Silica aerogel composites with embedded fibres: a review on their preparation, properties and applications

Silica aerogels are among the lightest weight solid materials and exhibit other unique properties, in particular an outstanding insulation performance. However, these nanostructured highly porous materials show inherent brittleness that makes their processing and handling difficult and constrains their use in common daily applications. One of the most convincing and effective strategies to reinforce the silica aerogel structure is the manufacturing of aerogel composites with embedded fibres, which significantly contributes to widening their applications. This review encompasses a complete survey on scientific achievements related to silica aerogel composites reinforced with all types of fibres (natural, man-made, organic, inorganic and nanofibres), describing their synthesis approaches and properties. The influence of the embedment of different fibres on the final properties of the composites is thoroughly reported, considering their amount in the matrix and/or their specific characteristics, namely morphology, orientation and optical features. The applications linked to the fibre-reinforced silica aerogel composites are briefly addressed as well, evincing developments in typical functions of aerogels, as thermal and/or acoustic insulators and adsorbents, and also in emerging uses, for example as sensors or technical and protective apparel. Silica aerogels are among the lightest solid materials but they are also very fragile. Fibres embedment is the most versatile and effective method to preserve a monolithic shape during drying, even at large scale, thus widening their applications.