Abstract
Excellent mechanical and adhesive properties make epoxy an ideal coating, but speedy pyrolysis rate, excessive gas products, and low residual char lead to low ablation efficiency, limiting the application in long-time thermal protection environments. In this paper, through branching structure design including pre-curing and alcohol exchange reactions, highly silicon-branched epoxy resins with different degrees of branching and silicon contents were synthesized. And the synthesis of highly silicone-branched epoxy resins with different branching degrees was verified by FTIR and viscosity curves. Through the analysis of thermal stability and pyrolysis history, the influence of the branched structure and content of silicone on the ablation mechanism of epoxy resin was investigated in detail. With 90 phr addition, the char residue increased to 42.3 %, and the release of pyrolysis products including a variety of flammable products was significantly inhibited. Furthermore, under a torch test of 160 kW/m2, due to the deposition mechanism in the gas and liquid phases of degradation products, a compact porous char was constructed during the ablation. The linear ablative rate of EP-3M@90P was reduced by more than 60 %, and the maximum value of back-surface temperature decreased by 48 °C compared to EP. Besides, the silicone-branched epoxy resin exhibits excellent mechanical properties, and the impact strength of EP-3M@90P nearly doubled compared to EP. Predictably, the design of silicone-branched structures to achieve control of the degradation history of epoxy resins provides a superior method for the preparation of high-strength and high-toughness thermal protective coatings.
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