Study on a Novel Integrated Wet Mixing and Devolatilization Extrusion Process for High‐Performance Polyimide Short Fiber Reinforced EPDM Ablation‐Resistant Composites

Polyimide short fiber (PISF) reinforced Ethylene‐Propylene‐Diene monomer (EPDM) composites are commonly employed as ablation resistant inner insulation layers. However, traditional dry mixing tends to cause nonuniform fiber dispersion and substantial fiber breakage. In this study, a novel integrated process combining solution wet mixing with devolatilization extrusion was developed. This method uses the volumetric stretching flow field generated by a mono screw devolatilization extruder to efficiently break up filler agglomerates. The effects of several wet mixing processes on fiber dispersion, filler distribution, degassing efficiency, mechanical properties, thermal stability, and ablation resistance of PISF/EPDM composites were systematically compared. Experimental results show that the novel process achieves a fiber length retention rate exceeding 95%, shortens devolatilization time to 2 h, and lowers residual volatile content to below 1%. The resulting composite exhibits a linear ablation rate as low as 0.051 mm/s, a dense carbonized layer, and a tensile strength of 12.85 MPa, which is comparable to that of dry mixed composites. Overall, this approach offers notable benefits in fiber and filler dispersion, processing efficiency, and comprehensive performance, thereby providing an effective technical route for high performance ablation resistant composites.