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Silica aerogels are highly porous materials with exceptional thermal insulation performance. They become even more attractive if combined thermal and acoustic insulation is achieved. Silica aerogel composites reinforced with fibres are an ingenious way to surpass the fragility stemmed from the aerogel's intrinsic porosity, and textile fibres are good sound absorption materials. Reclaimed fibres are a relatively low-cost feedstock and were obtained in this work exclusively through mechanical processes from textile wastes, thus promoting the concept of circular economy, namely for cotton, polyester and wool fibres. These reclaimed fibres were used as reinforcement matrices for silica aerogel composites obtained from sol–gel transformation of tetraethyl orthosilicate and isobutyltriethoxysilane/or vinyltrimethoxysilane precursors and dried at ambient pressure after silylation. Silica aerogel composites reinforced with reclaimed cotton fibres had the best sound absorption coefficient (a peak value of 0.89), while the polyester-reinforced composite exhibited the lowest thermal conductivity (k = ~24 mW m−1 K−1, Hot Disk). The better combined results on thermal and acoustic insulation were achieved by the wool-reinforced composites. The thermal conductivity values were less than 27 mW m−1 K−1, and the sound absorption coefficient achieved a peak value of 0.85. Therefore, the aerogel composites developed here can be selected for thermal or/and acoustic barriers by choosing a suitable type of fibre. Their design and preparation protocol followed environmental-friendly and cost-effective approaches. [ABSTRACT FROM AUTHOR]

Silica aerogels are highly porous materials with exceptional thermal insulation performance. They become even more attractive if combined thermal and acoustic insulation is achieved. Silica aerogel composites reinforced with fibres are an ingenious way to surpass the fragility stemmed from the aerogel’s intrinsic porosity, and textile fibres are good sound absorption materials. Reclaimed fibres are a relatively low-cost feedstock and were obtained in this work exclusively through mechanical processes from textile wastes, thus promoting the concept of circular economy, namely for cotton, polyester and wool fibres. These reclaimed fibres were used as reinforcement matrices for silica aerogel composites obtained from sol–gel transformation of tetraethyl orthosilicate and isobutyltriethoxysilane/or vinyltrimethoxysilane precursors and dried at ambient pressure after silylation. Silica aerogel composites reinforced with reclaimed cotton fibres had the best sound absorption coefficient (a peak value of 0.89), while the polyester-reinforced composite exhibited the lowest thermal conductivity (k = ~24 mW m−1 K−1, Hot Disk). The better combined results on thermal and acoustic insulation were achieved by the wool-reinforced composites. The thermal conductivity values were less than 27 mW m−1 K−1, and the sound absorption coefficient achieved a peak value of 0.85. Therefore, the aerogel composites developed here can be selected for thermal or/and acoustic barriers by choosing a suitable type of fibre. Their design and preparation protocol followed environmental-friendly and cost-effective approaches.

Silica aerogel composites reinforced with reclaimed cotton fibers obtained from textile industry wastes are here presented. These fibers were obtained from fabric leftovers of textile clothing industry, using only mechanical processes for reverting wasted fabric scraps to elementary fibers. The syntheses were carried out following environmentally friendly solutions. The post-gelation silylation/washing steps were performed applying ethyl acetate, recognized as a non-hazardous solvent. The tetraethyl orthosilicate-based aerogel composites were developed with a co-precursor having a non-hydrolysable bulky branch, isobutyltriethoxysilane, aiming to reduce brittleness and increase hydrophobicity. The aerogel matrix composition used here, reinforcement conception and modification solvent are being presented for the first time in the literature. The composites, manufactured in small cylindrical-shape (diameter ~3 cm) and disk-shape (diameter ~9 cm and ~14 cm) were silylated with hexamethyldisilazane and ambient pressure dried. Thermal conductivities were assessed by non-stationary and steady-state methods, the later yielding values 25–37% lower, achieving a value as low as 21 ± 3 mW m–1 K–1. The composites exhibit a high degree of flexibility conferred by the embedded cotton fibers, that imparted as well good acoustic insulation, since at frequencies near 1300 Hz, the sound absorption coefficient is 0.8. Cotton fibers are well known by their moisture buffering. By taking advantage of that water adsorption/desorption, the thermal regulation ability of the aerogels is studied here as a novel application for these materials. At 85% of relative humidity, silica aerogel composites with ~15 wt% of cotton fibers adsorbed 2.6 wt% of moisture and the process reversibility was confirmed. Highlights: Cotton-silica aerogel composites reinforced with waste fibers obtained from fabric scraps. Reclaimed industrial cotton fibers mechanically processed, without detrimental chemicals. A non-hazardous solvent, ethyl acetate, used for the first time for aerogel manufacturing. Multifunctional silica-aerogel composite: moisture regulator and thermal/acoustic barrier. [ABSTRACT FROM AUTHOR]