Study On The Nanostructure Based On The Surface Of Carbon Fiber And The Properties Of CF/MPSR Composites

Carbon fiber(CF) reinforced methylphenylsilicone resin(MPSR) composites serve as ideal structural materials for thermal protection in aerospace industries because of their superior properties, such as excellent thermal stability, good dielectric properties, light weight, low heat expansion coefficient, high weather and radiation resistance. However, applications of CF/MPSR composites are greatly restricted due to the weak interfacial adhesion between CF and MPSR. Therefore, it is necessary to modify the interface between CF and MPSR in order to enhance the interfacial adhesion and heat resistance. MPSR is a semi-inorganic thermosetting resin with the main backbone siloxane structure, which can be difficult to be modified for improving the interfacial performance. Therefore, smooth and inert fiber surface are needed to be activated to enhance interfacial strength. In this paper, based on the structure characteristics of MPSR, silica nanoparticles(Si O2), Tri Silanol Phenyl POSS and multiwall carbon nanotubes(CNTs) were introduced into the interface of composites by surface treatment of CFs. Three grafting methods improve the wettability, mechanical joggling, Van der Waals effect and chemical bonding between CF and MPSR aiming to enhance the interfacial performance and heat resistance of composites simultaneously.Acid modification, amidation functionalization and the sol-gel polymerization of tetraethoxysilane(TEOS) were combined to modify the fiber surface, and then silica nanoparticles were introduced into the interphase of composites. The relationship between fiber surface morphology and interfacial strength between CF and MPSR was investigated systematically by changing the concentration of TEOS. Introduction of silica nanoparticles helped to enhance the fiber surface energy and roughness, maximize the degree of the molecular contact, and improve mechanical interlocking between CF and MPSR. Therefore, the interfacial performance of composites was enhanced significantly. Experimental results showed that when TEOS concentration was 0.05mol/L, the quality of fiber surface morphology and the properties of composites were the best. Many silica nanoparticles without agglomeration were scattered uniformly onto the fiber surface and the grooves. The interlaminar shear strength(ILSS) and interfacial shear strength(IFSS) of the obtained hybrid fiber(CF/Si O2) composites were enhanced by 35.36% and 75.12%, respectively, and impact toughness of composites was improved by 26.91%. Meanwhile, the 5% weight loss temperature of CF/Si O2 hybrid fiber composites was 12.30 oC higher than that of untreated CF composites, and ILSS of the hybrid fiber composites increased from 23.28 MPa for untreated CF composites to 29.85 MPa by 28.22% after pyrolysis at 400 oC for 30 min. Therefore, the heat resistance of CF/Si O2 hybrid fiber composites was slightly enhanced.TriSilanol Phenyl-POSS was introduced onto the surface of CFs by chemical grafting, and then POSS nanoparticles were introduced into the interphase of composites. Introduction of POSS increased fiber surface roughness to create better mechanical interlocking between fiber and matrix resin. Moreover, the hydroxyl groups on the surface of the obtained hybrid fiber(CF-POSS) could react with MPSR, and form interfacial bonding between CF and MPSR, which enhanced the interfacial strength significantly. After POSS grafting, the fiber tensile strength had no discernable decrease in comparison with that of untreated CF. Compared with the untreated CF composites, ILSS and IFSS of CF-POSS hybrid fiber composites were increased by 45.30% and 89.54%, respectively, and impact toughness was improved greatly by 31.12%. Meanwhile, the 5% weight loss temperature of CF-POSS hybrid fiber composites was 67.16 oC higher than that of untreated CF composites, and ILSS of composites increased from 23.28 MPa for untreated CF composites to 33.26 MPa by 42.87% after 400 oC treatment for 30 min. Therefore, Introduction of POSS improved greatly the heat resistance of CF-POSS hybrid fiber composites.Acid modification, hydroxyl functionalization and chemical modified method were combined to introduce APS and CNTs onto the fiber surface by chemical grafting aiming to prepare a binary grafted multi-scale reinforcement(CF-APS-CNT). Experimental results indicated that CNTs distributed uniformly at different angles on the fiber surface, and CNTs formed an interconnected hierarchical network with few agglomerates. The grafting processes did not decrease fiber tensile strength. Compared to untreated CF composites, ILSS and IFSS of CF-APS-CNT composites were improved significantly by 56.50% and 102.10%, respectively, and the impact toughness was enhanced by 35.00%. Meanwhile, the 5% weight loss temperature of CF-APS-CNT composites was 114.88 oC higher than that of untreated CF composites, and ILSS of composites had an obvious increase to 37.96 MPa by 63.06% compared to untreated CF composites after 400 oC treatment for 30 min. Therefore, the heat resistance of CF-APS-CNT composites was enhanced remarkably.