Thermally Insulating and Moisture‐Resilient Foams Based on Upcycled Aramid Nanofibers and Nanocellulose

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Abstract

Low‐density foams and aerogels based on upcycled and bio‐based nanofibers and additives are promising alternatives to fossil‐based thermal insulation materials. Super‐insulating foams are prepared from upcycled acid‐treated aramid nanofibers (upANF _A) obtained from Kevlar yarn and tempo‐oxidized cellulose nanofibers (CNF) from wood. The ice‐templated hybrid upANF _A/CNF‐based foams with an upANF _A content of up to 40 wt% display high thermal stability and a very low thermal conductivity of 18–23 mW m ⁻¹ K ⁻¹ perpendicular to the aligned nanofibrils over a wide relative humidity (RH) range of 20% to 80%. The thermal conductivity of the hybrid upANF _A/CNF foams is found to decrease with increasing upANF _A content (5–20 wt%). The super‐insulating properties of the CNF‐upANF _A hybrid foams are related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANF _A and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar, and this study can hopefully inspire efforts to upcycle textile waste into high‐performance products.

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Adsorption of Gases in Multimolecular Layers

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Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide.

Bernd Wicklein, Andraž Kocjan, German Salazar-Alvarez … (2015)

High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m(-1) K(-1), which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.