New cardanolsucrose epoxy blends for biobased coatings

Progress in Organic Coatings 83(2015)47–54Contents lists available at ScienceDirectProgress in OrganicCoatingsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /p o r g c o atNew cardanol/sucrose epoxy blends for biobased coatingsEmilie Darroman a ,Nelly Durand b ,Bernard Boutevin a ,Sylvain Caillol a ,∗a UMR 5253CNRS-UM2-ENSCM-UM1,Institut Charles Gerhardt Montpellier,Equipe I.A.M.,8Rue de l’Ecole Normale,34296Montpellier Cedex 5,France bSogatra Nouvelle,784chemin de la Calladette,30350Lezan,Francea r t i c l ei n f oArticle history:Received 8June 2014Received in revised form 24December 2014Accepted 5February 2015Keywords:Epoxy resins Cardanol Sorbitol IsosorbideBiobased polymersa b s t r a c tCommercial epoxidized cardanol,from cashew nutshell liquid (CNSL)is a biobased reactant with inter-esting aromatic structure.Cured with two different amines,isophorone diamine and Jeffamine T403,the materials exhibit good properties but not enough to replace the bisphenol A diglycidyl ether (BADGE)in epoxy networks.Two kind of sucrose epoxy derivatives,sorbitol and isosorbide,were used as blends to enhance the properties of the epoxy cardanol-derived materials.These epoxy networks with differ-ent ratios were characterized by thermogravimetric analysis and differential scanning calorimetry;their hardness and brightness were measured as well as their resistance to chemical solvents.Biobased epoxy blends exhibit interesting properties for coating applications.©2015Elsevier B.V.All rights reserved.1.IntroductionEpoxy resins are an important class of thermoset polymers used for coating applications.Bisphenol A (BPA),a reactant that was ini-tially synthesized as a chemical estrogen [1],is nowadays the most used monomer for the production of epoxy resins.The aromatic ring of BPA is particularly interesting since it confers good thermal resistance to epoxy resins.But this endocrine disruptor can mimic the hormones of the human body and may lead to several negative health effects [2–5].Thus,a recent review [6]about studies of low-dose effects of BPA found that 94of the 115publications reported significant effects.Effects include alterations in brain chemistry,in the immune system,in the enzyme activity,in the male and female reproductive systems in a variety of animals,including snails,fish,frogs and mammals [6].The negative impact of BPA on human health and on environment necessarily implies the elimination of BPA especially since some countries,such as Canada or France,have recently banned the use of BPA in food contact materials.Therefore there is an increasing interest of chemical industries for non-harmful reactants allowing the synthesis of epoxy resins without BPA.Moreover,thermoset polymers cannot be recycled due to their cross-linked networks and for that reason they need to be biobased to ensure less environmental impacts.Thus,non-toxic biobased epoxy reactants are highly needed and studied [7].Few commercial∗Corresponding author.Tel.:+33467144327;fax:+33467147220.E-mail address:sylvain.caillol@enscm.fr (S.Caillol).biobased epoxy reactants are available with the exception of veg-etable epoxidized oils which are the most used biobased monomers [8].Despite their cross-linked networks,epoxidized vegetable oil based resins have low T g due to the long aliphatic chain (T g =−38◦C with epoxidized-linseed oil cured with amine-functionalized grape seed oil [9])and low reaction enthalpy.However,coatings need to have excellent thermal and mechanical properties,brought by compounds bearing aromatic rings or a high cross-linked network.Biobased aromatic epoxy reactants would give good properties to coatings as the BPA based resins.Even if literature reports some very interesting works based on natural flavonoids [10]or lignin,these resources exhibit strong drawbacks.Indeed,low purity and high molar masses of these resources limit their development in chemistry.Depolymerization of lignin [11,12]is an alluring route to give an access to biobased aromatic compounds,required by chemical industries,however this route remains deceptive since,like vanillin [13],very interesting product,the availability of this resource is not sufficient.Cardanol [14],extracted from cashew nut shell liquid (CNSL),a non-edible by-product of CNSL industries,is a really promising aromatic renewable resource,available in large quantity and would be suitable for food contact [15].Cardanol is a yellow pale liquid composed of four meta-alkyl phenols differing by unsaturation degree of aliphatic chain:saturated chains (SC)8.4%,mono-olefinic (MO)48.5%,di-olefinic (DO)16.8%and tri-olefinic (TO)29.33%chains [16,17].Cardanol was already extensively stud-ied for material synthesis,through direct polymerization [18],as a polyol in new polyurethanes [19],in polyester compositions [20],with partial or total substitution of phenol in thermoset resins such/10.1016/j.porgcoat.2015.02.0020300-9440/©2015Elsevier B.V.All rights reserved.48 E.Darroman et al./Progress in Organic Coatings83(2015)47–54Fig.1.Idealized structure of epoxidized cardanol by Cardolite and the structure defined by our team[28].as Novolac resins[21–23],vinyl esters[24,25]and also in epoxy resins modification[26,27].Our team previously worked on epoxidized cardanol[28]pro-vided by Cardolite and depicted the detailed chemical structure compared to the one given by the technical data sheet(Fig.1). In fact,this commercial epoxidized cardanol is not a dimer but appeared to be a mix of oligomers of cardanol and phenol with various molar masses,with opened epoxy rings and a mean func-tionality of2.3epoxy functions per molecule[28].Despite a120◦C curing of epoxidized cardanol formulations,the glass transition temperatures,T g,of cardanol resins were too low,and in order to increase them,blends with other epoxy reactants are needed. Some academic products such as isosorbide or prototypes,deriva-tives from sugar as sorbitol could also be proposed as candidates to substitute bisphenol A in coatings.The objective of this work is to obtain blends of epoxy resins with good thermal and mechan-ical properties in order to meet required properties for coating applications.In literature,to the best of our knowledge,few works reported the study of blends of biobased epoxy whereas this is cru-cial since it will be hard to substitute bisphenol A diglycidyl ether (BADGE)by an unique molecule.Our resins were formulated,cured at room temperature and characterized to measure their resistance as coatings in contact with acid or basic solvents.This publication is thefirst one to compare different biobased commercial epoxy reactants in coating applications.2.Materials and methods2.1.MaterialsTrifunctional polyetheramine Jeffamine T403(amine hydro-gen equivalent weight(AHEW)=81g/eq),isophorone diamine Aradur42BD(AHEW=42.5g/eq)were purchased from Hunts-man(Switzerland).Diglycidyl ether of cardanol NC-514(epoxy equivalent weight(EEW)=400g/eq)was obtained from Car-dolite(Belgium).Polyglycidyl ether of sorbitol Denacol EX622 (EEW=188g/eq),and two epoxidized isosorbide Denacol GSR100 (EEW=155g/eq)and Denacol GSR102(EEW=158g/eq)were pur-chased from Nagase(Japan).Bisphenol A diglycidyl ether(BADGE) (EEW=187g/eq),ethyl acetate,and sodium hydroxide were pur-chased from ThaïOrganic Chemicals Co,Brenntag and Univar, respectively.Glacial acetic acid and deionized water were pur-chased from Analytic Lab.All reactants were used as received.2.2.FormulationsSeveral mixtures were obtained from diglycidyl ether of car-danol NC-514(EEW=400g/eq)at different massic ratios(100wt%, 75wt%,50wt%and25wt%)with various epoxy reactants:polygly-cidyl ether of sorbitol Denacol EX622(EEW=188g/eq),and two epoxy reactants of isosorbide Denacol GSR100(EEW=155g/eq) and Denacol GSR102(EEW=158g/eq).These mixtures were cured at room temperature with two commercial amines,trifunctional polyetheramine Jeffamine T403and isophorone diamine Aradur 42BD,and were compared to the formulation obtained with DGEBA.Theoretically,all the formulations should be prepared in1:1M ratio of epoxy group to active H of amine in the view to obtaining the maximal crosslinking density of cured epoxy agent.Therefore, we used the given data(EEW and AHEW)from technical sheet of the different reactants.Each formulation is carried out with75g of epoxy resin which EEW is given by the technical sheet for mass content of100wt%or calculated as below:mol%epoxy1=m epoxy1EEW1(m epoxy1/EEW1)+(m epoxy2/EEW2)×100(1)where mol%epoxy1,m epoxy1,m epoxy2,EEW1and EEW2are respec-tively the molar percentage of epoxy1,the mass(g)of epoxys1and 2,and the epoxy equivalent weight of epoxys1and2.EEW mixture=EEW1×mol%epoxy1+EEW2×(1−mol%epoxy1)(2) where EEW mixture,mol%epoxy1,EEW1and EEW2are respectively the epoxy equivalent weight of the mixture of epoxys1and2,the molar percentage of epoxy1,and the epoxy equivalent weight of epoxys1and2.The mass of curing agent is determined as below:m curing agent=m epoxy×AHEWEEW(3) where m curing agent,m resin,AHEW and EEW are respectively the mass of the amine curing agent,the mass of epoxy or mixture of epoxys, the amine hydrogen equivalent weight and the epoxy equivalent weight of epoxy or mixture of epoxys.Formulations were carried out without solvent.After weigh-ing,reactants were mixed and vigorously manually stirred during 3min.Then mixtures were poured in a silicon mold and on a sable glass.These preparations were cured at22◦C during at least5days.2.3.Analytical techniquesViscosity and density of different mixtures were performed at 33◦C with a DV-E Brookfield viscosimeter and an Erichsen pyc-nometer(100mL,model290/1).Gel times were measured on a mixture of100g with a Trombo-mat purchased from Matériau Ingénierie.The micro-applicator(BYK)allowed us to cast a layer of500␮m on the glass(length:165mm,width:110mm and thickness:4mm).The brightness was evaluated by a Picogloss560MC on different places on the glass.Swelling index:The study of swelling is based on the materials cured in the silicon molds with different solvents and conditions. These materials were immerged into100mL(high:150mm and diameter:40mm)of the simulants as below:-in3wt%of acetic acid solution at40◦C during10days;-in3wt%of sodium hydroxide solution at22◦C during10days; -in ethyl acetate at22◦C during30min.The swelling index SI is given by following equation:SI=m1−m0×100(4)where SI,m1and m0are respectively,the swelling index,the mass in grams of the sample after being in the simulant and the initial mass of the sample.Thermogravimetric analyses(TGA)were performed on a Q50 from TA Instrument.10mg of sample in an aluminum pan was heated from room temperature to580◦C under nitrogenE.Darroman et al./Progress in Organic Coatings83(2015)47–5449Fig.2.Structure of IPDA and Jeffamine T403.(60mL/min).The experiments were carried out at a heating rate of10◦C/min.Differential scanning calorimetry(DSC)analyses were carried out on a NETZSCH DSC200calorimeter.Cell constant calibration was performed using indium,n-octadecane and n-octane stan-dards.Nitrogen was used as the purge gas.10–15mg samples were sealed in hermetic aluminum pans.The thermal properties were analyzed at10◦C/min between−100and280◦C to observe the glass transition as well as crystallization/fusion processes.All the reported temperatures are inflexion values.For each sample,the thermal history was erased with afirst heating ramp up to100◦C. The T g value was measured at the second ramp.3.Results and discussion3.1.Raw materialsWe formulated various epoxy-amine resins at room temper-ature with a view to replacing the bisphenol A diglycidyl ether (BADGE).Firstly,two amines were used as hardeners:isophorone diamine(IPDA)and a polyetheramine,Jeffamine T403.Isophorone diamine is a classic cyclic amine,often used as a hardener for epoxy resins.Jeffamine T403is a classic polyetheramine,and its use is approved by Huntsman as a non-toxic reactant and suitable for food contact(Fig.2).BADGE,Fig.3,is used as a reference in order to compare the properties of our new epoxy-amine resins.Epoxidized cardanol comes from cashew nut shell liquid and was obtained from Cardolite.Epoxidized cardanol was studied by our team[25,28],indeed we already reported some new epoxy networks with this product.Epoxy sorbitol and epoxy isosorbide are issued from sugar and isosorbide is obtained by a double-reaction of dehydration of the sorbitol.In Fig.3,idealized structure of the different epoxy reactants are presented.3.2.Gel timeGel time at room temperature wasfirstly studied to evaluate the start time of crosslinking of the different epoxy formulations (Table1).At22◦C,BADGE takes15h and3.5h to become a gel with Jeffamine T403and IPDA,respectively.Indeed,structures of the Jeffamine T403and IPDA have an influence on their reactivity. The methyl groups in˛position of Jeffamine T403contribute to the steric hindrance and decrease the reactivity of the primary amines [29].All the other epoxy reactants exhibit lower gel time that BADGE with IPDA.Indeed,epoxidized cardanol is cured with IPDA in3h, epoxidized isosorbide100and102in1.5and2h,respectively.The more reactive is the epoxidized sorbitol,with a gel time of0.9h with IPDA.The epoxidized sorbitol is more reactive due to the presence of six epoxide groups compared to two epoxy groups in epoxide cardanol and epoxidized isosorbide100and102.With Jeffamine T403,epoxidized isosorbide networks cannot be obtained without thermal cure.3.3.Thermogravimetric analysisThermogravimetric analyses on the different resins have been carried out under nitrogen atmosphere(Table1).The reference with BADGE gives the best thermal resistance with a degrada-tion temperature around365◦C at30%weight loss,whatever the diamine used.For the new renewable epoxy compounds cured with IPDA,the epoxidized isosorbide100is the best substitute to BADGE since it leads to higher T g(109◦C)and degradation temperature (362◦C)than isosorbide102;therefore we keep this isosorbide100 for further formulations.Then epoxidized cardanol and epoxidized isosorbide102are good candidates,however epoxidized sorbitol is not enough stable as its temperature degradation is285◦C.Despite its high crosslinking density,the epoxidized sorbitol cannot reach the thermal stability of aromatic or cycloaliphatic compounds.For the networks crosslinked with Jeffamine T403,the epoxy cardanol is enough resistant contrary to epoxy sorbitol which its degradation temperature is277◦C.Indeed the aromatic ring of the epoxy cardanol ensure a good thermal stability whereas the epoxy sorbitol is not enough resistant because its structure do not provide to its resin good resistance.3.4.Glass transition temperatureThe glass transition temperatures(T g)of the various epoxy-amine networks were studied by differential scanning calorimetry (Table1).The highest T g are obtained with IPDA,whereas Jeffamine T403leads to the lowest T g.The highest T g is121◦C,corresponding to the BADGE-IPDA works based on epoxidized car-danol exhibit the lowest T g:41◦C and23◦C,respectively with IPDA and Jeffamine T403.This low T g is due to the aliphatic chain of the cardanol which bringsflexibility to the networks.The T g of epoxy isosorbide100–IPDA material is109◦C,close to the T g of BADGE-IPDA whereas the resin obtained with epoxy isosorbide102and IPDA has a lower T g of72◦C.This difference can be explained by the oligomerization of the epichlorhydrine which can lead to an epoxy isosorbide with a higher rate of cycloaliphatic ring.More-over,the molar mass is increased as well as the functionality of isosorbide which lead to an higher T g[30],Fig.4.The glass transi-tion temperature depends of the epoxy isosorbide structure too,as the oligomer would not have the same properties with the epoxy isosorbide monomer.Epoxidized sorbitol cured with IPDA has a T g of82◦C,higher than the material from epoxy isosorbide102. Fig.3.BADGE,idealized structure of epoxy cardanol NC-514,polyglycidyl ether of sorbitol EX622and diglycidyl ether of isosorbide.50 E.Darroman et al./Progress in Organic Coatings83(2015)47–54 Table1Gel time,degradation temperature,glass transition of the different epoxy compounds cured with IPDA or Jeffamine T403.Curing agent Epoxy reactants Gel time(h)Degradation temperatureat30%weight loss(◦C)Glass transition temperature T g(◦C)IPDA BADGE 3.5367121 Epoxidized cardanol335041 Epoxidized sorbitol0.928582 Epoxidized isosorbide100 1.5362109 Epoxidized isosorbide102234572Jeffamine T403BADGE1536470 Epoxidized cardanol1035223 Epoxidized sorbitol627748 Epoxidized isosorbide100No curing at room temperatureEpoxidized isosorbide102Fig.4.Possible structures of the epoxidized isosorbide.An article studied the thermal and mechanical properties of Jeffamine T403-crosslinked with isosorbide resins at100◦C for 4h[31]and the properties were compared to BADGE resins.The mechanical properties were very good and permitted to use them as coatings.Nevertheless,the glass transition temperature obtained with epoxy isosorbide is lower than for resin based on BADGE:48◦C and90◦C,respectively.The T g obtained without cure of the resin BADGE-Jeffamine T403is70◦C which indicates the crosslinking is not complete.The lack of crosslinking could not give the best prop-erties regarding the chemical resistance,the thermal stability and the glass transition temperatures.Finally,the T g is a really important parameter in the coat-ing applications and epoxidized cardanol leads to materials with too low T g values.To substitute BADGE,blends with other epoxy compounds could increase the glass transition temperature and enhance the materials properties.To raise the T g of epoxidized car-danol resins,we proposed to mix epoxidized cardanol reactant with other renewable epoxy reactants such as sorbitol or isosorbide100.3.5.Blends with epoxidized sorbitolThe different mixtures of epoxy cardanol with epoxy sorbitol are presented in Table2.3.5.1.Thermogravimetric analysisWhen the epoxy sorbitol content increases,the degradation temperature decreases whatever the diamine used to cure the epoxy network,Fig.5.This is an expected result since epoxy sor-bitol resins with IPDA or Jeffamine T403previously exhibited theTable2Composition of the different epoxy system of epoxidized cardanol and epoxidized sorbitol.wt%epoxidized cardanol mol%epoxidizedcardanolmol%epoxidizedsorbitolEEW mixture(g/eq)1001000400 7558.541.5312 503268256 2513.586.5217 00100188 Reference BADGE––187lower thermal resistance.From50%weight of epoxy sorbitol,the degradation temperature at30%weight loss is under300◦C.3.5.2.Glass transition temperatureWhen the epoxy sorbitol content increases,the glass transi-tion temperature increases whatever the diamine used to cure the epoxy network,Fig.6.This is an expected result since epoxy sor-bitol networks with IPDA or Jeffamine T403previously exhibited higher glass transition temperature than epoxy cardanol networks. However,the glass temperature is not high enough to replace the BADGE resins in all applications as they are respectively of60◦C and37◦C at50wt%of epoxidized sorbitol in the resin with IPDA and Jeffamine T403.3.5.3.BrightnessThere is a slight tendency in Fig.7showing that the resins are brighter with the increase of epoxidized sorbitol content,but the evolution is verylow.Fig.5.Thermogravimetric analyses under nitrogen atmosphere of the epoxidized cardanol resin mixed with epoxidized sorbitol.E.Darroman et al./Progress in Organic Coatings 83(2015)47–5451Fig.6.Differential scanning calorimetry of the epoxidized cardanol and epoxidized sorbitol resins.3.5.4.HardnessWhen the epoxidized sorbitol content increases,the hardness of the materials increases whatever the diamine used to cure the epoxy networks,Fig.8.The largest change is observed for the resins cured with Jeffamine T403.Indeed,the hardness of pure epoxi-dized cardanol with Jeffamine T403is 56whereas the blend of epoxidized cardanol/epoxidized sorbitol with a ratio of 25/75,the hardness reaches 99.The structure of epoxidized sorbitol and its high functionality permit to have an equivalent hardness to BADGE resins.3.5.5.Swelling indexAll the epoxy networks are insoluble and exhibit very low swelling in sodium hydroxide (Table 3).The influence of epoxi-dized sorbitol is very low.In acetic acid,the swelling index of the resins cured with IPDA slightly increases.The epoxidized sorbitol is not enough resistant to acid treatment.However,a stability of the resins cured with Jeffamine T403is observed.In ethyl acetate,the swelling index is reduced with the addition of sorbitol.The epoxidized sorbitol enhances the stability regarding ethyl acetatetreatment.Fig.7.Evolution of the brightness of epoxidized cardanol resins with the content of epoxidizedsorbitol.Fig.8.Evolution of hardness with the content of epoxidized sorbitol in epoxy car-danol resins.Table 3Swelling index of the different epoxy resins in sodium hydroxide,acetic acid and ethyl acetate solutions.Curing agentRatio epoxidized cardanol/epoxidized sorbitolSwelling (%)Sodium hydroxide Acetic acid Ethyl acetate IPDABADGE 011100/001475/2501150/5015125/750400/100140Jeffamine T403BADGE 132100/002475/2507250/5010125/750000/10023.6.Blends with epoxidized isosorbideThe different mixtures of epoxy with epoxidized isosorbide 100are presented in Table 4.3.6.1.Thermogravimetric analysisWhen the epoxidized isosorbide content increases,the degrada-tion temperature slightly decreases whatever the diamine used to cure the epoxy networks,Fig.9.But all these networks are still good candidates to substitute the BADGE in epoxy resins since the degra-dation temperature at 30%weight loss is over 300◦C whatever the blend and the diamine used.Table 4Composition of the different epoxy system of epoxidized cardanol and epoxidized isosorbide 100.wt%epoxidized cardanolmol%epoxidized cardanolmol%epoxidized isosorbide 100EEW mixture (g/eq)10010004007553.846.22875027.972.12232511.488.618300100155Reference BADGE––18752E.Darroman et al./Progress in Organic Coatings 83(2015)47–54Fig.9.Thermal stability of the epoxy resins cured withisosorbide.Fig.10.Evolution of the glass transition temperature with the content of epoxidized isosorbide.3.6.2.Glass transition temperatureWhen the epoxidized isosorbide content increases,the glass transition temperature increases whatever the diamine used to cure the epoxy network,Fig.10.This is an expected result since epoxidized isosorbide networks with IPDA or Jeffamine T403previously exhibited higher glass transition temperature than epoxy cardanol resins.The blend of a ratio epoxidized car-danol/epoxidized isosorbide 100of 25/75cured with IPDA leads to a glass transition temperature of 83◦C which is a good T g for coating.3.6.3.BrightnessThe isosorbide content has not influence on the brightness,Fig.11.3.6.4.HardnessWhen the epoxidized isosorbide content increases,the hard-ness of the materials increases whatever the diamine used to cure the epoxy network,Fig.12.The largest change is observed for the resins cured with Jeffamine T403.Indeed,the hardness of pure epoxidized cardanol with Jeffamine T403is 56whereas the blendofFig.11.Brightness of the resins cured with different amounts of isosorbide.E.Darroman et al./Progress in Organic Coatings83(2015)47–5453Fig.12.Evolution of the hardness with different isosorbide content in epoxy cardanol resins.Table5Swelling index of the different epoxy networks in sodium hydroxide,acetic acid andethyl acetate solutions.Curing agent Ratio epoxidized cardanol/epoxidized isosorbide100Swelling(%)SodiumhydroxideAceticacidEthylacetateIPDA BADGE011 100/0014 75/250142 50/501251 25/755420 0/10011430Jeffamine T403BADGE132 100/0024 75/250292 50/501490 25/757750 0/100Not testedepoxidized cardanol/epoxidized sorbitol with a ratio of25/75,the hardness reaches91.The structure of epoxidized isosorbide with its two cycloaliphatic rings permits to have an equivalent hardness to BADGE resins.3.6.5.Swelling indexThe addition of epoxidized isosorbide100slightly increases the swelling index in sodium hydroxide(Table5)but the swelling index is very high in acetic acid.Indeed,increasing contents of isosorbide in the resin leads to a high swelling content of networks in acetic acid due to the affinity of isosorbide for water.Nevertheless,in ethyl acetate,the swelling index decreases with the isosorbide content.4.ConclusionEven if epoxidized cardanol-based networks cannot replace BADGE networks,the blends of epoxy cardanol with other biobased epoxy reactants could improve the properties of the networks. 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