| High-modulus carbon fiber/cyanate ester composites are widely used in the fields of satellites and space stations due to their excellent fatigue and corrosion resistance,which are also exposed to a variety of complex service environments such as temperature and humidity.The damage and cracking of resin-fiber interface can be caused after hydrothermal aging,leading to the degradation of mechanical properties of composites,which ultimately affects the dimensional stability of structural components.Therefore,improving the interfacial and anti-hydrothermal properties of HMCF/CE composites is significant for improving their environmental adaptability.The method of synchronously modifying CE resin matrix and HMCF surface by using organic-inorganic hybrid nanoparticles——epoxy-functionalized polyhedral oligomeric silsesquioxane(POSS)was proposed in this paper.The correlation of low hygroscopic resin matrix and rigid interphase with the antihygrothermal aging of composites was investigated,and the improvement of interfacial and anti-hygrothermal aging properties of composites were synchronously achieved.(1)PCE resin matrix with high modulus and low hygroscopicity was designed by the copolymerization of POSS and CE.The molecular structure,modulus and moisture uptake of CE and PCE resin matrix were studied.The P-HMCF was prepared by treating HMCF surface with POSS sizing.The physical and chemical properties of HMCF and P-HMCF surfaces were studied.The tensile and flexural modulus of PCE resin matrix were increased by 13.9% and 21.2% compared to CE resin matrix,respectively,which was achieved through mechanical restraint of rigid silicon cages and chemical crosslinking of epoxy and resin matrix.Compared with CE resin matrix,the moisture uptake of PCE resin matrix was decreased by 25% after immersion in water at 95 ℃ for 30 days.Compared with HMCF,a layer of nanoparticles was coated uniformly on P-HMCF surface,which caused the enhancement of chemical activity and average roughness of P-HMCF surface.The wettability and surface energy of P-HMCF surface were improved.(2)The interfacial properties and micromorphology of HMCF/CE,HMCF/PCE,P-HMCF/CE,and P-HMCF/PCE unidirectional and monofilament composites were compared,respectively.The interfacial modulus distribution and carbon element change trend of the four kinds of composites were analyzed through f-AFM and EDS,and the interfacial reinforcement mechanism of composites was proposed.Compared to HMCF/CE,the interlaminar shear strength(ILSS)of HMCF/PCE,PHMCF/CE,and P-HMCF/PCE were increased by 15.0%,36.8%,and 48.9%,respectively.The interfacial shear strength(IFSS)showed the same trend of improvement,and the failure mode of composites changed from the weakest adhesion failure of HMCF/CE to the strongest cohesive failure of PHMCF/PCE.The interfacial modulus transition of HMCF/PCE composites was widened,and the modulus intermediate layer of interphase was constructed in P-HMCF/CE and P-HMCF/PCE composites,which was attributed to the rigid interphase with modulus platform from the interaction between the rigid POSS on carbon fiber surface and resin matrix,contributing to transferring stress concentration and inhibiting crack propagation.(3)The moisture uptake and interlaminar shear strength(ILSS)of HMCF/CE,HMCF/PCE,P-HMCF/CE,and P-HMCF/PCE composites were compared during hydrothermal aging.The effects of hydrothermal aging on the structural changes of the interphase in various composites were characterized by peak force quantitative nano-mechanics(PF-QNM)mode of AFM.After immersion in water at 95 ℃ for 30 days,the P-HMCF/PCE composite exhibited the lowest moisture uptake(0.8%)and the highest ILSS retention(84.9%).Also,the crack growth of interphase was hardly emerged and the thickness of interphase was hardly changed in P-HMCF/PCE composite.The mechanism of anti-hydrothermal aging was proposed: the decrease of moisture uptake in PCE matrix and the enhancement of interfacial bonding between P-HMCF and PCE synergistically improved the antihydrothermal properties of composites. |
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