Ethylene propylene diene monomer (EPDM) foams have received considerable attention owing to their low weight, low thermal conductivity, and mechanical flexibility. However, their poor ablative resistance and low thermal stability make their use in severe conditions, such as the combustion chamber of a solid rocket motor, difficult. In this study, EPDM foams reinforced with aramid fibers (AFs) and carbon fibers (CFs) are prepared through a hot-pressing-induced foaming process. The effects of the fibers on the cellular structure, thermal stability, and mechanical, ablating, and insulating properties of the EPDM foams are investigated. The results show that the addition of CFs enhanced the thermal stability and mechanical properties of the EPDM foams, whereas the use of AFs lowered the thermal conductivity and ablation rate. In particular, when 2.5 phr (parts per hundred parts of rubber) AF and 2.5 phr CF are added, the linear ablation rate tested using oxyacetylene is 0.33 mm s −1 , and the back-face temperature is 53 °C, revealing a good balance in terms of ablative resistance and thermal insulation. Thus, the hybrid-fiber-reinforced EPDM foams possess several advantages, such as low weight, good thermal insulation, ablative resistance, and mechanical robustness, suggesting considerable potential for application in the aerospace industry.

No abstract

Ethylene–propylene–diene monomer (EPDM) composites were usually enhanced with ablative additives to protect solid rocket motor (SRMs) casings. However, the poor thermal insulation caused by the high thermal conductive ablative fillers can lead to rocket motor failure. Herein, the novel EPDM composites containing alternating layers of ablative EPDM (AM) and heat-insulated EPDM (HM) were prepared through layer-multiplying extrusion. Compared with conventional EPDM ablative material, the multilayer composites showed enhanced thermal insulation and mechanical properties that could be further improved by tuning the number of layers. The ablation and thermal insulation properties possessing in AM and HM layers could be combined by forced assembly during co-extrusion, and the alternating multilayer composite was capable of showing the effect of each component. In particular, compared with AM, the maximum back-face temperature with 40 alternating layers of AM/HM decreased from 96.2 °C to 75.6 °C during oxyacetylene test, while the good ablation properties were preserved in the AM component. This significant improvement was attributed to the planar orientation and densification of ablative additives, and the interruption of conductive pathways in the through-plane direction of AM/HM alternating laminate. The anisotropic EPDM composites featuring mechanical robustness, good ablative resistance and thermal insulation suggest considerable potential application in the aerospace industry.

No abstract