Preparation And Properties Of Novel UV-curable Resin From Castor Oil And Cardanol

Biomass resources have many advantages such as natural renewability,abundance,low price,and biodegradability.Thus the synthesis of polymer materials from biomass has attracted great attention.On the other hand,ultraviolet(UV)-curing technology possesses a variety of advantages that traditional curing technology doesn't have,such as no inert solvent volatilization,short curing time,and low temperature curing.Regarding as a new generation of green technology,this technology has been widely used in coatings,inks and glues,adhesives,and other fields.The combination of UV-curing technology and biomass resources to prepare bio-based UV-curable coatings can not only promote the sustainable development of coatings industry,but also may alleviate the petrochemical resources and reduce environmental pollution.UV-curable coating usually comprises prepolymer,diluent,and small amounts of initiator and additive.At present,polyurethane acrylate(PUA)prepolymers derived from biomass have problems of low C=C functionality,leading to far inferior properties compared to petroleum-based products,so it is desirable to synthesize highly-functional biobased PUA prepolymers.Meanwhile,when using petroleum-based low-molar-mass diluents with highly-fuctional biobased prepolymers to prepare UV-curable coatings,volumetric shrinkage of the obtainded materials was serious and the biobased content was reduced clearly.In order to solve these problems,a series of research works have been carried out:(1)Using castor oil(CO),isophorone diisocyanate,and pentaerythritol triacrylate as raw materials,highly-functional castor oil-based prepolymer(COPUA)was synthesized by a two-step process.The structure of COPUA was confirmed by FT-IR,1H NMR,and gel chromatography(GPC).Then UV-curable coatings were prepared by blending COPUA with a petroleum-based diluent,hydroxyethyl methacrylate(HEMA),and the final properties and UV-curable kinetics of the obtained materials were investigated.The results showed that the performance of pure COPUA resin material was excellent.For example,the tensile strength(?),tensile modulus(E)and glass transition temperature(Tg)reached 10.16MPa,130.09MPa and 31.81?,respectively.This good performance was mainly due to the high C=C functionality of COPUA,resulting in high crosslink density of the material.In addition,as the content of HEMA increased from 0 to 25%,the a,E,Tg,initial decomposition temperature(T5),maximum thermal weight loss rate(Tp),and hydrophobicity of the obtained COPUA/HEMA materials increased clearly.When the content of HEMA was 25%,the ?,E,Tg,T5,Tp,contact angle,and water absorption of the UV-curable COPUA/HEMA resin increased to 18.13MPa,296.35MPa,31.81?,357.0?,428.6?,105.77°,and 1.23%,respectively.Finally,with the increase of HEMA content,the final C=C conversion of COPUA/HEMA resin increased,and the initial conversion rate decreased.As the functionality of diluent increased,the final C=C conversion of the resin decreased,and the initial conversion rate increased.(2)Using cardanol as raw material,a polyfunctional cardanol-based PUA(C-PUA)prepolymer were synthesized via the similar two-step process mentioned above and the corresponding UV-curable materials were prepared by using HEMA as diluent.The results showed as the content of HEMA increased from 0 to 40%,the viscosity of the C-PUA/HEMA resin decreased from 8360 mPa·s to 115 mPa·s.The a of the obtained materials increased from 12.4 MPa to 32.0 MPa,E rose from 107.2 MPa to 782.7 MPa,and Tg was improved from 74.1? to 123.0?Finally,the C-PUA/HEMA resins showed good coating properties like flexibility and adhesion as well as low water absorption(3)A cardanol-based acrylate diluent,cardanyl acrylate(CA),was synthesized by reacting cardanol with acryloyl chloride,and then employed to modify COPUA.A petroleum-based diluent,hydroxyethyl acrylate(HEA),was used for comparison.The results showed that although the dilution ability of CA was slightly inferior to that of HEA,CA showed better effects than HEA on improving the biobased content and reducing the volume shrinkage of the obtained UV-cured materials.For example,when the content of CA was 30%,the biobased content,viscosity,and volumetric shrinkage of the COPUA/CA resin were 62.8%,1013mPa·s,and 9.51%,respectively,while the three values in the COPUA/HEA system with 30%of HEA were 50.8%,490 mPa·s and 21.94%,respectively.The lower shrinkage can be attributed to that CA possessed a lower C=C concentration than COPUA and the residual structures of CA like benzene ring and C15 alkyl chain can fill in the crosslinked unit.In addition,with the increase of CA content,the Tg,Tp,hardness of coating,and contact angle of the obtained COPUA/CA materials showed an increasing trend Finally,the curing kinetics indicated that the final C=C conversion of the COPUA/CA resin gradually increased with the growth of CA content(4)Epoxized cardanyl acrylate(ECA)diluent was synthesized via acrylation and epoxidation of cardanol,and then used to modify COPUA.For comparison HEA diluent was also used.The results showed that although the dilution ability of ECA diluent was not as good as that of HEA,CA demonstrated a much better effect on reducing the volume shrinkage of the resultant materials.For example,the volume shrinkage of the COPUA/HEA system with 30%of HEA was 21.9%,while the volume shrinkage of the COPUA/ECA system with 30%of ECA was only 3.7%.The reasons for the sharp reduction probably lies in that:firstly,ECA has a low C=C concentration and its residual structures can also fill in the crosslinked unit as CA diluent;secondly,the epoxy groups on ECA can simultaneously polymerize during the free-radical polymerization and form a interpenetrating polymer network(IPN).In addition,as the ECA content increased,the Tg,Tp,hardness of coating,and hydrophobicity of the obtained COPUA/ECA materials showed an increasing trend.When ECA content increased to 30%,the Tg,Tp,hardness,and contact angles of the resulting materials reached 32.5?,478.3?,5H and 95.5°,respectively.Finally,photocuring kinetics indicated that the final C=C conversion of the COPUA/ECA system approached to 97%(5)Epoxidized cardanol glycidyl ether(ECGE)diluent was synthesized by reacting cardanol with epichlorohydrin firstly and epoxidation of the side chain of CA subsequently.The resultant ECGE diluent was employed to modify COPUA.The results showed that when the content of ECGE increased to 50%,the biobased content was 66.2%,the viscosity was 1587mPa·s,and the volume shrinkage rate decreased to 3.9%for the obtained COPUA/ECGE resin.In addition,as the content of ECGE increased,the ?,E,and Tg of the UV-cured COPUA/ECGE resins decreased,while the contact angle increased.Finally,the COPUA/ECGE system demonstrated good flexibility and adhesion of coating,and the final C=C conversion reached 85%(6)A polyfunctional castor oil-based acrylate diluent(COPERAA)was synthesized via alcoholysis and acrylation of castor oil,which showed a C=C functionality up to 2.92.The COPREAA was used to prepare UV-curable coatings with acrylated epoxized soybean oil(AESO)and compared to a petroleum-based polyfunctional diluent,trimethylolpropane triacrylate(TMPTA).The results showed that although the dilution ability of COPERAA was slightly inferior to TMPTA,COPERAA showed better effects than TMPTA on improving the biobased content and inhibiting the volume shrinkage of the obtained materials.For example,as the content of diluent was 40%,the biobased content of AESO/COPERAA was 8.5%higher than that of AESO/TMPTA,while the volumetric shrinkage of AESO/COPERAA was 2.28%lower than that of AESO/TMPTA.In addition,when the content of COPERAA increased,the ?,E,and Tg of the AESO/COPERAA resin increased.The adhesion of AESO/COPERAA coatings was better than that of the AESO/TMPTA coatings.Finally,the photocuring kinetics showed that the initial C=C conversion rate of AESO/COPERAA was comparable to that of AESO/TMPTA,while the final C=C conversion rate of AESO/COPERAA was slightly better than that of AESO/TMPTA.