Preparation of ceramifiable and ablatively resistant epoxy resins by microphase structure modulation of silicones

Abstract

The development of ceramic-polymer composites is a focal point in the research of thermal protection systems, and the control of microstructure is crucial for fabricating high-performance resins. In order to investigate the effect of the silicon phase structure on the properties of epoxy resins and preparate the ablation-resistant ceramifiable resins, the homogeneous and “sea-island” phases of epoxy resins with different amounts of silicones were prepared by ring-opening and grafting reactions. The reaction mechanism and the microphase structure of silicone were verified by SEM and TEM. It was found that the homogeneous silicone-epoxy resins exhibited exceptional ablation resistance, with mass and linear ablation rates of 0.0646 g/s and 0.0073 mm/s, which were 78.61 % and 98.36 % lower than those of epoxy resins, and exceeded most of the resin-based ablation-resistant materials reported in the literatures. The homogeneous silicone further slows down the pyrolysis rate of the epoxy resin and inhibits the release of pyrolysis products. During the carbonization and ceramization, the carbothermal reduction reaction between silicon and carbon occurs sufficiently in the homogeneous system, which enhanced the content of SiC ceramics in the carbon layer. Eventually, a dense char layer with low porosity and a highly graphitized structure constructed in situ on the ablative surface, which greatly improves the ablative resistance. Furthermore, its exceptional mechanical properties render it capable of substituting conventional resin-based thermal protection materials, thereby meeting the stringent demands of challenging environments.