Thermally Insulating Cellulose Nanofiber Aerogels from Brewery Residues

Abstract

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

Harnessing the Flexibility of Lightweight Cellulose Nanofiber Composite Aerogels for Superior Thermal Insulation and Fire Protection

“…According to several studies, CNF aerogels are found to have low density and high porosity, which makes them thermally insulating. 27,28 On the other hand, CNF aerogels are associated with some drawbacks, such as flammability, high moisture sensitivity, and low mechanical properties. To overcome these problems, MTMS, PU, and APP were used for the synthesis of a PU-based CNF aerogel.…”

A Novel, Controllable, and Efficient Method for Building Highly Hydrophobic Aerogels

“…Aerogels made from silane [1][2][3][4][5], carbon [6][7][8][9], biomass [10][11][12][13][14][15][16][17][18][19][20][21][22][23], polymers [24][25][26], metal oxides [27], inorganic salts [28,29], etc., have the advantages of low density, high porosity, and high specific area [18]. This combination of properties makes them have a huge number of applications in the fields of industry [30], architecture [8,31,32], agriculture [17], etc., some of which have been commercialized already. Among them, aerogels made from a soluble polymer matrix by freeze-drying have the potential to be applied to thermal or sound insulation because of their low cost, easy preparation, and low heat conductivity [1,9,30].…”

“…Moreover, when water droplets condense on or are absorbed by the porous structure, the skeleton of the aerogel will be destroyed by capillary force and collapse [24]. Therefore, hydrophobic modification is a necessary precondition for the practical application of aerogels [15,31].…”

Characterization of holocellulose extracted from agricultural and food processing byproducts via ecofriendly delignification pulping process

“…However, pulping, the process by which wood is reduced to a fibrous mass, requires strong chemical process resulting in emissions of sulfur compounds, suspended solids, and wastewater 7,8 . There has been also increasing efforts to keep wood in its solid form rather than disintegrating it to its biopolymeric constituents 9 . Utilizing plant‐based byproducts generated from agricultural production and food processing, as a nonwood cellulose resource, has huge benefits considering their sufficient resources and the smaller amount of lignin that requires less use of chemicals and energy to produce cellulose‐based materials 10 …”