4-Hydroxybenzenesulfonic acid triggers rapid preparation of phenolic aerogel composites by ambient pressure drying

Abstract

Phenolic aerogel composites, as an excellent thermal insulation material, have been used in aerospace to resist extreme working conditions of severe heating and intense mechanical stress. However, the high cost and lengthy preparation process seriously restricts their more extensive application. Herein, a novel strategy for rapid preparation of aerogel composites by ambient pressure drying is enabled by copolymerization with 4-hydroxybenzenesulfonic acid. That is, the reactive 4-hydroxybenzenesulfonic acid can serve as the acid catalyst to accelerate both the protonation step and the gelation step during the preparation process of phenolic aerogel. After copolymerization with 4-hydroxybenzenesulfonic acid, these sulfonic acid groups significantly accelerate the protonation of benzoxazine intermediates, leading to more carbocation formation. The activation energy of curing reaction is significant decreased from 300 kJ∙mol−1 to 90 kJ∙mol−1. Thus, 4-hydroxybenzenesulfonic acid containing phenol formaldehyde resin (PFS) aerogel precursors exhibit much faster gelation reaction (within 4 h) than phenol formaldehyde resin (PF) aerogel precursor (12 h), which further facilitates the preparation of phenolic aerogel composites with needled quartz fiber felt by ambient pressure drying. Importantly, the PFS aerogel composites exhibit excellent thermal insulation performance under low heat flux and good fire safety under high heat flux. Rapid gelation of PFS triggered by 4-hydroxybenzenesulfonic acid provides a new approach to develop phenolic aerogel composites with low energy consumption, low cost and short preparation cycle.