Preparation and properties of polyacrylonitrile pre-oxidized fiber/silicone rubber ablation composites
Polyacrylonitrile pre-oxidized fiber(PANOF)is an emerging flame retardant material with low cost and high performance,showing a promising application potential as thermal protection materials in the aerospace field. Pretreated PANOF(t-PANOF)was obtained by the process of oil removing with acetone and surface modification using silane coupling agent KH570 in turn. Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS)were employed to figure out the changes of morphology and chemical structure of the fibers before and after pretreatment and their interfacial properties with silicone rubber(SR). Effects of t-PANOF on the mechanical and thermal performances of SR were further investigated. With the presence of ceramic forming agent(CFA),the ablation responsive behaviors of CFA/t-PANOF/SR ternary composites were researched as well. The results show that the level of interfacial adhesion between fibers and rubber is significantly enhanced contributed from the pretreatment of PANOF,and the tensile strength of the composites is improved accordingly.However,with the increasing content of t-PANOF,the comprehensive mechanical properties of t-PANOF/SR composites show the trend that increase first and then decrease,indicating that the optimal dosage of the fibers is 5 to 10 phr. t-PANOF skeleton helps to not only enhance the dimensional stability of SR in high temperature and oxygen-rich environment,but also improve the ablation performance of CFA/t-PANOF/SR composites. The antioxidation ceramic layer with fiber skeleton as the main structure is formed on the surface of CFA/t-PANOF/SR composites under the high temperature aerobic gas with the heat flux density of 2 MW/m2,the corresponding linear and mass ablation rate are only 0.02 mm/s and 0.02 g/s respectively,which is expected to be utilized as an ablation material to satisfy the demands of the new generation of aerospace vehicles.
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