Effects of heat exposure on the properties and structure of aerogels for protective clothing applications

Abstract

Abstract In this paper, an attempt has been made to investigate the effects of heat and thermal radiation on the structure and properties of hydrophobic aerogels intended for use in textile materials for protective clothing. A novelty is a comprehensive approach to the subject by considering all aspects relevant to the using of aerogels in clothing protecting against heat and adaptation of test methods commonly used to assess the protective properties of clothing materials for the needs of aerogel testing. The weight changes of aerogels upon heat and radiation exposure was determined by the gravimetric method and thermogravimetric analysis (TGA). The nano- and micro-structure of untreated and heat-treated aerogels was characterized by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, Fourier transform infrared spectroscopy (FTIR) and contact angle technique was used to study the chemical structure and hydrophobicity of the aerogels, respectively. Textural characteristics (specific surface area, pore volume, pore size distribution) were determined based on adsorption/desorption isotherms of N2 at 77 K. It was found that the exposure of aerogels to heat led to a reduction in their weight, for example at 180 °C the weight loss was about 2% (irrespective of treatment time), whereas at 350 °C the loss was three times greater and amounted to approx. 7%. The weight loss at 350 °C indicates a slow removal of the surface –CH3 groups, which has been confirmed by the FTIR analysis. The oxidation of methyl groups provides also change the hydrophobic nature of the aerogels demonstrated on the basis of the results of water contact angles. From SEM and AFM images it can be observed that exposure to heat changed the structure and morphology of silica aerogel granules, while aerogel powder was resistant to temperature treatment. The scale of observed changes of the structure and weight of silica aerogels allows their potential use in the design of protective clothing.