Silica aerogel-embedded thermal liner: fabrication, properties, and potential for extreme heat protective clothing

Abstract

Silica aerogel was developed in situ aramid needle punched nonwoven thermal liner via sol-gel process followed by ambient pressure drying technique using tetraethoxysilane (TEOS) as a precursor. The thermal liner was augmented with silica aerogel at three different add-on percentages relative to the weight of the nonwoven fabric. This incorporation aimed to investigate the influence of the aerogel add-on percentage on the thermal protective performance of the tested thermal liner. The wet gel surface was modified through a silylation process, varying concentrations of silylating agent, trimethylchlorosilane (TMCS), in hexane. The characterization of the aerogel-embedded thermal liner samples encompassed evaluations of thickness, air permeability, thermal conductivity, thermal stability (measured by TGA), and examination 
through Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy. The heat transfer index (HTI24) was measured for every sample under radiant and flame heat exposure. An investigation using Analysis of Variance was carried out to evaluate how the percentage of aerogel add-on and concentrations of silylating agent affect the HTI24 heat transfer index (HTI24) of the aerogel-embedded thermal line. Aerogel embedded thermal liner, irrespective of aerogel add-on percentages and TMCS concentrations, provides higher protection under both radiant and flame exposure than non-aerogel nonwoven thermal liner. Both aerogel add-on percentage and TMCS concentration positively impact the HTI24 value for both radiant and flame heat exposure. Higher protection against radiant and flame heat exposure makes aerogel-embedded thermal liners more suitable for extreme heat-protective clothing.