Synthesis Of Biphenyl Liquid Crystalline Polyurethane And Toughening Modification Of Epoxy Resin

Epoxy resin is widely promoted for its excellent physical and chemical properties.However,the disadvantage of poor toughness of the cured product limits its application in the high-end field,so it is necessary to toughen and modify it.However,most toughening methods impair its thermal and mechanical properties.To overcome this shortcoming,this paper is toughened with biphenyl liquid crystal polyurethane?LCPU?.First,a diphenol intermediate?BP₆?was synthesized using 4,4'-p-hydroxybiphenol and6-chloro-1-hexanol,and then BP₆ was reacted with toluene diisocyanate?TDI?to obtain an LCPU using FT-IR,DSC,POM,XRD means to characterize it.0 wt%,1 wt%,3 wt%,5 wt%,7 wt%of LCPU was blended with epoxy resin and cured by DDS to form the castables.The optimum toughening system was determined by mechanical properties,SEM,DSC and TG tests,the rheological properties and curing properties of the lipid system were studied.Finally,five glass fiber reinforced composites with resin system were prepared by compression molding process,and the mechanical properties were studied.The results of FT-IR proved that BP₆ and LCPU were successfully synthesized.The POM results show that LCPU is a typical thermotropic liquid crystal polymer and has birefringence.Combined with DSC curve analysis,the liquid crystal interval of LCPU is10?.XRD results show that BP₆ and LCPU have good liquid crystal characteristics and crystallization characteristics.The mechanical properties of the castables show that the 1 wt%LCPU/E-51 system has the best toughness,the impact toughness is 42.27 kJ·m^-2,which is71.90%higher than the pure resin 24.59 kJ·m^-2,and the bending and tensile properties are better than the pure resin.The SEM photograph shows that the section of the system is rough and is ductile fracture,which is consistent with the impact test results.From the TG and DSC analysis,it is known that the addition of LCPU increases the thermal decomposition temperature and glass transition temperature of the resin system.The dynamic and isothermal viscosity tests of 1 wt%LCPU/E-51/DDS and pure resin systems were carried out to understand the difference in rheological properties and the longest process operation period.According to the non-isothermal curing kinetics,the curing behavior of the resin system was studied,and the activation energy E?was solved.The kinetic model was established and compared with the experimental values.The results show that LCPU promotes the curing of epoxy resin,and the calculated values of the model are in good agreement with the experimental values.The rate equation can better analyze and calculate the curing process.The relationship between the exothermic state,reaction rate and temperature of 1 wt%LCPU/E-51/DDS system was studied by isothermal curing kinetics.The relationship between reaction rate and conversion rate was simulated by Kamal model.The model analysis showed that the system was dominated by autocatalytic reaction.The mechanical properties of the composites show that the mechanical properties of the1 wt%LCPU/E-51/DDS/glass fiber system is the best,and the interlaminar shear strength is increased by 32.56%compared with the E-51/DDS/glass fiber system;the bending strength and modulus are improved respectively 9.15%,16.36%;tensile strength,modulus and elongation at break increased by 5.14%,2.93%and 13.93%,respectively.