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

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.