Effects of inorganic nanofibers and high char yield fillers on char layer structure and ablation resistance of ethylene propylene diene monomer composites

Abstract

Influences of fillers [including multi-walled carbon nanotubes (MWCNTs), SiC nanowires, methyl-polyhedral oligomeric silsesquioxanes (methyl-POSS) and boron phenolic resin] on the characteristics of porous structure in char layers of ethylene propylene diene monomer (EPDM) composites were studied using experimental solid rocket motor (SRM). Comparing to basic formulation (Porosity: 78.25%), char layers of fillers formulation present lower porosity (Ranging from 64.03% to 67.69%) and showed significant trends of overall or local densification. Further analysis revealed different densification mechanisms: CNTs and SiC nanowires can promote chemical vapor deposition (CVD) reaction in char layers and reduce its porosity, which can be referred as “CVD-promotion densification”; boron phenolic resin is relatively high in char yield and char residue would densify the microstructure of char layers, which can be referred as “char residue densification”; methyl-POSS show a combination of both mechanisms, which lead to the lowest mass ablation rate [170.4 g/(m2·s)] and the best ablation performance.