Preparation of Organic/Inorganic Composite Aerogel through Gelation and Supercritical Fluid Drying of Para-Aramid Fibril/Silicon Alkoxide Dispersion

Abstract

Organic/inorganic composite aerogels were obtained from poly-paraphenylene terephthalamide (PPTA) micro-fibrils and methyltrimethoxysilane (MTMS). They are prepared using the following four-step process: the gelation of 1.0 wt% PPTA fibril dispersion containing MTMS by cooling, dehydration condensation of MTMS by immersing the wet gel in a catalyst solution, substituting the solvent in the wet gel, and supercritical drying of the wet gel. When the PPTA/MTMS dispersion containing 1.0 wt% MTMS was gelatinized, the PPTA fibrils strongly adhered to each other, and the PPTA/MTMS composite wet gel obtained better morphological stability. Furthermore, the wet gel prevented shrinkage during the catalyst soaking and supercritical fluid drying processes, and the resulting aerogel had a minimum density of < 0.03 g/cm³. It also had a composite network structure with silica spheres of approximately 30 nm attached to the PPTA fibril network. In contrast, when the PPTA/MTMS dispersions containing 5.0 or 10 wt% MTMS were gelatinized, the obtained composite aerogels had an entangled structure of PPTA fibril networks around silica spheres ranging from 500 nm to 700 nm in size. Moreover, aerogels comprising PPTA/MTMS dispersion with 10 wt% MTMS had a specific surface area of 610 m²/g and retained 70 % of their weight after the heat resistance evaluation at 600°C.