Improvement of the Mechanical Properties of Silica Aerogels for Thermal Insulation Applications through a Combination of Aramid Nanofibres and Microfibres.

Reinforcement of silica aerogels, remarkable lightweight mesoporous materials with outstanding insulation performance, is still a challenging research topic. Among the strategies used to overcome their brittleness, one of the most effective is the manufacturing of aerogel composites with embedded fibres. In this work, the incorporation of nanofibres together with microfibres in a tetraethoxysilane-vinyltrimethoxysilane matrix is investigated for the first time for the development of novel aerogel nanocomposites. The nanofibres, synthesized from different aramid fibres, including Kevlar ® pulp, Technora ® , Teijinconex ® and Twaron ® fibres, were used in different combinations with microaramids and the resulting nanocomposites were thoroughly investigated for their physicochemical and thermomechanical features. The properties depended on the type and amount of the nano/microfibre used. While the microfibres exhibited low interaction with the silica matrix, the higher surface of the nanofibres ensured increased contact with the gel matrix. A low bulk density of 161 kg m -3 and thermal conductivity of 38.3 mW m -1 K -1 (Hot Disk ® ) was achieved when combining the nanofibres obtained from Kevlar ® pulp with the Technora ® or Teijinconex ® long fibres. The nanofibres showed higher dispersion and random orientation and in combination with microfibres led to the improvement by a factor of three regarding the mechanical properties of the aerogel nanocomposites reinforced only with microfibres. The scale-up process of the samples and simulated tests of thermal cycling and vacuum outgassing successfully conducted indicate good compliance with space applications.