翻译定稿

Easy estimation估计of the progress of artificial Weathering风化侵蚀of palm棕榈fiber-polypropylene composites by chemiluminescence化学发光
Date palm leaves were compounded with polypropylene (PP) and UV stabilizers安
定装置稳定器to form composite materials. Residual剩余的thermo-oxidation stability of such composites undergone to accelerated 加速的weathering in Xenotest has been investigated by chemiluminescence method.It has been found that composites are much more stable 稳定的than PP alone which wasattributed to the direct interaction 交互作用of cellulose纤维素fibres (reinforcing effect) and lignin 木质素(anti-oxidation 抗氧化effect) with polypropylene peroxyl过氧化氢radicals. Samples in which polypropylene is compatibilized with cellulose by Epolene E-43 wax are generally less stable than uncompatibilized ones probably because of the pro-initiation正面的开始effect of cellulose on polypropylene oxidation.
1. Introduction
Since 1990 one can register记录登记an increasing interest in the development of industrial and consumer products that combine联合lignocellulosic fibers and plastics. The primary 主要的impetus推动力has come from one of these goals:目标1. To reduce material costs by combining a lower cost material acting as担当filler or extender with a higher cost material.2. To develop products that can utilize利用recycled再循环materials.3. To produce a composite material that exhibits展示specific properties that are superior compared to either ofthe component 成分materials alone (e.g. increased strength to weight ratio, improved abrasion resistance, etc.) The processing temperature of thermoplastics热塑性塑料withcellulosic fibers is limited due to the cellulose degradation降解at higher temperatures. However, it has been reported that no deterioration变坏退化of properties of composite materials containing cellulose was observed观察when processing temperatures are maintained维持below 200.C The composites of cellulose fibers with thermoplastics can withstand抵挡higher stresses压力than either their individual constituent要素because the fibers and matrix interact and redistribute重新分布the stresses. The ability of these two constituents to exchange stresses depends critically主要的on the effectiveness效力of the coupling耦合or bonding黏结between fiber and matrix [6]. It is well known that compatibility兼容性between lignocellulosic materials and the polymer matrix plays a crucial只管紧要的role in determining the properties of a composite. Lignocellulosic materials,which have polar极性hydroxyl groups on the surface, have difficulty in forming well bonded interfaces界面with nonpolar polymer matrix materials such as polyethylene and polypropylene. Various各种各样的chemical reagents试剂have been employed to enhance the compatibility between the constituent materials. These include Epolene E-43 (Maleic anhydride modified polypropylene) [2,7, 8, 11–13],
poly[methylene(polyphenyl isocyanate)](PMPPIC), γ
-methacryloxypropyltrimethoxysilane,poly(propylene acrylic acid) and
poly(propyleneethylene acrylic acid) [7], etc. From the practical viewpoint, the resistance抵抗力of the above materials towards thermo-oxidation should be of
interest重要性影响as it determines the remaining保留service life of the material. Until now very few studies investigating the artificial weathering of polypropylene/cellulose fiber composites exist. On the other hand, the antioxidant抗氧化剂properties of lignin木质素in polypropylene were reported several times [14–16]. The authors underline the necessity of compatibilization of lignin with polypropylene to explore the maximum of its antioxidant properties
due to hydroxyl groups involved in monomer unit.
Objective目的of this report is to show how the extent程度范围of stabilization of polypropylene/date palm cellulose fiber composites changes with the time of exposition暴光of sample to artificial ageing. The chemiluminescence method has been used for an easy characterization of the remaining thermo-oxidation stability.The thermal oxidation of polypropylene alone was Examined调查by this method many times and the agreement between induction time\诱导时间so determined and those determined by other methodswas several times reported. The method itself is typical with extreme极度的sensitivity敏感but the chemiluminescence behavior of polymers may differ each from the other. There are polymers, polypropylene including, which give typical sigmoidal S形的autocatalytic 自身催化的increase of the light emission光发射under isothermal等温的conditions条件which coincides with与..相符the oxidation runs融化的determined by other methods.On the other hand, cellulose has a relatively short length of kinetic oxidation chains and does not give an autocatalytic自身催化的shape of chemiluminescence runs. Intensity强度of the light emission of oxidized cellulose decays衰退steadily有规则的稳定的from the initial最初的level. Different authors indicate that the elementary初步的基本的processes from the oxidation mechanism which might be responsible for the light emission are not quite clear but the predominating 占优势opinions favor the recombination再结合of peroxyl过氧化氢radicals which proceeds according to Russel’s scheme.In the Equation 1 asterix denotes显示the excited singlet state of oxygen and excited triplet三重态state of carbonyl羰基groups on the polymer chain, respectively. The light comes from the transfer of these excited particles粒子极少量to their ground states. Together with this emissive发射的route路程路线of deactivation钝化惰性化of excited states there occur发生quenching淬火processes. Non-emissive way of transfer of excited into ground state may be much more significant and may modulate调整调节the proportionality constant比例常数in linear
relation线性关系between chemiluminescence intensity强度I and the rate of oxidation氧化.I = _ · rate of oxidation (2)
2. Experimental2.1. Materials Polypropylene used in the study was supplied by Saudi Basic Industries Corporation (SABIC). The brand name商标for it is LADENE PP570P. It is a homopolymer均聚物used for producing rigid刚性的injection molded注模articles商品. Details of the polymer are given in Table I. Maleated 马来酸盐的polypropylene was used as a compatibilizer and was supplied by Eastman Chemicals Two stabilizers稳定器Irgastab and Tinuvin-783
were used to stabilize the composites for thermal and UV degradation降解during processing and weathering. Polypropylene wax was added to facilitate促进推动the injection molding喷射摸塑法of the composites. The formulations明确的表达used in preparation预备of composites are shown in
2.2. Fiber preparation
Branches分支obtained获得from palm trees were cut into pieces about 6 inch long. Thereafter,随后they were air dried风干for 48 h at room temperature. The pieces of branches were then granulated颗粒状的to a small size using a Granulator造粒机The fibers were then size依大小排列separated分开by using sieving筛分machine. Only the large fraction片断of fibers was used in this study. The fibers size distribution was characterized
using a digital vernier caliper.数字的游标卡尺The average length of the fibers was 4.7 mm with a standard deviation标准偏差of 1.7 mm and an aspect ratio纵横比of 10.8. The fibers obtained were then cleaned to remove the volatile organic compounds.有机挥发性化合物The chemicals化学药品used for cleaning were Ethanol乙醇and Toluene甲苯in the ratio比率of (1:2) (V/V). The mixture of these two chemicals was prepared in a large container.容器The fibers were soaked in吸收the mixture for 24 h.
The fibers were then washed with water and dried in a vacuum oven真空电炉at 105.C for 24 h to remove residual moisture.残留水分
2.3. Compounding混合and molding成型
The composite components were compounded using a Brabender Measuring Head, Model S-650, No:G126 mounted with安放a single screw extruder.螺杆挤压机The fibers were hand mixed with和..混合polypropylene and other additives添加剂prior to在前compounding. In both cases the fibers and
the resins were first hand mixed in a bowl and then transferred to转the
mixer/extruder.搅拌器挤压机The conditions of mixing were varied in such a way to determine the optimum conditions最佳条件that will produce samples with maximum最大量最大限度dispersion散布of fibers, good mechanical properties, good color and smell. The mixed compositesobtained
from the extruder were granulated颗粒状的then molded浇铸using an injection molding machine 注模机at 200.C. The composite specimen样品were molded into standard ASTM (American Society of Testing Materials, 美国材料实验协
会)D-648–94B specimen, which were then weathered and characterized.
2.4. Weathering trials试验
The complete details详细资料of the trials may be seen below: Equipment used: Xenotest Beta-LM Total duration of exposure:暴露时间2000 h
Parameters参数of Xenotest Beta-LM Irradiance:发光45 w/m2 between 300–400 nm Black panel temp. (BPT): 63. ± 3.C Black sensor temp. (BST): 70. ± 3.C Humidity:湿度50 5%
2.5. Characterization of aged samples
The composite materials exposed to使易受artificial weathering trials were
characterized by mechanical testing parameter such as stress at break. The samples were tested using an Instron 5560 Mechanical Testing Machine.机械试验The tests were conducted操作at a constant不变的恒量strain张力rate of 2 mm/min. The measured quantity测定量was the stress at maximum load in MPa. The melting temperatures of the samples were characterized using a Perkin Elmer DSC instrument. 10 mg samples were used for the tests.The temperature range of each scan was 50–190.C andthe heating and cooling rates were 10.C/min.
2.6. Chemiluminescence measurements
Chemiluminescence experiments were performed on the photon counting光子计数instrument Lumipol 3 manufactured by the Polymer Institute of Slovak Academy of Sciences, Bratislava, Slovakia. The instrument dark
count rate was 2–4 counts/s at 40.C. The measurements were carried out完成实现
in an oxygen flow氧化流程of 3 L/h.Polymer composite samples for chemiluminescence measurements were cut by microtome knife切片力from standard samples for mechanical testing and placed into aluminium
pans. The average weight of the samples was 12 mg. Isothermal等温的CL runs were performed at temperatures between 140 and 180.C. Non-isothermal runs were performed so that the sample was kept at 40.C
for 10 minutes, then temperature started to increase by the rate of heating 2.5.C min.1 till 200.C and cooled subsequently随后by the same rate to 180.C. At this temperature measurement continued as an isotherm.等温线
3. Results and discussion
Fig. 1 shows two cases of the chemiluminescence intensity强度runs in time provided that temperature of the sample changes according to the program described by the dotted有点的line. The residual stability 剩余的稳定性of more aged samples was lower and chemiluminescence light emission
started to increase earlier. At the same time, the maximum intensity at 200.C is higher for aged sample. For unaged and thus从而the most stabilized稳定PP-2 sample there may be observed some induction period诱导期when
continuing连续的with isothermal heating等温加热at 180.C after the nonisothermal run from 40 to 200.C. This is not the case for the aged sample where a sharp increase of the CL intensity is observed already during nonisothermal temperatureramping (Fig. 1).The whole set of experiments of artificially人工的aged samples may be seen in the Fig. 2. The residual stability of the aged samples is dependent on the time of ageing exposure. The higher the time of sample ageing, the more significant shift of the chemiluminescence signal towards lower temperatures occurs.Quite of相当的interest is comparison比较对照of isothermal experiments at temperatures between 140 and 180.C.Several zones 地域may be observed on isothermal runs. First(I) is typical by a steady decay of chemiluminescence intensity, the second (II) characterizes the end of induction period,诱导期where chemiluminescence intensity starts to increase, the third (III) is the region地域of the maximum light emission and the fourth (IV) is accompanied 伴随by
the newemission decay. The surprising observation has been done, namely也就是
that the induction period of oxidation which is well observable for pure polypropylene cannot be observed at 140.C and lower temperatures. As it is seen in the Fig. 3, a considerable increase of CL signal for composite materials and thus well distinguished显著的induction period of oxidation may be seen above 170.C, only when polypropylene melts and the mobility活动性of the macromolecular chains becomes released.释放One can see the large difference between runs of chemiluminescence signal of PP-2 aged 2000h and measured at 170 and 180.C in oxygen. The increase of temperature from 170 to 180.C brings about here more than 10 times stronger maximum chemiluminescence signal, while the corresponding相应的ratio between 170 and 160.C is about 3, approximately.近似的The reinforcing effect of cellulose fibers seems to be from that quite evident.明显的Palm leaves fibers reduce the mobility of the polypropylene chains when compared to polypropylene alone and it is quite possible that the mechanism of chemiluminescence changes, too. We remind提醒here that
both Irgastab 410 and Tinuvin 783 used in our experiments are very weak antioxidants抗氧化剂and that their effect on prolongation延伸of induction time is negligible可以忽略under the conditions of thermo-oxidation experiments.The compatibilized samples PP-2 are less stable than uncompatibilized PP-1. This is seen in Fig. 5 where PP-1 and PP-2 are compared after 400 h of ageing. \This result is somewhat surprising; in compatibilized比较两个samples the contact of接触联系hydroxyl groups羟基from cellulose and/or lignin is definitely明确的better than in uncompatibilized ones and one should expect that compatibilization
has to lead to a better stabilization of the composite.The explanation互相证明of such a contradiction may consist in pro-initiation effect of cellulose itself. Its monomer unit contains 5 tertiary carbon atoms叔碳原子which are rather susceptible to易手影响的the direct interaction with oxygen which
subsequently leads to free radical 自由基process. The compatibilizer is likely to facilitate the transfer reaction of hydrogen peroxyl radicals or peroxyl radicals formed in cellulose bacbone with polypropylene tertiary carbons and oxidation of polypropylene may thus be more
pronounced.显著的From Arrhenius化学家plots结构of chemiluminescence intensity on temperature, the breaking points may be found
at which the oxidation passes from the region of lower activation energy characterized by a lower slope倾斜to accelerated加速region区域ofoxidation where the chemiluminescence increase is determined by the chain reaction of accumulating hydroperoxides (Fig. 6). It is of interest that the lower slopes correspond to相符activation energy活化能between 50–70 kJ/mol, while those at accelerating加速的
催化的region are higher than 200 kJ/mol. The temperatures corresponding to the breaking points decrease with the
time of sample ageing indicating 标志again a lower residual剩余的
stability of artificially aged composite when compared with non-aged
samples.Which is the reason of a low activation energy for the first stages of
non-isothermal oxidation run? Theanswer may follow from the Fig. 4 where the decay of chemiluminescence intensity was observed for unaged
sample PP-2 for time as long as 100 000 s. When oxidation process is in the region of induction period and the heating takes place with linearly线性的increasing temperature,the corresponding chemiluminescence response is
composed from two parts. The first which corresponds to the kinetics of the light emission decay which is superposed with the increase. In non-isothermal experiments this ultimately 最后基本上leads to a lower activation energy of chemilu-minescence increase when compared with the situation after induction period.Melting temperatures of the artificially aged samples decrease with time of ageing as well. The melting temperature of PP alone dropped sharply from 164
to138.C already after 800 h of exposure; then it continued to decrease at a slower rate. The uncompatibilized
and compatibilized samples showed similar tendencies in stabilities and their melting temperatures showing only a 5% drop (Fig. 7). The correspondence with the temperature of the start of oxidation in non-isothermal
chemiluminescence tests is quite evident. The stress at maximum load of the artificially aged samples for both the co mpatibilized and uncompatibilized
samples indicates also much higher stabilities than the PP without any cellulose fiber. The drop in the strength does not exceed 20% after 2000 h of ageing exposure (Fig. 8). The PP alone shows a slight decrease in strength in the first 500 h of exposure followed by a sharper drop.暴跌After 2000 h of exposure, the PP alone loses 85% of its strength. The fast rate of degradation
in the accelerated ageing might offset抵消弥补any enhancement in interfacial界面的adhesion 支持caused by degradation and as a consequence, no increase in strength is observed.
4. Conclusions
PP/date palm cellulose fiber composites are found to be much more stable towards thermal oxidation than polypropylene alone while the continuous accelerated weathering reduces the thermo-oxidation stability according
to the extent of 到..的程度ageing. Compatibilized samples are generally less stable than uncompatibilized ones.This may be the result of an complementary补充的补足的initiation开始of oxidation coming from cellulose itself. In addition to除..之外enhanced stability imparted给予的by presence of存在the fibers in the composites, enhanced interfacial adhesion resulting from oxidation of the polymer matrix can be the source
of retention of mechanical strength. The progress of the sample degradation due to artificial weathering may be easy estimated by non-isothermal chemiluminescence runs. The samples which are more degraded are shifted
distinctly to清楚的显然的lower temperatures.
Acknowledgment
The authors would like to acknowledge KACST for supporting this research under grant number 科研补助金AR-18-14. The authors would also like to acknowledge答谢the support provided by KFUPM. The authors (L. M. R.
and J.R.) acknowledge the support from grant agency VEGA (project No.
2/3053/23).。