| If carbon fiber composite materials want to be truly used in automobile industries,it must satisfy the production demands of automobile industries,like high production,high manufacturing speed and low cost.It calls for new technique of large-scale,automatic production and rapidly moulding composite.The existing carbon fiber composites represented by epoxy resin matrix will be fabricated within 3-4 hours.Its application has been limited with the long moulding cycle.In this article,high-temperature-toughed epoxy resin was designed and synthesized from the level of molecular structure,a rapidly moulding prepreg system was developed based on high-temperature-toughed epoxy resin matrix and regulated by the high reactive activity of modified curing system.The unification of rapidly mouldig process of carbon fiber composites and processing operability of the prepreg was realized.1.Isocyanate-terminated polyurethane prepolymer(PPU400,PPU600,PPU1000)were designed and synthesized from liquefied 4,4’-diphenylmethane diisocyanate(L-MDI)and poly propylene glycol(PPG400,PPG600,PPG 1000).High-temperature-toughed epoxy resin(HTTEP400,HTTEP600,HTTEP1000)were synthesized by the reaction betweem isocyanate group and epoxy group,introducing polyurethane flexible segment and oxazolidinone rigid ring to the main chain of epoxide.The structure of PPU was confirmed by FTIR spectra.After 3 hours,the isocyanate content and molecular weight of PPU run up to theoretical value.HTTEP were confirmed by FTIR and NMR spectra,its molecular weight and epoxy value is accordant with theoretical values.2.Three prepreg resin systems were prepared with high-temperature-toughed epoxy(HTTEP400,HTTEP600,HTTEP 1000).Its thermal properties,mechanical properties including impact toughness were compared with Control(pure epoxy resin system),and the toughening mechanism was analyzed.The use of HTTEP improved the glass transition temperature at a range from 20～40℃.The static test of mechanical properties suggested that modulus of HTTEP system increased as the decrease of PPG molecular.HTTEP improved the toughness of resin system,the longer PPG molecular,the higher prepreg resin system toughness.PPU flexible chain segment was separated out from epoxy matrix and formed microphase area.The presence of well-dispersed and proper-sized microphase resulted to excellent toughness of resin system.3.The curing kinetics of four kinds of resin systems were studied respectively.The analysis of non-isothermal DSC calculated the curing reaction activation energy(Ea)during curing respectively,suggested that they all fitted autocatalytic model.The Ea of HTTEP400 resin system was the lowest,had highest reactivity.Isothermal DSC showed that HTTEP resin system can cure within 5 minutes at 150℃,which is benefit to rapidly cure.4.Prepregs of HTTEP400 resin system and Control resin system were prepared with hot melt method.And the processing performance of prepregs was regulated,composites moulding by prepregs is tested on thermal,mechanical properties and micro structure.Viscosity-temperature curve indicated that HTTEP resin system had a suitable processing flow window.Short-term composites had good heat resistant properties with high Tg at 188℃.The toughness of resin matrix and carbon fiber matched well,with Gic at 639J/m2,GⅡc at 1552J/m2,and interlaminar shear strength at 86.29Mpa.Fracture surface micrographs revealed that its resin matrix had good coating on carbon fiber at Short-term composites,and the interface bonding between resin matrix and carbon fiber was strong. |
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