TEMPO-Mediated Oxidation of Native Cellulose
1高碘酸钠催化微晶纤维素的氧化精要.
1高碘酸钠催化微晶纤维素的氧化【作者】陶芙蓉；王丹君；宋焕玲；丑凌军；【Author】 TAO Fu-rong 1,2,WANG Dun-jun 1,2,SONG Huan-ling 1,CHOU Ling-jun 1(1.State Key Laboratory for Oxo Synthesis and Selective Oxidation,Lanzhou Institute of Chemical Physics,Chinese Academy of Sciences,Lanzhou 730000,China;2.Graduate School of Chinese Academy of Sciences,Beijing 100049,China)【机构】中国科学院兰州化学物理研究所羰基合成与选择氧化国家重点实验室；中国科学院研究生院；【摘要】主要讨论了使用高碘酸钠(NaIO4)溶液氧化微晶纤维素的过程及性能,用红外光谱(IR)验证了氧化纤维素的生成;通过扫描电镜(SEM)、热重分析(TG-DSC)以及X射线衍射(XRD)对比了反应前后纤维素的变化;考察了氧化时间、氧化温度、氧化剂的浓度以及溶液的pH值对氧化纤维素的产率及醛基含量的影响;结果表明,反应前后纤维素的晶型和形貌基本没有变化,随着氧化程度的加深,氧化纤维素的热稳定性越来越差;并且随着氧化温度的提高和氧化剂浓度的增大,醛基含量相应提高,而氧化时间和pH值对醛基含量存在相对最高值。
【关键词】纤维素；氧化；氧化纤维素；高碘酸钠；∙【文献出处】分子催化, Journal of Molecular Catalysis, 编辑部邮箱, 2011年02期∙【DOI】10.16084/ki.issn1001-3555.2011.02.001∙【分类号】O643.32∙【被引频次】14∙【下载频次】508【参考文献】说明：反映本文研究工作的背景和依据中国期刊全文数据库∙[1] 李琳,赵帅,胡红旗. 纤维素氧化体系的研究进展[J]. 纤维素科学与技术. 2009(03) ∙[2] 姜锋,马丁,包信和. 酸性离子液中纤维素的水解[J]. 催化学报. 2009(04)∙[3] 叶代勇,黄洪,傅和青,陈焕钦. 纤维素化学研究进展[J]. 化工学报. 2006(08)∙[4] 孟舒献,冯亚青,梁足培,吕玮,徐嘉. 微晶纤维素的氧化及吸附性能[J]. 精细化工.2005(02)∙[5] 刘燕,冯亚青,李熙凤,张卫红. 氧化纤维素的制备研究[J]. 化学工程. 2002(06)外文题录数据库∙[1] Tao F R,Song HL,Chou L J. Chemsuschem . 2010∙[2] Salmon S,Hudson S M. J Macromol.Sci.Rev.Mac-romol.Chem.Phys . 1997∙[3] Stephen M B,John G,Andrew D T. Journal of Materials Chemistry . 1998∙[4] Camy S,Montanari S,Rattaz A,et al. The Journal ofSupercritical Fluids . 2009∙[5] Hassan R M,Ahmed S M,Fawzy A,et al. Catalysiscommunication . 2010∙[6] Xu F,Ding H S,Tejirian A. Enzyme and MicrobialTechnology . 2009∙[7] Sirvio J,Hyvakko U,Liimatainen H,et al. Carbohy-drate Polymers . 2011∙[8] Marte R L,Owens M L. Analytical Chemistry . 1956∙[9] Mascal M,,Nikitin E B. Angew Chem.Int.Ed . 2008∙[10] Fukuoka A,Dhepe P L. Angewandte Chemie International Edition . 2006【引证文献】说明：引用本文的文献。
tempo改性纤维素【SCI全文】
INFLUENCE OF BUFFER SOLUTION ON TEMPO-MEDIATED OXIDATIONMei Xu, Hongqi Dai,* Xuan Sun, Shumei Wang, and Weibing WuTEMPO-mediated oxidation has been reported to effectively convert C6primary hydroxyl groups to carboxyl groups for better water-solubility.However, the pH decreases continuously during the oxidation process,and it is therefore difficult to maintain the stability of the reaction. Thecontrol of pH at a constant level throughout the oxidation process is acomplicated task. The applicability of a carbonate buffer system and aborax buffer system with various continuous addition rate of sodiumhypochlorite solution was considered. Carbonate buffer solution andborax buffer solution can efficiently buffer the pH. The results of carboxylcontent and DP of celluloses proved that the activities of sodiumhypochlorite solution can be maintained when sodium hypochlorite isadded with controlled flow rates without adjusting pH by hydrochloricacid. Buffer solutions created a milder reaction environment in which thedamage of celluloses would be buffered. The conclusion was consistentwith DP tests of celluloses. Compared with carbonate buffer, the boraxbuffer with high ability of penetration could enhance the depth and widthof oxidation, which was demonstrated by the results of X-ray diffractionpatterns and carboxyl content of celluloses.Keywords: TEMPO; Cellulose; Oxidation; Buffer solution; Drop rate; Carboxyl contentContact information: Jiangsu Provincial Key Lab of Pulp and Paper Science and Technology, Nanjing Forestry University, Nanjing Jiangsu, 210037, P. R. China*Corresponding author: hgdhq@INTRODUCTIONPiperidine radicals are noted for their high stability. The 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO)/NaBr/NaClO has been reported to effectively convert C6 primary hydroxyl groups of cellulose to carboxyl groups via a reactive aldehyde-intermediate (de Nooy et al. 1995). Regioselective oxidations of C6 primary hydroxyls of polysaccharides to carboxyl groups have been developed, in which 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and sodium bromide have been used as catalysts under aqueous conditions at pH from 10 to 11 (Isogai et al. 1998). Such modifications of cellulose are usually achieved by converting some of the surface OH moieties of cellulose into carboxyl groups (Saito et al. 2004). Neither the crystalline type of cellulose nor the width of the crystalline region is changed in the oxidation process. In addition, the oxidation process could increase the carboxyl content of cellulose, which as a consequence, would increase the hydrophilicity of cellulose (Saito et al. 2005).The pH value is a key factor that affects the reaction of TEMPO/NaClO/NaBr, with the optimal value under aqueous conditions within the range 10 to 11. A stable pH ensures high quality of products. Recently it was reported that under acidic conditionscurdlan and other polysaccharides could be oxidized by 4-acetamide-TEMPO/NaClO/ NaClO2with 100 mL of 0.2M acetate buffer at pH 4.7 (Tamura et al. 2010). In this process, the sodium hypochlorite solution was added all at once. Regioselective oxidation transforms C6 primary hydroxyls on cellulose to aldehyde groups at the beginning of the reaction under acidic conditions. Then the C6 primary aldehyde groups on cellulose are oxidized to carboxyl groups by NaClO2. The Na2CO3-NaHCO3 buffer system was also applied in the selective oxidation of ethanol by Liaigre (2005). It can be seen from the two examples above, alkaline buffer solution has the potential to be applied in the TEMPO/NaClO/NaBr aqueous system, because it does not affect the normal reaction and can maintain the reaction pH continuously.A carbonate buffer system and borax buffer system can be used at pH 10.5. A carbonate buffer system is stable and does not react with cellulose. In the oxidation process, it only maintains a certain pH with a huge buffering capacity. In the borax-sodium hydroxide system, however, the outer electronic structure of boron atoms determined that it can form bonds with cellulose, and thus promoting the penetration of the reaction solution. The borax-sodium hydroxide buffer system also demonstrated a small buffering capacity. Thus, the sodium hypochlorite solution was not added all at once. Simultaneously, it can create a mild reaction environment when the TEMPO-mediated oxidation is started by trickling sodium hypochlorite with controlled flow rates.In general, cotton fiber (Dai et al. 2011), softwood pulps (Dang et al. 2007), hardwood pulps (Fukuzumi et al. 2010, Mishra et al. 2011), lignocellulosic fibers (Hamid et al. 2011), and regenerated cellulose (Sun et al. 2005) can be oxidized by a TEMPO/ NaClO/NaBr aqueous system. During the reaction, sodium hypochlorite solution is typically added all at once before the reaction (Qin et al. 2011). Sodium hydroxide solution was added continuously to maintain the pH (Saito et al. 2006). During oxidation of alcohols, da Silva Perez et al. (2003) controlled the reaction by adding sodium hypochlorite solution drop by drop. The problem of buffer capacity of the borax buffer was solved with the method of da Silva Perez. In this study, the applicability of the carbonate buffer system and the borax buffer system with various dropping rate of sodium hypochlorite solution was considered. This method further simplified the control of TEMPO oxidation, which has a potential to be applied in mass production. EXPERIMENTALMaterialsThe softwood bleached kraft pulp used in this study was a commercial pulp supplied by Celgar Co., Ltd., Canada. TEMPO (2,2,6,6-tetramethyl piperidine-1-oxyl radical) was purchased from Johnson Metthey Co., UK. Sodium bromide and sodium hypochlorite solution (ca. 8.6% active chlorine) were supplied by Jiuyi Chemicals Reagent (Shanghai China). All other chemicals were analytically pure (Shanghai Chemicals Co., Ltd, China) and were used without further purification.Carbonate buffer (pH 10.5) was prepared with 0.1 M sodium carbonate (500 mL) and 0.1 M sodium bicarbonate (250 mL) at room temperature. Borax buffer solution (pH 10.5) was prepared with 0.05 M borax (320 mL), 0.2 M sodium hydroxide (145 mL), and deionized water (285 mL) at room temperature.MethodsTEMPO-mediated oxidationThe fibers (10 g) were suspended in buffer solution (750 mL, pH 10.5) containing TEMPO (0.025 g) and sodium bromide (0.25 g). The TEMPO-mediated oxidation was conducted in carbonate buffer solution (pH 10.5) and borax buffer solution (pH 10.5) at room temperature respectively for two hours with agitation. The TEMPO oxidation was started by trickling sodium hypochlorite at controlled flow rates. One gram of celluloses required 8 mmol of sodium hypochlorite solution. The solution of sodium hypochlorite was added, respectively, within 15 min, 30 min, 45 min, and 60 min to control the flow rates. The TEMPO-oxidized cellulose was thoroughly washed with water and stored at 4°C before further treatment or analysis.Reaction rateDuring the oxidation process, the generation of carboxyl groups was monitored by recording the pH value every 5 minutes. The slope of the time-pH curve was applied to reflect the generation rate of the carboxyl content.Determination of carboxyl groupsThe carboxyl content of the TEMPO-oxidized cellulose was determined by an electrical conductivity titration method (Saito et al. 2007). In the electrical conductivity titration method, sodium carboxyl groups in the TEMPO-oxidized cellulose were converted to free carboxyl groups by ion-exchange treatment. Fibers (3g) were suspended in water (450 mL). The slurry was adjusted to pH 2 to 3 with 0.1 M hydrochloric acid, and allowed to sit for 1 hr, followed by thorough washing with water. This process was repeated one more time (Mao et al. 2008).Determination of degree of polymerizationThe degree of polymerization of cellulose was estimated, since cellulose samples with different DP need to use different amounts in order to achieve a target viscosity during the test. Celluloses (0.15 g) before oxidation and TEMPO-mediated celluloses (1g) were dissolved respectively in copper ethylenediiamine solution to determinate the degree of polymerization of cellulose by capillary viscometer (Shi et al. 2010).X-ray diffraction patterns of oxidized cellulosesThe softwood fiber samples were converted to powder substrates and then subjected to X-ray diffraction analysis from 5° to 60°at 5°/min of diffraction angle 2θusing the reflection method by means of a D/Max-3A (Japan) with a Nifiltered CuKa radi ation (λ=0.1548nm) at 40 kV and 100 mA. The crystallinity indices based on 2θ scan from 5° to 60° were calculated according to Segal’s method,002002()100%/AM Crystallinity I I I =−× (1)where 002I was identified with the intensity at 22.5, and AM I was the intensity at 16.5.RESULTS AND DISCUSSIONThe Effects of Dropping Rate of Sodium Hypochlorite Solution on Oxidation The first series of experiments involved the effect of adding sodium hypochlorite solution by different modes of oxidation. Aqueous systems, in the absence of buffer, were applied in the oxidation process. In the default method, sodium hypochlorite solution was pH-adjusted in advance and added at once. By contrast, sodium hypochlorite was added dropwise in a continuous manner. In Table 1, experimental conditions were designed to determine the effects of the dropping rate of sodium hypochlorite solution on oxidation.Obviously, a mild reaction environment can be created when the TEMPO-mediated oxidation is started by used of a trickling sodium hypochlorite with controlled flow rates. The results of carboxyl content and DP reflected that the activities of sodium hypochlorite solution can be maintained without adjusting pH by hydrochloric acid. With other parameters held constant, the optimal flow rate was when the sodium hypochlorite was added gradually within 30 min. Under this condition, celluloses were protected and the oxidation reaction progressed extensively.Table 1. Reaction Conditions in the Aqeuous SystemReaction system Add way ofNaClOsolutionpHReactiontimeAmount of NaClO/ mmol·g-1 fiberCarboxylcontent /mmol·g-1 fiberDPAqueousmediaadd all at once 10.52hr 80.48 106Aqueous media add graduallywithin 15 min10.52hr 80.5670 107Aqueous media add graduallywithin 30 min10.52hr 80.6011 109Aqueous media add graduallywithin 45 min10.52hr 80.5701 104Aqueous media add graduallywithin 60 min10.52hr 80.5456 106The Effect of Buffer System On TEMPO-Oxidized CellulosesFluctuations in pH inevitably resulted when sodium hypochlorite was controlled by flow rates without pH adjustment. Buffer solution used for this situation can moderate the impact of sodium hypochlorite (pH 12.6) and generation of carboxyl groups. The function of buffer was to keep the pH value of the solution in a proper rang. The pH value of buffer was maintained by the equilibrium state of conjugate acid-base pairs (Jia et al. 2002). It provided a milder environment for TEMPO-mediated oxidation.A carbonate buffer system and borax buffer system are two kinds of common alkali buffer solution that can be used at pH 10.5. In the following experiments, a carbonate buffer system and a borax buffer system were applied in the oxidation process. Experiments in Table 2 were designed to determine the effects of drop rate of sodium hypochlorite solution on oxidation in the buffer system.Table 2. Reaction Conditions in the Buffer System Reaction system Add way of NaClO solution pH Reaction time Amount ofNaClO /mmol·g -1Carboxyl content /mmol·g -1 fiber DP Carbonate buffer system add gradually at 15min 10.5 2hr 80.5917 110 Carbonate buffer system add gradually at 30min 10.5 2hr 80.6068 110 Carbonate buffer system add gradually at 45min 10.5 2hr 80.5968 108 Carbonate buffer system add gradually at 60min 10.5 2hr 80.5567 110 Borax buffer system add gradually at 15min 10.5 2hr 80.6126 116 Borax buffer system add gradually at 30min 10.5 2hr 80.6076 116 Borax buffer system add gradually at 45min 10.5 2hr 80.6133 113 Borax buffersystem add gradually at 60min 10.5 2hr8 0.6369 116In the buffer, pH was not entirely the same. This was due both to the generation of carboxyl groups during the reaction and a variety of other chemical reactions that changed the ratio of conjugate acid-base pairs. During the oxidation process, the generation of carboxyl groups was monitored by recording the pH value every 5 minutes. Figures 1 and 2 show the changes in pH value in the carbonate buffer and borax buffer, respectively, during the reaction.0204060801001209.510.010.511.0p HReaction time (min) adding within 15minadding within 30minadding within 45minadding within 60min0204060801001209.09.510.010.511.0p HReaction time (min) adding within 15min adding within 30min adding within 45min adding within 60minFig. 1. Variation of pH under different sodiumhypochlorite drop rate in the carbonate buffer Fig. 2. Variation of pH under different sodium hypochlorite drop rate in the borax bufferAccording to time-pH curve, the relationship between time and reaction rate can be obtained. The slope of the time-pH curve was applied to reflect the rate of generation of the carboxyl content. Figures 3 and 4 reflect the relationship between time and reaction rate.In the control group, the pH of the system was stable with carbonate buffer when fiber was not added during the reaction, while other conditions were not changed. As shown in Fig. 1, the pH of the system was stable between the pH of 10.5 to 10 withcarbonate buffer. From Fig. 3, it can be seen that sodium hypochlorite concentration had little effect on the reaction. The optimal addition rate of sodium hypochlorite was adding it gradually within 30 min. This was due to the fact that the reaction was finished at 2 h. Under other addition rates, time needs to be extended, because the reactions did not end with a low reaction rates. In addition, comparing Table 1 with Table 2, it can be seen that the oxidation regulation of carbonate buffer solution was the same as that of the water system. With the increasing flow rate of sodium hypochlorite, the carboxyl content of the products increased then decreased. The carboxyl content and DP were all optimal when the sodium hypochlorite was added gradually within 30 min. Reaction was rapid under high flow rate. Cellulose macromolecules were degraded under high sodium hypochlorite concentration. At reduced flow rate the cellulose can be protected. But the reaction activities were also low. In addition, cellulose molecules would be cleaved when the flow of sodium hypochlorite was added continuously at the end of the reaction. Therefore, satisfactory results could not be achieved if the dropping rate of sodium hypochlorite was too fast or too slow. Experimental results shown that a milder reaction environment can be provided by a moderate dropping rate.0204060801001200.0000.0020.0040.0060.0080.010O x i d a t i o n r a t e Reaction time (min) adding within 15min adding within 30min adding within 45min adding within 60min 0204060801001200.0000.0050.0100.0150.0200.0250.0300.035O x i d a t i o n r a t eReaction time (min) adding within 15min adding within 30min adding within 45min adding within 60minFig. 3. The relationship between time andreaction rate in the carbonate buffer Fig. 4. The relationship between time and reaction rate in the borax bufferAs shown in Fig. 2, the buffering capacity of the borax buffer was smaller compared with the carbonate buffer. Therefore, the dropping rate of sodium hypochlorite was a key factor in the borax buffer. As shown in Fig. 4, both high dropping rate and a slow dropping rate were beneficial to the reaction rate. Obviously, borax buffer was different from carbonate buffer in oxidation regulation. The sodium hypochlorite concentration was not the only influencing factor. The penetration of the reaction solution can be promoted in a borax buffer. For this reason, the penetration time was also an important influencing factor. The carboxyl content was high when the reaction rate was fast under high flow rate of sodium hypochlorite. The carbonate buffer system itself did not play a role in cellulose. In the borax buffer, the buffer had a swelling effect on celluloses. Because the structure of B atom is 2s22p1, and the main oxidation number is 3. It could form a 4- or 6-coordination compound. Since the B atom has a small atomic radius, it usually forms a 4-coordination structure (Zhang et al. 2010). Because of the structure of borax, it could form chemical bonds with the hydroxyl groups of cellulose (Zhang et al. 1998). Thus, the reaction solutions were promoted to penetrate into cellulose with the increase of soaking time. If a steady stream of sodium hypochloritewas added continuously with the increase of soaking time, a higher carboxyl group content was obtained with borax buffer. According to its small capacity and its infiltration, the experiment condition was optimal when the sodium hypochlorite was being added gradually within 60 min. The conclusion was consistent with Table 2. Structural Analyses of the Oxidized Celluloses with Different ConditionsX-ray diffraction was used to further understand the structure of celluloses after being subjected to different conditions. Five reaction conditions of cellulose and their X-ray results are shown in Fig. 5. The crystallinity of celluloses is shown in Table 3.Table 3. Results of X-ray Diffraction PatternsReaction Number Reaction Condition DPCrystallinity/%0 Fibers before oxidation 1100 77.43%1 Fibers were oxidized by adding sodium hypochlorite atonce.106 77.30%2 Fibers were oxidized by adding sodium hypochloritegradually within 30min in water system.109 77.37%3 Fibers were oxidized by adding sodium hypochloritegradually within 30min in carbonate system.110 78.05%4 Fibers were oxidized by adding sodium hypochloritegradually within 30min in borax system.116 91.12%As shown in Fig. 5, the crystal types of celluloses were not changed after oxidation. In the buffer-free system, the pH value of reaction was not stable and celluloses would be damaged in that changing oxidation environment.Fig. 5. X-ray diffraction patterns of the original (0), after the TEMPO-mediated oxidation with adding sodium hypochlorite at once (1), after the TEMPO-mediated oxidation with adding sodium hypochlorite gradually within 30 min in water system (2), after the TEMPO-mediated oxidationwith adding sodium hypochlorite gradually within 30 min in carbonate system (3), after the TEMPO-mediated oxidation with adding sodium hypochlorite gradually within 30min in borax system (4) at room temperature.According to the results, the crystallinity degrees of cellulose were not changed in the buffer-free system and carbonate system. It can be concluded that the carboxyl groups were not formed inside crystallites during the TEMPO-mediated oxidation; the significant amounts of carboxyl groups formed in the water-insoluble fractions were mostly present on the crystal surfaces and in amorphous regions.In borax system, the crystallinity of cellulose increased markedly. Most part of the amorphous region of the cellulose tended to become ordered in the borax buffer, and the crystallinity of cellulose increased. The borax solution could form chemical bonds with the hydroxyl groups of cellulose. In the process of washing celluloses, some borax solution was removed by water, and a small amount of borax solution was locked in the new crystalline region of cellulose. This was why a water peak appeared in the X-ray map of borax buffer solution (Chen et al. 1990). The results further indicated that the borax solution could form chemical bonds with the hydroxyl groups of cellulose. Therefore, the borax buffer solution could enhance the depth and width of oxidation in the TEMPO-mediated system.CONCLUSIONS1. In a buffer-free aqueous system, the results for carboxyl content and DP of cellulose demonstrated that the activities of sodium hypochlorite solution can be maintained when sodium hypochlorite is added with controlled flow rates without use of hydrochloric acid to adjust the pH.2. Buffer solutions created a milder reaction environment in which the damage of celluloses would be minimized. This conclusion was supported by observations of the DP of cellulose. Compared with carbonate buffer, the borax buffer showed a high ability to penetrate into the fibers, and it was able to enhance the depth and width of oxidation, which was shown by X-ray diffraction patterns and carboxyl content of celluloses.3. The oxidation regulation of carbonate buffer solution was same as that of the buffer-free system. The sodium hypochlorite concentration was the key factor. The optimum condition involved adding sodium hypochlorite gradually within 30 min.4. A borax buffer was different from the carbonate buffer in oxidation regulation. The penetration time was another important factor. Therefore, the optimum condition involved adding sodium hypochlorite gradually within 60 min. ACKNOWLEDGMENTSThe research has been financially supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.REFERENCES CITEDChen, J. (1990). Pulping Chemistry, M. Light Industry Press, 36-37.Dai, L., Dai, H., Yuan, Y., Sun X., and Zhu Z. (2011). "Effect of TEMPO oxidation system on kinetic constants of cotton fibers," BioResources 6(3), 2619-2631. Dang, Z., Zhang, J., and Ragauskas, A. J. (2007). "Characteriaing TEMPO-mediated oxidation of ECF bleached softwood kraft pulps," Carbohydrate Polymers. 70, 310-317.da Silva Perez, D., Montanari, S., and Vignon, M. R. (2003). "TEMPO-mediated oxidation of cellulose III," Biomacromolecules 4(5), 1417-1425.De Nooy, A. E. J., Besemer, A. C., and van Bekkum, H. (1995). "Highly selective nitroxyl radical-mediated oxidation of primary alcohol groups in water-solubleglucans," Carbohydrate Research 269, 89-98.Fukuzumi, H., Saito, T., Okita, Y., and Isogai, A. (2010). "Thermal stabilization of TEMPO-oxidized cellulose," J . Polymer Degradaation and Stability 95, 1502-1508. Kaddami, H., Sbiai, A., Sautereau, H., Maazouz, A., and Fleury, E. (2011). "TEMPO-mediated oxidation of lignocellulosic fibers from date palm leaves," Carbohydrate Polymers 86(4), 1445-1450.Isogai, A., and Kato, Y. (1998). "Preparation of polyuronic acid from cellulose by TEMPO-mediated oxidation," Cellulose 5, 153-164.Jia, Z., Zhang, S., He, Q., and Xuan, D. (2002). Inorganic and Analytical Chemistry, M.Higher Education Press, 128-129.Liaigre, D., Breton, T., and Belgsir, E. I. M. (2005). "Kinetic and selectivity control of TEMPO electro-mediated oxidation of alcohols," Electrochemistry Communications 7, 312-316.Mao, L. S., Law, K. N., Brouillette, F., and Daneault, C. (2008). "Effect of 4-acetamido-TEMPO-mediated oxidation conditions on the formation of carboxylic acid groups on mechanical pulp fibers," Journal of Pulp and Paper Science 34(4), 198-202. Mishra, S. P., Thirree, J., Manent, A.-S., Chabot, B., and Daneault, C. (2011)."Ultrasound-catalyzed TEMPO- mediated oxidation of native cellulose for theproduction of nanocellulose: Effect of process variables," BioResources 6(1), 121-143. Qin, Z.-Y., Tong, G.-L., Chin, Y. C. F., and Zhou, J.-C. (2011). "Preparation of ultrasonic-assisted high carboxylate content cellulose nanocrystals by TEMPOoxidation," BioResources 6(2), 1136-1146.Saito, T., and Isogai, A. (2004). "TEMPO-mediated oxidation of native cellulose. The effect of oxidation conditions on chemical and crystal structures of the water -Insoluble fractions," Biomacromolecules 5, 1983-1989.Saito, T., Kimura, S., Nishiyama, Y., and Isogai, A. (2007). "Cellulose nanofibers prepared by TEMPO-mediated oxidation of native cellulose," Biomacromolecules 8, 2485-2491.Saito, T., Okita, Y., Nge, T. T., Sugiyama, J., and Isogai, A. (2006). "TEMPO-mediated oxidation of native cellulose: Microscopic analysis of fibrous fractions in the oxidized products," Carbohydrate Polymers 65, 435-440.Saito, T., Shibata, I., Isogai, A., Suguri, N., and Sumikawa N. (2005). "Distribution of carboxylate groups introduced into cotton linters by the TEMPO-mediatedoxidation," Carbohydrate Polymers. 61, 414-419.Shi, J., He, F. (2010). Analysis and Detection of Pulp and Paper, M. Light Industry Press, 67-71.Sun, B., Gu, C., Ma, J., and Liang, B. (2005). "Kinetic study on TEMPO-mediated selective oxidation of regenerated cellulose," Cellulose 12, 59-66.Tamura, N., Hirota, M., Saito, T., and Isogai, A. (2010). "Oxidation of curdlan and other polysaccharides by 4-acetamide-TEMPO/NaClO/NaClO2 under acid conditions,"Carbohydrate Polymers. 81, 592-598.Zhang, D., Xi, P., and Wang, Q. (1998). "The application of borax in konjac production,"Science and Technology of Food Industry. 3, 37-38.Zhang, X., Li, J., and Li, C. (2010). "The research of IR and crystal structure in borax," J.Guangdongchemical 37(8), 77-79.Article submitted: October 30, 2011; Peer review completed: December 10, 2011; Revised version received: January 5, 2012; Second revision received and accepted: February 11, 2012; Published: February 14, 2012.。
水利部、工业和信息化部印发造纸等七项工业用水定额
《中国造纸》2021年第40卷第2期［31］Yousif Ahmed M ，Zaid Osama F ，El -Said Waleed A ，et al.SilicaNanospheres Coated Nanofibrillated Cellulose for Removal and Detection of Copper （II ）Ions in Aqueous Solutions ［J ］.I &ECResearch ，2019，58（12）：4828-4837.［32］Hokkanen Sanna ，Doshi Bhairavi ，Srivastava Varsha ，et al.Arsenic （III ）removal from water by hydroxyapatite -bentonite clay -nanocrystalline cellulose ［J ］.Environmental Progress &Sustainable Energy ，2019，38（5）：13147.［33］Zhou Yiming ，Fu Shiyu ，Zhang Liangliang ，et al ，Use ofcarboxylated cellulose nanofibrils -filled magnetic chitosan hydrogelbeads as adsorbents for Pb （II ）［J ］.Carbohydrare Polymers ，2014，101：75-82.［34］Wei Jie ，Yang Zhixing ，Sun Yun ，et al.Nanocellulose -basedmagnetic hybrid aerogel for adsorption of heavy metal ions fromwater ［J ］.Polymers ，2019，54（8）：6709-6718.［35］Li Jian ，Xu Zhaoyang ，Wu Weibing ，et al.Nanocellulose/Poly （2-（dimethylamino ）ethyl methacrylate ）Interpenetrating polymer network hydrogels for removal of Pb （II ）and Cu （II ）ions ［J ］.Colloids and Surfaces A ，2018（538）：474-480.［36］Li Jian ，Zuo Keman ，Wu Weibing ，et al.Shape memory aerogelsfrom nanocellulose and polyethyleneimine as a novel adsorbent for removal of Cu （II ）and Pb （II ）［J ］.Carbohydrate Polymers ，2018，196：376-384.［37］TANG Juntao ，SONG Yang ，ZHAO Feiping ，et pressiblecellulose nanofibril （CNF ）based aerogels produced via a bioinspired strategy for heavy metal ion and dye removal ［J ］.Carbohydrate Polymers ，2019（208）：404.［38］Shahnaz Tasrin ，Fazil S Mohamed Madhar ，Padmanaban V C ，etal.Surface modification of nanocellulose using polypyrrole for theadsorptive removal of Congo red dye and chromium in binary mixture ［J ］.Biological Macromolecules ，2020（151）：322-332.［39］Maatar Wafa ，Boufi Sami.Poly （methacylic acid -co -maleic acid ）grafted nanofibrillated cellulose as a reusable novel heavy metalions adsorbent ［J ］.Carbohydrate Polymers ，2015（126）：199-207.［40］Hokkanen Sanna ，Repo Eveliina ，SillanpääMika.Removal ofheavy metals from aqueous solutions by succinic anhydride modified mercerized nanocellulose ［J ］.Chemical Engineering Journal ，2013（223）：40-47.［41］YU Xiaolin ，TONG Shengrui ，GE Maofa ，et al.Adsorption ofheavy metal ions from aqueous solution by carboxylated cellulose nanocrystals.［J ］.Journal of Enviromental Science ，2013，25（5）：933-943.［42］QIN Famei ，FANG Zhiqiang ，ZHOU Jie ，et al.Efficient Removalof Cu 2+in Water by Carboxymethylated Cellulose Nanofibrils ：Performance and Mechanism ［J ］.Biomacromolecules ，2019，20（12）：4466-4475.［43］Sharma Priyanka R ，Chattopadhyay Aurnov ，Sharma Sunil K ，etal.Nanocellulose from Spinifex as an Effective Adsorbent to Remove Cadmium （II ）from Water ［J ］.ACS Sustailable Chenistry&Engineering ，2018，6（3）：3279-3290.［44］Yao C ，Wang F ，Cai Z ，et al.Aldehyde -functionalized porousnanocellulose for effective removal of heavy metal ions from aqueoussolutions ［J ］.RSC Advances ，2016，6（95）：92648-92654.［45］GENG Biyao ，WANG Haiying ，WU Shuai ，et al.Surface -TailoredNanocellulose Aerogels with Thiol -Functional Moieties for Highly Efficient and Selective Removal of Hg （II ）Ions from Water ［J ］.ACS Sustainable Chemistry &Engineering ，2017，5（12）：11715-11726.［46］Alipour A ，Zarinabadi S ，Azimi A ，et al.Adsorptive removal of Pb（II ）ions from aqueous solutions by thiourea -functionalized magnetic ZnO/nanocellulose composite ：Optimization by responsesurface methodology （RSM ）［J ］.Int.J.Biol.Macromol ，2020（151）：124-135.［47］Anirudhan T S ，Shainy F ，Deepa J R.Effective removal of Cobalt（II ）ions from aqueous solutions and nuclear industry wastewater usingsulfhydrylandcarboxylfunctionalisedmagnetitenanocellulose composite ：batch adsorption studies ［J ］.Chemistryand Ecology ，2019，35（3）：235-255.［48］Hong Hye -jin ，Lim Jin Seong ，Hwang Jun Yeon ，et al.Carboxymethlyated cellulose nanofibrils （CMCNFs ）embedded in polyurethane foam as a modular adsorbent of heavy metal ions ［J ］.Carbohydrate Polymers ，2018，195：136-142.［49］Mo Liuting ，Pang Huiwen ，Tian Yi ，et al.3D multi -wall perforatednanocellulose -based polyethylenimine aerogels for ultrahigh effcient and reversible removal of Cu 2+ions from water ［J ］.ChemicalEngineering Journal ，doi ：10.106/j ，eej.2019.122157.［50］Li Weixue ，Ju Benzhi ，Zhang Shufen.Preparation of cysteamine -modified cellulose nanocrystal adsorbent for removal of mercury ionsfrom aqueous solutions ［J ］.Cellulose ，2019，8（26）：4971-4985.［51］Zhang Nan ，Long Guo ，Chen Zang ，et al.A novel TEMPO -mediated oxidized cellulose nanofibrils modified with PEI ：Preparation ，characterization ，and application for Cu （II ）removal ［J ］.Hazardous Materials ，2016（316）：11-18.CPP（责任编辑：董凤霞）·消息·水利部、工业和信息化部印发造纸等七项工业用水定额2020年12月30日，为深入推进节约用水工作，水利部联合工业和信息化部印发造纸等七项工业用水定额的通知，定额标准自2021年3月1日起施行。
TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展
TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展徐媚;徐梦蝶;戴红旗;王淑梅;吴伟兵【摘要】2,2,6,6-四甲基哌啶氧自由基(TEMPO)共氧化剂体系被广泛应用于选择性氧化纤维素的C6位伯醇羟基.在氧化过程中,纤维素的聚合度大幅度降低,因此被应用于制备纳米纤维素.随着TEMPO/NaClO/NaBr氧化技术的发展成熟,TEMPO/NaClO/NaClO2和4-乙酰胺基-TEMPO/NaC1O/NaClO2体系都得到了广泛关注.随着研究的深入,TEMPO及其衍生物氧化体系已经成为一种高效且全pH范围适用的选择性氧化体系.TEMPO/NaC1O/NaBr氧化体系在pH范围9～11活性最高,TEMPO/NaC1O/NaC1O2体系能够应用于pH中性的条件下,4-乙酰胺基-TEMPO/NaClO/NaC1O2体系一般的pH使用范围为3.5～6.8.传统的TEMPO氧化过程需要持续手动控制pH恒定,操作繁琐,可控性差,应用缓冲溶液可控制TEMPO氧化过程中pH在一定范围内恒定,从而实现了TEMPO氧化体系的智能控制.文章综述了TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展.【期刊名称】《纤维素科学与技术》【年(卷),期】2013(021)001【总页数】8页(P70-77)【关键词】2,2,6,6-四甲基哌啶氧自由基(TEMPO);TEMPO衍生物;纳米纤维素;自动调节【作者】徐媚;徐梦蝶;戴红旗;王淑梅;吴伟兵【作者单位】南京林业大学江苏省制浆造纸科学与技术重点实验室,江苏南京210037;南京林业大学江苏省制浆造纸科学与技术重点实验室,江苏南京210037;南京林业大学江苏省制浆造纸科学与技术重点实验室,江苏南京210037;南京林业大学江苏省制浆造纸科学与技术重点实验室,江苏南京210037;南京林业大学江苏省制浆造纸科学与技术重点实验室,江苏南京210037【正文语种】中文【中图分类】O636.112,2,6,6-四甲基哌啶氧自由基（TEMPO）属于亚硝酰自由基类，是一种稳定的自由基，其结构式如图1所示[1]。
TEMPO-Mediated Oxidations
6 TEMPO-Mediated Oxidations6.1.IntroductionIn1965,Golubev,Rozantsev,and Neiman reported1that treatment of oxoam-monium salt11with excess of ethanol led to the formation of acetaldehyde.In1975,Cella et al.demonstrated2that alcohols can be oxidized to carboxylic acids by treatment with m-chloroperbenzoic acid in the presence of a catalytic amount of2,2,6,6-tetramethylpiperidine(12).Apparently,MCPBA oxidizes the amine12,resulting in a catalytic quantity of the stable radical2,2,6,6-tetramethylpiperidine-1-oxyl(13),normally called TEMPO,that is further oxidized to the oxoammonium cation14that operates as the primary oxidant.7980IntroductionCella made a very important seminal contribution to the TEMPO-mediated obtention of carboxylic acids by showing that oxoammonium salts can be employed catalytically in the transformation of primary alcohols into carboxylic acids.On the other hand,Cella’s procedure involves the use of a peracid as secondary oxidant,which is a strong oxidant that interferes with many functional groups.In 1987,Anelli et al .published 3a landmark paper in which they showed that primary alcohols can be oxidized either to aldehydes or to carboxylic acids in a highly efficient and convenient manner,by treating the alcohol in a CH 2Cl 2–water biphasic mixture with chlorine bleach (sodium hypochlorite)in the presence of sodium bicarbonate,potassium bromide,and a catalytic amount of the TEMPO derivative 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (15)(4-MeO-TEMPO).The oxidation can be stopped at the aldehyde stage by running it for a short time.Alternatively,it can be brought to the carboxylic acid stage by adding a phase-transfer catalyst that causes a great acceleration of theoxidation.One important limitation of Anelli’s procedure is the need to utilize sodium hypochlorite as stoichiometric oxidant,a compound that has a great tendency to produce chlorinations in some sensitive substrates.This tendency to chlorination can be mitigated by employing Zhao’s modification of Anelli’s procedure,which was published 4in 1999.In this modification,the secondary oxidant—sodium hypochlorite—is used in catalytic amounts rather than in excess,the reagent being regenerated by addition of stoichiometric sodium chlorite,a compound that lacks the strong chlorinating tendency of sodium hypochlorite.Edited by Foxit Reader Copyright(C) by Foxit Software Company,2005-2008For Evaluation Only.Chapter 681In 1999,Epp and Widlanski described 5the oxidation of alcohols to carboxylic acids using catalytic TEMPO,with bis(acetoxy)iodobenzene—PhI OAc 2,commonly referred as BAIB—as secondary oxidant in an acetonitrile–aqueous buffer mixture.This procedure for the oxidation of primary alcohols possesses the distinctive advantage of producing the rather benign iodobenzene and acetic acid as side compounds.Furthermore,in contrast to other oxidation procedures,it is possible to perform the oxidation of Epp and Widlanski in the absence of metallic salts.MechanismThe available experimental data are consistent with a mechanism,4 6as shown below,in which the secondary oxidant transforms TEMPO,or a related stable radical,in an oxoammonium salt that operates as the primary oxidant,trans-forming the alcohol into the corresponding aldehyde.This results in the formation of a hydroxylamine that is oxidized to a TEMPO radical,thus completing the catalytic cycle.The catalytic cycle can in fact be more complex,because TEMPO radicals can dispro-portionate into oxoammonium salts and hydroxylamines under acidic catalysis.6a82Introduction The aldehyde,in the presence of water,equilibrates with the corresponding hydrate that can be oxidized via a similar mechanism to the corresponding acid, as shown below.Interestingly,TEMPO inhibits the oxidation of aldehydes to carboxylic acids when this oxidation proceeds via a radical mechanism.That is why Anelli’s oxidation can be carried out under air and be easily stopped at the aldehyde stage with no competing overoxidation due to the presence of gaseous oxygen.7While in all TEMPO-mediated oxidations of primary alcohols to carboxylic acids, oxoammonium salts are the primary oxidants for the transformation of alcohols into aldehydes,the subsequent oxidation of aldehydes to carboxylic acids may sometimes be effected by the oxidant present in excess rather than by oxoammonium salts.In such cases,the secondary oxidant for the transformation of alcohols into aldehydes is the primary oxidant for the oxidation of aldehydes to carboxylic acids.The oxidation of primary alcohols with oxoammonium salts can work either via a compact five-membered transition state under basic conditions or via a linear transition state under acidic conditions,as shown below.Under basic conditions the oxidation is quicker and possesses a greater selectivity for primary alcohols versus secondary ones.The five-membered transition state under basic conditions is more compact,leading to aquicker reaction rate and greater selectivity for oxidation of primary alcohols relative tosecondary ones.Chapter683Stoichiometric OxidantsThe most common stoichiometric oxidants in TEMPO-mediated transformations of primary alcohols into carboxylic acids are sodium hypochlorite(NaOCl)—Anelli’s oxidation—,3sodium chlorite NaClO2 —Zhao’s modification ofAnelli’s oxidation—,4and PhI OAc2—oxidation of Epp and Widlanski.5Other stoichiometric oxidants less commonly used include MCPBA,2Ca ClO2 (swimming pool bleach),8t-BuOCl,9CuCl−O2,10NaBrO2,11Cl2,12Br212,and trichloroisocyanuric acid.13It is possible to perform the oxidation under electro-chemical conditions in the presence of catalytic TEMPO.14Amino1-Oxyl RadicalsTEMPO and analogue compounds can be prepared starting with a simple conden-sation of ammonia with acetone,15and their cost is quite affordable.They are stable radicals because they are flanked by two quaternary carbons that provide a bulky environment.For these reasons,TEMPO and analogue compounds,that is, 2,2,6,6-tetramethylpiperidine-1-oxyl radicals,are almost exclusively employed in oxidations mediated by amino1-oxyl radicals.TEMPO is a volatile compound soluble in organic solvents and water.It can be recovered by extraction with Et2O14or by azeotropic distillation with water.16Although some differences in the chemical behavior of different TEMPO derivatives were noticed,17the selection of a particular derivative is normally dictated by price and convenience.As far as the authors are aware,no profound study of the efficacy of different TEMPO derivatives in the oxidation of alcohols has been carried out.TEMPO entrapped within a silica matrix has been employed as a recyclable catalyst in the selective oxidation of primary alcohols using NaOCl as stoichiometric oxidant.186.2.Anelli’s OxidationIn1987,Anelli et al.made a key contribution to TEMPO-mediated oxida-tions by showing that the very cheap reagent chlorine bleach(aqueous NaOCl) can function very effectively as a stoichiometric oxidant for alcohols in the presence of traces of4-MeO-TEMPO.3They established a protocol involving a reaction run at0 C in a biphasic CH2Cl2–water mixture in the presence of excess of NaOCl,NaHCO3,KBr,and catalytic4-MeO-TEMPO for oxidation to aldehydes.Under these conditions the oxidation to acids is quite slow.If the acid is desired,it is advisable to add a phase-transfer catalyst to speed up the oxidation.84Anelli’s OxidationThe oxidation of a primary alcohol using Anelli’s procedure without the addition of aphase-transfer catalyst allows the preparation of74%of the corresponding aldehyde.The addition of1mol%of tetrabutylammonium bisulfate as phase-transfer catalyst produces a great acceleration of the oxidation that allows the isolation of the correspondingacid in91%.19The following experimental data are relevant regarding Anelli’s oxidation:•Primary alcohols are transformed into the corresponding aldehydes—with no need to add a phase-transfer catalyst—normally in only about3minutes.The oxidation of benzyl alcohols possessing electron donatinggroups in the aromatic ring can be much slower,a fact that canbe explained by the presence of a negative charge in the transitionstate for the oxidation involving oxoammonium salts under basicconditions.•The addition of some KBr produces a substantial acceleration of theoxidation,because of the generation of HOBr.20This reagent is formedfrom HOCl and KBr,and is apparently a much better oxidant for theregeneration of oxoammonium salts than HOCl.•The reaction is rather slow at the pH of commercial bleach(ca.12.7),being much quicker at a pH of ca.8.6,generated by the additionof NaHCO3as buffer.This fact can be explained assuming that at avery high pH the regeneration of the oxoammonium salt,rather thanthe oxidation of the alcohol by the oxoammonium salt via a five-membered transition state,becomes rate-determining.At a very basicpH the concentration of HOBr,which is the oxidant regenerating theoxoammonium salt,becomes very low relative to the concentration ofthe hypobromite anion BrO– .•The reaction can fail in substrates possessing a high hydrophilicity.Apparently,the oxidation takes place in the organic phase,where suchsubstrates are present in a very low concentration.•The oxidation can be substantially accelerated by the addition ofquaternary ammonium salts as a phase-transfer catalyst.Thus,while inthe absence of phase-transfer catalyst the reaction is easily stopped atChapter685 the aldehyde stage,the addition of catalytic amounts of a quaternaryammonium salt normally allows the oxidation to carboxylic acidto be completed in5minutes at0 C.As in the oxidation toaldehydes,electronic effects can be very important,and oxidationsyielding benzoic acids possessing electron donating groups can be muchslower.•Somehow unexpectedly,the reaction speed decreases by increasing thetemperature,a fact due to the decomposition of oxoammonium salts,which are very stable at0 C,but decompose very quickly in the presenceof water at25 C.•The transformation of aldehydes into carboxylic acids is apparentlymediated by oxoammonium salts,rather than by some other oxidantin excess;for,in the absence of TEMPO radicals,this reaction israther slow.The above facts are illustrated in the following scheme:SolventAnelli‘s oxidation is most often carried out in a biphasic system consisting of CH2Cl2and water.As the oxidation takes place in the organic phase,this biphasic system fails in water-soluble substrates.That is why when Anelli’s oxidation is applied to sugars,water is normally employed as the sole solvent.21 Furthermore,acetone/water is a solvent combination quite often utilized,22while86Anelli’s Oxidation MeCN/water23and EtOAc/water24are less used.When water or an aqueous mixture is employed as solvent,the reaction may fail in lipophilic substrates because of lack of solubility.25The primary alcohols,in a cyclodextrin possessing the secondary alcohols protected as methyl ethers,are oxidized in a monophasic MeCN–water mixture providing93%of the corresponding heptacarboxylate.Under these conditions there is no oxidation in substrates where the secondary alcohols are protected as benzyl or allyl ethers,due to their much greaterlipophilicity.25CatalystSimple TEMPO is usually employed as catalyst in the Anelli’s oxidation of primary alcohols to acids,although other TEMPO derivatives such as4-MeO-TEMPO,3 264-HO-TEMPO,27or4-AcNH-TEMPO19are equally effective.A trace quantity of1mol%of catalyst is normally enough for an efficient oxidation,although because of the low price of TEMPO and its very easy elimi-nation during the workup,the use of ca.4–10mol%is common.TEMPO is sometimes added in amounts as high as1–1.5equivalents;this may help to prevent side reactions produced by excess of HOCl.22a b 28According to the authors:“Direct oxidation of the primary alcohol to the desired sensitive carboxylic acid was accomplished best using N-oxoammonium salts in combination with NaOCl in a buffered solution(2equivalents of4–6%NaOCl,1.1equivalents of TEMPO,0.1 equivalents of KBr,acetone-5%aqueous NaHCO3 0 C,2h,78%).In the optimization of this reaction it was found that1.1equivalents of TEMPO were necessary to obtain the desired oxidation product.If a catalytic amount(ca.0.1equivalents)of TEMPO was employed or Ca OCl 2was substituted for NaOCl,the chlorinated aromatic derivative was isolated as the major product.Presumably the TEMPO scavenges any chlorine which is liberated during the reaction.”Observe that no phase-transfer catalyst is needed in this reaction performed in asingle acetone–water phase.22aChapter687Phase-Transfer CatalystAlthough no phase-transfer catalyst is needed in oxidations carried out in a single phase—such as in water,MeCN/water,or acetone/water—an ammonium salt such as n-Bu4NCl,29n-Bu4NBr,30n-Bu4NHSO4,19or Aliquat®336(tricapry-lylmethylammonium chloride)31is normally added in oxidations performed in a biphasic CH2Cl2/water mixture.pHCommercial chlorine bleach is prepared by reacting chlorine with an aqueous NaOH solution,and contains ca.3–6%of NaOCl.Excess of NaOH is employed to stabilize the NaOCl,which otherwise would disproportionate into NaCl and NaClO3.This results in bleach possessing a pH between11and13,which is too basic for a normal Anelli’s oxidation.The addition of NaHCO3allows lowering the pH to a value of ca.8.6–10,which is normally ideal for Anelli’s oxidations. Some NaOH is sometimes added additionally to fine tune the pH to a value of ca.10.25 32Figure3shows the influence of pH on the rate of oxidation of methyl -d-glucopyranoside.There is a very sharp increase in speed from pH8 to pH10,while a higher pH produces no further acceleration of reaction speed.The generation of carboxylic acid during the oxidation may cause a lowering of pH that produces a decrease of oxidation speed and of selectivityFigure3.Influence of pH on the rate of oxidation of methyl -D-glucopyranoside using 0.007eq.of TEMPO,2.2eq.of a15%NaOCl solution,and0.4eq.of NaBr at2 C,adding 4M HCl to adjust the pH.6b Reprinted from Carbohydrate Research,Vol.269,Nooy,A.E.J.; Besemer,A.C.;van Bekkum,H.,“Highly selective nitroxyl radical-mediated oxidation of primary alcohol groups in water-soluble glucans,”pages89–98,©1995,with permission from Elsevier.88Anelli’s Oxidation for oxidation of primary alcohols versus secondary ones.This may be avoided by continuous adjustment of the pH by addition of NaOH.21b 33Some functional groups,such as esters,may be sensitive to the mildly basic pH normally used in Anelli‘s oxidations,and in some cases it may be necessary to adjust the precise reaction conditions to avoid interferences.29aThe reaction time must be kept to a minimum to avoid the hydrolysis of the acetate under thebasic reaction conditions.29aIn some cases,Anelli’s oxidation must be carried out under acidic condi-tions to obtain an optimum yield.27In this oxidation the pH is adjusted below7by bubbling CO2into the sodium hypochlorite solution.The reaction fails when it is performed at a pH above7,due tothe sensitivity of propargyl alcohol to NaOCl under basic conditions.It is possible toincrease the yield to50–66%by performing acontinuous oxidation.27SelectivityOne of the most useful features of the oxidation of primary alcohols to carboxylic acids under Anelli’s conditions is the great selectivity achieved for the oxidation of primary alcohols versus secondary ones.8 9b 34This selectivity is the result of the steric hindrance around the oxoammonium functionality in the oxoammonium salts derived from TEMPO-like radicals,resulting in a much easier attack by the relatively less hindered primary alcohols.Chapter689Research neededThe employment of amino oxyl radicals,yielding oxoammonium salts with agreater steric hindrance than those derived from TEMPO-like radicals,in theselective oxidation of primary alcohols must be investigated.Treatment of the starting triol under Anelli’s conditions in water at pH10–11allows the selective oxidation of the primary alcohol in90%.The use of gaseous oxygen in the presence of platinum on carbon under Heyns’conditions provides a more modest50%yield of thedesired carboxylic acid.9aUnder basic conditions there is a compact and sterically demanding five-membered transition state for the oxidation of alcohols with oxoammonium salts, while under acidic conditions a less sterically demanding linear transition state operates.This results in both greater oxidizing speed and greater selectivity for oxidation of primary alcohols under Anelli’s conditions at high pH.Furthermore, under less basic conditions hypohalous acids may compete with oxoammonium salts for the direct oxidation of alcohols6b resulting in even less selectivity. In fact,under acidic conditions the selectivity greatly decreases and secondary alcohols may even be oxidized more rapidly.6aIt is possible to oxidize selectively the two primary alcohols in d-glucitol in89%underAnelli’s conditions at pH11.7,with minor formation of side compounds resulting from incomplete oxidation or oxidative breakage at the secondary alcohols.Lowering of the pH to 10.5produces a much less selective oxidation,resulting in only27%of the desired diacid thatis isolated as the disodium salt.34b90Anelli’s OxidationA primary alcohol is selectively oxidized in a complex molecule containing a secondaryalcohol,using Anelli’s conditions in a CH2Cl2–water biphasic system.266.2.1General Procedure for Oxidation of Primary Alcoholsto Carboxylic Acids by Anelli’s OxidationA mixture of1equivalent of alcohol with ca.0.002–0.1—typically0.01—equivalent of TEMPO(MW156.25),a b ca.1.75–8—typically2—equivalents of NaOCl(MW74.44),c ca.0.1–0.7equivalent of KBr(MW119.01),d and ca.0.05–0.12—typically0.06—equivalent of a phase-transfer catalyst e in a biphasic buffered f g system containing water and CH2Cl2,h is vigorously stirred at0 C i until most of the starting alcohol is consumed.j The reaction mixture is optionally quenched by addition of methanol or ethanol.When the reaction is carried out using a mixture of acetone and water,the removal of acetone in vacuo may facilitate the rest of the workup.The elimination of acetone sometimes causes the crystallization or precipitation of the sodium salt of the acid that can be isolated by filtration.Generally,the remainder of the workup of the reaction can be made according to three alternative protocols: Workup A:The reaction mixture is optionally washed with an organic solvent like Et2O or CH2Cl2.When the product—even as a sodium carboxylate—is very lipophilic,it may be convenient to adjust the pH above 12by the addition of concentrated NaOH before the washing with an organic solvent.The pH is brought to ca.2–6by the addition of hydrochloric acid or10%aqueous citric acid.WARNING:this may cause the evolution of poisonous chlorine gas.The mixture is extracted with an organic solvent like EtOAc or CH2Cl2.The collected organic phases can be optionally washed with water or brine.The organic phase is dried with Na2SO4or MgSO4and concentrated,giving a crude acid that may need further purification.This workup may not be suitable for products like many sugars,possessing a very low solubility in organic solvents.The acidification sometimes causes the precipitation or crystallization of the acid that can be isolated by simple filtration.Alternatively,in the case of organic acids with a high solubility in water,the precipitation of the organic acid from an acidic aqueous phase may be induced sometimes by addition of an organic solvent miscible with water such as ethanol.Workup B:The reaction mixture is fractioned between EtOAc and water.The organic phase is separated and can be optionally washed withChapter691 water,10%HCl,or brine.The organic phase is dried with Na2SO4or MgSO4 and concentrated,giving a crude acid that may need further purification. This workup is suitable for lipophilic organic acids possessing a very low solubility in water even when present as sodium salts.Workup C:The reaction mixture is optionally neutralized by the addition of hydrochloric acid.The solvent is removed either by concentration at reduced pressure or lyophilization.The resulting residue containing the desired acid—either free or as a sodium salt contaminated with inorganic salts—is purified by chromatography.a Other TEMPO derivatives such as4-AcO-TEMPO(MW214.28),4-HO-TEMPO(MW172.24),or4-AcNH-TEMPO(MW213.30)are equally effective.b A quantity as high as1–1.5equivalents of TEMPO is sometimes employed in order tomitigate some side reactions induced by the stoichiometric oxidant,such as unwanted chlorinations.22a b 28c Sodium hypochlorite is sold as a ca.3–13%aqueous solution(chlorine bleach)containingsome NaOH to provide a pH of11–13,which helps to stabilize the reagent against dispro-portionation in NaCl and NaClO3.Household bleach is perfectly effective.d KBr is added to generate HOBr,which is a more effective secondary oxidant than HOCl.Failure to add KBr leads to a slower oxidation that nevertheless may prove useful.NaBr is equally effective.e Quaternary ammonium salts such as n-BuNCl(MW277.9),29n-Bu4NBr(MW322.37),304n-Bu4NHSO4(MW339.53),19or Aliquat®336(tricaprylylmethylammonium chloride,MW 404.17)31are used as phase-transfer catalysts.Failure to add a phase-transfer catalyst results in a much slower reaction that may lead to isolation of aldehyde.No phase-transfer catalyst is needed when the oxidation is performed in a monophasic system.f The addition of bleach causes the mixture to reach a very basic pH that may prove detrimentalfor many substrates.Thus,although the oxidation velocity increases under basic conditions, the pH is normally lowered to ca.8.5–10in order to attain a good balance of oxidation speed versus base-induced deleterious side reactions.The optimum pH is very substrate dependent.When the selective oxidation of a primary alcohol in the presence of a secondary one is desired,a pH as high as11.7may be advisable.34b On the other hand,in oxidations occurring in the presence of esters the pH must be lowered to8–9to avoid unwanted hydrolysis.g The pH is normally lowered to8.6–10by the addition of an aqueous solution of NaHCO3 possessing a concentration between5%and saturation.A higher pH can be adjusted by the subsequent addition of aqueous NaOH.A final fine tuning of the pH can require the addition of some HCl.A phosphate buffer is sometimes used.The formation of carboxylic acid in the course of the oxidation leads to lowering of pH as the reaction proceeds,causing a decrease in the oxidation rate.This can be avoided by the sequential addition of some aqueous NaOH.h A ca.7:2to3:5water:CHCl2mixture is normally employed.Normally,ca.15–60mL of2solvent mixture is used per mmol of alcohol.Sometimes,ca.2–19mL of brine per mmol of alcohol is also added.The reaction can also be performed in a monophasic system consisting of water,water:acetone(ca.3:4to7:4),or water:MeCN(ca.29:26to9:5).In a water:CH2Cl2 biphasic system the oxidation takes place in the organic phase,therefore,this system is very suitable for lipophilic substrates but fails in substrates—like most sugars—possessing a high solubility in water.In such cases the oxidation is best carried out in water or in a monophasic solvent mixture.92Anelli’s Oxidation i The primary oxidants,which consist of oxoammonium salts,are very quickly decomposedby water at room temperature,leading to an actual decrease of oxidation rate with increasing temperature.Therefore,the reaction temperature must be kept close to0 C during the mixing of the reagents as soon as oxoammonium salts are generated.This may demand the slow addition of some reagents.j It normally takes between30minutes and20hours.An attempted oxidation using Jones reagent resulted in extensive decomposition due to the acid-sensitivity of the spiro system.The employment of Anelli’s oxidation under mildly basic conditions allowed the isolation of the desired acid in very good yield.31aAccording to the authors:“Oxidation of the hydroxymethyl function to a carboxylic acid, without simultaneous oxidation of the benzyl to a benzoyl group,proved to be a challenging problem.Neither pyridinium dichromate in dimethylformamide nor Jones oxidation gave the desired product in acceptable yield.Oxidation with ruthenium tetraoxide predictably gave a mixture of the benzyl-and the benzoylepoxy acids.The problem was overcome by oxidation with hypochlorite in the presence of catalytic amounts of oxoammonium salt generated from 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO,free radical).The product,(2R,3R)-3-(benzyloxy)methyloxirane-2-carboxylic acid,was obtained in excellent yield(88%)andhigh purity.”31bAccording to the authors:“Problems were encountered in the attempted oxidation of theprimary alcohol to a carboxylic acid.After screening of various oxidation methods,theoxoammonium salt mediated oxidation using a couple TEMPO-NaOCl was selected for further optimization.Chlorination of the electron-rich aromatic ring was found to be the major side reaction.However,when the reaction temperature was carefully maintained between −5 C and0 C,the desired acid was obtained in good yield.”35Chapter693This oxidation under Anelli’s conditions in which a quantity of TEMPO as high as1.06equivalents is utilized,probably to avoid side reactions,proved to be superior than thePDC/DMF system.22bIn this remarkable transformation,a total of21primary alcohols in one molecule are oxidized to carboxylic acids in a94%yield,which means that each individual alcohol oxidation isperformed in greater than99.7%yield.326.3.Zhao’s Modification of Anelli’s OxidationIn1999,Zhao et al.published4a variation of Anelli’s procedure for the transfor-mation of primary alcohols into carboxylic acids,in which side reactions induced by the presence of sodium hypochlorite were lessened by using this reagent in catalytic rather than stoichiometric quantity.In this modified procedure sodium chlorite NaClO2 is employed as stoichiometric oxidant,which serves both to regenerate NaOCl and to operate as the primary oxidant36for the transformation of the intermediate aldehyde into carboxylic acid.The mechanism represented in the following scheme indicates the catalytic cycles in this oxidation:94Zhao’s Modification of Anelli’s OxidationInterestingly,there is no need for sodium chlorite to regenerate directly NaOCl by oxidation of NaCl,because as soon as some aldehyde is formed,the aldehyde is very quickly oxidized by sodium chlorite resulting in the formation of NaOCl.Thus,NaOCl is in fact regenerated via oxidation of the aldehyde.If the reaction is carried out in the absence of added NaOCl,there is a long induction period during which NaClO2 generates the aldehyde in a very inefficient way.Once some aldehyde is formed, it is very quickly oxidized by NaClO2,resulting in the formation of NaOCl that is very efficient in the generation of an N-oxoammonium salt,resulting in a very quick acceleration of the whole oxidation.Zhao et al.optimized the reaction conditions seeking to minimize unwanted chlorinations rather than increasing the oxidation speed.This resulted in an oxidation protocol involving the simultaneous addition of NaClO2and catalytic NaOCl in the form of dilute bleach to a stirred mixture kept at35 C,containing the alcohol,acetonitrile,an aqueous phosphate buffer at pH6.7,and catalytic TEMPO.WARNING:sodium chlorite and bleach must not be mixed before being added to the reaction,because the resulting mixture is unstable.Subse-quent authors tended to follow very closely the original oxidation protocol of Zhao et al.Zhao’s modification of Anelli’s oxidation is reported4to give generally better yields of carboxylic acids than the original Anelli’s procedure. WARNING:Zhao’s procedure involves the use of stoichiometric NaClO2,which is a very powerful oxidant that can explode in the presence of organic matter. Therefore,Zhao’s procedure must be employed,particularly on a big scale,only on substrates for which it proves to be clearly superior.6.3.1General Procedure for Oxidation of Primary Alcoholsto Carboxylic Acids by Zhao’s Modification of Anelli’sOxidationWARNING:NaClO2and NaOCl must not be mixed before being added to the reaction because the resulting mixture is unstable.Approximately,from2to5—typically2—equivalents of aqueous ca.1.1–2M NaClO2(MW90.44)a and ca.0.02–0.32—typically0.02—equivalent of NaOCl(MW74.44)contained in ca.0.28–0.65%—typically0.30%—bleach b are slowly c added over a vigorously stirred mixture,kept at a certain temperature between room temperature and45 C,d typically35 C,containing 1equivalent of the alcohol,ca.0.07–0.125—typically0.1—equivalent of TEMPO(MW156.25),acetonitrile,e and a phosphate buffer at pH6.6–6.8.f g The resulting mixture is stirred at a certain temperature between35and50 C until most of the starting alcohol is consumed.hThe reaction mixture is cooled to room temperature.At this point the addition of some(cold)water may help to carry out the rest of the workup.。
TEMPO选择性氧化对纤维形态及成纸性能的影响
摘要 ：通过 2，2，6，6- 四甲基哌啶氧化物自由基（TEMPO）/NaClO/NaBr 混合氧化体系在碱性条件下对漂白桉木
浆进行选择性氧化，制备了不同羧基含量的氧化纸浆。用光学显微镜观察氧化前后纤维形态，未发现明显变化。将
TEMPO 氧化纸浆与未氧化桉木原浆按比例配抄，研究氧化浆的羧基含量及氧化浆添加量对成纸强度性能的影响。
22
2010 年 10 月 第29卷 第 10 期
试验研究
浆在水中分散，分散浓度为 2.0%， 向 其 中 加 入 TEMPO 和 NaBr， TEMPO 用 量 0.1mmol.g-1（绝 干 浆），NaBr 用 量 1mmol.g-1（绝 干 浆），分散均匀后调节体系的 pH 为 10.0，逐滴加入 9% 的 NaClO 溶 液，并用 0.1mol.L-1 NaOH 控制体 系 pH 为 10±0.1，控 制 NaClO 的 用量，制备不同羧基含量的桉木氧 化浆，氧化浆料经洗涤后备用。 1.3.2 氧 化 纸 浆 羧 基 含 量 的 测 定
改善纸页性质及其纸张的回收性
能等。本文对漂白蝴蝶桉木浆在
TEMPO/NaClO/NaBr 体系中进行 催化氧化，制备了不同羧基含量的 氧化纸浆，将不同氧化程度的氧化 纸浆与桉木原浆按比例配抄，研究 氧化浆用量和氧化浆中羧基含量 对成纸强度性能的影响。
1 实验
1.1 原料与试剂
纸 浆，蝴 蝶 桉 木 漂 白 浆， TEMPO，次 氯 酸 钠（分 析 纯）， 溴 化 钠（分 析 纯），PAE， （固 含 量 12.9%），CPAM，阳离子淀粉 （catosize 380）。
结果表明 ：紧度未因氧化浆的加入而明显变化 ；纸张的抗张指数、耐破指数随氧化浆添加量及氧化浆中羧基含量的
tempo氧化纳米纤维素的的制备与表征
导言1.1 研究背景在材料科学领域，纳米纤维素作为一种重要的纳米材料，具有广泛的应用前景。
它不仅具有天然纤维素的优良性能，如高强度、高韧性，还具有纳米材料的独特性质，如高比表面积、可调控的孔径结构等。
制备和表征纳米纤维素的方法备受关注。
1.2 研究意义tempo氧化纳米纤维素是一种常见的纳米纤维素材料，其制备过程及表征方法对于相关领域的研究具有重要意义。
通过深入了解tempo氧化纳米纤维素的制备与表征方法，可以为材料科学领域的研究和应用提供重要的参考和指导。
2. tempo氧化纳米纤维素的制备2.1 材料及试剂准备制备tempo氧化纳米纤维素的首要步骤是准备所需的材料和试剂。
通常情况下，项目包括纤维素原料、tempo氧化剂、辅助剂等。
2.2 制备方法制备tempo氧化纳米纤维素的常用方法包括氧化-还原法、溶剂交换法、机械处理法等。
其中，氧化-还原法是一种较为常见的方法，其步骤主要包括氧化反应、还原反应和纤维素的再结晶。
2.3 影响因素制备tempo氧化纳米纤维素的过程中，存在多种影响因素，如温度、反应时间、氧化剂浓度、pH值等。
这些因素对产品的纳米纤维素结构和性能具有重要影响。
3. tempo氧化纳米纤维素的表征3.1 形貌表征通过透射电镜（TEM）、扫描电镜（SEM）等技术对tempo氧化纳米纤维素的形貌进行表征，可以获得其纤维形态、尺寸分布、表面形貌等信息。
3.2 结构表征采用X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）等技术对tempo氧化纳米纤维素的结构进行表征，可以了解其晶体结构、化学键类型、官能团等信息。
3.3 性能表征常用的性能表征方法包括比表面积测定、孔径分布测试、力学性能测试等，这些测试可以揭示tempo氧化纳米纤维素的比表面积、孔径结构、力学性能等重要参数。
4. 结论与展望通过对tempo氧化纳米纤维素的制备与表征方法进行系统归纳和总结，可以得出一些结论性的观点。
也可以对未来的研究方向和应用前景进行展望，为相关领域的研究工作提供参考。
姜黄素通过下调HO-1
姜黄素通过下调HO -1/NQO1保护肝癌模型小鼠*牟海军， 陈幸幸， 刘安安， 张丽， 朱加兴， 金海△（遵义医科大学附属医院消化病医院，遵义医科大学附属医院消化内科，贵州 遵义 563000）［摘要］ 目的：观察姜黄素对N -亚硝基二乙胺（DEN ）联合四氯化碳（CCl 4）诱导的C57BL/6J 小鼠肝癌模型的作用并探索其机制。
方法：取14日龄雄性C57BL/6J 小鼠腹腔注射DEN （25 mg/kg ），随机分成模型组和姜黄素（100、200和400 mg/kg ）给药组，另取同龄雄性小鼠10只作为正常对照组。
模型组和姜黄素给药组从第8周开始灌胃给予10% CCl 4（5 mL/kg ），每周2次；同时，给药组开始灌胃姜黄素，正常对照组灌胃等体积的蒸馏水，每天1次，连续14周。
给药结束后处死小鼠，检测小鼠血清丙氨酸转氨酶（ALT ）和天冬氨酸转氨酶（AST ）活性，观察肝组织病理学变化，检测血红素加氧酶1（HO -1）和NAD （P ）H -醌氧化还原酶1（NQO1）的mRNA 表达水平，以及HO -1、NQO1和Ki67蛋白表达水平。
结果：与正常对照组比较，模型组小鼠体重显著降低（P <0.01），肝脏指数显著增加（P <0.01），血清ALT 和AST 活性显著升高（P <0.01），HO -1和NQO1的mRNA 表达水平无显著差异（P >0.05），HO -1和NQO1蛋白表达水平显著升高（P <0.05），Ki67阳性表达率显著增加（P <0.05）。
姜黄素治疗后，小鼠体重显著升高（P <0.01），肝脏指数无明显变化（P >0.05），癌结节数量显著减少（P <0.05或P <0.01），血清AST 活性显著降低（P <0.01），HO -1和NQO1的mRNA 及蛋白表达水平显著降低（P <0.05），Ki67阳性表达率显著降低（P <0.05）。
R-(-)-扁桃酸的生物合成研究进展
Tetrahedron:Asymmetry,2004,15(2):207-211.
[3]Takahashi E,Nakamichi K,Furui M,et a1.R-(-)-Mandelicacid production from Racemic mandelic acids by pseudomonaspolycolor with asymmetric degrading activity[J].Journal ofFermentation and Bioengineering,1995,79(5):439-442.
3水解酶生物催化合成R-扁桃酸
腈水解酶是一类可以将腈转化成相应酸及氨基的酶。当以扁桃腈为底物时，脂肪族水解酶立体选择性地生成R型扁桃酸，最重要的是其理论动力学反应产物收率为100％。具体作用机制如图4所示。
ATRP法制备以_环糊精为核的两臂PGMA聚合物
1 实验部分
1． 1 仪器与试剂 红外光谱采用 Nicoler 750 红外光谱仪测试，
KBr 压片; 核磁氢谱采用 AVANCE III 核磁共振谱 仪( Bruker Biospin) ，氘岱 DMSO 为溶剂，TMS 为 内标; GPC 采用 Waters 515 测定，THF 为流动相， 流速 1 mL / min．
14
吉林化工学院学报
2011 年
12 mL 的 N，N-二 甲 基 甲 酰 胺 中． 再 依 次 加 入 2． 64 mL ( 20 mmol) 的甲基丙烯酸缩水甘油酯和 0． 031 2 g( 0． 2 mmol) 的 2，2'-联吡啶，通氮气 1 h． 在氮气保护的条件下加入 0． 028 7 g ( 0． 2 mmol) 的溴化亚铜，继续通氮气 0． 5 h，后在 60 ℃ 下反应
得出该聚合物的Mn = 3． 7 × 104 ，Mw = 5． 5 × 104 ， 相对分子质量分布窄，Mw / Mn 为 1． 41．
3结 论
本文首先以 β-环糊精为母体，将其酰溴化，合 成了大分子引发剂 β-环糊精-BIBB． 后在 CuBr /2， 2'-联吡啶催化体系中，采用原子转移自由基聚合 法，引发 GMA 单体聚合，得到分子量分布较窄的以 β-环糊精为核的两臂聚合物 β-环糊精-PGMA，并用 GPC，FT-IR，1 HNMR 对其结构进行了表征．
高羧基含量TEMPO氧化纤维素的制备与表征
收稿日期:２０１８－０３－３０修回日期:２０１８－０７－０２基金项目:国家重点研发计划项目(２０１８ＹＦＤ０６００３０２)ꎻ国家自然科学基金项目(２１７７４０２１ꎬ３１４７０５９８)ꎻ闽江学者奖励计划(ＫＸＮＡＤ００２Ａ)ꎻ福建农林大学校国际科技合作与交流项目(ＫＸＢ１６００２Ａ)ꎮ第一作者简介:吴慧(１９７７－)ꎬ男ꎬ教授ꎬ博士生导师ꎬ从事植物资源化学与新材料研究ꎮＥｍａｉｌ:ｗｕｈｕｉ＠ｆａｆｕ.ｅｄｕ.ｃｎꎮＤＯＩ:１０.１３３２４/ｊ.ｃｎｋｉ.ｊｆｃｆ.２０１９.０１.０１５高羧基含量ＴＥＭＰＯ氧化纤维素的制备与表征吴㊀慧ꎬ汤祖武ꎬ卢生昌ꎬ胡会超ꎬ黄六莲ꎬ陈礼辉(福建农林大学材料工程学院ꎬ福建福州３５０１０８)摘要:为提高２ꎬ２ꎬ６ꎬ６￣四甲基哌啶氧化物(ＴＥＭＰＯ)试剂制备的氧化纤维素的氧化度ꎬ采用ＤＭＡｃ/ＬｉＣｌ体系ꎬ通过两步法制备高羧基含量ＴＥＭＰＯ氧化纤维素ꎮ第一步采用ＤＭＡｃ/ＬｉＣｌ溶解体系破坏纤维素Ⅰ结构来获得纤维素粉末ꎬ第二步利用ＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ体系对纤维素粉末进行ＴＥＭＰＯ氧化ꎬ获得高羧基含量㊁高氧化度的氧化纤维素ꎮ用顶空气相色谱法㊁电导率法㊁傅里叶变换红外光谱(ＦＴＩＲ)㊁核磁分析仪(１３ＣＮＭＲ)和Ｘ射线衍射(ＸＲＤ)对产物的结构进行了表征ꎬＦＴＩＲ和１３ＣＮＭＲ结果表明ＴＥＭＰＯ氧化纤维素制备成功ꎬＸＲＤ分析表明纤维素Ⅰ结构完全被溶剂破坏ꎮ顶空气相色谱法测得ＴＥＭＰＯ氧化纤维素羧基含量高达２.０２ｍｍｏｌ ｇ－１ꎬ电导率法测得氧化度为９７％ꎮ关键词:羧基含量ꎻ纤维素ꎻ氧化度ꎻＴＥＭＰＯ氧化中图分类号:ＴＱ３５２.４文献标识码:Ａ文章编号:２０９６－００１８(２０１９)０１－００８８－０７ＰｒｅｐａｒａｔｉｏｎａｎｄｃｈａｒａｃｔｅｒｉｚａｔｉｏｎｏｆＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｗｉｔｈｈｉｇｈｃａｒｂｏｘｙｌｃｏｎｔｅｎｔＷＵＨｕｉꎬＴＡＮＧＺｕｗｕꎬＬＵＳｈｅｎｇｃｈａｎｇꎬＨＵＨｕｉｃｈａｏꎬＨＵＡＮＧＬｉｕｌｉａｎꎬＣＨＥＮＬｉｈｕｉ(ＣｏｌｌｅｇｅｏｆＭａｔｅｒｉａｌＥｎｇｉｎｅｅｒｉｎｇꎬＦｕｊｉａｎＡｇｒｉｃｕｌｔｕｒｅａｎｄＦｏｒｅｓｔｒｙＵｎｉｖｅｒｓｉｔｙꎬＦｕｚｈｏｕꎬＦｕｊｉａｎ３５０１０８ꎬＣｈｉｎａ)Ａｂｓｔｒａｃｔ:Ｔｏｉｎｃｒｅａｓｅｔｈｅｏｘｉｄａｔｉｏｎｄｅｇｒｅｅｏｆｔｈｅ２ꎬ２ꎬ６ꎬ６￣ｔｅｔｒａｍｅｔｈｙｌｐｉｐｅｒｉｄｉｎｅ￣１￣ｏｘｙｌ(ＴＥＭＰＯ)￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅꎬＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｗｉｔｈｈｉｇｈｏｘｉｄａｔｉｏｎｄｅｇｒｅｅａｎｄｈｉｇｈｃａｒｂｏｘｙｌｃｏｎｔｅｎｔｗａｓｐｒｅｐａｒｅｄｕｓｉｎｇＤＭＡｃ/ＬｉＣｌｓｙｓｔｅｍｂｙａｔｗｏ￣ｓｔｅｐｐｒｏｃｅｓｓｉｎｔｈｉｓｐａｐｅｒ.ＴｈｅｆｉｒｓｔｓｔｅｐｗａｓｔｏｄｅｓｔｒｏｙｔｈｅｃｅｌｌｕｌｏｓｅｃｒｙｓｔａｌⅠｂｙｕｓｉｎｇＤＭＡｃ/ＬｉＣｌｓｙｓｔｅｍｔｏｏｂｔａｉｎａｍｏｒｐｈｏｕｓｃｅｌｌｕｌｏｓｅｐｏｗｄｅｒ.ＴｈｅｓｅｃｏｎｄｓｔｅｐｗａｓｔｏｏｘｉｄｉｚｅｔｈｅｃｅｌｌｕｌｏｓｅｐｏｗｄｅｒｂｙＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ.ＴｈｅＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｗａｓａｎａｌｙｚｅｄｂｙｈｅａｄ￣ｓｐａｃｅｇａｓｃｈｒｏｍａｔｏｇｒａｐｈｙꎬｃｏｎｄｕｃｔｉｍｅｔｒｙꎬＦｏｕｒｉｅｒｔｒａｎｓｆｏｒｍｉｎｆｒａｒｅｄｓｐｅｃｔｒｏｓｃｏｐｙ(ＦＴＩＲ)ꎬｎｕｃｌｅａｒｍａｇｎｅｔｉｃ(ＮＭＲ)ꎬＸ￣ｒａｙｄｉｆｆｒａｃｔｉｏｎ(ＸＲＤ).ＲｅｓｕｌｔｓｏｆＦＴＩＲａｎｄＮＭＲｓｈｏｗｅｄｔｈａｔｔｈｅＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｗａｓｐｒｅｐａｒｅｄｓｕｃｃｅｓｓｆｕｌｌｙ.ＸＲＤａｎａｌｙｓｉｓｓｈｏｗｅｄｔｈａｔｔｈｅｃｒｙｓｔａｌｌｉｎｅｒｅｇｉｏｎｏｆｃｅｌｌｕｌｏｓｅⅠｗａｓｃｏｍｐｌｅｔｅｌｙｄｅｓｔｒｏｙｅｄｂｙｔｈｅｓｏｌｖｅｎｔ.Ｔｈｅｃａｒｂｏｘｙｌｃｏｎｔｅｎｔｍｅａｓｕｒｅｄｂｙｈｅａｄｓｐａｃｅｇａｓｃｈｒｏｍａｔｏｇｒａｐｈｙｗａｓｕｐｔｏ２.０２ｍｍｏｌ ｇ－１ꎬａｎｄｔｈｅｏｘｉｄａｔｉｏｎｄｅｇｒｅｅｍｅａｓｕｒｅｄｂｙｃｏｎｄｕｃｔｉｍｅｔｒｙｔｉｔｒａｔｉｏｎｗａｓ９７％.Ｋｅｙｗｏｒｄｓ:ｃａｒｂｏｘｙｌｃｏｎｔｅｎｔꎻｃｅｌｌｕｌｏｓｅꎻｏｘｉｄａｔｉｏｎｄｅｇｒｅｅꎻＴＥＭＰＯｏｘｉｄａｔｉｏｎ纤维素是自然界中最为丰富的天然高分子ꎬ是一种绿色环保的可再生资源ꎮ纤维素因来源丰富㊁价格低廉㊁可再生㊁且具有生物可降解性及生物相容性等而被广泛地应用在材料㊁化工㊁食品㊁医药㊁环境等领域[１]ꎮ进一步有效利用纤维素ꎬ对纤维素进行功能化改性[２－９]ꎬ开发具有高附加值和高性能的纤维素基产品成为国内外研发的重点ꎮ氧化纤维素作为一种纤维素衍生物ꎬ具有无毒无害㊁良好的生物相容性和生物可降解性等优点ꎬ已被广泛用在医疗㊁化工和材料等领域[１０－１１]ꎮ通常有两种方法来制备氧化纤维素[１２]:非选择性氧化和选择性氧化ꎮ非选择性氧化可同时氧化伯羟基和仲羟基ꎬ生成醛㊁酮㊁酸等多种基团ꎮ在氧化反应过程中ꎬ伴有多种副反应ꎬ分子链剧烈降解ꎬ不能有效控制氧化度和降解度ꎻ选择性氧化只单独氧化纤维素分子链上的伯羟基或仲羟基ꎬ可有效地减少副反应ꎮ选择性氧化纤维素的主要方法有氧化氮类体系氧化法[１３－１４]㊁高碘酸盐体系氧化法[１５]㊁ＴＥＭＰＯ氧化法[１６－１７]等ꎮＹＡＥＫＥＬｅｔａｌ[１３]在气相ＮＯ２条件下研究了纤维素Ｃ６位上选择性氧化ꎮ氧化纤维素因含氮而呈现黄到棕色ꎬ产物高度降解ꎬ氧化反应速度慢ꎮｄｅＮＯＯＹｅｔａｌ[１４]以ＮａＮＯ３作为氧化剂ꎬＮａＮＯ２作催化剂ꎬ在磷酸溶液中氧化纤维素ꎮ虽然Ｃ６位９５％以上的伯羟基被氧化成羧基ꎬ但Ｃ２和Ｃ３位上也有１０％~２０％的仲羟基被氧化成酮基ꎮＪＡＣＫＳＯＮｅｔａｌ[１５]用高碘酸钠溶液氧化棉纤维素来制备双醛纤维素ꎬ森林与环境学报㊀２０１９ꎬ３９(１):８８－９４第３９卷第１期ＪｏｕｒｎａｌｏｆＦｏｒｅｓｔａｎｄＥｎｖｉｒｏｎｍｅｎｔ２０１９年１月但此体系会破坏纤维素的主链结构ꎮ而ＴＥＭＰＯ氧化法可选择性氧化纤维素Ｃ６位上的伯羟基制备单羧基纤维素ꎬ具有污染小㊁条件温和㊁成本低㊁操作简单等优点ꎬ引起人们广泛地关注[１６－２９]ꎮＩＳＯＧＡＩｅｔａｌ[１８－２２]用ＴＥＭＰＯ/ＮａＣｌＯ２/ＮａＣｌＯ体系氧化阔叶木纤维素制备了ＴＥＭＰＯ氧化纤维素ꎮ当氧化纤维素羧基含量为０.７８ｍｍｏｌ ｇ－１时ꎬ可在水中解离成宽度为５ｎｍꎬ长度不低于２μｍ的高结晶度的纳米纤维[１８]ꎮ羧基含量在１.０９~１.４５ｍｍｏｌ ｇ－１的氧化纤维素可制成医用可吸收止血纱布ꎬ应用于手术治疗及整形外科手术中[２３]ꎮ但是制备医用品对氧化纤维素的羧基含量具有一定的要求ꎻ若羧基含量过低ꎬ不足以制备具有止血等功能的医药试剂[３０－３１]ꎮ因此ꎬ高羧基含量的氧化纤维素有利于其在水溶液中的分散或溶解ꎬ有利于其作为中间体进行进一步改性制备高附加值的产品ꎬ有助于其在膜材料㊁胶黏材料㊁复合材料㊁医疗用品等方面的应用ꎮ在目前的文献报道中ꎬ盐酸水解产生的ＴＥＭＰＯ氧化的囊泡晶须的最大氧化度约为１０％[３２]ꎮ将云杉木粉中的木质素去除后ꎬ通过ＴＥＭＰＯ氧化和超声波处理所制备的超薄纤维素微纤维的氧化度为５０％[３３]ꎮ本课题组[２９]曾将纤维素用ＮａＯＨ/尿素溶解ꎬ制备了氧化度为９１％的ＴＥＭＰＯ氧化纤维素ꎮ为了进一步提高ＴＥＭＰＯ氧化纤维素的氧化度ꎬ本研究以纤维素为原料ꎬ采用ＤＭＡｃ/ＬｉＣｌ溶解体系破坏纤维素Ⅰ结构来获得低结晶度的纤维素粉末ꎬ利用ＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ体系对纤维素粉末进行ＴＥＭＰＯ氧化ꎬ获得氧化度高达９７％的氧化纤维素ꎮ１㊀材料与方法１.１㊀试验原料竹溶解浆板(原纤维素)是由四川天竹竹资源开发有限公司提供ꎮ纸浆中的α￣纤维素㊁半纤维素和灰分的含量分别为９４.５％㊁５.２％和０.１％ꎮ凝胶渗透色谱法测定的重均分子量为１４１０００ꎬ数均分子量为５６０００ꎮ分析纯的２ꎬ２ꎬ６ꎬ６￣四甲基哌啶氧化物(ＴＥＭＰＯ)㊁次氯酸钠(ＮａＣｌＯ)㊁溴化钠(ＮａＢｒ)㊁氢氧化钠(ＮａＯＨ)㊁ＮꎬＮ￣二甲基乙酰胺(ＤＭＡｃ)㊁氯化锂(ＬｉＣｌ)㊁碳酸氢钠(ＮａＨＣＯ３)㊁盐酸(ＨＣｌ)㊁乙醇(Ｃ２Ｈ５ＯＨ)和氯化钠(ＮａＣｌ)购自中国天津国药集团化学试剂有限公司ꎮ１.２㊀ＴＥＭＰＯ氧化纤维素的制备高氧化度ＴＥＭＰＯ氧化纤维素采用两步法制备:第一步ꎬ将纤维素Ⅰ中的氢键用ＤＭＡｃ/ＬｉＣｌ溶解体系破坏ꎬ获得较低结晶度的纤维素粉末ꎬ第二步ꎬ通过ＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ氧化体系将羟甲基高度选择性氧化成羧基ꎮ在ＴＥＭＰＯ氧化过程中ꎬＮａＣｌＯ是主要的氧化剂ꎮ每消耗２ｍｏｌＮａＣｌＯꎬ１ｍｏｌ羟甲基转化为１ｍｏｌ羧酸盐基团[１６]ꎮ理论上每克纤维素需要使用１２.３ｍｍｏｌＮａＣｌＯ才能将羟甲基氧化成羧基ꎬ而本实验中ＮａＣｌＯ的用量为２５.５ｍｍｏｌꎬ比理论剂量要高很多ꎮ因此ꎬ本研究使用足够剂量的ＮａＣｌＯ来保证高氧化度ＴＥＭＰＯ氧化纤维素的制备ꎮＴＥＭＰＯ氧化纤维素的制备条件如下:将８０ｇＬｉＣｌ溶于１ＬＤＭＡｃ中ꎬ加入５ｇ竹纤维素并加热至１００ħ搅拌２ｈꎬ再常温搅拌１２ｈ制得０.５％的纤维素溶液[３４]ꎮ将此溶液在８０００ｒ ｍｉｎ－１的转速下常温离心１５ｍｉｎ移除少量不溶物得到透明纤维素溶液ꎮ将２０Ｌ超纯水逐滴滴入到纤维素溶液中并剧烈搅拌ꎬ过滤ꎬ冷冻干燥３ｄ得ＤＭＡｃ/ＬｉＣｌ处理的纤维素ꎮ将４.８ｇ处理后的纤维素放到５００ｍＬ超纯水中ꎬ搅拌使其完全分散ꎮ加入０.１６ｇＴＥＭＰＯ试剂和１２.７０ｇＮａＢｒꎬ用０.１ｍｏｌ Ｌ－１ＮａＯＨ溶液控制体系的ｐＨ值为１０左右(ｐＨ计检测)ꎮ待ＴＥＭＰＯ试剂完全溶解后ꎬ加入１１４ｍＬ质量分数为８％的ＮａＣｌＯ溶液进行ＴＥＭＰＯ氧化反应ꎮ反应过程中用０.１ｍｏｌ Ｌ－１ＮａＯＨ溶液维持体系的ｐＨ值在１０ʃ０.１ꎬ直到ｐＨ值不再变化ꎮ用５ｍＬ无水乙醇终止反应ꎮ先将此混合液转移到透析袋于超纯水中透析３ｄꎬ冷冻干燥后得到ＤＭＡｃ/ＬｉＣｌ处理的氧化纤维素ꎮ作为对比实验ꎬ采用ＴＥＭＰＯ体系直接将纤维素进行氧化ꎬ以获得直接ＴＥＭＰＯ氧化的纤维素ꎮ反应条件如下:将４.８ｇ竹纤维素加到５００ｍＬ水中ꎬ使其完全分散ꎮ加入０.１６ｇＴＥＭＰＯ㊁１２.７０ｇＮａＢｒ和１１４ｍＬ质量分数为８％ＮａＣｌＯ溶液在ｐＨ＝１０ʃ０.１反应６ｈꎮ将样品透析并冷冻干燥后获得直接ＴＥＭＰＯ氧化纤维素[２１ꎬ２９]ꎮ ９８ ㊀第１期吴慧ꎬ等:高羧基含量ＴＥＭＰＯ氧化纤维素的制备与表征１.３㊀表征与测试方法１.３.１㊀羧基含量的测定㊀准确称取０.０５４０ｇ已完全酸化的样品ꎬ置于容积为２０ｍＬ的顶空测试瓶中ꎮ加入４.０ｍＬ浓度为０.０８ｍｏｌ Ｌ－１ＮａＨＣＯ３溶液ꎮ摇晃测试瓶ꎬ使样品充分分散ꎬ进行顶空气相色谱测试ꎬ记录二氧化碳气相色谱峰的面积(Ａ)ꎮ校正系数的确定:在一组加有４.０ｍＬ浓度为０.０８ｍｏｌ Ｌ－１ＮａＨＣＯ３溶液的密封顶空样品瓶中分别加入０㊁１０㊁２０㊁３０㊁４０㊁５０μＬ浓度为０.０１ｍｏｌ Ｌ－１的盐酸溶液(重复３次)ꎬ进行顶空气相色谱检测并分别得到它们色谱图信号的峰面积ꎮ再以顶空样品瓶中所加入盐酸的绝对量(ｍｏｌ)为横坐标ꎬ以所得到相应色谱图信号的峰面积为纵坐标ꎬ绘制标准曲线ꎬ所得标准曲线的斜率即为校正系数ｋꎮ通过公式(１)计算羧基含量[３５]:ＣＣＯＯＨ＝Ａ－Ａ０ｋｍ(１)式中:ＣＣＯＯＨ为待测样品中羧酸基团的含量(ｍｍｏｌ ｇ－１)ꎻＡ为添加样品后检测到的二氧化碳信号峰面积ꎻＡ０为未添加样品时检测到的二氧化碳信号峰面积ꎻｋ为校正常数(ｍｍｏｌ－１)ꎻｍ为样品的绝干质量(ｇ)ꎮ１.３.２㊀氧化度的测定㊀氧化度(ｄｅｇｒｅｅｏｆｏｘｉｄａｔｉｏｎꎬＤＯ)为已被氧化的羟甲基基团的数量与总羟甲基基团数量的比值ꎮ电导滴定法的测定如下:５０ｍｇ纤维素样品完全分散在１５ｍＬ浓度为０.０１ｍｏｌ Ｌ－１ＨＣｌ溶液中ꎬ搅拌１０ｍｉｎ后ꎬ用０.００５ｍｏｌ Ｌ－１ＮａＯＨ溶液进行滴定ꎬ同时通过电导测定仪记录体系中电导率的变化ꎬ当溶液ｐＨ＝１１ꎬ测定终止ꎮ采用公式(２)计算氧化度[３２ꎬ３６]:ＤＯ＝１６２Ｃ(Ｖ２－Ｖ１)ｍ－３６Ｃ(Ｖ２－Ｖ１)ˑ１００％(２)式中:Ｃ为ＮａＯＨ溶液浓度(ｍｏｌ Ｌ－１)ꎻＶ２为对应于样品溶液总酸体积所消耗ＮａＯＨ溶液的量(ｍＬ)ꎻＶ１为对应于样品溶液ＨＣｌ溶液体积所消耗ＮａＯＨ溶液的量(ｍＬ)ꎻｍ为样品的绝干质量(ｍｇ)ꎮ１.３.３㊀ＦＴＩＲ分析㊀将ＴＥＭＰＯ氧化纤维素样品酸化ꎬ采用ＫＢｒ压片法在红外光谱仪(ＢＲＵＫＥＲＴＥＮＳＯＲⅡꎬＫａｒｌｓｒｕｈｅ)上测定样品的红外吸收谱图ꎮ样品与ＫＢｒ的质量比为１ʒ１００ꎬ扫描次数为６４次ꎬ测量波长范围为４０００~４００ｃｍ－１ꎮ１.３.４㊀１３ＣＮＭＲ分析㊀用核磁(ＡｖａｎｃｅⅢ５００ꎬＢｒｕｋｅｒ)对不同样品进行分析ꎬ操作条件是４ｍｍ魔角探头ꎬ转速５ｋＨｚꎬ脉冲宽度９０ꎬ交叉极化时间０.０５ｓꎬ采样间隔时间１０μｓꎬ接触时间２０００μｓꎬ弛豫时间１ｓꎬ采集数据点８１９２ꎮ１.３.５㊀ＸＲＤ分析㊀用Ｘ射线衍射仪(ＳｈｉｍａｔｚｕｄｉｆｆｒａｃｔｏｍｅｔｅｒꎬＸＲＤ６１００ꎬＫｙｕｓｈｕ)波长０.１５４０５ｎｍ分析不同样品的结晶度ꎬ这仪器是在２０ｋＶ和５ｍＡ条件下操作ꎬ扫描衍射角范围在５ʎ~６０ʎꎮ用结晶度指数(ＩＣｒ)来表示样品的结晶度ꎮ通过公式(３)计算结晶度[３７]:ＩＣｒ＝Ｉ２００－ＩａｍＩ２００ˑ１００％(３)式中:Ｉ２００为２００晶面衍射峰强度(纤维素Ⅰ的２θ＝２２.６ʎꎬ纤维素Ⅱ的２θ＝２１.７ʎ)ꎻＩａｍ为不定性区晶面衍射峰强度(纤维素Ⅰ的２θ＝１９.０ʎꎬ纤维素Ⅱ的２θ＝１６.０ʎ)ꎮ２㊀结果与讨论２.１㊀羧基含量纤维素改性前后的羧基含量通过顶空气相色谱法计算ꎬ其羧基含量如表１所示ꎮ原纤维素和ＤＭＡｃ/ＬｉＣｌ处理的纤维素的羧基含量约为０.０１ｍｍｏｌ ｇ－１ꎬ表明其中存有微量的羧基ꎮ经过ＴＥＭＰＯ氧化后ꎬ直接ＴＥＭＰＯ氧化纤维素的羧基含量为１.２７ｍｍｏｌ ｇ－１ꎬ表明ＴＥＭＰＯ试剂只氧化原纤维素表面上的伯羟基ꎬ并没有进入纤维素Ⅰ晶体的内部ꎬ故用足量的ＮａＣｌＯ也不能直接制备高羧基含量的ＴＥＭＰＯ氧化纤维素ꎮ而ＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素的羧基含量高达２.０２ｍｍｏｌ ｇ－１ꎬ远远大于直接ＴＥＭＰＯ氧化纤维素的羧基含量ꎮ这说明ＤＭＡｃ/ＬｉＣｌ溶解体系破坏了纤维素Ⅰ结晶区ꎬ羟甲基可以充分暴露出来并被ＴＥＭＰＯ试剂氧化ꎬ导致很高的羧基含量ꎮ０９ 森㊀林㊀与㊀环㊀境㊀学㊀报第３９卷㊀表１㊀纤维素改性前后的羧基含量、氧化度和结晶度Ｔａｂｌｅ１㊀Ｃａｒｂｏｘｙｌｃｏｎｔｅｎｔꎬｏｘｉｄａｔｉｏｎｄｅｇｒｅｅａｎｄｃｒｙｓｔａｌｌｉｎｉｔｙｉｎｄｅｘｏｆｃｅｌｌｕｌｏｓｅｂｅｆｏｒｅａｎｄａｆｔｅｒｏｘｉｄａｔｉｏｎ样品Ｓａｍｐｌｅ羧基含量Ｃａｒｂｏｘｙｌｃｏｎｔｅｎｔ/(ｍｍｏｌ ｇ－１)氧化度Ｏｘｉｄａｔｉｏｎｄｅｇｒｅｅ/％结晶度Ｃｒｙｓｔａｌｌｉｎｉｔｙ/％原纤维素Ｐｒｉｓｔｉｎｅｃｅｌｌｕｌｏｓｅ０.０１０.３７１.０ＤＭＡｃ/ＬｉＣｌ处理的纤维素ＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄｃｅｌｌｕｌｏｓｅ０.０１０.３直接ＴＥＭＰＯ氧化纤维素ＤｉｒｅｃｔＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ１.２７５３.０６９.５ＤＭＡｃ/ＬｉＣｌ处理后ＴＥＭＰＯ氧化纤维素ＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ２.０２９７.０２.２㊀氧化度纤维素改性前后的氧化度通过电导滴定曲线来计算ꎮ电导率值和ＮａＯＨ溶液消耗体积如图１所示ꎬ氧化度如表１所示ꎮ通过电导率滴定法测得原纤维素和ＤＭＡｃ/ＬｉＣｌ处理的纤维素的氧化度约为０.３％ꎮ直接ＴＥＭＰＯ氧化纤维素的氧化度为５３.０％ꎮ这说明在ＴＥＭＰＯ氧化过程中ꎬ原纤维素上约为５２.７％的羟甲基被氧化成羧基ꎮＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素的氧化度为９７.０％ꎮ在本研究中ꎬ由于ＤＭＡｃ/ＬｉＣｌ溶解体系破坏了纤维素Ⅰ的晶体结构ꎬＴＥＭＰＯ试剂可以充分与无定形纤维素中的羟甲基反应ꎬ使药剂的可及性提高ꎬ从而可得到高氧化度的ＴＥＭＰＯ氧化纤维素ꎮ电导滴定法结果与顶空气相色谱法计算的结果一致ꎮ(ａ)原纤维素Ｐｒｉｓｔｉｎｅｃｅｌｌｕｌｏｓｅ(ｂ)ＤＭＡｃ/ＬｉＣｌ处理的纤维素ＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄｃｅｌｌｕｌｏｓｅ(ｃ)直接ＴＥＭＰＯ氧化纤维素(ｄ)ＤＭＡｃ/ＬｉＣｌ处理后ＴＥＭＰＯ氧化纤维素ＤｉｒｅｃｔＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ图１㊀氧化度电导滴定曲线Ｆｉｇｕｒｅ１㊀Ｃｏｎｄｕｃｔｉｖｉｔｙｔｉｔｒａｔｉｏｎｃｕｒｖｅｏｆｏｘｉｄａｔｉｏｎｄｅｇｒｅｅ２.３㊀ＦＴＩＲ分析纤维素改性前后的ＦＴＩＲ图如图２所示ꎮ在未氧化纤维素的光谱中[图２(ａ)㊁(ｂ)]ꎬ１０６４ｃｍ－１为纤维素主链骨架Ｃ Ｏ的伸缩振动ꎬ并且不受ＴＥＭＰＯ氧化的影响[３８－３９]ꎮ在图２(ｃ)㊁(ｄ)的１７３０ｃｍ－１处出现了一个新峰ꎬ此峰为Ｃ＝Ｏ伸缩振动ꎮ这表明Ｄ￣葡萄糖单元的羟甲基成功转化为羧基ꎮＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素的Ｃ＝Ｏ的峰强度很强ꎬ而直接ＴＥＭＰＯ氧化纤维素的Ｃ＝Ｏ峰强度弱ꎬ表明ＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素的羧基数量最多ꎬ氧化程度最高ꎮ １９ ㊀第１期吴慧ꎬ等:高羧基含量ＴＥＭＰＯ氧化纤维素的制备与表征２.４㊀１３ＣＮＭＲ分析图３为纤维素及其ＴＥＭＰＯ氧化纤维素的１３ＣＮＭＲ谱图ꎮ在原纤维素(图３ａ)和ＤＭＡｃ/ＬｉＣｌ处理的纤维素(图３ｂ)的碳谱图中ꎬδ１０４.８处为Ｃ１峰ꎬδ７２.３处为Ｃ２峰ꎬδ７４.８处为Ｃ３峰ꎬδ８８.６处为Ｃ４峰ꎬδ８２.５处为Ｃ５峰ꎬδ６４.８处为Ｃ６峰[４０－４２]ꎮ图３ｃ是直接ＴＥＭＰＯ氧化纤维素的碳谱ꎬ可以看出在δ１７４.６处出现了一个新的谱峰ꎮ该峰为Ｃ６ᶄ的羧基峰ꎬ说明原纤维素中有羟甲基氧化为羧基ꎮ同时谱图上还可看见δ６４.８处有Ｃ６峰存在ꎬ说明直接ＴＥＭＰＯ试剂并没有完全氧化Ｃ６上的羟甲基ꎮ图３ｄ是ＤＭＡｃ/ＬｉＣｌ处理ＴＥＭＰＯ氧化纤维素的碳谱ꎬ可知位于δ１７４.６处Ｃ６ᶄ峰强度很大ꎬ而δ６４.８处的Ｃ６峰很弱ꎬ说明原纤维素经过ＤＭＡｃ/ＬｉＣｌ溶解体系处理后ꎬＣ６上羟甲基的氧化程度显著得到了提高ꎮ㊀㊀注:ａ代表原纤维素ꎻｂ代表ＤＭＡｃ/ＬｉＣｌ处理的纤维素ꎻｃ代表直接ＴＥＭＰＯ氧化纤维素ꎻｄ代表ＤＭＡｃ/ＬｉＣｌ处理ＴＥＭＰＯ氧化纤维素ꎮＮｏｔｅ:ａｒｅｐｒｅｓｅｎｔｓｐｒｉｓｔｉｎｅｃｅｌｌｕｌｏｓｅꎻｂｒｅｐｒｅｓｅｎｔｓＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄｃｅｌｌｕｌｏｓｅꎻｃｒｅｐｒｅｓｅｎｔｓｄｉｒｅｃｔＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅａｎｄｄｒｅ￣ｐｒｅｓｅｎｔｓＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ.图２㊀红外光谱图Ｆｉｇｕｒｅ２㊀ＦＴＩＲｓｐｅｃｔｒｕｍ(ａ)原纤维素Ｐｒｉｓｔｉｎｅｃｅｌｌｕｌｏｓｅ(ｂ)ＤＭＡｃ/ＬｉＣｌ处理的纤维素ＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄｃｅｌｌｕｌｏｓｅ(ｃ)直接ＴＥＭＰＯ氧化纤维素(ｄ)ＤＭＡｃ/ＬｉＣｌ处理后ＴＥＭＰＯ氧化纤维素ＤｉｒｅｃｔＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ图３㊀１３ＣＮＭＲ图Ｆｉｇｕｒｅ３㊀１３ＣＮＭＲｓｐｅｃｔｒｕｍ２.５㊀ＸＲＤ分析为了进一步验证两步法处理的效果ꎬ对纤维素氧化前后进行了ＸＲＤ表征ꎬ如图４所示ꎮ在原纤维素的ＸＲＤ曲线(图４ａ)中ꎬ２θ＝１４.８ʎ㊁１６.４ʎ㊁２２.６ʎ和３４.２ʎ处的衍射峰分别为(１１０)㊁(１１０)㊁(２００)和(０４０)晶面峰[４３]ꎬ显示出典型的纤维素Ⅰ型晶体结构[３２]ꎮ图４ｂ为ＤＭＡｃ/ＬｉＣｌ处理的纤维素ꎬ其纤维素 ２９ 森㊀林㊀与㊀环㊀境㊀学㊀报第３９卷㊀衍射峰的位置与原纤维素完全不同ꎬ只在２１ʎ处观测到一个纤维素Ⅱ型的(１１０)/(２００)晶面衍射峰ꎮ但是没法对其结晶度进行估算ꎮ这表明再生后的纤维素的晶型结构发生了变化ꎬ体系中的氢键受到严重破坏ꎬ由Ⅰ型晶体结构转变为Ⅱ型晶体或者无定形结构ꎮ在以前研究中[２９]ꎬ经过ＮａＯＨ/尿素处理的纤维素Ⅱ型的结晶度仍有６３.２％ꎮ这是由于ＮａＯＨ/尿素体系对纤维素的溶解不够完全ꎬ对晶体结构的破坏不够彻底ꎬ而ＤＭＡｃ/ＬｉＣｌ体系能更好地破坏纤维素的结晶区ꎮ在图４ｃ中ꎬ原纤维素被ＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ氧化后ꎬ没有观察到峰位置的变化ꎬ表明纤维素Ⅰ晶体具有显著的抗氧化性ꎮ这是因为原纤维素中氢键排列规整ꎬ结晶度高ꎬ使ＴＥＭＰＯ试剂的可及性降低ꎬ氧化反应难以破坏纤维素Ⅰ的晶体结构[３２]ꎮ图４ｄ是ＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素粉末的衍射图ꎬ除了在２９.５ʎ处存在一个很宽的散射峰外ꎬ很难辨认出结晶衍射峰的存㊀㊀注:ａ代表原纤维素ꎻｂ代表ＤＭＡｃ/ＬｉＣｌ处理的纤维素ꎻｃ代表直接ＴＥＭＰＯ氧化纤维素ꎻｄ代表ＤＭＡｃ/ＬｉＣｌ处理ＴＥＭＰＯ氧化纤维素ꎮＮｏｔｅ:ａｒｅｐｒｅｓｅｎｔｓｐｒｉｓｔｉｎｅｃｅｌｌｕｌｏｓｅꎻｂｒｅｐｒｅｓｅｎｔｓＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄｃｅｌｌｕｌｏｓｅꎻｃｒｅｐｒｅｓｅｎｔｓｄｉｒｅｃｔＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅａｎｄｄｒｅｐｒｅｓｅｎｔｓＤＭＡｃ/ＬｉＣｌ￣ｔｒｅａｔｅｄＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ.图４㊀ＸＲＤ图Ｆｉｇｕｒｅ４㊀Ｘ￣ｒａｙｄｉｆｆｒａｃｔｉｏｎｃｕｒｖｅｓ在ꎬ这表明经过ＤＭＡｃ/ＬｉＣｌ处理的ＴＥＭＰＯ氧化纤维素已经处于无定形状态ꎮ而ＮａＯＨ/尿素处理后ＴＥＭＰＯ氧化纤维素的结晶度是２６.６％[２９]ꎮ由此说明ＤＭＡｃ/ＬｉＣｌ体系能更彻底地破坏原纤维素的结晶区ꎬ使得ＴＥＭＰＯ试剂可以更加充分的进入纤维素内部氧化伯羟基ꎬ提高羧基含量ꎮ３㊀结论采用ＤＭＡｃ/ＬｉＣｌ体系ꎬ通过两步法制备高羧基含量㊁高氧化度的水溶性ＴＥＭＰＯ氧化纤维素ꎮ第一步采用ＤＭＡｃ/ＬｉＣｌ溶解体系破坏纤维素Ⅰ结构来获得低结晶度纤维素粉末ꎬ第二步利用ＴＥＭＰＯ/ＮａＢｒ/ＮａＣｌＯ体系对纤维素粉末进行ＴＥＭＰＯ氧化ꎮＤＭＡｃ/ＬｉＣｌ处理ＴＥＭＰＯ氧化纤维素的羧基含量高达２.０２ｍｍｏｌ ｇ－１ꎬ氧化度高达９７％ꎮ高氧化度的ＴＥＭＰＯ氧化纤维素可应用于医学㊁造纸㊁食品㊁电子产品等领域ꎮ参考文献[１]ＷＡＮＧＳꎬＬＵＡꎬＺＨＡＮＧＬＮ.Ｒｅｃｅｎｔａｄｖａｎｃｅｓｉｎｒｅｇｅｎｅｒａｔｅｄｃｅｌｌｕｌｏｓｅｍａｔｅｒｉａｌｓ[Ｊ].ＰｒｏｇｒｅｓｓｉｎＰｏｌｙｍｅｒＳｃｉｅｎｃｅꎬ２０１６ꎬ５３:１６９－２０６.[２]ＬＩＮＸＸꎬＭＡＷꎬＷＵＨꎬｅｔａｌ.Ｓｕｐｅｒｈｙｄｒｏｐｈｏｂｉｃｍａｇｎｅｔｉｃｐｏｌｙ(ＤＯＰＡｍ￣ｃｏ￣ＰＦＯＥＡ)/Ｆｅ３Ｏ４/ｃｅｌｌｕｌｏｓｅｍｉｃｒｏｓｐｈｅｒｅｓｆｏｒｓｔａｂｌｅｌｉｑｕｉｄｍａｒｂｌｅｓ[Ｊ].ＣｈｅｍｉｃａｌＣｏｍｍｕｎｉｃａｔｉｏｎｓꎬ２０１６ꎬ５２(９):１８９５－１８９８.[３]ＺＨＯＵＸＭꎬＬＩＮＸＸꎬＷＨＩＴＥＫＬꎬｅｔａｌ.Ｅｆｆｅｃｔｏｆｔｈｅｄｅｇｒｅｅｏｆｓｕｂｓｔｉｔｕｔｉｏｎｏｎｔｈｅｈｙｄｒｏｐｈｏｂｉｃｉｔｙｏｆａｃｅｔｙｌａｔｅｄｃｅｌｌｕｌｏｓｅｆｏｒｐｒｏｄｕｃｔｉｏｎｏｆｌｉｑｕｉｄｍａｒｂｌｅｓ[Ｊ].Ｃｅｌｌｕｌｏｓｅꎬ２０１６ꎬ２３(１):８１１－８２１.[４]ＷＵＨꎬＷＵＬＨꎬＬＵＳＣꎬｅｔａｌ.Ｒｏｂｕｓｔｓｕｐｅｒｈｙｄｒｏｐｈｏｂｉｃａｎｄｓｕｐｅｒｏｌｅｏｐｈｉｌｉｃｆｉｌｔｅｒｐａｐｅｒｖｉａａｔｏｍｔｒａｎｓｆｅｒｒａｄｉｃａｌｐｏｌｙｍｅｒｉ￣ｚａｔｉｏｎｆｏｒｏｉｌ/ｗａｔｅｒｓｅｐａｒａｔｉｏｎ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＰｏｌｙｍｅｒｓꎬ２０１８ꎬ１８１:４１９－４２５.[５]徐思佳ꎬ巫龙辉ꎬ卢生昌ꎬ等.纤维素接枝２￣(全氟辛基)乙基甲基丙烯酸酯共聚物的制备和表征[Ｊ].纤维素科学与技术ꎬ２０１６ꎬ２４(３):７－１１.[６]ＬＩＮＸＸꎬＭＡＷꎬＷＵＨꎬｅｔａｌ.Ｆａｂｒｉｃａｔｉｏｎｏｆｃｅｌｌｕｌｏｓｅｂａｓｅｄｓｕｐｅｒｈｙｄｒｏｐｈｏｂｉｃｍｉｃｒｏｓｐｈｅｒｅｓｆｏｒｔｈｅｐｒｏｄｕｃｔｉｏｎｏｆｍａｇｎｅｔｉ￣ｃａｌｌｙａｃｔｕａｔａｂｌｅｓｍａｒｔｌｉｑｕｉｄｍａｒｂｌｅｓ[Ｊ].ＪｏｕｒｎａｌｏｆＢｉｏｒｅｓｏｕｒｃｅｓａｎｄＢｉｏｐｒｏｄｕｃｔｓꎬ２０１７ꎬ２(３):１１０－１１５.[７]李国炜ꎬ林新兴ꎬ汤祖武ꎬ等.ＡＡＯ模板法制备纤维素纳米纤维[Ｊ].纤维素科学与技术ꎬ２０１７ꎬ２５(２):９－１４.[８]ＷＵＨꎬＨＩＧＡＫＩＹꎬＴＡＫＡＨＡＲＡＡ.Ｍｏｌｅｃｕｌａｒｓｅｌｆ￣ａｓｓｅｍｂｌｙｏｆｏｎｅ￣ｄｉｍｅｎｓｉｏｎａｌｐｏｌｙｍｅｒｎａｎｏｓｔｒｕｃｔｕｒｅｓｉｎｎａｎｏｐｏｒｅｓｏｆａｎｏｄｉｃａｌｕｍｉｎａｏｘｉｄｅｔｅｍｐｌａｔｅｓ[Ｊ].ＰｒｏｇｒｅｓｓｉｎＰｏｌｙｍｅｒＳｃｉｅｎｃｅꎬ２０１８ꎬ７７:９５－１１７.[９]黄六莲ꎬ卢生昌ꎬ黄慧华ꎬ等.柑橘渣的阳离子化改性及其对刚果红的吸附性能[Ｊ].森林与环境学报ꎬ２０１８ꎬ３８(３):２６５－２７１.[１０]ＳＡＩＴＯＴꎬＩＳＯＧＡＩＡ.Ａｎｏｖｅｌｍｅｔｈｏｄｔｏｉｍｐｒｏｖｅｗｅｔｓｔｒｅｎｇｔｈｏｆｐａｐｅｒ[Ｊ].ＴａｐｐｉＪｏｕｒｎａｌꎬ２００５ꎬ４(３):３－８.[１１]ＦＯＧＬＡＲＯＶＡＭꎬＰＲＯＫＯＰＪꎬＭＩＬＩＣＨＯＶＳＫＹＭ.Ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅ:ａｎａｐｐｌｉｃａｔｉｏｎｉｎｔｈｅｆｏｒｍｏｆｓｏｒｐｔｉｏｎｆｉｌｔｅｒｍａｔｅｒｉａｌｓ[Ｊ].ＪｏｕｒｎａｌｏｆＡｐｐｌｉｅｄＰｏｌｙｍｅｒＳｃｉｅｎｃｅꎬ２００９ꎬ１１２(２):６６９－６７８.[１２]李琳ꎬ赵帅ꎬ胡红旗.纤维素氧化体系的研究进展[Ｊ].纤维素科学与技术ꎬ２００９ꎬ１７(３):５９－６４. ３９ ㊀第１期吴慧ꎬ等:高羧基含量ＴＥＭＰＯ氧化纤维素的制备与表征４９ 森㊀林㊀与㊀环㊀境㊀学㊀报第３９卷㊀[１３]ＹＡＣＫＥＬＥＣꎬＫＥＮＹＯＮＷＯ.Ｔｈｅｏｘｉｄａｔｉｏｎｏｆｃｅｌｌｕｌｏｓｅｂｙｎｉｔｒｏｇｅｎｄｉｏｘｉｄｅ[Ｊ].ＪｏｕｒｎａｌｏｆｔｈｅＡｍｅｒｉｃａｎＣｈｅｍｉｃａｌＳｏｃｉｅｔｙꎬ１９４２ꎬ６４(１):１２１－１２７.[１４]ｄｅＮＯＯＹＡＥＪꎬＰＡＧＬＩＡＲＯＭꎬＶＡＮＢＥＫＫＵＭＨꎬｅｔａｌ.Ａｕｔｏｃａｔａｌｙｔｉｃｏｘｉｄａｔｉｏｎｏｆｐｒｉｍａｒｙｈｙｄｒｏｘｙｌｆｕｎｃｔｉｏｎｓｉｎｇｌｕｃａｎｓｗｉｔｈｎｉｔｒｏｇｅｎｏｘｉｄｅｓ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＲｅｓｅａｒｃｈꎬ１９９７ꎬ３０４(２):１１７－１２３.[１５]ＪＡＣＫＳＯＮＥＬꎬＨＵＤＳＯＮＣＳ.Ａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅｃｌｅａｖａｇｅｔｙｐｅｏｆｏｘｉｄａｔｉｏｎｂｙｐｅｒｉｏｄｉｃａｃｉｄｔｏｓｔａｒｃｈａｎｄｃｅｌｌｕｌｏｓｅ[Ｊ].ＪｏｕｒｎａｌｏｆｔｈｅＡｍｅｒｉｃａｎＣｈｅｍｉｃａｌＳｏｃｉｅｔｙꎬ１９３７ꎬ５９(１０):２０４９－２０５０.[１６]ｄｅＮＯＯＹＡＥＪꎬＢＥＳＥＭＥＲＡＣꎬＶＡＮＢＥＫＫＵＭＨ.ＨｉｇｈｌｙｓｅｌｅｃｔｉｖｅＴＥＭＰＯｍｅｄｉａｔｅｄｏｘｉｄａｔｉｏｎｏｆｐｒｉｍａｒｙａｌｃｏｈｏｌｇｒｏｕｐｓｉｎｐｏｌｙｓａｃｃｈａｒｉｄｅｓ[Ｊ].ＲｅｃｕｅｉｌＤｅｓＴｒａｖａｕｘＣｈｉｍｉｑｕｅｓＤｅｓＰａｙｓ￣Ｂａｓꎬ１９９４ꎬ１１３(３):１６５－１６６.[１７]ＣＨＡＮＧＰＳꎬＲｏｂｙｔＪＦ.Ｏｘｉｄａｔｉｏｎｏｆｐｒｉｍａｒｙａｌｃｏｈｏｌｇｒｏｕｐｓｏｆｎａｔｕｒａｌｌｙｏｃｃｕｒｒｉｎｇｐｏｌｙｓａｃｃｈａｒｉｄｅｓｗｉｔｈ２ꎬ２ꎬ６ꎬ６￣ｔｅｔｒａｍｅｔｈｙｌ￣１￣ｐｉｐｅｒｉｄｉｎｅｏｘｏａｍｍｏｎｉｕｍｉｏｎ[Ｊ].ＪｏｕｒｎａｌｏｆＣａｒｂｏｈｙｄｒａｔｅＣｈｅｍｉｓｔｒｙꎬ１９９６ꎬ１５(７):８１９－８３０.[１８]ＳＡＩＴＯＴꎬＨＩＲＯＴＡＭꎬＴａｍｕｒａＮꎬｅｔａｌ.Ｉｎｄｉｖｉｄｕａｌｉｚａｔｉｏｎｏｆｎａｎｏ￣ｓｉｚｅｄｐｌａｎｔｃｅｌｌｕｌｏｓｅｆｉｂｒｉｌｓｂｙｄｉｒｅｃｔｓｕｒｆａｃｅｃａｒｂｏｘｙｌａｔｉｏｎｕｓｉｎｇＴＥＭＰＯｃａｔａｌｙｓｔｕｎｄｅｒｎｅｕｔｒａｌｃｏｎｄｉｔｉｏｎｓ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００９ꎬ１０(７):１９９２－１９９６.[１９]ＳＡＩＴＯＴꎬＩＳＯＧＡＩＡ.ＴＥＭＰＯ￣ｍｅｄｉａｔｅｄｏｘｉｄａｔｉｏｎｏｆｎａｔｉｖｅｃｅｌｌｕｌｏｓｅ.Ｔｈｅｅｆｆｅｃｔｏｆｏｘｉｄａｔｉｏｎｃｏｎｄｉｔｉｏｎｓｏｎｃｈｅｍｉｃａｌａｎｄｃｒｙｓｔａｌｓｔｒｕｃｔｕｒｅｓｏｆｔｈｅｗａｔｅｒ￣ｉｎｓｏｌｕｂｌｅｆｒａｃｔｉｏｎｓ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００４ꎬ５(５):１９８３－１９８９.[２０]ＳＡＩＴＯＴꎬＳＨＩＢＡＴＡＩꎬＩＳＯＧＡＩＡꎬｅｔａｌ.ＤｉｓｔｒｉｂｕｔｉｏｎｏｆｃａｒｂｏｘｙｌａｔｅｇｒｏｕｐｓｉｎｔｒｏｄｕｃｅｄｉｎｔｏｃｏｔｔｏｎｌｉｎｔｅｒｓｂｙｔｈｅＴＥＭＰＯ￣ｍｅ￣ｄｉａｔｅｄｏｘｉｄａｔｉｏｎ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＰｏｌｙｍｅｒｓꎬ２００５ꎬ６１(４):４１４－４１９.[２１]ＳＡＩＴＯＴꎬＫＩＭＵＲＡＳꎬＮＩＳＨＩＹＡＭＡＹꎬｅｔａｌ.ＣｅｌｌｕｌｏｓｅｎａｎｏｆｉｂｅｒｓｐｒｅｐａｒｅｄｂｙＴＥＭＰＯ￣ｍｅｄｉａｔｅｄｏｘｉｄａｔｉｏｎｏｆｎａｔｉｖｅｃｅｌｌｕｌｏｓｅ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００７ꎬ８(８):２４８５－２４９１.[２２]ＩＳＯＧＡＩＡꎬＳＡＩＴＯＴꎬＦＵＫＵＺＵＭＩＨ.ＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｎａｎｏｆｉｂｅｒｓ[Ｊ].Ｎａｎｏｓｃａｌｅꎬ２０１１ꎬ３(１):７１－８５. [２３]ＳＡＦＥＲＳＴＥＩＮＬꎬＷＯＬＦＳꎬＫＡＭＰＬꎬｅｔａｌ.Ｐｒｏｃｅｓｓｆｏｒｐｒｅｐａｒｉｎｇａｎｅｕｔｒａｌｉｚｅｄｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｐｒｏｄｕｃｔａｎｄｉｔｓｍｅｔｈｏｄｏｆｕｓｅ[Ｐ].ＵＳ５１３４２２９:１９９２－０７－２８.[２４]杨建校ꎬ章丽萍ꎬ左宋林ꎬ等.ＴＥＭＰＯ氧化法制备氧化纤维素纳米纤维[Ｊ].东北林业大学学报ꎬ２０１１ꎬ３９(３):９６－９８. [２５]戴路ꎬ戴红旗ꎬ袁洋春ꎬ等.ＴＥＭＰＯ氧化体系氧化棉纤维的动力学研究[Ｊ].南京林业大学学报ꎬ２０１１ꎬ３５(２):９３－９８. [２６]ＤＡＩＬꎬＷＡＮＧＢꎬＬＯＮＧＺꎬｅｔａｌ.Ｐｒｏｐｅｒｔｉｅｓｏｆｈｙｄｒｏｘｙｐｒｏｐｙｌｇｕａｒ/ＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｎａｎｏｆｉｂｒｉｌｓｃｏｍｐｏｓｉｔｅｆｉｌｍｓ[Ｊ].Ｃｅｌｌｕｌｏｓｅꎬ２０１５ꎬ２２(５):３１１７－３１２６.[２７]戴磊ꎬ龙柱ꎬ张丹.ＴＥＭＰＯ氧化纤维素纳米纤维的制备及应用研究进展[Ｊ].材料工程ꎬ２０１５ꎬ４３(８):８４－９１. [２８]叶贵超ꎬ卢芸ꎬ殷亚方ꎬ等.ＴＥＭＰＯ氧化和高频超声下埃米级厚度纤维素纳米纤丝的制备[Ｊ].高分子学报ꎬ２０１７ꎬ４:６８３－６９１.[２９]ＴＡＮＧＺＷꎬＬＩＷＹꎬＬｉｎＸＸꎬｅｔａｌ.ＴＥＭＰＯ￣ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｗｉｔｈｈｉｇｈｄｅｇｒｅｅｏｆｏｘｉｄａｔｉｏｎ[Ｊ].Ｐｏｌｙｍｅｒｓꎬ２０１７ꎬ９(９):４２１.[３０]ＧＡＬＧＵＴＰＮ.Ｏｘｉｄｉｚｅｄｃｅｌｌｕｌｏｓｅｍｅｓｈ:Ⅰ.Ｂｉｏｄｅｇｒａｄａｂｌｅｍｅｍｂｒａｎｅｉｎｐｅｒｉｏｄｏｎｔａｌｓｕｒｇｅｒｙ[Ｊ].Ｂｉｏｍａｔｅｒｉａｌｓꎬ１９９０ꎬ１１(８):５６１－５６４.[３１]熊犍ꎬ叶君ꎬ吴奏谦ꎬ等.羧酸纤维素的制备及其抗凝血性能的研究[Ｊ].功能高分子学报ꎬ１９９７ꎬ４(１０):５５９－５６３. [３２]ＨＡＢＩＢＩＹꎬＣＨＡＮＺＹＨꎬＶＩＧＮＯＮＭＲ.ＴＥＭＰＯ￣ｍｅｄｉａｔｅｄｓｕｒｆａｃｅｏｘｉｄａｔｉｏｎｏｆｃｅｌｌｕｌｏｓｅｗｈｉｓｋｅｒｓ[Ｊ].Ｃｅｌｌｕｌｏｓｅꎬ２００６ꎬ１３(６):６７９－６８７.[３３]ＳＵＹꎬＢＵＲＧＥＲＣꎬＭＡＨꎬｅｔａｌ.Ｅｘｐｌｏｒｉｎｇｔｈｅｎａｔｕｒｅｏｆｃｅｌｌｕｌｏｓｅｍｉｃｒｏｆｉｂｒｉｌｓ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２０１５ꎬ１６(４):１２０１－１２０９.[３４]ＺＨＯＮＧＪＦꎬＣＨＡＩＸＳꎬＦＵＳＹ.Ｈｏｍｏｇｅｎｅｏｕｓｇｒａｆｔｉｎｇｐｏｌｙ(ｍｅｔｈｙｌｍｅｔｈａｃｒｙｌａｔｅ)ｏｎｃｅｌｌｕｌｏｓｅｂｙａｔｏｍｔｒａｎｓｆｅｒｒａｄｉｃａｌｐｏｌｙｍｅｒｉｚａｔｉｏｎ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＰｏｌｙｍｅｒｓꎬ２０１２ꎬ８７(２):１８６９－１８７３.[３５]侯庆喜ꎬ柴欣生ꎬ朱俊勇.应用顶空气相色谱测定纸浆纤维的羧基含量[Ｊ].中国造纸ꎬ２００５ꎬ２４(９):５－９. [３６]ＤＡＳＩＬＶＡＰＥＲＥＺＤꎬＭＯＮＴＡＮＡＲＩＳꎬＶＩＧＮＯＮＭＲ.ＴＥＭＰＯ￣ｍｅｄｉａｔｅｄｏｘｉｄａｔｉｏｎｏｆｃｅｌｌｕｌｏｓｅⅢ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００３ꎬ４(５):１４１７－１４２５.[３７]ＳＥＧＡＬＬＣꎬＣＲＥＥＬＹＪꎬＭＡＲＴＩＮＡＥＪꎬｅｔａｌ.ＡｎｅｍｐｉｒｉｃａｌｍｅｔｈｏｄｆｏｒｅｓｔｉｍａｔｉｎｇｔｈｅｄｅｇｒｅｅｏｆｃｒｙｓｔａｌｌｉｎｉｔｙｏｆｎａｔｉｖｅｃｅｌｌｕｌｏｓｅｕｓｉｎｇｔｈｅＸ￣Ｒａｙｄｉｆｆｒａｃｔｏｍｅｔｅｒ[Ｊ].ＴｅｘｔｉｌｅＲｅｓｅａｒｃｈＪｏｕｒｎａｌꎬ１９５９ꎬ２９(１０):７８６－７９４.[３８]ＦＲＩＳＯＮＩＧꎬＢＡＩＡＲＤＯＭꎬＳＣＡＮＤＯＬＡＭꎬｅｔａｌ.Ｎａｔｕｒａｌｃｅｌｌｕｌｏｓｅｆｉｂｅｒｓ:ｈｅｔｅｒｏｇｅｎｅｏｕｓａｃｅｔｙｌａｔｉｏｎｋｉｎｅｔｉｃｓａｎｄｂｉｏｄｅｇｒａ￣ｄａｔｉｏｎｂｅｈａｖｉｏｒ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００１ꎬ２(２):４７６－４８２.[３９]ＺＩＮＩＥꎬＳＣＡＮＤＯＬＡＭꎬＧＡＴＥＮＨＯＬＭＰ.Ｈｅｔｅｒｏｇｅｎｅｏｕｓａｃｙｌａｔｉｏｎｏｆｆｌａｘｆｉｂｅｒｓ.Ｒｅａｃｔｉｏｎｋｉｎｅｔｉｃｓａｎｄｓｕｒｆａｃｅｐｒｏｐｅｒｔｉｅｓ[Ｊ].Ｂｉｏｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ２００３ꎬ４(３):８２１－８２７.[４０]ＢＥＲＴＯＣＣＨＩＣꎬＫＯＮＮＷＩＣＺＰꎬＳＩＧＮＯＲＥＳꎬｅｔａｌ.Ｓｙｎｔｈｅｓｉｓａｎｄｃｈａｒａｃｔｅｒｉｓａｔｉｏｎｏｆｐｏｌｙｇｌｕｃｕｒｏｎａｎ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＰｏｌｙｍｅｒｓꎬ１９９５ꎬ２７(４):２９５－２９７.[４１]ＴＡＨＩＲＩＣꎬＶＩＧＮＯＮＭＲ.ＴＥＭＰＯ￣ｏｘｉｄａｔｉｏｎｏｆｃｅｌｌｕｌｏｓｅ:ｓｙｎｔｈｅｓｉｓａｎｄｃｈａｒａｃｔｅｒｉｓａｔｉｏｎｏｆｐｏｌｙｇｌｕｃｕｒｏｎａｎｓ[Ｊ].Ｃｅｌｌｕｌｏｓｅꎬ２０００ꎬ７(２):１７７－１８８.[４２]ＦＯＬＬＡＩＮＮꎬＭＯＮＴＡＮＡＲＩＳꎬＪＥＡＣＯＭＩＮＥＩꎬｅｔａｌ.Ｃｏｕｐｌｉｎｇｏｆａｍｉｎｅｓｗｉｔｈｐｏｌｙｇｌｕｃｕｒｏｎｉｃａｃｉｄ:ｅｖｉｄｅｎｃｅｆｏｒａｍｉｄｅｂｏｎｄｆｏｒｍａｔｉｏｎ[Ｊ].ＣａｒｂｏｈｙｄｒａｔｅＰｏｌｙｍｅｒｓꎬ２００８ꎬ７４(３):３３３－３４３.[４３]ＴＡＫＡＨＡＳＨＩＹꎬＭＡＴＳＵＮＡＧＡＨ.Ｃｒｙｓｔａｌｓｔｒｕｃｔｕｒｅｏｆｎａｔｉｖｅｃｅｌｌｕｌｏｓｅ[Ｊ].Ｍａｃｒｏｍｏｌｅｃｕｌｅｓꎬ１９９１ꎬ２４(１３):３９６８－３９６９.(责任编辑:卢凤美)㊀㊀。
tempo-mediated_oxidation含义_概述及解释说明
tempo-mediated oxidation含义概述及解释说明1. 引言1.1 概述在有机化学中，氧化反应是一个重要的研究领域。
其中一种被广泛研究和应用的氧化反应方法就是tempo-mediated oxidation。
Tempo是一种指示剂，可以催化某些有机物质的氧化反应。
它在近年来得到了广泛的关注和研究，因为它具有高效、选择性强以及环境友好等优点。
1.2 文章结构本文将首先对tempo-mediated oxidation进行详细阐述，并解释其包括的过程和反应机理。
接下来，将介绍其在有机合成中的应用与意义，并展望未来对于tempo-mediated oxidation进一步研究的方向和前景。
1.3 目的本文旨在全面介绍tempo-mediated oxidation，并深入探讨其涉及的定义、过程解释以及应用与意义。
通过这篇长文，读者将能够全面了解并理解tempo-mediated oxidation在有机合成领域中所扮演的重要角色，并展望其未来可能发展方向。
请继续完成文章“2. 正文”部分。
2. 正文在tempo-mediated oxidation的过程中，Tempo是一种常用的催化剂。
这种催化剂可以有效地将醇氧化成相应的酮或醛。
这个反应在有机合成中具有重要作用，因为它可以实现高效、高选择性和环境友好的氧化转化。
Tempo-mediated oxidation是一步法反应，即将Tempo（2,2,6,6-四甲基-1-哌啶氧化物）与底物一起反应得到产物。
在该反应中，Tempo作为催化剂稳定地存在于反应体系中，并且能够循环使用。
过程解释上来说，tempo-mediated oxidation涉及底物分子与Tempo之间发生氧化还原反应。
首先，Tempo通过与底物分子发生单电子转移形成一个自由基中间体。
然后，在适当条件下，氧气参与到反应中作为氧化剂。
在这个过程中，底物分子失去一个电子并被氧原子取代形成酮或醛产物。
三种不同分子量6-羧基壳聚糖的制备、表征及其溶解性
ＤＯＩ：１０．３９６９／Ｊ．ＩＳＳＮ．１６７２ ７９８３．２０２１．０１．００４三种不同分子量６ 羧基壳聚糖的制备、表征及其溶解性高风坤，陆 蕾，张文婧，程才红，侯文龙 ，杨越冬（河北科技师范学院河北省天然产物活性成分与功能重点实验室，河北秦皇岛，０６６００４）摘要：为确定不同分子量对６ 羧基壳聚糖氧化度的影响及其在乙酸乙酯，乙醇，甲醇，二氯甲烷，苯，水，ＤＭ ＳＯ，ＤＭＦ，０．３ｍｏｌ／ＬＮａＯＨ溶液，０．２ｍｏｌ／Ｌ乙酸溶液，吡啶中的溶解性，采用ＮＯ２氧化法将壳聚糖氧化为分子量分别为５０，２００，１０００ｋｕ的６ 羧基壳聚糖，并用Ｘ射线衍射仪（ＸＲＤ）、场发射扫描电子显微镜（ＦＥＳＥＭ）、傅立叶变换红外光谱仪（ＦＴＩＲ）和差热热重同步分析仪对样品的物相、形貌尺寸、分子结构和化学组成及热稳定性进行了表征与分析。
结果表明：使用ＮＯ２对壳聚糖进行氧化，成功将Ｃ ６位的醇羟基氧化为羧基得到６ 羧基壳聚糖，且壳聚糖分子量越大氧化效果越好，氧化度最高为５４．５４％；引入亲水性羧基后热稳定性相比壳聚糖降低；６ 羧基壳聚糖在水、稀乙酸中完全溶解，在二甲基亚砜（ＤＭＳＯ）、苯、吡啶和ＮａＯＨ溶液中部分溶解。
关键词：壳聚糖；氧化壳聚糖；氧化度；溶解性中图分类号：Ｒ３１８．０８ 文献标志码：Ａ 文章编号：１６７２ ７９８３（２０２１）０１ ００２１ ０７壳聚糖的分子量相对较大，小到数万大到数百万不等，独特的结构和较大的分子量使得其溶解性较差，在水中不溶解，可以溶解于弱酸，在很大程度上限制了它的应用［１，２］。
提高壳聚糖溶解性的方法之一是通过增加亲水性官能团来修饰分子结构。
壳聚糖含有多个羟基（Ｃ ６上的伯羟基和Ｃ ３上的仲羟基）和高活性（Ｃ ２）氨基［３］，可通过不同的方法进行修饰。
国内外研究者已对壳聚糖的氧化进行了大量的探究。
Ｃｏｓｅｒｉ等［４］研究表明，氮氧自由基２，２，６，６ 四甲基哌啶 １ 氧基（ＴＥＭＰＯ）催化氧化还原体系可以氧化脂肪族和芳香族醇，是一种有效的催化体系。
胆甾烷-3-醇及胆甾烷-3-酮的合成研究进展
胆甾烷-3-醇及胆甾烷-3-酮的合成研究进展刘强;龙可栋;李兴;常宏宏;魏文珑【摘要】甾族化合物在生物、医药等诸多方面具有很重要的利用价值.本文在大量文献的基础上对以胆固醇为原料,经还原反应制备胆甾烷-3-醇和以胆甾烷-3-醇为原料经氧化反应制备胆甾烷-3-酮的合成工艺进行了综述,重点对上述合成工艺的催化剂及催化方法进行了阐述,并分析了不同催化剂的优缺点,对今后的研究方向进行了归纳.【期刊名称】《广州化工》【年(卷),期】2011(039)007【总页数】3页(P25-27)【关键词】甾族化合物;胆固醇;胆甾烷-3-醇;胆甾烷-3-酮【作者】刘强;龙可栋;李兴;常宏宏;魏文珑【作者单位】太原理工大学化学化工学院,山西,太原,030024;太原理工大学化学化工学院,山西,太原,030024;太原理工大学化学化工学院,山西,太原,030024;太原理工大学化学化工学院,山西,太原,030024;太原理工大学化学化工学院,山西,太原,030024【正文语种】中文甾族化合物是广泛存在于生物体组织内的一类重要天然有机化合物,如性激素、肾上腺皮质激素、甾醇、胆汁酸、甾体生物碱等均属于此化合物,甾族化合物在结构上的共同点是均为氢化程度不同的 1,2-环戊烯并菲甾核,并且在甾核上一般连有三个侧链。
因目前发现许多甾体化合物具有十分重要的生物学功能,故甾体化合物在有机合成及医药工业中倍受关注。
对甾族化合物的合成研究一直是药物化学及合成化学领域关注的问题之一,甾族化合物可利用丰富的天然资源进行半合成[1]制备,本文重点对以胆固醇为原料合成胆甾烷 -3-醇、胆甾烷 -3-酮进行了综述,反应方程式如下:由于胆固醇中双键的空间位阻很大,使用铜、铝[2]等传统催化剂很难将其还原,且原料与产物的极性与溶解性[3]相似,因此选择合适的催化剂及确定适宜的反应条件是制备胆甾烷 -3-醇的关键问题。
早在1937年BruceW.F.等[4]用氧化铂做催化剂、冰醋酸做溶剂,在常压65～75℃下通氢气反应 2～4 h后,再经过氢氧化钠溶液水解、乙醇重结晶后得到胆甾烷 -3-醇,收率达 75%～85%。
TEMPO 氧化纤维素纳米纤维在膜材料中的研究进展
第38卷 第1期 陕西科技大学学报 V o l.38N o.1 2020年2月 J o u r n a l o f S h a a n x iU n i v e r s i t y o f S c i e n c e&T e c h n o l o g y F e b.2020* 文章编号:2096-398X(2020)01-0115-09T E M P O氧化纤维素纳米纤维在膜材料中的研究进展戴 磊1,2,程 婷1,王 岩1,席香菊1,王晓婉1,王 凡1,华飞果2,童树华2(1.陕西科技大学轻工科学与工程学院,陕西西安 710021;2.浙江金昌特种纸股份有限公司,浙江龙游324404)摘 要:以天然纤维素为原料,采用2,2,6,6-四甲基哌啶-1-氧自由基(T E M P O)催化氧化体系(即T E M P O/N a B r/N a C l O体系)预处理,并结合适当的均质处理可以制备得到纳米纤维素(即T E M P O氧化纤维素纳米纤维,T O C N s),其良好的成膜性及优异的纳米材料特点(如高比表面积,高强度等)使其在膜材料领域具有诸多应用可能,前景广阔.综述了T O C N s在膜材料中的应用情况,其中主要涉及气体阻隔膜㊁过滤膜㊁吸附膜及导电膜等,并对未来的研究发展进行了展望.关键词:纤维素;T E M P O;纳米纤维;膜材料中图分类号:T B324 文献标志码:AT E M P O-o x i d i z e d c e l l u l o s e n a n o f i b e r s i n f i l m m a t e r i a l s:Ar e v i e wD A IL e i1,2,C HE N G T i n g1,WA N G Y a n1,X IX i a n g-j u1,WA N G X i a o-w a n1,WA N GF a n1,HU AF e i-g u o2,T O N GS h u-h u a2(1.C o l l e g e o f B i o r e s o u r c e sC h e m i c a l a n dM a t e r i a l sE n g i n e e r i n g,S h a a n x iU n i v e r s i t y o f S c i e n c e&T e c h n o l o g y,X i'a n710021,C h i n a;2.Z h e j i a n g J i n c h a n g S p e c i a l t y P a p e rC o.,L t d.,L o n g y o u324404,C h i n a)A b s t r a c t:N a n o c e l l u l o s ec a n b e p r e p a r e dv i a2,2,6,6-t e t r a m e t h y l p i p e r i d i n e-1-o x y lr a d i c a l(T E M P O)-m e d i a t e do x i d a t i o no f n a t u r a l c e l l u l o s e,f o l l o w e db y a p p r o p r i a t eh o m o g e n i z a t i o n,a n d t h er e s u l t a n tn a n o c e l l u l o s e i sc a l l e d T E M P O-o x i d i z e dc e l l u l o s en a n o f ib e r s(T O C N s).T O C N s f i n d sv a r i o u sa p p l i c a t i o n s i nf i l ma r e a,d u e t o i t s g o o df i l mf o r m i n gp r o p e r t i e sa n d o u t s t a n d i n g n a n o m a t e r i a l c h a r a c t e r i s t i c s(s u c ha sh i g hs p e c i f i cs u r f a c ea r e aa n ds t r e n g t h).T h i s p a p e r r e v i e w s t h e a p p l i c a t i o n s o fT O C N s i n f i l m s,i n c l u d i n gg a sb a r r i e r f i l m s,f i l t r a t i o n m e m b r a n e s,a d s o r p t i o n f i l m s a n d c o n d u c t i v e f i l m s.O u t l o o k a n d f u t u r e p r o s p e c t s a r e p r o v i d e da sw e l l.K e y w o r d s:c e l l u l o s e;T E M P O;n a n o f i b e r;f i l m*收稿日期:2019-10-05基金项目:国家外国专家局高端外国专家项目(G D T20186100425);陕西省科技厅自然科学基础研究计划项目(2019J Q-784)作者简介:戴 磊(1988-),男,江苏镇江人,副教授,博士,研究方向:生物质功能材料Copyright©博看网 . All Rights Reserved.陕西科技大学学报第38卷0 引言近年来,随着石化资源的不断减少及人们环保意识的提升,天然可再生材料正受到越来越多的关注[1-3].其中,源自植物㊁被囊类动物和细菌的纤维素作为地球上最为丰富的天然高分子,被视作未来材料的重要选择[4-7].天然纤维素经物理㊁化学或生物等方法处理可制成纳米尺寸纤维,即纳米纤维素[8,9].纳米纤维素作为一种纳米材料因其独特的结构特点而具有许多显著的性能:如高强度㊁优异的光学性㊁流变性㊁可降解性㊁生物相容性及可再生性等[10,11].使其在高性能复合材料领域显现出极大的应用价值[12].迄今为止,经报道的纳米纤维素大致可分为3类:(1)通过天然纤维素的酸水解制备获得的纤维素纳米晶体或纤维素纳米晶须(C N C s)[13,14].纤维素分子链中包含无定形区及结晶区.该类方法通过提取纤维素微纤维中的结晶区以获得纤维素纳米晶体[15],经硫酸水解能够将纤维的尺寸从微米级降低至纳米级(宽度为5~10n m),为进一步防止纤维间因强氢键驱动而聚集,通常所制备的C N C s 需经过冷冻干燥处理,以便于其后续能够快速再分散[16,17].除此以外,拥有纳米颗粒特征的C N C s还具有优异的强度和光学性能.(2)通过机械瓦解纤维素纤维,并在部分羧甲基化或纤维素酶辅助处理下制备微纤化纤维素(M F C s)[18-20].以木质纤维素为原料,采用高剪切机械均质法能够制备10~2000n m宽的M F C s, M F C s由瓦解的微纤维聚集体组成,具有较高的刚度[21].从木浆中分离得到M F C s可用于高性能的聚合物纳米复合材料,这些纳米复合材料的杨氏模量可高达20G P a,其聚合物分子在生物合成过程中以长链构象结晶,形成横向尺寸约为4n m的微纤丝[22].在木材中,纤维素微纤丝表现出较好的取向,且通常与轴向纤维方向接近.为此,基于木浆M F C s的纳米复合材料是一种具有超高机械性能的材料[23].(3)通过2,2,6,6-四甲基哌啶-1-氧自由基(T E M P O)催化氧化天然纤维素纤维,并将氧化后的纤维素纤维经过机械处理而制备的纳米纤维素[24].T E M P O催化氧化结合均质处理目前已成为制备纳米纤维素的重要方法,其利用T E M P O/ N a B r/N a C l O体系,对纤维素纤维进行有效氧化预处理,选择性将纤维素C6位伯醇羟基氧化成羧基[25,26](如图1所示),随后经温和的均值化处理制得纳米纤维素(T O C N s)[27,28](如图2所示).图1 T E M P O氧化纤维素纳米纤维非晶态与晶界示意图[26](a)0.5mm o l/g (b)1.0mm o l/g(c)1.8mm o l/g图2 不同羧基含量的T O C N s的S E M图像[28]与前两类纳米纤维素相比,T O C N s宽度基本一致,均为3~4n m,且长度可达几微米,具有较大的长径比(>50)[29](如图3所示),并以单个纳米纤维的形式在水中均匀分散,且具有优异的成膜性,干燥后可制成透明的T O C N s薄膜.此外,通过在其他表面亲水性基膜上涂覆T O C N s可以制备出具有T O C N s层的复合薄膜[30].T O C N s还可以与其他材料复合制成功能化复合膜材料,通过从光学㊁力学㊁气阻性等方面对T O C N s涂层薄膜进行研究,使其应用于不同领域.本课题组长期从事T O C N s复合膜材料研究,相继开发了一系列含T O C N s的膜材料[31-33].(a)棉纤维 (b)云杉纤维㊃611㊃Copyright©博看网 . All Rights Reserved.第1期戴 磊等:T E M P O氧化纤维素纳米纤维在膜材料中的研究进展(c)竹纤维图3 各类纤维经T E M P O氧化分解处理后的T E M图像[29]近年来,作为一种可生物降解的环保型薄膜材料,纳米纤维素膜材料已在众多技术领域取得了丰富的应用成果[34].其中,T O C N s膜材料更是具有诸多特点,如纯T O C N s膜具有较高透光率(> 80%),且透光率随着T O C N s自身长度的减小而增大.而随着T O C N s长度的增加,其膜的拉伸强度和断裂伸长率均显著提高[34].本文主要针对近几年T O C N s在膜材料领域的研究进展进行综述,包括气体阻隔膜㊁过滤膜㊁吸附膜及导电膜等,以期为今后该领域的研究提供指导与参考.1 含T O C N s的功能膜材料1.1 气体阻隔膜由于T O C N s表面具有高密度的羟基与羧基等功能性基团,因而其具有极高的表面自由能,此外,得益于纳米纤维素的微小尺寸,其所形成的膜具有非常致密的结构,具有优异的氧气阻隔性,且其氧气阻隔性随着厚度的增加而提高[34].F u k u z u-m i等[34]利用三种不同纳米纤维长度(平均长度分别为200㊁680㊁1100n m)的T O C N s研究了其长度对自组装T O C N s及T O C N s涂覆聚对苯二甲酸乙二醇酯(P E T)及聚乳酸(P L A)薄膜气体阻隔性的影响.研究发现,在相对湿度(R H)为0%时, T O C N s涂覆P E T及P L A薄膜的透氧率(O T R)极低,但随着R H的增加,O T R呈指数增长.其中,在0~50%R H范围内,T O C N s的阻氧性能最高.此外,随着T O C N s长度的增加,T O C N s涂覆的P E T和P L A膜的氧气阻隔性能明显增加.相比之下,T O C N s长度对水蒸气阻隔性则几乎没有影响.F u k u z u m i等[12]的研究也证实将T O C N s在P L A膜上浇铸可制成高阻氧膜.其中,未改性的P L A膜的氧气渗透率约为746m L m-2d a y-1 P a-1,而T O C N s层的形成将氧气渗透率显著降低至1m L m-2d a y-1P a-1.T O C N s涂覆的P L A膜具有与高阻氧功能的聚偏二氯乙烯和聚乙烯-聚乙烯醇共聚物膜相近的氧气阻隔效果,这种高阻氧的生物质膜可用作食品㊁药品包装,及显示面板和其他电子设备等.此外,研究表明T O C N s所携带基团对气体阻隔性具有重要影响.F u k u z u m i等[35]分析了T O C-N s膜和T O C N s涂覆P E T膜对O2㊁N2㊁C O2㊁H2及其混合气体的阻隔性.结果表明具有游离羧基的T O C N s-C O O H和具有羧酸钠基团的T O C N s-C O O N a对O2㊁N2㊁C O2等气体的阻隔性差异性较小,但T O C N s-C O O N a对H2的阻隔性比T O C-N s-C O O H层高一个数量级.气体动力学直径与渗透率之间的良好相关性表明T O C N s层的气体渗透行为主要可由扩散机理解释(如图4所示),即气体分子的动力学直径越小,两层的透气性越高.相应地,F u j i s a w a等[36]研究发现T O C N s-C O O H膜比T O C N-C O O N a膜具有更高的透氧性,前者为0.049m Lμm m-2d a y-1k P a-1,而后者则为0.0017m Lμm m-2d a y-1k P a-1,但值得注意的是两者均明显低于P E T膜的透氧值(15.5m Lμm m-2d a y-1k P a-1).图4 T O C N-C O O H膜选择性渗透H2示意图[35]T O C N s也能够与其他材料结合使用,实现气体阻隔作用.R o i l o等[37]研究发现在P L A基体上以T O C N s/T i O2纳米复合物进行涂敷可获得厚度均匀㊁无缺陷的涂层,因而能够有效阻碍O2㊁C O2㊁N2等气体的穿透.其中,纳米T i O2通过聚集形成约100n m的团聚体,进一步增加了纳米复合涂层中渗透迁移路径的弯曲度,从而降低了气体渗透扩散率.W u等[38]研究发现在T O C N s薄膜中添加蒙脱土(MT M)可以进一步改善其氧气阻隔性(如图5所示).其中,添加1%MT M后,氧气透过率从0.03降至0.006m Lμm m-2d a y-1k P a-1.并且,当T O C N s/MT M复合材料中MT M含量增加至50%时,其氧气阻隔性进一步提高至0.0008m L μm m-2d a y-1k P a-1.因此,采用混合㊁干燥等简单工艺便可制备出具有高透明性和柔韧性的T O C N/ M T M复合膜,该轻质㊁透明㊁高强㊁高韧的新型生物㊃711㊃Copyright©博看网 . All Rights Reserved.陕西科技大学学报第38卷质基纳米复合膜材料具有广阔的应用前景.(a)T O C N/M T M薄膜透光性 (b)复合膜T E M图像图5 T O C N/MT M复合薄膜[38]S o n i等[39]以壳聚糖为基体,T O C N s为增强剂制备了透明㊁高性能的生物阳极复合膜(壳聚糖/ T O C N s膜).研究发现,T O C N s的加入能够显著降低复合膜的氧气透过率(O T R)及水蒸气透过率(WV P R).与100%壳聚糖(WV P R为3.28×10-8 g P a-1h-1m-1)膜相比,随着T O C N s含量的增加,薄膜的水蒸气阻隔性逐渐增强(80%/20%的壳聚糖/T O C N s,WV P R为2.89×10-8g P a-1h-1 m-1;75%/25%的壳聚糖/T O C N s,WV P R为2.63×10-8g P a-1h-1m-1).同样地,含T O C N s的纳米复合膜具有更高的氧气阻隔性.据了解,高氧阻隔膜的O T R范围约为1~10c c(m-2d a y-1).而100%壳聚糖膜的平均O T R为0.45c c(m-2 d a y-1),壳聚糖基质中加入T O C N s的复合膜O T R则进一步下降至0.05~0.21c c(m-2 d a y-1).这些结果表明,壳聚糖/T O C N s生物质纳米复合膜可以保护食品免受氧化变质,在食品包装方面具有广阔的应用前景.当前该类气体阻隔膜实际仍然主要围绕纳米纤维素膜的氧气阻隔性开展,此外,虽然研究者们均已认识到纳米纤维素膜水蒸气阻隔性能的缺陷,但仍然缺乏有效的改善手段.1.2 过滤膜工业及生活污水(如含油废水)等对自然环境具有严重影响,对其进行有效处理意义重大.基于生物质材料的新型超滤膜近年来得到各领域研究者的青睐.M a等[40]以T O C N s为顶层阻隔层(厚度为0.10±0.02μm),聚丙烯腈(P A N)静电纺丝支架为中间层,P E T无纺布为支撑基材,制备了一种新型超滤(U F)纳米纤维复合膜(T F N C),该膜最大孔径约为55n m.以直径为0.10±0.01μm的微球测试U F膜效率发现该膜的渗透通量比使用不含T O C N s阻隔层的商品超滤膜(如P A N10)高约5倍.对于油/水乳液的超滤,其渗透通量比商业P A N10膜高约8倍.此外,该T F N C薄膜更是显示出优异的耐化学性和广泛的p H适用范围. K o n g等[41]以T O C N s与三乙酸纤维素(C T A)通过反相法制备均相C T A/T O C N s超滤膜.T O C N s 的加入能够大幅提高超滤膜的纯水通量,原因在于T O C N s的加入增大了孔隙率,并提高了膜的亲水性(如图6所示).此外,T O C N s表面的羧基有助于氢键的产生,进而提高纯水通量.因此该超滤膜的通量恢复率(F R R)较高,且由于T O C N s的高亲水性,所以吸附的蛋白质也较易冲洗掉.(a)不含T O C N s (b)0.5w t%T O C Ns(c)1.0w t%T O C N s (d)1.5w t%T O C Ns(e)2.0w t%T O C N s (f)2.5w t%T O C N s图6 不同含量T O C N s对C T A/T O C N s膜形貌结构的影响[41]除此以外,H a s s a n等[42]研究发现使用4'-氯[2,2':6',2″]三联吡啶(T p y)与C u2+形成络合物修饰的T O C N s能够制成具有抗菌性能和高水通量的T O C N s-C u-T p y超滤膜,该膜可以高效去除再生纤维造纸废水流出物中的亚微米级悬浮颗粒,因而可用以处理造纸厂废水,实现水资源的循环利用.M a等[43]将T O C N s浸渍渗透到静电纺P A N 纳米纤维(直径约150n m)支架中,开发出具有高通量,低压降和高效截留细菌与噬菌体的复合纳米纤维微滤(M F)膜(如图7所示).该M F膜具有良好的机械性能和高表面电荷密度.相较于商业M F 膜,该膜对染料的吸附能力是商业产品的16倍.研究证明,随着T O C N s的加入,纳米纤维支架的孔径减小,纯水的流量减少约28%.因此该膜非常适合用于湖泊㊁河流和池塘的低能耗饮用水净化.纳米纤维素具有优异的生物可降解性,因而,其所制成的水过滤膜的使用寿命具有天然的限制,有待进一步研究提高.㊃811㊃Copyright©博看网 . All Rights Reserved.第1期戴 磊等:T E M P O氧化纤维素纳米纤维在膜材料中的研究进展(a )过滤前 (b)过滤后图7 M F 复合膜过滤前后的照片[43]传统的超滤(U F )或纳滤(N F)水处理过滤器通常是基于多孔膜,由浸渍法制造.其中扭曲孔隙率会导致相对较低的通量率.而高通量静电纺(E S)纳米纤维膜以其高孔隙率㊁良好的互连性和高比表面积,引起了人们对超滤或纳滤应用的极大兴趣.C a o 等[44]介绍了一种新型双层P A N 静电纺纳米纤维膜,并用T E M P O 选择性氧化黄麻纤维素纳米晶(J C N s )增强的J C N s -P A N 复合纳米纤维膜.对其性能表征发现,该复合膜具有良好的过滤性能.通过以乳化油/水混合物为原料,采用紫外可见光谱法对J C N s 包覆的P A N 膜进行超滤.结果表明,该膜的抑油率达99.5%以上,且滤液含油浓度小于5.5p p m ,完全符合废水排放环境标准(<10p p m ).由此可见,该复合膜系统是处理油水废水的良好选择.在过滤分离过程中,若薄膜被污染堵塞,会直接导致分离效率的大幅下降.W a n g 等[45]以交联聚乙二醇(P E G )和T O C N s 制备了纳米纤维超滤膜.交联P E G 填充了T O C N s 间的空隙,从而减小了P E G /T O C N s 孔径(约为5n m ),进而得到结构更为致密的超滤膜.所得的复合阻隔层亲水性好,防污能力高.此外,该膜在防污性能和回收能力等方面显著优于具有类似过滤性能的商业膜(如P a l l L i f eS c i e n c e so m e g a 膜和K o c h H F K328膜).在长时间的测试中,复合膜的通量大约是商业膜的两倍,且污垢阻隔性保持在90%以上.另外,鉴于该膜的高密度㊁小孔径及亲水性,其可用于蛋白质分离或药物应用等.1.3 吸附膜近年来,纳米纤维素㊁氧化石墨烯(G O )及其复合材料因其独特的吸附能力㊁机械特性㊁表面电荷密度㊁配位过渡金属离子能力等在水净化领域引起了大量研究人员的关注.Z h u 等[46]采用真空过滤法将T O C N s 与氧化石墨烯片或氧化石墨烯纳米胶体杂化物复合,以期用作水净化的自组装吸附膜材料(如图8所示).由于T O C N s 对C u2+具有良好的吸附能力,且吸附后的C u 2+可实现T O C N s和G O 间的离子交联,在水中形成独特的 吸附态”.因此该复合膜在多次吸附-解吸循环和强超声作用下仍能保持独特的水解稳定性及可回收性.得益于T O C N s /G O 膜的高吸附容量㊁柔韧性㊁水解稳定性及机械强度,该复合膜有望成为具有协同性能的新型水净化膜.图8 T O C N s /G O 生物混合膜[46]由于T O C N s 与带正电荷的金属离子通过表面羧基的静电吸引而发生相互作用,因此T O C N s 显示出净化污水中金属离子的生物修复潜力.有研究表明,C u 2+在T O C N s 上的吸附随羧酸基团含量的增加呈线性增加.由于T O C N s 在低p H 下具有较低的金属结合能力,因此可以在酸性环境中回收金属[47](如图9所示).此外,研究发现T O C N s 与甲壳素纳米纤维在P E T 膜表面进行层层自组装修饰所得的膜具有亲水性,且对带电或不带电的染料均有较强的吸附作用[48].Y a n g 等[49]则以T O C N s 嵌入静电纺P A N 支架中,并在T O C N s 上接枝半胱氨酸,通过化学改性,在提高了T O C N s 比表面积的同时更赋予了其新的硫醇基团.大大提升了对C r 6+和P b 2+的吸附能力.结果证实改性T O C N s /P A N 复合膜对C r 6+和P b2+两种重金属离子的吸附能力分别可达87.5m g /g 及137.7m g /g.与此同时,该膜结构性能稳定,可多次回用,不失为一种绿色有发展前景的材料.吸附性能与材料本身的结构具有较大关系,因此,通过纳米纤维素膜材料的结构调控,以进一步提高其吸附能力仍然需要进一步研究.(a )吸附前 (b)吸附后图9 吸附铜(I I )前后T O C N s 膜的S E M 图像[47]S o n e 等[50]将具有羧酸钠基团的T O C N s -N a 分散在水中,其所携带的N a+通过简单的离子交换处理,可以与其他金属离子(M n+)进行有效交㊃911㊃Copyright©博看网 . All Rights Reserved.陕西科技大学学报第38卷换,在一定条件下,获得均匀的T O C N s -M 水分散体,将其涂覆在滤纸上可以形成一层复合薄膜.经研究发现,以含有C u 2+的T O C N s -C u 及A g +的T O C N s -A g 涂覆的滤纸具有很好的吸附除臭作用,能够有效分解或吸附H 2S 和C H 3S H 气体.基于此,该膜适用于除臭剂方面应用.一直以来,温室气体引起的气候变化及全球变暖是全人类共同面对的严重环境问题,而全球变暖的首要因素即由过量的C O 2气体排放导致.同时,农业废弃物中也释放出以N H 3气体为主的含氮气体.为控制温室气体排放,现有的吸附气体材料中,碳㊁金属㊁半导体等功能纳米材料由于体积过小㊁毒性过强而受到限制.因此,合适的支架对于吸附材料具有重要意义.S h a h 等[51]采用T O C N s 与阳离子和阴离子交换有机黏土(锂皂石㊁绢云母㊁水滑石)杂交,加载聚(酰氨基胺)树枝状大分子制备出有机黏土/T O C N s 复合薄膜用于气体吸附.研究发现,随着有机黏土量的增加,吸附在阳离子树枝状大分子上的C O 2分子和吸附在阴离子树枝状大分子上的N H 3分子相应增加(如图10所示).其中,不含有机黏土的T O C N s 膜吸附N H 3约9~10m g /g (T O C -N s ),明显高于C O 2吸附量(低于2.5m g /g (T O C -N s )).而不同有机黏土复合T O C N s 对该两种气体的吸附经测试可知,水滑石/T O C N s 薄膜对其两种气体的吸附率最高,可达约30m g /g .因此,本研究将有助于开发具有选择性吸附特定气体的吸附剂.图10 C O 2和NH 3气体吸附在有机黏土/T O C N s 薄膜上的示意图[51]1.4 导电膜T O C N s 热膨胀性低且电解质吸收性能好,是超级电容器的良好基材.并且,与传统基材(如玻璃㊁塑料)相比,T O C N s 无需使用任何表面预处理.W a n g 等[52]在研究中将G O 纳米片和聚(3,4-乙烯二氧噻吩:聚苯乙烯磺酸盐)(P E D O T -P S S)纳米颗粒为载体,分别以带正电荷的聚苯胺(P A N I)纳米线在T O C N s 纸上沉积,制备出多层薄膜电极.进而制备了两种不同的透明柔性薄膜超级电容器S -P G -8和S -P P -8.进一步通过氢碘酸(H I)酸化还原转化为导电T O C N s /[P A N I -R G O ]n (C P R G -n )膜.电化学测试结果显示,C P R G -8电极可以有效促进电解质离子扩散,其电化学性能更为优异,而原因在于还原氧化石墨烯(R G O )的双电层(E D L )电容性和P A N I 的伪电容性的协同作用.当电流密度为0.0043m Ac m -2时,S -P G -8的面积电容可达5.86m Fc m -2.而在相同电流密度时,S -P P -8的面积电容仅为4.22m Fc m -2.同时,S -P G -8也表现出良好的循环稳定性.然而,S -P P -8电容在长期循环中是不稳定的.此外,良好的透明性是透明柔性器件的关键,透明柔性薄膜超级电容器具有良好的弯曲稳定性.其中,S -P G -8的透射率约为47.1%(550n m ),而S -P P -8的透射率仅约为30.6%(550n m ).由此得以看出,拥有各项优异性能的C P R G -n 导电膜将具有良好的应用前景.K o g a 等[53]利用T O C N s 作为基体,将含有大量羧酸钠基团的T O C N s 与经硝酸处理过的表面带有羧基的单壁碳纳米管(C N T s )混合浇铸成膜,从而制备了具有超强㊁超薄㊁柔韧㊁透明㊁导电的纳米复合膜材料.其中,表面阴离子化的T O C N s 可以作为C N T s 的分散剂,促进C N T s 在水中均匀分散.并且,T O C N s 表面大量的羧酸钠基团能够实现离子传导,有效提高C N T s /T O C N s 复合膜的导电性(如图11所示).经研究对比发现,C N T s /T O C N s 薄膜比其他C N T s /聚合物薄膜(包括再生纤维素[54]㊁细菌纤维素[55]㊁聚乙烯(P E )[56]㊁聚苯乙烯(P S )[57]㊁及聚酰胺-6[58])具有更高的导电性(高达10Sc m -1),并且C N T s /T O C N s 薄膜的电阻更是低至300Ω,充分表明了其优异的导电性.该研究表明该膜不仅有望应用于下一代柔性电子产品,更为实现绿色柔性电子器件提供了一条很有前景的途径.(a )C N T s /T O C N s 膜 (b )C N T s /P E T 膜光学光学图像及电阻值图像及电阻值㊃021㊃Copyright©博看网 . All Rights Reserved.第1期戴 磊等:T E M P O氧化纤维素纳米纤维在膜材料中的研究进展(c)基于C N T s/T O C N s涂覆P E T透明导电薄膜L E D响应图11 基于C N T s/T O C N s复合薄膜导电性[53] J r a d i等[26]采用水介质中吡咯表面化学聚合诱导吸附法,以F e C l3为氧化剂,通过吡咯溶液化学氧化聚合使聚吡咯纳米粒子连续均匀地包覆在T O C N s网络表面,原位合成了兼具优异力学性能和高导电性的T O C N s/聚吡咯(P P y)柔性复合薄膜,其整体电导率(氁)约为3Sc m-1.此外,研究还证实通过添加聚乙烯醇(P V A)可以进一步提高复合膜的柔韧性(可弯曲至180°)(如图12所示),且对导电性没有不利影响.该T O C N s/P P y复合薄膜以其优异的力学㊁导电性能有望应用于传感器㊁柔性电极等导电柔性薄膜领域.图12 P V A/T O C N/P P y复合薄膜卷曲的光学图像[26]由于锂离子电池具有能量密度高㊁功率密度大㊁长期稳定的特点[59],因而柔性锂离子电池被视为未来发展柔性电子器件的关键部件,在可弯曲和可穿戴电子设备中的应用受到人们越来越多的关注[60]. T O C N s可作为一种具有良好机械性能的柔性锂离子电池粘结剂,L u等[61]发现在制备电极时,4w t%的T O C N s便具有良好的结合性能.该研究采用传统造纸工艺,将具有不同重量比的L i F e P O4㊁石墨㊁S u p e r-P碳及T O C N s的悬浮液经真空过滤,并在110℃下真空干燥制备得到柔性纸电极(如图13所示).研究表明,将碳酸亚乙烯酯(V C)添加到电解质中对L i F e P O4电极和石墨电极的比容量和库仑效率(C E)均有积极影响.并且在制备电极期间增加干燥时间可改善L i F e P O4电极的电化学性能,但对石墨电极则具有明显的负面影响.(a)柔性正纸电极 (b)弯曲电池图13 T O C N s对柔性电极的影响[61]2 结论T O C N s不仅具有纤维素的诸多优点,而且其良好的成膜性及纳米尺寸效应使其能够制成功能性膜材料,在诸多领域具有潜在应用.今后的研究应当继续着力于新型功能膜材料的开发,在充分发挥T O C N s自身特点的同时,借助其他功能性物质赋予膜材料新的结构与功能,如纳米纤维素膜对水蒸气的阻隔性以及相应功能膜材料的性能优化,以此充分打开T O C N s下游市场.这不但能够为纳米纤维素的生产制造技术的提升与改进提供动力,降低销售价格,而且能够加速纳米纤维素的产业化应用推广,真正使其能够服务于国民生产生活.参考文献[1]D i n c e r I.R e n e w a b l e e n e r g y a n ds u s t a i n a b l ed e v e l o p m e n t:A c r u c i a lr e v i e w[J].R e n e w a b l ea n d S s t a i n a b l e E e r g yR v i e w s,2000,4(2):157-175.[2]B l e d z k iA K,G a s s a nJ.C o m p o s i t e s r e i n f o r c e dw i t hc e l l u-l o s eb a s e df i b r e s[J].P r o g r e s s i nP y m e rS i e n c e,1999,24(2):221-274.[3]K l e mm D,H e u b l e i nB,F i n k H P,e ta l.C e l l u l o s e:F a s c i-n a t i n g b i o p o l y m e r a n d s u s t a i n a b l e r a w m a t e r i a l[J].A n g e-w a n d t e C h e m i e I n t e r n a t i o n a l E d i t i o n,2005,44(22):3358-3393.[4]B r o w n J rR M,S a x e n a IM,K u d l i c k aK.C e l l u l o s eb i o s y n-t h e s i s i nh i g h e r p l a n t s[J].T r e n d s i nP l a n t S s c i e n c e,1996,1(5):149-156.[5]Št u r c o váA,D a v i e sGR,E i c h h o r nS J.E l a s t i cm o d u l u s a n ds t r e s s-t r a n s f e r p r o p e r t i e so ft u n i c a t ec e l l u l o s e w h i s k e r s[J].B i o m a c r o m o l e c u l e s,2005,6(2):1055-1061.[6]Röm l i n g U.M o l e c u l a rb i o l o g y o fc e l l u l o s e p r o d u c t i o ni nb ac t e r i a[J].R e s e a r c h i n M i c r o b i o l o g y,2002,153(4):205-212.[7]H a b i b iY,L u c i aL A,R o j a sOJ.C e l l u l o s en a n o c r y s t a l s:C h e m i s t r y,s e l f-a s s e m b l y,a n da p p l i c a t i o n s[J].C h e m i c a lR e v i e w s,2010,110(6):3479-3500.[8]C h a r r e a u H,L F o r e s t iM,V a z q u e zA.N a n o c e l l u l o s e p a-t e n t s t r e n d s:Ac o m p r e h e n s i v e r e v i e wo n p a t e n t s o n c e l l u-l o s en a n o c r y s t a l s,m i c r o f i b r i l l a t e da n db a c t e r i a lc e l l u l o s e[J].R e c e n tP a t e n t so n N a n o t e c h n o l o g y,2013,7(1):56-80.㊃121㊃Copyright©博看网 . All Rights Reserved.陕西科技大学学报第38卷[9]D eF r a n c eKJ,H o a r eT,C r a n s t o nED.R e v i e wo f h y d r o-g e l s a n da e r o g e l sc o n t a i n i n g n a n o c e l l u l o s e[J].C h e m i s t r y o fM a t e r i a l s,2017,29(11):4609-4631.[10]K i mJH,S h i mBS,K i m HS,e t a l.R e v i e wo f n a n o c e l l u-l o s ef o rs u s t a i n a b l ef u t u r e m a t e r i a l s[J].I n t e r n a t i o n a l J o u r n a lo f P r e c i s i o n E n g i n e e r i n g a n d M a n u f a c t u r i n g-G r e e nT e c h n o l o g y,2015,2(2):197-213.[11]C h i r a y i l CJ,M a t h e wL,T h o m a sS.R e v i e wo f r e c e n t r e-s e a r c h i nn a n o c e l l u l o s e p r e p a r a t i o n f r o md i f f e r e n t l i g n o-c e l l u l o s i c f i b e r s[J].R e v i e w so nA d v a n c e d M a t e r i a l sS c i-e n c e,2014,37:20-28.[12]F u k u z u m iH,S a i t o T,I w a t a T,e ta l.T r a n s p a r e n ta n dh i g h g a s b a r r i e r f i l m s o f c e l l u l o s e n a n o f i b e r s p r e p a r e d b yT E M P O-m e d i a t e d o x i d a t i o n[J].B i o m a c r o m o l e c u l e s, 2008,10(1):162-165.[13]D o n g X M,R e v o l JF,G r a y D G.E f f e c t o fm i c r o c r y s t a l-l i t e p r e p a r a t i o nc o n d i t i o n so nt h ef o r m a t i o n o fc o l l o i dc r y s t a l s o f c e l l u l o s e[J].C e l l u l o s e,1998,5(1):19-32.[14]M a r c h e s s a u l tR H,M o r e h e a dF F,W a l t e rN M.L i q u i dc r y s t a ls y s t e m sf r o m f i b r i l l a r p o l y s a c c h a r ide s[J].N a-t u r e,1959,184(4686):632-633.[15]P e n g BL,D h a rN,L i uH L,e t a l.C h e m i s t r y a n d a p p l i c a-t i o n so fn a n o c r y s t a l l i n ec e l l u l o s ea n di t sd e r i v a t i v e s:A n a n o t e c h n o l o g yp e r s p e c t i v e[J].T h eC a n a d i a nJ o u r n a l o fC h e m i c a l E n g i n e e r i n g,2011,89(5):1191-1206.[16]J o h a rN,A h m a dI,D u f r e s n eA.E x t r a c t i o n,p r e p a r a t i o na n d c h a r a c t e r i z a t i o no f c e l l u l o s e f ib r e sa n dn a n oc r y s t a l sf r o mr i c eh u s k[J].I n d u s t r i a l C r o p s a n dP r o d u c t s,2012,37(1):93-99.[17]L uP,H s i e hY L.P r e p a r a t i o na n d p r o p e r t i e so f c e l l u l o s e n a n o c r y s t a l s:R o d s,s p h e r e s,a n dn e t w o r k[J].C a r b o h y-d r a t eP o l y me r s,2010,82(2):329-336.[18]H e n r i k s s o n M,H e n r i k s s o n G,B e r g l u n dL A,e ta l.A ne n v i r o n m e n t a l l yf r i e n d l y m e t h o d f o r e n z y m e-a s s i s t e dp r e p a r a t i o no fm i c r o f i b r i l l a t e dc e l l u l o s e(M F C)n a n o f i-b e r s[J].E u r o p e a nP o l y m e r J o u r n a l,2007,43(8):3434-3441.[19]N a k a g a i t o A N,Y a n o H.T h ee f f e c to f m o r p h o l o g i c a lc h a n g e sf r o m p u l p f i b e rt o w a rd sn a n o-s c a l ef i b r i l l a te dc e l l u l o s eo nt h e m e c h a n i c a l p r o p e r t i e so fh i g h-s t r e n g t hp l a n t f i b e rb a s e dc o m p o s i t e s[J].A p p l i e d P h y s i c s A, 2004,78(4):547-552.[20]Wãg b e r g L,D e c h e rG,N o r g r e n M,e t a l.T h eb u i l d-u p o f p o l y e l e c t r o l y t e m u l t i l a y e r s o f m i c r o f i b r i l l a t e d c e l l u l o s e a n d c a t i o n i c p o l y e l e c t r o l y t e s[J].L a n g m u i r,2008,24(3): 784-795.[21]B a t t i s t a O A.M i c r o c r y s t a l p o l y m e rs c i e n c e[M].N e wY o r k:E l s e v i e r,1975:624-625.[22]H u l tEL,I v e r s e nT,S u g i y a m a J.C h a r a c t e r i z a t i o no f t h e s u p e r m o l e c u l a r s t r u c t u r e o f c e l l u l o s e i nw o o d p u l p f i b r e s [J].C e l l u l o s e,2003,10(2):103-110.[23]H e n r i k s s o n M,H e n r i k s s o n G,B e r g l u n dL A,e ta l.A ne n v i r o n m e n t a l l yf r i e n d l y m e t h o d f o r e n z y m e-a s s i s t e dp r e p a r a t i o no fm i c r o f i b r i l l a t e dc e l l u l o s e(M F C)n a n o f i-b e r s[J].E u r o p e a nP o l y m e r J o u r n a l,2007,43(8):3434-3441.[24]I s o g a iA,S a i t oT,F u k u z u m iH.T E M P O-o x i d i z e dc e l l u-l o s en a n o f i b e r s[J].N a n o s c a l e,2011,3(1):71-85.[25]S a i t oT,K i m u r aS,N i s h i y a m aY,e t a l.C e l l u l o s en a n o f i-b e r s p r e p a r e db y T E M P O-m e d i a t e do x i d a t i o no fn a t i v ec e l l u l o s e[J].B i o m a c r o m o l e c u l e s,2007,8(8):2485-2491.[26]J r a d iK,B i d e a u B,C h a b o tB,e ta l.C h a r a c t e r i z a t i o no fc o nd u c t i v ec o m p o s i t ef i l m sb a se do n T E M P O-o x i d i z e dc e l l u l o s e n a n o f i b e r s a nd p o l y p y r r o l e[J].J o u r n a l o fM a-t e r i a l s S c i e n c e,2012,47(8):3752-3762.[27]M i s h r a SP,T h i r r e e J,M a n e n tAS,e t a l.U l t r a s o u n d-c a t-a l y z e dT E M P O-m e d i a t e d o x i d a t i o n o f n a t i v e c e l l u l o s e f o r t h e p r o d u c t i o no fn a n o c e l l u l o s e:E f f e c to f p r o c e s sv a r i a-b l e s[J].B i oR e s o u rc e s,2011,6(1):121-143.[28]J o h n s o n R K,Z i n kS h a r p A,G l a s s e r W G.P r e p a r a t i o na n d c h a r a c t e r i z a t i o no f h y d r o p h ob icde r i v a t i v e so fT E M-P O-o x i d i z e dn a n o c e l l u l o s e s[J].C e l l u l o s e,2011,18(6): 1599-1609.[29]S a i t oT,K i m u r aS,N i s h i y a m aY,e t a l.C e l l u l o s en a n o f i-b e r s p r e p a r e db y T E M P O-m e d i a t e do x i d a t i o no fn a t i v ec e l l u l o s e[J].B i o m a c r o m o l e c u l e s,2007,8(8):2485-2491.[30]F u k u z u m iH,S a i t oT,I s o g a i A.I n f l u e n c e o fT E M P O-o x-i d i z e d c e l l u l o s en a n o f i b r i l l e n g t ho nf i l m p r o p e r t i e s[J].C a r b o h y d r a t eP o l y m e r s,2013,93(1):172-177.[31]D a i L,W a n g B,L o n g Z,e t a l.P r o p e r t i e s o f h y d r o x y p r o p-y l g u a r/T E M P O-o x i d i z e d c e l l u l o s e n a n o f i b r i l s c o m p o s i t ef i l m s[J].C e l l u l o s e,2015,22(5):3117-3126.[32]D a i L,L o n g Z,C h e nJ,e t a l.R o b u s t g u a r g u m/c e l l u l o s e n a n o f i b r i l sm u l t i l a y e r f i l m sw i t h g o o db a r r i e r p r o p e r t i e s [J].A C S A p p l i e d M a t e r i a l s&I n t e r f a c e s,2017,9(6): 5477-5485.[33]D a i L,L o n g Z,Z h a oY,e t a l.C o m p a r i s o no f h y d r o x y p r o-p y l a n d c a r b o x y m e t h y l g u a r f o r t h e p r e p a r a t i o no f n a n o-c e l l u l o s ec o m p o s i t ef i l m s[J].C e l l u l o s e,2016,23(5): 2989-2999.[34]F u k u z u m iH,S a i t oT,I s o g a i A.I n f l u e n c e o fT E M P O-o x-i d i z e d c e l l u l o s en a n o f i b r i l l e n g t ho nf i l m p r o p e r t i e s[J].C a r b o h y d r a t eP o l y m e r s,2013,93(1):172-177.[35]F u k u z u m iH,F u j i s a w aS,S a i t oT,e t a l.S e l e c t i v e p e r m e-a t i o no f h y d r o g e n g a s u s i n g c e l l u l o s en a n o f ib r i l f i l m[J].B i o m a c r o m o l e c u l e s,2013,14(5):1705-1709.[36]F u j i s a w aS,O k i t aY,F u k u z u m iH,e t a l.P r e p a r a t i o na n dc h a r a c t e r i z a t i o no fT E M P O-o x id i ze dc e l l u l o s en a n of i b r i l f i l m sw i t h f r e ec a r b o x y lg r o u p s[J].C a r b oh y d r a t eP o l y-m e r s,2011,84(1):579-583.[37]R o i l oD,M a e s t r iC A,S c a r p a M,e ta l.G a sb a r r i e ra n do p t i c a l p r o p e r t i e so fc e l l u l o s e n a n o f i b e rc o a t i n g s w i t hd i s pe r s e d T i O2n a n o p a r t i c l e s[J].S u rf a c ea n d C o a t i ng sT e c h n o l o g y,2018,343:131-137.㊃221㊃Copyright©博看网 . All Rights Reserved.第1期戴 磊等:T E M P O氧化纤维素纳米纤维在膜材料中的研究进展[38]W uCN,S a i t oT,F u j i s a w aS,e t a l.U l t r a s t r o n g a n dh i g hg a s-b a r r i e r n a n o c e l l u l o s e/c l a y-l a y e r e d c o m p o s i t e s[J].B i-o m a c r o m o l e c u l e s,2012,13(6):1927-1932. [39]S o n iB,S c h i l l i n g M W,M a h m o u d B.T r a n s p a r e n tb i o-n a n o c o m p o s i t e f i l m s b a s e d o n c h i t o s a n a n dT E M P O-o x i-d i ze d c e l l u l o s en a n of i b e r sw i t he n h a n c e dm e c h a n i c a l a n db a r r i e r p r o p e r t i e s[J].C a r b o h y d r a t e P o l y m e r s,2016,151:779-789.[40]M aH,B u r g e r C,H s i a oBS,e t a l.F a b r i c a t i o n a n d c h a r a c-t e r i z a t i o no fc e l l u l o s en a n o f i b e rb a s e dt h i n-f i l m n a n o f i-b r o u s c o m p o s i t e m e m b r a n e s[J].J o u r n a lo f M e m b r a n e S c i e n c e,2014,454:272-282.[41]K o n g L,Z h a n g D,S h a oZ,e t a l.S u p e r i o r e f f e c t o fT E M-P O-o x i d i z e d c e l l u l o s en a n o f i b r i l s(T O C N s)o nt h e p e r-f o r m a n c eo fc e l l u l o s et r i a c e t a t e(C T A)u l t r a f i l t r a t i o nm e m b r a n e[J].D e s a l i n a t i o n,2014,332(1):117-125.[42]H a s s a n M,H a s s a nE,F a d e l S M,e t a l.M e t a l l o-t e r p y r i-d i n e-m o d i f ie dc e l l u l o s en a n of i b e rm e m b r a n e s f o r p a p e r-m a k i n g w a s t e w a t e r p u r i f i c a t i o n[J].J o u r n a l o f I n o r g a n i ca n d O r g a n o m e t a l l i c P o l y m e r sa n d M a t e r i a l s,2018,28(2):439-447.[43]M aH,B u r g e rC,H s i a oBS,e t a l.N a n o f i b r o u sm i c r o f i l-t r a t i o n m e m b r a n eb a s e do nc e l l u l o s en a n o w h i s k e r s[J].B i o m a c r o m o l e c u l e s,2011,13(1):180-186.[44]C a oX,H u a n g M,D i n g B,e t a l.R o b u s t p o l y a c r y l o n i t r i l e n a n o f i b r o u s m e m b r a n e r e i n f o r c e d w i t h j u t e c e l l u l o s e n a n o w h i s k e r sf o r w a t e r p u r i f i c a t i o n[J].D e s a l i n a t i o n, 2013,316:120-126.[45]W a n g Z,M aH,H s i a oBS,e t a l.N a n o f i b r o u su l t r a f i l t r a-t i o n m e m b r a n e sc o n t a i n i n g c r o s s-l i n k e d p o l y(e t h y l e n e g l y c o l)a n dc e l l u l o s en a n o f i b e rc o m p o s i t eb a r r i e rl a y e r[J].P o l y m e r,2014,55(1):366-372..[46]Z h uC,L i uP,M a t h e w AP.S e l f-a s s e m b l e dT E M P Oc e l-l u l o s en a n o f i b e r s:G r a p h e n eo x i d e-b a s e d b i o h y b r i d sf o r w a t e r p u r i f i c a t i o n[J].A C S A p p l i e d M a t e r i a l s&I n t e r-f a c e s,2017,9(24):21048-21058.[47]S e h a q u iH,d eL a r r a y aU P,L i uP,e t a l.E n h a n c i n g a d-s o r p t i o no fh e a v y m e t a l i o n so n t ob i o b a s e dn a n o f i b e r s f r o m w a s t e p u l p r e s i d u e sf o ra p p l i c a t i o ni n w a s t e w a t e r t r e a t m e n t[J].C e l l u l o s e,2014,21(4):2831-2844.[48]Q iZ D,S a i t o T,F a n Y,e ta l.M u l t i f u n c t i o n a lc o a t i n gf i l m s b y l a y e r-b y-l a y e r d e p o s i t i o no f c e l l u l o s ea n dc h i t i nn a n o f i b r i l s[J].B i o m a c r o m o l e c u l e s,2012,13(2):553-558.[49]Y a n g R,A u b r e c h tKB,M aH,e t a l.T h i o l-m o d i f i e d c e l l u-l o s en a n o f i b r o u s c o m p o s i t e m e m b r a n e sf o rc h r o m i u m (V I)a n d l e a d(I I)a d s o r p t i o n[J].P o l y m e r,2014,55(5): 1167-1176.[50]S o n eA,S a i t oT,I s o g a iA.P r e p a r a t i o no f a q u e o u s d i s p e r-s i o n s o fT E M P O-o x i d i z e d c e l l u l o s e n a n o f i b r i l sw i t hv a r i-o u s m e t a lc o u n t e r i o n sa n dt h e i rs u p e rd e o d o r a n t p e r-f o r m a n c e s[J].A C S M a c r oL e t t e r s,2016,5(12):1402-1405.[51]S h a hKJ,I m a eT.S e l e c t i v e g a s c a p t u r e a b i l i t y o f g a s-a d-s o r b e n t-i n c o r p o r a t e dc e l l u l o s en a n o f i b e rf i l m s[J].B i o-m a c r o m o l e c u l e s,2016,17(5):1653-1661.[52]W a n g X,G a oK,S h a oZ,e t a l.L a y e r-b y-l a y e r a s s e m b l e dh y b r i dm u l t i l a y e r t h i n f i l me l e c t r o d e s b a s e do n t r a n s p a r-e n t c e l l u l o s e n a n o f i b e r s p a p e r f o r f l e x i b l e s u p e r c a p a c i t o r s a p p l i c a t i o n s[J].J o u r n a lo fP o w e rS o u r c e s,2014,249: 148-155.[53]K o g aH,S a i t oT,K i t a o k aT,e t a l.T r a n s p a r e n t,c o n d u c-t i v e,a n d p r i n t a b l e c o m p o s i t e s c o n s i s t i n g o fT E M P O-o x i-d i z e dn a n o c e l l u l o s ea n dc a r b o nn a n o t u b e[J].B i o m a c r o-m o l e c u l e s,2013,14(4):1160-1165.[54]K i m D H,P a r kSY,K i mJ,e t a l.P r e p a r a t i o n a n d p r o p e r-t i e s o f t h e s i n g l e-w a l l e d c a r b o nn a n o t u b e/c e l l u l o s e n a n o-c o m p o s i t e s u s i n g N-m e t h y l m o r p h o l i n e-N-o x i d e m o n o-h y d r a t e[J].J o u r n a lo fA p p l i e dP o l y m e rS c i e n c e,2010, 117(6):3588-3594..[55]Y o o nSH,J i nHJ,K o o k M C,e t a l.E l e c t r i c a l l y c o n d u c-t i v e b a c t e r i a l c e l l u l o s eb y i n c o r p o r a t i o no f c a r b o nn a n o-t u b e s[J].B i o m a c r o m o l e c u l e s,2006,7(4):1280-1284.[56]O'C o n n o r I,D eS,C o l e m a nJN,e ta l.D e v e l o p m e n to ft r a n s p a r e n t,c o n d u c t i n g c o m p o s i t e sb y s u r f a c ei n f i l t r a-t i o no fn a n o t u b e si n t oc o mm e r c i a l p o l y m e rf i l m s[J].C a r b o n,2009,47(8):1983-1988.[57]M u M,W a l k e rA M,T o r k e l s o n JM,e t a l.C e l l u l a r s t r u c-t u r e s o f c a r b o nn a n o t u b e s i na p o l y m e rm a t r i xi m p r o v e p r o p e r t i e sr e l a t i v et oc o m p o s i t e s w i t h d i s p e r s e d n a n o-t u b e s[J].P o l y m e r,2008,49(5):1332-1337.[58]M e i n c k eO,K a e m p f e rD,W e i c k m a n n H,e t a l.M e c h a n i-c a l p r o p e r t i e s a nde l e c t r i c a l c o n d u c t i v i t y of c a r b o n-n a n o-t u b e f i l l e d p o l y a m i d e-6a n d i t sb l e n d sw i t ha c r y l o n i t r i l e/b u t a d i e n e/s t y r e n e[J].P o l y m e r,2004,45(3):739-748.[59]E t a c h e r iV,M a r o m R,E l a z a r iR,e t a l.C h a l l e n g e s i nt h ed e v e l o p m e n t o f a d v a n c e dL i-i o nb a t t e r i e s:Ar e v i e w[J].E n e r g y&E n v i r o n m e n t a lS c i e n c e,2011,4(9):3243-3262.[60]L iW,Y a n g L,W a n g J,e t a l.T h r e e-d i m e n s i o n a l l y i n t e r-c o n n e c t e dT a S3n a n o w i r e n e t w o r k a s a n odef o r h ig h-p e r-f o r m a n c e f l e x i b l e l i-i o nb a t t e r y[J].A C SA p p l i e dM a t e r i-a l s&I n t e r f a c e s,2015,7(10):5629-5633.[61]L uH,B e h m M,L e i j o n m a r c kS,e t a l.F l e x i b l e p a p e r e l e c-t r o d e s f o r l i-i o nb a t t e r i e s u s i n g l o wa m o u n t o fT E M P O-o x i d i z e d c e l l u l o s en a n o f i b r i l sa sb i n d e r[J].A C S A p p l i e dM a t e r i a l s&I n t e r f a c e s,2016,8(28):18097-18106.【责任编辑:陈 佳】㊃321㊃Copyright©博看网 . All Rights Reserved.。
TEMPO氧化细菌纤维素基纳米复合凝胶的制备及其结构表征
第40卷 第1期 陕西科技大学学报 V o l.40N o.1 2022年2月 J o u r n a l o f S h a a n x iU n i v e r s i t y o f S c i e n c e&T e c h n o l o g y F e b.2022* 文章编号:2096-398X(2022)01-0007-06T E M P O氧化细菌纤维素基纳米复合凝胶的制备及其结构表征钱 鑫,徐永建(陕西科技大学轻工科学与工程学院轻化工程国家级实验教学示范中心陕西省造纸技术及特种纸品开发重点实验室中国轻工业纸基功能材料重点实验室,陕西西安 710021)摘 要:通过微波辅助溶剂热原位合成反应,制备了C d S负载量更高的氧化细菌纤维素(T O-B C)@硫化镉(C d S)纳米复合凝胶材料.F T-I R㊁S E M㊁ED S㊁X R D和R a m a n结果表明,在羧基的络合作用下,立方晶型C d S纳米团簇以类似细胞感受器的形貌主要吸附在T O B C纤维非结晶区域,形成了较为稳定的有机无机杂化结构.这为高效㊁简洁制备纳米复合纤维素凝胶提供了良好的思路.关键词:T E M P O氧化;细菌纤维素;C d S纳米团簇;纳米复合凝胶中图分类号:T Q352 文献标志码:AP r e p a r a t i o na n d s t r u c t u r a l c h a r a c t e r i z a t i o no fT E M P O-o x i d i z e db ac t e r i a l c e l l u l o s e-b a s e dn a n o c o m p o s i t e g e lQ I A N X i n,X U Y o n g-j i a n(C o l l e g e o fB i o r e s o u r c e sC h e m i c a l a n d M a t e r i a l sE n g i n e e r i n g,N a t i o n a lD e m o n s t r a t i o nC e n t e r f o rE x p e r i m e n-t a lL i g h t C h e m i s t r y E n g i n e e r i n g E d u c a t i o n,S h a a n x i P r o v i n c eK e y L a b o r a t o r y o f P a p e r m a k i n g T e c h n o l o g y a n d S p e c i a l t y P a p e r,K e y L a b o r a t o r y o fP a p e rB a s e d F u n c t i o n a l M a t e r i a l so fC h i n a N a t i o n a lL i g h tI n d u s t r y, S h a a n x iU n i v e r s i t y o f S c i e n c e&T e c h n o l o g y,X i'a n710021,C h i n a)A b s t r a c t:O x i d i z e db a c t e r i a l c e l l u l o s e(T OB C)@c a d m i u ms u l p h i d e(C d S)n a n o c o m p o s i t e g e lw i t hh i g hC d S l o a d i n gp e r c e n t a g ew a s o b t a i n e d t h r o u g hm i c r o w a v e-a s s i s t e d s o l v o t h e r m a l i n-s i t u s y n t h e s i s r e a c t i o n.T h e r e s u l t s o fF T-I R,S E M,E D S,X R Da n dR a m a nr e v e a l e d t h a t c e l l r e c e p t o r-l i k e c u b i cC d Sn a n o c l u s t e r sw e r em a i n l y a t t a c h e d t o a m o r p h o u s r e g i o no fT O B C f i-b e r v i ac o m p l e x a t i o no f c a r b o x y l g r o u p,w h i c h f o r m i n g s t a b l e o r g a n i c-i n o r g a n i c h y b r id s t r u c-t u r e.T h eh i g h-e f f i c i e n t a n d s a m p l em e t h o d p r o v i d e s n e w i d e a s t o p r e p a r e n a n o c o m p o s i t e c e l-l u l o s e g e l.K e y w o r d s:T E M P Oo x i d i z a t i o n;b a c t e r i a l c e l l u l o s e;C d Sn a n o c l u s t e r s;n a n o c o m p o s i t e g e l*收稿日期:2021-08-20基金项目:国家自然科学基金项目(31170559);陕西科技大学学科带头人培育计划项目(2013X S D25)作者简介:钱 鑫(1983-),男,陕西西安人,实验师,在读博士研究生,研究方向:细菌纤维素功能化Copyright©博看网 . All Rights Reserved.陕西科技大学学报第40卷0 引言1886年,英国人B r o w n首次发现并报道了细菌纤维(B a c t e r i a lC e l l u l o s e,B C)的存在[1].B C是由细菌(主要为木醋杆菌)在液体培养基中发酵产生的不含半纤维素和木质素的纯纳米纤维,呈凝胶状[2].B C作为新型生物材料,具有无毒㊁无害㊁绿色㊁环保,以及较强的生物兼容性和可降解性的特点;B C分子链表面的活性羟基可进行羧基化㊁磺酸化㊁酯化㊁醚化等多种原位反应,从而获得应用性能更强的B C基材[3-5].改性B C基材在食品㊁医疗㊁组织工程材料㊁声学材料㊁造纸㊁纺织㊁化妆品㊁电池㊁水处理㊁催化等领域都有应用的潜力[6-12].在仿生制备技术的启发下,提出了利用天然生物质材料作为模板来制备小尺寸纳米材料的新思路[13].在前期研究工作中,通过原位化学反应成功将纳米硫化镉颗粒(C d Sn a n o p a r t i c l e s)负载到了B C凝胶基质上,制备出B C@C d S纳米复合凝胶[14].由于羟基络合能力较弱,所以导致了B C基质上硫化镉的负载量偏低,这也在一定程度上影响了B C@C d S纳米复合凝胶的最终应用.为了进一步提高C d S在B C凝胶上的负载量,首先采用2, 2,6,6-四甲基哌啶-1-氧化物自由基(T E M P O)介导氧化法对B C基材进行氧化,得到络合能力更强的氧化B C(T O B C);再利用T O B C为模板,通过微波辅助溶剂热原位反应将C d S纳米颗粒负载到T O B C基质上,从而制备出C d S负载量更高的T O B C@C d S纳米复合凝胶,并采用F T-I R㊁S E M㊁E D S㊁R a m a n等对T O B C@C d S纳米复合凝胶进行表征.1 实验部分1.1 主要材料与试剂细菌纤维素,购自海南热带水果加工有限公司;氢氧化钠(N a O H,分析纯),氯化镉(C d C l2)㊁溴化钠(N a B r)㊁次氯酸钠(N a C l O),购自天津市科密欧化学试剂有限公司;硫脲(H2N S C N H2)㊁无水乙醇(C H3C H2O H),购自天津市富宇精细化工有限公司;T E M P O试剂,购自美国S i g m a公司.实验用去离子水均是由定量分析型超纯水机R O取水,水质标准优于中国国家实验室用水(G B6682-92)三级水标准,电导率≤20毺S㊃c m-1 (25℃).1.2 主要仪器X射线衍射仪(D8A d v a n c e,德国布鲁克B r u k e r公司);拉曼光谱(D X R x i,美国赛默飞T h e r m o f i s h e r公司);扫描电子显微镜及能谱仪(S4800,日本日立H I T A C H I公司;V E G A-3-S B H,捷克泰思肯T E S C A N公司);傅里叶红外光谱仪(V e r t e x70,德国布鲁克B r u k e r公司);微波合成仪(m o n o w a v e100,澳大利亚安东帕公司). 1.3 T O B C的制备采用超声波协同T E M P O介导氧化法来制备T O B C(机理如图1所示)[15].具体方法如下:取一定量B C凝胶经压榨排水后,剪成小碎片浸入T E M P O/N a B r(0.06g/120m L)混合溶液中,充分搅拌混合均匀放入超声波发生器内.取一定量0.6 m o l㊃L-1的N a C l O溶液,在超声波辅助下逐滴加入上述混合液中,进行原位氧化反应,同时监测体系的p H值,用0.5m o l㊃L-1的N a O H溶液保持体系p H始终稳定在10.0~11.0之间.反应一定时间后,向混合液中加入一定量无水乙醇终止反应,再用0.5m o l㊃L-1H C l调节p H值为7.0.过滤取出氧化后的B C凝胶,经充分洗涤后,即得到T O B C凝胶[16-18].图1 T E M P O介导氧化纤维素机理示意图[15] 1.4 T O B C@C d S纳米复合凝胶的制备将羧基含量最高的T O B C凝胶浸入C d C l2乙醇水溶液(v/v,2/3)中,机械搅拌,吸附平衡后,用去离子水反复冲洗3次,去除表面未吸附固定的C d2+.然后,采用微波辅助溶剂热法原位合成C d S 纳米颗粒到T O B C凝胶上:将吸附C d2+的T O B C 凝胶转入过量的浓度比为1∶1(C d C l2:硫脲)的硫脲乙醇水(v/v,2/3)溶液中,置于微波合成仪中反应,所得复合材料经去离子水反复洗涤后得到㊃8㊃Copyright©博看网 . All Rights Reserved.第1期钱 鑫等:T E M P O 氧化细菌纤维素基纳米复合凝胶的制备及其结构表征T O B C @C d S 纳米复合凝胶,制备过程中实物如图2所示.图2 T O B C @C d S 纳米复合凝胶制备过程中实物图1.5 T O B C @C d S 纳米复合凝胶中C d S 负载量测定C d S 的负载量根据公式(1)计算所得 W t %(C d S )=W TO C -W T OW TO C×100%(1) 式(1)中:W t 为C d S 的百分含量,%;W T O C 为T O B C @C d S 纳米复合凝胶的绝干质量,g ;W T O 为T O B C 凝胶的绝干质量,g.1.6 羧基含量测定采用氯化钠-碳酸氢钠法测定T O B C 的羧基含量[19],具体计算如公式(2): 羧基含量=V 1-V 2+V 2M 0æèçöø÷éëêêùûúú100×C ×400Mmm o l /100g 样品(2) 式(2)中:V 1为空白试验耗用盐酸标准溶液体积,m L ;V 2为滴定滤液耗用盐酸标准溶液体积,m L ;C 为H C l 标准溶液浓度,m o l ㊃L -1;M 0为T O B C 湿浆中水的质量,g ;M 为T O B C 的绝干质量,g.1.7 结构形貌表征采用F T -I R 分析B C ㊁T O B C 的官能团;采用S E M 观察B C ㊁T O B C 以及T O B C @C d S 凝胶的微观形貌;采用E D S 分析T O B C@C d S 凝胶的元素分布;采用X R D ㊁R a m a n 光谱表征T O B C @C d S 凝胶的成分与结构.2 结果与讨论2.1 T O B C 凝胶的结构和形貌表征2.1.1 T O B C 凝胶的F T -I R 表征图3为B C 凝胶及T O B C 凝胶的F T -I R 光谱图.由图可知,T E M P O 氧化后,对应于-C=O 伸缩振动的1650c m -1吸收峰明显加强,说明T O B C凝胶具有更多的-C O O H.此外,3350c m -1峰对应于-O H 的伸缩振动峰,1415c m -1峰对应于二聚羧酸的-C =O 伸缩振动峰,以及1050c m -1峰对应于C -O-C 的伸缩振动峰[20],这些峰都显示出同样的变化规律,也能佐证T O B C 凝胶含有大量的-C O O H.F T -I R 结果表明,采用超声波协同T E M P O 介导氧化法成功制备了高羧基含量的T O B C .图3 B C 和T O B C 凝胶的F T -I R 图2.1.2 氧化条件对T O B C 凝胶羧基含量的影响为了得到羧基含量较高的T O B C 凝胶,对氧化时间和N a C l O 用量进行了优化研究,结果如图4所示.从图4(a )可以看出,随着氧化时间的延长,T O B C 凝胶的羧基含量逐渐升高,表明B C 中C 6位羟基被更多地氧化成羧基,这与廖世波等人的研究结果一致[21].当反应120m i n 后,N a C l O 消耗殆尽,T O B C 凝胶的羧基含量达到0.6092m m o l ㊃k g -1,趋于稳定.氧化时间相同时,N a C l O 用量增大,可以得到羧基含量较高的T O B C ,但当N a C l O 用量增大到一定量时,T O B C 的羧基含量上升趋于平缓如图4(b)所示.这表明T E M P O 氧化主要针对B C 分子链中结构松散㊁能势较低的非结晶区[22];当N a C l O 用量增大到一定量后,N a C l O 针对B C 分子链非结晶区中C 6位羟基呈过饱和状态,进一步提高N a C l O 用量,T O B C 的羧基含量也不再显著增加.综上所述,确定N a C l O 用量为8m L ㊃g -1,反应时间为120m i n,可以获得羧基含量较高的T O B C 凝胶.㊃9㊃Copyright©博看网 . All Rights Reserved.陕西科技大学学报第40卷(a )氧化时间与T O B C凝胶羧基含量(b )氧化剂用量与T O B C 凝胶羧基含量图4 T E M P O 氧化与T O B C 凝胶羧基含量相关性2.1.3 T O B C 凝胶的微观形貌图5为B C 及T O B C 凝胶的微观形貌图.从图5可以看出,B C (图5(a ))呈现纳米级三维网络结构,纤维宽度约为50~100n m ,网络孔道较为致密.T O B C 凝胶(图5(b ))的微观网络结构较为疏松,网孔直径大而疏,网络分支减少.说明T E M P O氧化后,B C 分子链降解,长度减小,这与M o h a m -m a d k a z e m i F 等[23]的研究结果一致.(a )B C凝胶(b )T O B C 凝胶图5 B C 凝胶及T O B C 凝胶的S E M 图2.2 T O B C @C d S 纳米复合凝胶的结构和形貌表征2.2.1 T O B C @C d S 纳米复合凝胶拉曼光谱表征从T O B C @C d S 纳米复合凝胶的拉曼光谱图(图6)可以看出,T O B C@C d S 纳米复合凝胶的拉曼光谱出现了C d S 590c m -1和296c m -1两个特征吸收峰,与纯C d S 的拉曼光谱图相对应[24],表明C d S 成功负载到了T O B C 基质上.同时,T O B C@C d S 纳米复合凝胶并未出现对应于-C=O 的1450c m -1吸收峰,且2950c m -1处的-O H 吸收峰强度没有明显衰减,表明T O B C 凝胶主要通过-C O O H 来吸附C d S 纳米颗粒.图6 T O B C @C d S 纳米复合凝胶的拉曼光谱图2.2.2 T O B C @C d S 纳米复合凝胶的结晶结构表征图7为B C ㊁T O B C 和T O B C @C d S 纳米复合凝胶的X R D 衍射图.从图7可以看到,2毴为14.6°㊁16.9°㊁22.8°的衍射峰,分别对应于T O B C 的(100)㊁(010)㊁(110)晶面,符合纤维素Ⅰ的特征结构,这与B C 的结晶结构一致[25],说明T E M P O 氧化并没有改变B C 的晶型结构.当T O B C 上负载C d S 纳米颗粒后,由于C d 和S 元素的插入,这三个衍射峰强度有所下降,但出峰位置没有改变.说明基质T O B C 的结晶结㊃01㊃Copyright©博看网 . All Rights Reserved.第1期钱 鑫等:T E M P O氧化细菌纤维素基纳米复合凝胶的制备及其结构表征构没有发生变化,仍为纤维素Ⅰ型结构.另外,2毴为26.4°㊁43.9°㊁52.0°的衍射峰分别对应于C d S闪锌矿立方相晶体结构的(111)㊁(220)㊁(311)晶面(p u r e C d S s t a n d a r dc a r dJ C P D S65-2887)[26],这表明C d S 以立方晶型成功的负载到了T O B C基质上.图7 B C、T O B C凝胶和T O B C@C d S纳米复合凝胶的X R D图2.2.3 T O B C@C d S纳米复合凝胶的微观形貌及元素组成图8(a)为T O B C@C d S纳米复合凝胶的微观形貌图.从图中可以看到,C d S纳米颗粒聚集在T O B C分子结构的末端,形成了类似细胞感受器的结构.这表明T E M P O首先选择与B C分子链中结构松散㊁能势较低的非结晶区相结合并氧化,产生较多的羧基;富含羧基的T O B C区域对C d2+的吸附作用更强,形成了原位合成C d S纳米颗粒的反应 活性区域”.当遇到S2-时,C d S纳米颗粒迅速生成并聚集.从T O B C@C d S纳米复合凝胶E D S 图(图8(b))可以看出,吸附聚集在T O B C纤维上的纳米颗粒团簇主要为C d和S元素,说明通过微波辅助溶剂热原位法成将C d S原位合成并负载到了T O B C上.(a)T O B C@C d S纳米复合凝胶的S E M图(b)T O B C@C d S纳米复合凝胶的E D S图图8 T O B C@C d S纳米复合凝胶的微观形貌图表1对比了T O B C凝胶与B C凝胶C d S负载量.可以看出,T O B C较B C基质而言,C d S的负载量明显提高.经过T E M P O氧化处理的B C,其羧基含量显著提高,因而与C d S的结合能力增大,这是显著提高C d S的负载量的原因.表1 C d S在T O B C凝胶与B C凝胶上负载量的对比样品干基材质量/m g干样品质量/m gC d S负载率/%B C@C d S7.258.2812.4±0.3 T O B C@C d S7.209.3923.3±0.2 3 结论采用超声波辅助T E M P O介导氧化法氧化B C,制备出了羧基含量最高为0.6092mm o l㊃k g-1的T O B C基材.再采用微波辅助溶剂热原位合成法,以简洁㊁高效的方法成功制备了T O B C@ C d S纳米复合凝胶.F T-I R㊁S E M㊁E D S㊁X R D和R a m a n结果表明T O B C@C d S纳米复合凝胶具有稳定的有机无机杂化纳米纤维复合结构;在羧基的络合作用下,立方晶型C d S纳米团簇主要吸附在T O B C纤维上的非结晶区域,其形貌类似神经细胞感受器;C d S在T O B C上的负载量明显高于在B C 上的负载量,达到23.3±0.2%.参考文献[1]J i n g W a n g,J a v a dT a v a k o l i,Y o u h o n g T a n g.B a c t e r i a l c e l-l u l o s e p r o d u c t i o n,p r o p e r t i e sa n da p p l i c a t i o n sw i t hd i f f e r-e n tc u l t u r e m e t h o d s-A r e v i e w[J].C a r b o h y d r a t e P o l y-m e r s,2019,219:63-76.[2]J o z a l aAF,L e n c a s t r eN,L e t i c i aC,e t a l.B a c t e r i a l n a n o c e l-l u l o s e p r o d u c t i o na n d a p p l i c a t i o n:A10-y e a r o v e r v i e w[J].㊃11㊃Copyright©博看网 . All Rights Reserved.陕西科技大学学报第40卷A p p l i e d M i c r o b i o l o g y a n dB i o t e c h n o l o g y,2016,100: 2063-2072.[3]H u W,C h e nS,Y a n g J,e t a l.F u n c t i o n a l i z e db a c t e r i a l c e l-l u l o s ed e r i v a t i v e sa n dn a n o c o m p o s i t e s[J].C a r b o h y d r a t e P o l y m e r s,2014,101:1043-1060.[4]W a n g J,T a v a k o l i J,T a n g Y H.B a c t e r i a l c e l l u l o s e p r o d u c-t i o n,p r o p e r t i e s a n d a p p l i c a t i o n s w i t h d i f f e r e n tc u l t u r e m e t h o d s-Ar e v i e w[J].C a r b o h y d r a t eP o l y m e r s,2019,219: 63-76.[5]G a l l e g o sA M A,C a r r e r aS H.B a c t e r i a l c e l l u l o s e:As u s-t a i n a b l e s o u r c et od e v e l o p v a l u e-a d d e d p r o d u c t s-ar e v i e w [J].B i o r e s o u r c e s,2016,11(2):5641-5655.[6]K a i y a nQ i u,A n i lN.N e t r a v a l i.Ar e v i e wo f f a b r i c a t i o n a n da p p l i c a t i o n so fb ac t e r i a lc e l l u l o s e b a s ed n a n o c o m p o s i te s [J].P o l y m e rR e v i e w s,2014,54(4):598-626. [7]C i e l e c k a I,S z u s t a k M,K a l i n o w s k aH,e t a l.G l y c e r o l-p l a s-t i c i z e db a c t e r i a ln a n o c e l l u l o s e-b a s e dc o m p o s i t e s w i t he n-h a n c e df l e x i b i l i t y a n dl i q u i ds o r p t i o nc a p a c i t y[J].C e l l u-l o s e,2019,26(9):5409-5426.[8]汤卫华,贾士儒,王 芃,等.细菌纤维素在造纸工业中的应用[J].中国造纸学报,2013,28(1):62-64. [9]C h a i y a s a tA,J e a r a n a i S,C h r i s t o p h e rLP,e t a l.N o v e l s u-p e r a b s o r b e n tm a t e r i a l s f r o m b a c t e r i a l c e l l u l o s e[J].P o l y-m e r I n t e r n a t i o n a l,2019,68(1):102-109.[10]G o r g i e v a S,T rˇc e k J.B a c t e r i a l c e l l u l o s e:P r o d u c t i o n,m o d-i f i c a t i o na n d p e r s p e c t i v e s i nb i o m e d i c a l a p p l i c a t i o n s[J].N a n o m a t e r i a l s,2019,9(10):1352.[11]P o r t e l aR,L e a lC R,A l m e i d aPL,e t a l.B a c t e r i a l c e l l u-l o s e:Av e r s a t i l eb i o p o l y m e r f o rw o u n dd r e s s i n g a p p l i c a-t i o n s[J].M i c r o b i a l B i o t e c h n o l o g y,2019,12(4):586-610.[12]S a t h i s hSK,V i t t aS.B a c t e r i a l c e l l u l o s eb a s e dn a n o c o m-p o s i t e s f o re l e c t r o n i ca n de n e r g y a p p l i c a t i o n s[J].E n c y-c l o p e d i ao fR e n e w a b l ea n dS u s t a i n a b l e M a t e r i a l s,2020, 3:16-25.[13]M a g h s o u d iG a n j e h M,L i nL Q,W a n g X D.B i o i n s p i r e dd e s i g no fh y b r i dc o m p o s i t e m a t e r i a l s[J].I n tJS m a r tN a n oM a t e r,2019,10(1):90-105.[14]Q i a n X,X u Y,Y u eX,e ta l.M i c r o w a v e-a s s i s t e ds o l v o-t h e r m a l i n-s i t u s y n t h e s i s o f C d S n a n o p a r t i c l e s o n b a c t e r i-a l c e l l u l o s em a t r i x f o r p h o t o c a t a l y t i c a p p l i c a t i o n[J].C e l-l u l o s e,2020,27(10):5939-5954.[15]戴 磊,龙 柱,张 丹.T E M P O氧化纤维素纳米纤维的制备及应用研究进展[J].材料工程,2015,43(8):84-91.[16]J i aYY,Z h e n g M M,X uQQ,e t a l.R h e o l o g i c a l b e h a v i o r s o f p i c k e r i n g e m u l s i o n s s t a b i l i z e db y T E M P O-o x i d i z e db a c t e r i a lc e l l u l o s e[J].C a r b o h yd r a t eP o l y me r s,2019,215:263-271.[17]K e r s t i n,S c h l u f t e r,T h o m a s,e t a l.C a r b o x y m e t h y l a t i o no fb ac t e r i a l c e l l u l o s e[J].M a c r o m o l e c u l a rS y m p o s i a,2010, 294(2):117-124.[18]C h e nY,C h e n S,W a n g B,e t a l.T E M P O-o x i d i z e d b a c t e r i-a l c e l l u l o s en a n o f ib e r s-s u p p o r t e d g o l dn a n o p a r t ic l e sw i t h s u p e r i o r c a t a l y t i c p r o p e r t i e s[J].C a r b o h yd r a t eP o l y me r s, 2017,160:34-42.[19]W a n g J,L i uM.P r e p a r a t i o n a n d c h a r a c t e r i z a t i o n o f c e l l u-l o s e-b a s e d a d s o r b e n t a n d i t s a p p l i c a t i o n i nh e a v y m e t a l i-o n s r e m o v a l[J].C a r b o h y d r a t eP o l y m e r s,2019,206:837-843.[20]P a h l e v a n M,T o i v a k k a M,A l a m P.M e c h a n i c a l p r o p e r t i e so fT E M P O-o x i d i s e db a c t e r i a lc e l l u l o s e-a m i n oa c i d b i o m a t e r i a l s [J].E u r o p e a nP o l y m e r J o u r n a l,2018:101:29-36. [21]廖世波,奚廷斐,赖 琛,等.T E M P O-N a B r-N a C l O体系对细菌纤维素的氧化过程研究[J].中国生物医学工程学报,2013,32(6):699-707.[22]S o g a iA,S a i t oT,F u k u z u m iH.T E M P O-o x i d i z e dc e l l u-l o s e n a n o f i b e r s[J].N a n o s c a l e,2011,3(1):71-85. [23]M o h a mm a d k a z e m iF,B a r a n g e n a n iR K,K o o s h a M.D e-v e l o p m e n to fo r g a n i c-i n o r g a n i co x i d i z e db a c t e r i a lc e l l u-l o s en a n o b i o c o m p o s i t e s:T e r n a r y c o m p l e x e s[J].C e l l u-l o s e,2019,26(10):6009-6022.[24]P r a b h uRR,K h a d a rM A.S t u d y o f o p t i c a l p h o n o nm o d e s o fC d Sn a n o p a r t i c l e s u s i n g R a m a ns p e c t r o s c o p y[J].B u l-l e t i no fM a t e r i a l sS c i e n c e,2008,31(3):511-515. [25]F r e n c hAD.I d e a l i z e d p o w d e r d i f f r a c t i o n p a t t e r n s f o r c e l-l u l o s e p o l y m o r p h s[J].C e l l u l o s e,2014,21(2):885-896.[26]X i nL,C h e nS,H u W,e t a l.I n s i t u s y n t h e s i s o f C d Sn a n-o p a r t i c l e s o nb a c t e r i a l c e l l u l o s en a n o f i b e r s[J].C a r b o h y-d r a t eP o l y m e r s,2009,76(4):509-512.【责任编辑:蒋亚儒】㊃21㊃Copyright©博看网 . All Rights Reserved.。
TEMPO氧化体系选择性氧化未漂非木浆的研究
TEMPO氧化体系选择性氧化未漂非木浆的研究张德志;李海龙;蒙启骏;詹怀宇【摘要】以未漂麦草浆和竹浆为原料,研究了TEMPO-NaBr-NaClO体系氧化前后纸浆性质及纤维形貌的变化情况,并对其氧化过程进行了动力学分析.结果表明,未漂麦草浆和竹浆的TEMPO氧化过程均遵循二级反应动力学方程.经TEMPO氧化后,麦草浆和竹浆的羧基含量大幅提高,分别达569.8 μmol/g和716.7 μmol/g,而纸浆黏度和热稳定性则均显著下降.此外,氧化前后纤维微观形貌、尺寸变化不大,而结晶度则有所增加,但仍保持了天然纤维素Ⅰ型的结晶结构.【期刊名称】《中国造纸》【年(卷),期】2017(036)001【总页数】6页(P9-14)【关键词】未漂非木浆;TEMPO氧化;纸浆性质;纤维形貌【作者】张德志;李海龙;蒙启骏;詹怀宇【作者单位】华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640【正文语种】中文【中图分类】TS71我国森林资源短缺,非木材纤维原料如麦草、竹子、蔗渣等资源丰富。
非木材纤维制浆造纸在我国具有悠久的历史,非木材是我国造纸工业的重要纤维原料[1]。
然而,非木材原料制浆造纸存在的诸多技术和环保问题限制了其发展。
探寻新工艺和新技术是突破非木材纤维高值化利用壁垒、实现清洁生产的关键。
非木材纤维原料在纤维形态、生物结构和化学组成等方面差异较大,这使得大量的非木材纤维资源得不到有效利用[2-3]。
因此,如何结合非木材原料的特点,科学、高效、合理地利用非木材纤维资源,提高其应用价值,具有重要意义。
2,2,6,6-四甲基哌啶-1-氧化物自由基(TEMPO)属于亚硝酰自由基类,是一种具有稳定氮氧自由基结构的环状化合物[4]。
TEMPO(2,2,6,6-四甲基哌啶-1-氧基)对乳酸的电氧化研究
TEMPO(2,2,6,6-四甲基哌啶-1-氧基)对乳酸的电氧化研究张文彬;廖新艳;张静雅【摘要】TEMPO(2,2,6,6-四甲基哌啶-1-氧基)被证明可以用于乳酸的电催化氧化反应,电氧化峰值电流密度随水溶液pH升高而增大,同一条件下,4-乙酰氨基-TEMPO对L-乳酸的电催化能力强于TEMPO,这可以归结于乙酰氨基官能团的吸电子能力.同时,由于可能的位阻效应,TEMPO对L-乳酸的电催化能力大于其对D-乳酸的电氧化能力.【期刊名称】《宜春学院学报》【年(卷),期】2018(040)006【总页数】3页(P8-10)【关键词】乳酸;电催化;氮氧自由基;手性;pH【作者】张文彬;廖新艳;张静雅【作者单位】宜春学院化学与生物工程学院,江西宜春336000;宜春学院化学与生物工程学院,江西宜春336000;宜春学院化学与生物工程学院,江西宜春336000【正文语种】中文【中图分类】TQ243乳酸是一种常见的有机酸，它在许多生物化学过程中都有着重要意义，在一般的新陈代谢和运动中人体会不断产生乳酸。
作为一种重要的工业原料，乳酸可用于药物合成、化妆品，食品、农业和绿色化工等领域，比如，乳酸可以经不同类型化学反应和电化学反应生成各种目标小分子。
在常见的乳酸相关电化学反应中，Ni-PTFE 电极[1]等已被证明都可用于乳酸的电化学氧化反应，为拓宽乳酸电化学氧化反应体系，论文将探讨氮氧自由基(主要是TEMPO)在碱性条件对乳酸的电化学催化氧化过程。
包括TEMPO在内的氮氧自由基是一种少见稳定存在的自由基，已被广泛用于醇及胺类的电氧化反应[2,3]，新的涉及氮氧自由基的电化学体系也在不断被开发，如Shannon S.Stahl等报道了(2,2'-联吡啶)铜/氮氧自由基共催化剂体系相对于纯氮氧自由基体系可用于更快速的电化学醇氧化反应[4]。
雷爱文等发现TEMPO可用于N-杂环的电催化无溶剂脱氢[5]，但目前将包括TEMPO在内的氮氧自由基用于乳酸电催化氧化的研究还未见报道。
木素对TEMPO氧化竹浆制备纳米纤维素的影响
木素对TEMPO氧化竹浆制备纳米纤维素的影响杜超;李海龙;蒙启骏;刘梦茹;詹怀宇【摘要】TEMPO-oxidation cellulose nanofibers (TOCNs) were prepared from unbleached kraft bamboo pulps (SHK,Kappa No.=25.5;SLK,Kappa No.=11.7) by means of TEMPO/NaBr/NaC1O oxidation and subsequent homogenization.The TOCN films were prepared by vacuumfiltration.During the TEMPO-oxidation processes,the properties of TEMPO oxidized pulps,TOCNs and TOCN films of SHK and SLK were compared,the effect of lignin on TEMPO-oxidation process and TOCN production was studied.Results showed that the TEMPO-oxidation rate of SHK was faster than SLK,but the carboxyl content of SLK-TEMPO oxidized pulp was 1.01 mmol/g,much higher than SHK-TEMPO oxidized pulp (0.89 mmol/g).The obtained TOCNs exhibited a fibril-like structure,with a narrow width ranging from 5 nm to 8 nm and a high aspect ratio (＞ 100),and the TOCNs were cellulose-I.The suspension transparency and crystalline index of SLK-TOCN were higher than SHK-TOCN.The two kinds of TOCN films displayed good optical and mechanical performance,and the Yong's modules,tensile strength,and the elongation of SLK-TOCN film were 2.6 GPa,92 MPa,and 10.9％,respectively,all of them were higher than the SHK-TOCN film which were 2.4 GPa,90 MPa,and 8.7％,respectively.%以卡伯值不同的2种未漂硫酸盐竹浆(卡伯值为25.5和11.7的竹浆分别标记为SHK和SLK)为原料,通过TEMPO/NaBr/NaClO体系氧化及高压均质处理,制备了TEMPO氧化纳米纤维素(TOCN),并利用抽滤法制备TOCN膜.系统地研究了2种竹浆的TEMPO氧化过程、TEMPO氧化浆性能、TOCN性能及TOCN膜的力学性能等,探讨了木素对竹浆TEMPO氧化过程和TOCN制备的影响.结果表明,SHK的TEMPO氧化速率高于SLK,但SLK-TEMPO氧化浆的羧基含量达到1.01 mmol/g,高于SHK-TEMPO氧化浆的羧基含量(0.89 mmol/g).2种TOCN形态结构差异不大,均呈纤丝状结构,直径约为5～8 nm,长径比＞100,且均保持纤维素Ⅰ的晶型结构;SLK-TOCN的结晶度和悬浮液的透光度均略高于SHK-TOCN.2种TOCN膜均具有优良的光学性能和力学性能,SLK-TOCN膜的杨氏模量、拉伸强度及裂断伸长率分别为2.6 GPa、92 MPa和10.9％,均高于SHK-TOCN膜的2.4 GPa、90 MPa和8.7％.【期刊名称】《中国造纸学报》【年(卷),期】2017(000)002【总页数】6页(P1-6)【关键词】未漂竹浆;TEMPO氧化;纳米纤维素;薄膜;强度【作者】杜超;李海龙;蒙启骏;刘梦茹;詹怀宇【作者单位】华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640;华南理工大学制浆造纸工程国家重点实验室,广东广州,510640【正文语种】中文【中图分类】TS721木质纤维原料主要包括木材、草类、能源作物、农业废弃物等,是地球上最丰富的可再生资源。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
TEMPO-Mediated Oxidation of Native Cellulose.The Effect of Oxidation Conditions on Chemical and Crystal Structures of theWater-Insoluble FractionsTsuguyuki Saito and Akira Isogai*Graduate School of Agricultural and Life Sciences,The University of Tokyo,1-1-1Yayoi,Bunkyo-ku,Tokyo113-8657,JapanReceived April15,2004;Revised Manuscript Received June1,2004Cellulose cotton linter was oxidized with sodium hypochlorite with catalytic amounts of sodium bromide and2,2,6,6-tetramethylpiperidine-1-oxyl radical(TEMPO)under various conditions.After this TEMPO-mediated oxidation,water-insoluble fractions were collected and characterized in terms of carboxylate and aldehyde contents,crystallinities and crystal sizes,degrees of polymerization,morphology,and water retention values.Carboxylate and aldehyde groups were introduced into the water-insoluble fractions up to about0.7 and0.3mmol/g,respectively,by the oxidation,where recovery of the water-insoluble fractions were generally higher than80%.Crystallinities and crystal sizes of cellulose I were nearly unchanged during the oxidation, and thus,carboxylate and aldehyde groups were introduced selectively on crystal surfaces and in disordered regions of the water-insoluble fractions.Water retention values of cotton linter can be increased from60% to about280%through the introduction of hydrophilic carboxylate groups and morphological changes from fibrous forms to short fragments by the TEMPO-mediated oxidation.IntroductionWater-soluble and stable nitroxyl radicals such as2,2,6,6-tetramethylpyperidine-1-oxyl(TEMPO)have been widely studied for catalytic and selective oxidation of primary hydroxyl groups of polysaccharides under aqueous condi-tions.Nooy et al.1-3first applied the TEMPO-mediated oxidation to water-soluble polysaccharides such as potato starch,amylodextrin,and pullulan,where NaClO was used as a primary oxidant with catalytic amounts of NaBr and TEMPO at pH10-11.Highly selective oxidation of the C6 primary hydroxyl groups of the polysaccharides to carboxyl ones was achieved,and the corresponding polyuronic acids were obtained quantitatively.Chang and Robyt4applied the TEMPO-mediated oxidation to water-soluble natural polysaccharides,water-soluble polysac-charide derivatives,and water-insoluble natural polysaccha-rides such as cellulose and chitin.In the case of the oxidation of native celluloses,however,the oxidized products are not completely soluble in water even after extended oxidation time,because most of the C6primary hydroxyl groups in native celluloses remain as they are in the oxidized prod-ucts.5,6When regenerated or mercerized celluloses are used as the starting materials for the TEMPO-mediated oxidation, in contrast,the aqueous cellulose slurry turns to a clear solution at room temperature within1h as the oxidation proceeds,and -1,4-linked polyglucuronic acid sodium salt (cellouronic acid Na salt)having a homogeneous chemical structure can be obtained quantitatively as the oxidized product.5,6The oxidation resistance of native celluloses is ascribed to their high crystallinities and low accessibilities to the reagents.Perez et al.7revealed from their detailed studies using various cellulose I and III samples that significant increases in water-soluble fractions were achieved by using cellulose samples having cellulose III crystal structures, which were prepared by treating native celluloses with either liquid ammonia or ethylenediamine.It is well-known that partial decrystallization occurs on native celluloses by the cellulose III conversion treatments at atmospheric pressure.8 Cellouronic acid is a water-soluble polyelectrolyte with many possible functionalities,and extensive studies have been carried out to characterize its properties and to control its molecular mass values.9-11TEMPO-mediated oxidation of native celluloses,on the other hand,is a surface effect in which anionic carboxylate groups are introduced as func-tional groups at solid cellulose surfaces.12-14When bleached hardwood kraft pulp after beating to a standard level was used as the starting material for the TEMPO-mediated oxidation,some interesting results were obtained in charac-terizations of the oxidized pulps with various carboxylate contents and the handsheets prepared thereof.12,13However, because the kraft pulp used contained about15%noncellu-losic polysaccharides(hemicellulose),pure cellulose must be adopted for obtaining fundamental information about TEMPO-mediated oxidation of native cellulose.In this study,the TEMPO-mediated oxidation was applied to cotton linter under various conditions,and the water-insoluble fractions in the oxidized products were collected by filtration and characterized from various aspects for obtaining fundamental information about the surface-modi-fied celluloses with various functional groups.*To whom correspondence should be addressed.Phone:+8135841 5538.Fax:+81358415271.E-mail:aisogai@mail.ecc.u-tokyo.ac.jp.1983Biomacromolecules2004,5,1983-198910.1021/bm0497769CCC:$27.50©2004American Chemical SocietyPublished on Web07/09/2004Materials and MethodsMaterials.Cellulose cotton linter(Ash-less filter pulp, Advantec Toyo Co.,Ltd.,Japan)was used as a native cellulose sample.TEMPO,sodium bromide and9mass% sodium hypochlorite solution,and other chemicals and solvents were of laboratory grades(Wako Pure Chemicals, Co.,Japan)and used without further purification.Cotton linter was immersed in liquid ammonia at about-70°C and atmospheric pressure for1h,and the cellulose/ammonia complex thus formed was soaked in water to prepare a low-crystalline cellulose I sample.TEMPO-Mediated Oxidation of Cellulose.Cellulose(5g)was suspended in water(375mL)containing TEMPO(0.0125g)and sodium bromide(0.125g).A designed amount of the9%NaClO solution,corresponding to0-9.67 mmol/g cellulose,was added slowly to the cellulose slurry,and the pH of the mixture was maintained to be10.5at room temperature by adding0.5M NaOH using a pH stat for 0.25-24h.After stirring for a designed time,the oxidation was quenched by adding ethanol(ca.5mL).The oxidized cellulose was washed thoroughly with water and then ethanol on a filter paper set in a Bu¨chner funnel.The water-insoluble fractions thus obtained were then dried by lyophilization followed by vacuum-drying at40°C for48h,and weighed to measure the mass recovery ratios.Determination of Carboxylate and Aldehyde Contents. The carboxylate content of the water-insoluble fractions was determined by the electric conductivity titration method.To a dried sample(0.3g)were added water(55mL)and0.01 M NaCl(5mL),and the mixture was sufficiently stirred to prepare a well-dispersed slurry.Then,0.1M HCl was added to the mixture to set the pH value in the range of2.5-3.0. A0.04M NaOH solution was added at the rate of0.1mL/ min up to pH11by using a pH stat.The carboxylate content of the sample was determined from the conductivity and pH curves.14The aldehyde content in the water-insoluble frac-tions was measured according to the following standard method.15The water-insoluble fractions were further oxidized with sodium chlorite at pH4-5for selective conversion of the aldehyde groups in the samples to carboxylate ones,and carboxylate content was determined by the above-mentioned electric conductivity titration method.A cellulose slurry with 10%consistency was prepared beforehand,and then this slurry(20g)was added to a mixture containing NaClO2(1.81 g),5M CH3COOH(20mL),and water(57mL).Oxidation was carried out by stirring the mixture at room temperature for48h,followed by washing thoroughly with water by filtration.The carboxylate groups formed by the NaClO2 oxidation were regarded as aldehyde groups present in the original water-insoluble fractions.X-ray Diffraction.The water-insoluble fractions having fiber and/or powder forms were converted to pellets using the KBr disk apparatus for IR measurements and subjected to X-ray diffraction measurement using the reflection method by means of a Rigaku RINT2000with a Ni-filtered Cu K R radiation at40kV and40mA.Crystallinity indices and crystal sizes of the200direction of cellulose I were calculated from the X-ray diffraction patterns according to the conventional methods.16,17DPv Measurement.Intrinsic viscosities of the water-insoluble fractions were obtained by a capillary viscometer using0.5M copper ethylenediamine(cuen)as the solvent, and these values were converted to viscosity average degrees of polymerization(DPv)by the reported method.18 Water Retention Value.The never-dried water-insoluble fractions after the oxidation were centrifuged at1500gravity and20°C for15min,and water retention values(WRVs) were calculated from the following equation:where W w is the mass of the wet sample after the centrifuga-tion and W d is that after drying of the wet sample at105°C for3h.Results and DiscussionKinetics of TEMPO-Mediated Oxidation of Cellulose. Figure1shows relationships between oxidation time and either carboxylate or aldehyde content in the water-insoluble fraction,where4.84mmol NaClO(per gram cellulose)was applied to the cellulose slurry at room temperature and pH10.5.Both carboxylate and aldehyde groups were formed ina similar manner up to0.5h,and then the aldehyde content nearly reached a plateau level around0.2-0.3mmol/g,which corresponded to approximately one aldehyde group per20-30monomer-repeating units.The carboxylate content,on the other hand,further increased up to0.74mmol/g with increasing oxidation time,and no clear increase in carboxy-late content was observed in the water-insoluble fractions during the oxidation from4to24h.The0.74mmol/g carboxylate content corresponds to approximately one car-boxylate group per8monomer-repeating units on average. The aldehyde groups formed in the water-insoluble frac-tions are due to C6aldehydes present as the intermediate structure during the TEMPO-mediated oxidation and reduc-ing ends formed from glycoside bonds by -elimination at pH10.5during the oxidation.In the case of TEMPO-mediated oxidation of water-soluble polysaccharides,sig-nificant amounts of C6aldehydes,aldehyde hydrates,and hemiacetals are formed as intermediate structures during the oxidation process.19,20In the homogeneous oxidationsystems, Figure1.Carboxylate and aldehyde contents of the water-insoluble fractions in the products prepared from cotton linter by the TEMPO-mediated oxidation with4.84mmol NaClO(per g of cellulose)at room temperature and pH10.5for various reaction times.WRV(%))100×(Ww-Wd)/Wd1984Biomacromolecules,Vol.5,No.5,2004Saito and Isogaihowever,these aldehyde-related structures are completely oxidized to carboxylate groups as the oxidation proceeds.Therefore,it is an unexpected result that significant amounts of aldehyde groups remain in the water-insoluble fractions even after the extended oxidation up to 24h.These aldehyde groups,probably forming intra-and intermolecular hemiac-etals with cellulose hydroxyls in the solid water-insoluble fractions,are likely to have high resistance to the next TEMPO-mediated oxidation step by steric hindrance.This is discussed in a latter section.Figure 2plots relationships between oxidation time and NaOH consumption in the experiment of Figure 1.Recovery mass percentages of the water-insoluble fractions are also plotted in this figure.The recovery ratio of the water-insoluble fraction decreased with increasing oxidation time,and approximately 20%of the original cotton linter was lost after oxidation for 24h by the washing/filtration process.Thus,a part of the water-insoluble fractions become water-soluble and is removed as a filtrate during the washing process,when the carboxylate content in average exceeds the value of ca.0.8mmol/g.The NaOH consumption due to atmospheric CO 2adsorp-tion to the oxidation medium at pH 10.5can be regarded as negligible.On the other hand,the NaOH consumption was clearly detected in the cellulose/NaBr/NaClO system without TEMPO,and especially a significant amount of NaOH was consumed after stirring the mixture for 24h.Probably,ClO -and BrO -gradually attack cellulose in the slurry without TEMPO to form some carboxyl groups,which in turn consume NaOH to maintain the pH of 10.5.The NaOH consumption in the cellulose/NaBr/TEMPO/NaClO system at pH 10.5corresponded well with the total amount of carboxylate and aldehyde groups formed in the water-insoluble fraction up to 0.5h;not only carboxyl groups but also aldehyde groups formed in the water-insoluble fractions stoichiometrically consume NaOH for maintaining the pH of 10.5.However,after that,the difference between the NaOH consumption and the total carboxylate and aldehyde contents increased with increasing oxidation time.Because the recovery of the water-insoluble fraction decreased with increasing oxidation time,the excess NaOH is likely to be consumed to neutralize carboxyl groups in the water-soluble fractions formed by the TEMPO-mediated oxidation.These results of the oxidation kinetics as well as the pattern of therecovery ratio show that the TEMPO-mediated oxidation takes place in accessible regions in cotton linter as reported by Perez et al.7Figure 3depicts relationships between the amount of NaClO added as the primary oxidant to the cellulose/NaBr/TEMPO system and either carboxylate or aldehyde content in the water-insoluble fractions.The carboxylate and alde-hyde contents increased in a similar manner by the addition of NaClO up to 0.6mmol per gram cellulose.Carboxylate groups were further formed up to about 0.6mmol/g by the NaClO addition,whereas the content of aldehyde groups was unchanged around 0.2mmol/g.Thus,neither carboxylate nor aldehyde content in the water-insoluble fractions exceeds a certain level even by the excess NaClO addition.The recovery of the water-insoluble fraction and the amount of NaOH consumed in the experiment of Figure 3are plotted in Figure 4.In this case also,the NaOH consumption stoichiometrically proceeded up to 0.6mmol NaClO per gram cellulose,corresponding to the carboxyl and aldehyde groups in the water-insoluble fractions.The clear difference between the NaOH consumption and the total amounts of carboxylate and aldehyde groups appeared at the NaClO addition of more than 1.2mmol per gram cellulose.Along with this result,the recovery ratio of the water-insoluble fraction decreased;the excess NaOH was consumed to neutralize carboxyl groups in the water-soluble fractions formed during the TEMPO-mediatedoxidation.Figure 2.Changes in the amount of NaOH consumed,that of carboxylate and aldehyde groups formed in the water-insoluble fractions,and recovery of the water-insoluble fractions by the TEMPO-mediated oxidation of cotton linter under the conditions in Figure1.Figure 3.Carboxylate and aldehyde contents of the water-insoluble fractions in the products prepared from cotton linter by the TEMPO-mediated oxidation with various amounts of NaClO at room temper-ature and pH 10.5for 2h.Figure 4.Changes in the amount of NaOH consumed,that of carboxylate and aldehyde groups formed in the water-insoluble fractions,and recovery of the water-insoluble fractions by the TEMPO-mediated oxidation of cotton linter under the conditions in Figure 3.TEMPO-Mediated Oxidation of Native Cellulose Biomacromolecules,Vol.5,No.5,20041985Thus,significant amounts of carboxylate and aldehyde groups can be introduced into solid cellulose by the TEMPO-mediated oxidation of cellulose cotton linter,and the amounts of these functional groups are controllable by selecting the oxidation conditions.Changes in Crystallinity and Crystal Size of Cellulose during TEMPO-Mediated Oxidation.Table 1shows carboxylate content and recovery of the water-insoluble fractions in the products prepared from cotton linter and the low-crystalline cellulose I sample by the TEMPO-mediated oxidation at room temperature and pH 10.5for 2h.The low-crystalline cellulose I sample gave recovery ratios lower than those for cotton linter,when the oxidation was applied under the same conditions,showing that the oxidation takes place in accessible or disordered regions in these cellulose I samples.The carboxylate contents in the water-insoluble fractions,on the other hand,were within the range of 0.52-0.76mmol/g.When the carboxylate contents on average are more than about 0.8mmol/g,the oxidized products turn to have higher water-solubility and thus are removed to the filtrates during the washing process.Figure 5illustrates X-ray diffraction patterns of the cellulose I samples before and after the TEMPO-mediated oxidation.Although recovery ratios decreased by oxidation,the X-ray diffraction patterns were nearly unchanged evenafter the oxidation.The 200diffraction peak position of cotton linter and the 110diffraction pattern of the low-crystalline cellulose I sample slightly changed by the oxidation.These slight changes may reflect the introduction of significant amounts of carboxylate and aldehyde groups on cellulose I crystal surfaces.Figure 6plots changes in crystallinity of cellulose I and crystal size of the 200direction of the water-insoluble fractions during the TEMPO-mediated oxidation with various amounts of NaClO,whose oxidation conditions correspond to those in the experiment of Figures 3and 4.Even though significant amounts of carboxylate and aldehyde groups were formed in the water-insoluble fractions by the oxidation,crystallinity was nearly unchanged for cotton linter,and slightly increased for the low-crystalline cellulose I sample.Crystal sizes were unchanged for the two cellulose I samples.These results show that neither carboxylate nor aldehyde groups are formed inside cellulose I crystallites during the TEMPO-mediated oxidation;the significant amounts of carboxylate and aldehyde groups formed in the water-insoluble fractions are mostly present on the crystal surfaces and in disordered regions.Thus,even though the carboxylate content of,for example,0.74mmol/g in the water-insoluble fractions corresponds to about one carboxylate group per 8monomer-repeating units in average,the crystal surfaces and disordered regions have carboxylate groups with much higher densities.The slight increase in crystallinity for the low-crystalline cellulose I sample by oxidation is due to partial loss of the disordered regions during the washing process because of their increased water-solubility.Similar results were observed in steam-explosion of native cellulose samples,where some disordered regions are hydrolyzed and removed to water-soluble fractions.21Thus,the TEMPO-mediated oxidation of cellulose cotton linter can introduce carboxylate and aldehyde groups with high densities on crystal surfaces and in disordered regions,maintaining the water-insoluble states.Changes in Degree of Polymerization of Cellulose during TEMPO-Mediated Oxidation.Generally,some depolymerization is inevitable in the TEMPO-mediated oxidation of regenerated cellulose to prepare cellouronic acid,and some radical species formed in situ in theoxidationFigure 5.X-ray diffraction patterns of the original cotton linter (A1),low-crystalline cellulose I (B1),and those of the water-insoluble fractions (A2and B2,respectively)after the TEMPO-mediated oxidation with NaClO of 4.84mmol/g cellulose at room temperature for 2h.Table 1.Carboxylate Content and Recovery of Water-Insoluble Fractions in the Products Prepared from Cotton Linter andLow-Crystalline Cellulose I by the TEMPO-Mediated Oxidation at Room Temperature and pH 10.5for 2hsampleNaClO added (mmol/g cellulose)carboxylate content (mmol/g)recovery as(%)cellulose cotton linter 4.840.60919.680.5484low-crystalline cellulose I a4.840.76849.680.5278aPrepared by soaking cotton linter/ammonia complex inwater.Figure 6.Changes in crystallinity (empty symbols)and average crystal size (filled symbols)of the 200plane of cellulose I in the water-insoluble fractions by the TEMPO-mediated oxidation of cotton linter and low-crystalline cellulose I with different amounts of NaClO at room temperature for 2h.1986Biomacromolecules,Vol.5,No.5,2004Saito and Isogaisystem rather than -elimination at pH 10.5are likely to participate in the depolymerization mechanism.8Figure 7plots changes in viscosity average degree of polymerization (DPv)of the water-insoluble fractions.The DPv of the original cotton linter dropped from 480to about 200within 0.5h in the oxidation.Similar results were obtained also in the TEMPO-mediated oxidation of bleached hardwood kraft pulp with different amounts of NaClO.12However,because the cuen solution used for the viscosity measurement is alkaline,some of these DPv reductions must have occurred on the water-insoluble fractions during the dissolution process in cuen by -elimination of the glycoside bonds.Not only the presence of C6carboxylate groups but also that of C6aldehyde and C2or C3ketones formed in the water-insoluble fractions by the TEMPO-mediated oxidation accelerates the -elimination under the alkaline conditions.12The phenomenon observed in Figure 7is well-known as the leveling-off DP patterns in diluted acid hydrolysis of higher plant celluloses,even though the result in Figure 7was obtained under alkaline conditions.The periodical distribution of disordered regions present along microfibrils in higher plant celluloses 22has probably brought about such leveling-off DP behavior.This is because the TEMPO-mediated oxidation introducing carboxylate and aldehyde groups into solid cellulose,which in turn lead to -elimina-tion during the dissolution process in cuen,occurs on the disordered regions in cotton linter accessible to reagents in the oxidation medium.Studies on real molecular mass without -elimination and molecular mass distribution of the water-insoluble fractions will be reported in the following paper.The amounts of reducing ends in the water-insoluble fractions were calculated from the DPv values in Figure 7on the assumption that the DPv/DPn values were 2.5and 1.5for the original cotton linter and the samples having the leveling-off DPv,respectively.23Because the DPv values of the oxidized samples in Figure 7must be lower than real ones,as described above,the quantities of reducing ends plotted in Figure 7are somewhat overestimated.Neverthe-less,these values are still far lower than those determined as aldehyde contents in Figure 1.Thus,most of the aldehyde groups formed in the water-insoluble fractions by the oxidation (Figure 1)are not due to reducing ends formed by -elimination of glycoside bonds under the oxidation condi-tions at pH 10.5but to C6aldehydes formed as the intermediate structures during the TEMPO-mediated oxida-tion.Morphological Changes of Cellulose Fibers during TEMPO-Mediated Oxidation.Optical microphotographs with or without cross-polarizers of the original cotton linter and the TEMPO-oxidized water-insoluble fractions are shown in Figure 8.After the oxidation for 2h,significant amounts of carboxylate and aldehyde groups were formed in the water-insoluble fraction,0.60and 0.22mmol/g,respectively (Figure 3).However,most of the long fibers were morphologically similar to those of the original cotton linter,whereas some fine particles formed by the oxidation were observed (Figure 8B).Fibrillation of long fibers and formation of fine particles were clearly observed after the oxidation for 4h (Figure 8C).Most of the long cellulose fibers turned to short fragments by cutting perpendicularly to the fiber axis after oxidation for 24h,and simultaneously,each short fragment increased in width by fibrillation (Figure 8D).Depolymerization occurring in thenoncrystallineFigure 7.Changes in degree of polymerization (DPv)of the water-insoluble fractions prepared from cotton linter by the TEMPO-mediated oxidation of cotton linter with 4.84mmol NaClO (per gram cellulose)at room temperature and pH 10.5for 2h.Contents of reducing end groups are calculated from the DPv values obtained (see thetext).Figure 8.Optical microphotographs of cotton linter (A)and the water-insoluble fractions in the products prepared from cotton linter by the TEMPO-mediated oxidation with 4.84mmol NaClO (per gram cellulose)at room temperature and pH 10.5for 2(B),4(C),and 24h (D).Photographs were taken with and without cross polarizers.TEMPO-Mediated Oxidation of Native Cellulose Biomacromolecules,Vol.5,No.5,20041987regions as the side reaction during the oxidation (Figure 7)is likely to cause the formation of short fragments.These short fragments were still observed as bright parts with cross-polarizers,showing that the crystal structure of cellulose I remained in there.Thus,the fibrous morphology of cotton linter changes together with the introduction of carboxylate and aldehyde groups into cellulose by the TEMPO-mediated oxidation,depending on the oxidation conditions.When oxidation time of cotton linter was extended to 24h,the fibrous form turned to short fragments,and simultaneously,recovery ratios of water-insoluble fractions decreased,al-though carboxylate and aldehyde contents were nearly unchanged.Changes in Water Retention Values of Cellulose during TEMPO-Mediated Oxidation.Figure 9depicts water retention values (WRVs)of the water-insoluble fractions obtained by the different TEMPO-mediated oxidation times.The WRV increased roughly linearly with increasing the carboxylate content of the water-insoluble fraction up to an oxidation time of 4h.Although the carboxylate contents were nearly equal between the samples oxidized for 4and 24h,a large difference in WRV was observed between them.Generally,WRVs are influenced by the content of fines fraction as well as swelling ability and degrees of fibrillation of the long fibers.24The remarkable increase in WRV for the sample prepared by oxidation for 24h is probably due to the formation of a significant amount of fines by the extended oxidation time,as observed in the microphoto-graphs of Figure 8D.Thus,TEMPO-mediated oxidation can be used to impart cellulose cotton linter with various WRVs by controlling the oxidation conditions.In the case of the TEMPO-mediated oxidation of bleached kraft pulp after beating,WRVs were mostly unchanged for the pulps oxidized under various conditions.7However,because the original kraft pulp contained hydrophilic hemi-cellulose of about 15%and had a high WRV of about 150%after beating,no clear increases in WRVs were observed for these oxidized pulps.In the case of cotton linter,in contrast,because its WRV is sufficiently low (about 60%),clear increases in WRVs can be achieved by the TEMPO-mediated oxidation,where both chemical and morphological changes take place on cellulose.ConclusionsWhen TEMPO-mediated oxidation is applied to cellulose cotton linter,carboxylate and aldehyde groups can be introduced into the water-insoluble fractions up to about 0.7and 0.3mmol/g,respectively.Recovery ratios of the water-insoluble fractions vary,depending on the oxidation condi-tions and are generally higher than 80%.Sodium hypochlorite and NaOH used in the oxidation are consumed not only for the formation of carboxyl and aldehyde groups in the water-insoluble fractions but also for the formation of water-soluble fractions,especially under harsh conditions such as extended oxidation time or excess NaClO addition.Crystallinities and crystal sizes of cellulose I are mostly unchanged for cotton linter even after introduction of significant amounts of carboxylate and aldehyde groups into the water-insoluble fractions by the oxidation.Thus,these functional groups must be present on crystal surfaces and in disordered regions with quite high densities.The fibrous form of cotton linter can be maintained to some extent by selecting the oxidation conditions,where significant amounts of carboxylate and aldehyde groups are introduced into the water-insoluble fractions.However,the extended oxidation time causes the formation of fine fragments by cutting perpendicularly to the fiber directions and fibrillation.Water retention values of cotton linter increase from 60%to about 280%by the introduction of carboxylate groups and morphological changes through the TEMPO-mediated oxidation.Thus,the TEMPO-mediated oxidation allows unique chemical modifications selectively on crystal surfaces and in disordered regions together with some morphological changes for cotton linter under aqueous and moderate conditions.Acknowledgment.This research has been supported by a Grand-in-Aid for Scientific Research (Grant Number 11660160,13660157,and 15380116)from the Japan Society for the Promotion of Science (JSPS).References and Notes(1)de Nooy,A.E.;Besemer,A.C.;van Bekkum,H.Carbohydr.Res.1995,269,89.(2)de Nooy,A.E.;Besemer,A.C.;van Bekkum,H.Tetrahedron 1995,51,8023.(3)Bragd,P.L.;van Bekkum,H.;Besemer,A.C.Top.Catal.2004,27,49.(4)Chang,P.S.;Robyt,J.F.J.Carbohydr.Chem.1996,15,819.(5)Isogai,A.;Kato,Y.Cellulose 1998,5,153.(6)Tahiri C.;Vignon,M.R.Cellulose 2000,7,177.(7)Da Silva Perez;Montanari,S.;Vignon,M.R.Biomacromolecules2003,4,1417.(8)Isogai,A.;Usuda,M.Mokuzai Gakkaishi 1992,38,562.(9)Kato,Y.;Habu,N.;Yamaguchi,J.;Kobayashi,Y.;Shibata,I.;Isogai,A.;Samejima,M.Cellulose 2002,9,75.(10)Shibata,I.;Isogai,A.Cellulose 2003,10,151.(11)Shibata,I.;Isogai,A.Cellulose 2003,10,335-341.(12)Kitaoka,T.;Isogai,A.;Onabe,F.Nordic Pulp Paper Res.J.1999,14,274.(13)Kitaoka,T.;Isogai,A.;Onabe,F.Nordic Pulp Paper Res.J.2000,15,177.(14)Araki,J.;Wada,M.;Kuga,ngmuir 2001,17,21.(15)Parks,E.J.;Hebert,R.L.Tappi J.1972,55(10),1510.(16)Segal,L.;Creely,J.J.;Martin,A.E.,Jr.;Conrad,C.M.Textile Res.J.1959,29,786.(17)Alexander,L.E.In X-ray Diffraction Methods in Polymer Science ;Krieger:New York,1979;p 423.(18)Sihtola,H.;Kyrklund,B.;Laamanen,L.;Palenlus,I.Paperi ja Puu1963,45,225.(19)de Nooy,A.E.;Besemer,A.C.;van Bekkum,H.;van Dijk,J.A.P.P.;Smit,J.A.M.Macromolecules 1996,29,6541.Figure 9.Changes in water-retention values of the water-insoluble fractions prepared from cotton linter by the TEMPO-mediated oxida-tion with 4.84mmol NaClO (per gram cellulose)at room temperature and pH 10.5for various reaction times.1988Biomacromolecules,Vol.5,No.5,2004Saito and Isogai。