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

Abstract

Low‐density foams and aerogels based on upcycled and bio‐based nanofibers and additives are promising alternatives to fossil‐based thermal insulation materials. We have prepared super‐insulating foams from upcycled acid‐treated aramid nanofibers (upANFA) obtained from Kevlar® yarn and tempo‐oxidized cellulose nanofibers (CNF) from wood. The ice‐templated hybrid upANFA/CNF‐based foams with an upANFA content of up to 40 wt.% displayed 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 upANFA/CNF foams was found to decrease with increasing upANFA content (5‐20 wt.%). The super‐insulating properties of the CNF‐upANFA hybrid foams were related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANFA and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar®, and this study could hopefully inspire efforts to upcycle textile waste into high‐performance products.This article is protected by copyright. All rights reserved

Hybrid Foams based on Multi‐Walled Carbon Nanotubes and Cellulose Nanocrystals for Anisotropic Electromagnetic Shielding and Heat Transport

“…The thermal conductivity in the radial direction (Figure 4a) is 4 to 7 times lower than the thermal conductivity in the axial direction (Figure 4b), which is consistent with previous studies on anisotropic nanocellulose-based hybrid foams. [59,60] The thermal conductivity in the axial direction (Figure 4b) increased with increasing relative humidity (RH) while the thermal conductivity in the radial direction (Figure 4a) displayed a U-shaped RH-dependence. Previous studies on hygroscopic CNC and CNF-based anisotropic foams [53,61] found a similar RH-dependence of the radial thermal conductivity, which was related to a competition between a humidity-induced swelling that increased phonon scattering at low and intermediate RH, and a replacement of air with water at higher relative humidity.…”