Synthesis,Hybridization And Modification Of The Bio-based Non-isocyanate Polyurethane

Polyurethane(PU)is one of the most commercially viable polymers,and has a wide range of applications in industry and daily life,such as coatings,foams,adhesives,sealants,synthetic leather,thin films and elastomers.The main raw materials of traditional PU are fossil raw materials.In order to cope with the gradual depletion of these non-renewable resources in the future,the raw materials for green and sustainable development are important subjects worthy of in-depth study.Besides,the synthesis of traditional PU needs to use isocyanate as the essential raw material,which is the derivative of phosgene,a highly toxic gas,harmful to human body and the environment.Except this problem,isocyanate itself is also very sensitive to water,easy to produce bubbles in the synthesis process to affect the properties of the material.Therefore,the development of the non-isocyanate polyurethane(NIPU)materials with renewable resources as the main raw materials is one of the better ways to transform traditional PU.Therefore,in this work,with renewable dimer acid as raw material,NIPU was respectively synthesized by immobilized enzyme catalysis method or melting method and then crosslinked by epoxy resin to obtain different hybrid non-isocyanate polyurethane(HNIPU).The influence of epoxy value and secondary amine number on their properties for HNIPU was studied.Then,in order to endow HNIPU with better performance,composites containing modified MWCNTs and MWCNTs-GNPs mixtures were synthesized respectively,and the properties of HNIPU were also investigated.The main research contents and results of the study are summarized below:1.Dimer acid cyclocarbonate(DACC)was synthesized by dimer acid(DA)and glyceryl carbonate as raw materials and Novozyme 435 as catalyst.The synthesis conditions were optimized by single factor analysis,and the optimum conditions were obtained:glyceride carbonate/dimer acid ratio 8.00,the reaction time 10 h,the enzyme concentration 8 wt%(recycled twice),the reaction temperature 50°C,the molecular sieve content 60 wt%,the shaking speed 200 rpm,and acetonitrile as solvent.After optimization,the maximum yield was 76.00%and the minimum acid value was 43.82 mg KOH/g.Then,NIPUs were synthesized with DACC and five different diamines,and their thermal properties were analyzed.It was found that the secondary amine groups on the diamines do not react with the cyclic carbonates.2.HNIPUs were prepared by one-step reaction of the synthesized DACC with diamines and epoxy resins,and applied to coatings.The effects of different amount of secondary amines and epoxy resins with different epoxy value on properties of HNIPU were examined.It was found that HNIPU-4551,synthesized from tetraethylenepentamine and epoxy resin E51,had the largest T_g and Td_5%.HNIPU-2351 had the lowest water absorption rate of 2.8%.This shows that,for the one-step synthesis of HNIPU,a larger epoxy value and a higher secondary amine content are beneficial to improving the thermal properties of the materials.The effect of secondary amine content on storage modulus and pencil hardness of the material is greater than the epoxy value.The water resistance of the materials is mainly affected by the density of carbamate.3.The four chemical intermediate bis(hydroxyethyloxycarbonylamino)alkanes(BHAs)were synthesized from diamines and ethylene carbonate.Then,NIPU prepolymer was obtained by BHA and DA via melting method,and then crosslinked with epoxy resin to obtain HNIPU.The effects of secondary amine number and epoxy value on the properties of HNIPU were studied.It was found that BHA-4551-HNIPU had the highest T_g and Td_5%.Meanwhile,it was also found that the influence of epoxy value on the crosslinking density was greater than that of secondary amine number.4.Four different modified MWCNTs were synthesized and characterized using MWCNTs as raw materials.Subsequently,they were added to HNIPU substrates to obtain composites,and the effects of different modified MWCNTs on the properties of composites were further investigated.It was found that the composites containing modified MWCNTs had better thermal properties than those containing unmodified MWCNTs and pure HNIPU.MWCNTs-COOH-Au-HNIPU composites had the highest T_gand Td_5%.5.The dispersion and crystal conditions of MWCNTs and GNPs mixtures with different proportions were characterized.The mixtures of different proportions were then added into HNIPU to obtain five composites materials.The effects of different MWCNTs and GNPs mixture ratios on the properties of HNIPU composites were further investigated.The result showed that the dispersion of pure MWCNTs or GNPs alone in HNIPU was not as good as the mixture of MWCNTs and GNPs.The Td_5%of pure MWCNTs modified HNIPU was 104.2°C higher than that of pure GNPs modified HNIPU,and the water absorption rate was 1.9%lower.It shows that the increase of the proportion of GNPs would weaken the thermal stability and water resistance of HNIPU.In conclusion,in this study,bio-based raw material dimer acid was used as the main structure of polymer,and NIPUs were synthesized by enzyme catalysis and non-catalytic melting method,respectively,and HNIPUs with crosslinking network structure were then obtained by reaction with epoxy resin.Subsequently,HNIPUs were further modifited by nano materials,the properties of the obtained composites were all improved to some extent,and show great potential for application in functional coatings.