Thermally Insulating Cellulose Nanofiber Aerogels from Brewery Residues

Brewery spent grain(BSG), the main waste of the brewery industry,is often disposed of or sold as an animal feed at low prices, neglectingthe potential for further valorization. In this work, BSG was usedfor the first time to produce cellulose nanofiber aerogels for greenthermal insulating applications. Cellulose nanofibers (CNFs) wereextracted from BSG through microfluidization with and without TEMPO-oxidationpretreatment to obtain bio-based building blocks for aerogels. TheTEMPO-treated CNFs exhibited a finer diameter (5.4 nm) with a morehomogeneous size distribution (2-10 nm) than that of nonoxidizedsamples. All of the produced aerogels demonstrated low densities (0.009-0.031g/cm(3)), low thermal conductivities (32.3-37.7 mW/mK),and a compressive Young's modulus in the range of 4-311kPa. Unidirectional freezing and TEMPO-oxidation showed a distinctimprovement in the thermal conductivity and mechanical propertiesof the aerogels compared to the random frozen samples. Specifically,the unidirectional frozen aerogel with the highest investigated CNFconcentration of 3 wt % exhibited the lowest thermal conductivity(32.4 mW/mK), highest Young's modulus (311 kPa), and good thermalstability. These results show that the BSG-derived nanocellulose isa valuable resource for producing eco-friendly, biodegradable, andthermally insulating aerogels.