Nano-hydroxyapatite filled EPDM nanocomposite: towards green elastomeric thermal insulating coating with superior mechanical, thermal, and ablation properties

Abstract

ABSTRACT Heat-shielding composite materials containing asbestos has been used for thermal insulation of aerospace rocket motors. However, asbestos has carcinogenic effects on both human and environment. This study was directed to the development of novel elastomeric nanocomposite thermal-shielding coating (asbestos-free); the developed elastomeric nanocomposite was based on hydroxyapatite (HA) nanoparticles (NPs) in an ethylene propylene diene monomer (EPDM) matrix. HA is a bio-ceramic material with 18.5 wt % phosphorus; HA can act as nano phosphorus-based fire extinguisher. HA NPs were synthesized by continuous hydrothermal technique; high crystalline HA nanoplates of 350 nm length, and 100 nm width were successfully developed. HA NPs were integrated into EPDM matrix; uniform dispersion of HA particles was verified via EDAX analysis. The impact of HA NPs on EPDM tensile strength, elongation-at-break, hardness, density, thermogravimetric analysis (TGA), thermal conductivity test, and ablation test was assessed to asbestos fibers. HA/EPDM secured superior mechanical properties compared with Asbestos/EPDM; HA NPs secured an increase the tensile strength, elongation at break by 16.2% and 105.3% respectively. HA with surface hydroxyl groups could be integrated into EPDM matrix via chemical bonding. HA offered novel thermal shielding properties; HA secured a decrease in thermal conductivity coefficient by −21.1%; and the best ablation resistance was increased by + 31.5%. Residual weight was increased by 13%, compared with asbestos fibers.