EPDM-based heat-shielding materials modified by hybrid elastomers of silicone or polyphosphazene

Abstract

The erosion resistances of ethylene propylene diene monomer (EPDM) insulations are often inadequate for advanced solid rocket motor (SRM) applications. EPDM modification by blending secondary matrixes is a feasible approach to improve the ablative properties of EPDM insulations. The addition of flexible inorganic hybrid rubbers as a secondary matrix, such as silicones and polyphosphazenes, may impart EPDM insulations with better ablative performance. The blends of EPDM/hybrid rubbers represent the state-of-the-art heat-shielding materials for SRM. In the present work, methyl-phenyl silicone/EPDM and poly(diaryloxyphosphazene)/EPDM insulation systems with various blending ratios of secondary matrixes have been prepared. The ablative properties of the insulations were examined by oxy-acetylene ablation tests, and the results showed that these properties could be enhanced accordingly by blending with hybrid rubbers under appropriate proportions. The unique charred layers resulting from the hybrid rubbers contributed to their excellent ablation properties. For example, the silicone/EPDM insulations exhibited a more significant improvement of ablation resistance properties. With a 1:1 blending ratio of silicone/EPDM, the linear ablation rate was 0.06 mm s−1 after 20 s of oxy-acetylene ablation. The enhancement in the ablative resistance was attributed to the charred layers with bunches of embedded compact microtubes with a length of 2–3 mm, which consisted of silicon carbide, silicon dioxide, and Si–O–C ceramics.

Evaluation of elastomeric heat shielding materials as insulators for solid propellant rocket motors: A short review

“…However, the poor mechanical properties associated with silicones severely restrict their utility [46]. Regarding ablation performance, Wu et al [47] have concluded that with a 1:1 blending ratio of silicone/EPDM, the linear ablation rate was 0.06 mm/s after 20 s of the oxy-acetylene ablation test compared to the much lower result of the EPDM insulation (0.215 mm/s). This result highlights the usefulness of silicone as additive in EHSM formulations.…”

Ablation Response Behavior under Different Heat Flux Environments for Liquid Silicone Rubber Composites

“…They show unique advantages in complex deformation and dynamic structure, which can effectively make up for the drawback of rigid insulators. To date, the most widely used elastomeric matrices include nitrile butadiene rubber (NBR), ethylene propylene diene monomer rubber (EPDM), − and silicone rubber (SR). , Among them, SR, as an inorganic (semi-organic) material, has received more and more attention due to its excellent oxidation resistance and heat resistance, which is attributed to its special structure with Si–O–Si. Liquid silicone rubber-based ablative materials exhibit great development prospects in thermal protection fields due to their good properties and excellent designability …”

Performances of novel poly(diaryloxyphosphazene) based heat shielding materials with various fibrous reinforcements

“…The PA/PDPP and CF/PDPP composites produced relatively compact charred surface and fewer macro fractures. Remarkably, the charred region of PDPP composites was less prone to expand above the virgin material compared to the conventional fibers reinforced EHSMs 26,36 . This ablation behavior is different from Torre's report on EPDM based EHSMs, where the charred region tends to expand above the virgin material for the EPDM insulations based on different fibrous reinforcements 10,37,38 …”

“…Remarkably, the charred region of PDPP composites was less prone to expand above the virgin material compared to the conventional fibers reinforced EHSMs. 26,36 This ablation behavior is different from Torre's report on EPDM based EHSMs, where the charred region tends to expand above the virgin material for the EPDM insulations based on different fibrous reinforcements. 10,37,38 In terms of adhesion of ablative charred layers to the underneath virgin material, PA/PDPP based EHSMs exhibited the best adhesion performance among these different fibrous fillers.…”