(255a) Fabrication of Waste Biomass-Derived Aerogel Using Zinc Chloride Salt Hydrate

Aerogel is a highly porous material with unique properties including low density, thermal conductivity, and high water/oil retention capacity. It is mainly fabricated from synthesized polymers or cross-linked by additional chemical agents. With the increasing demand for green materials and sustainable processes, more attention has been drawn to developing aerogels directly from natural and renewable materials.

Cellulose is an abundant natural polymer and has been used for fabricating aerogels. It has advantages including its biocompatibility and non-toxicity. One of the cellulose-based aerogel fabrication approaches is the dissolution-regeneration process. However, one big challenge is the strong hydrogen bonds in and between cellulose chains impair the efficiency of most solvent systems.

Molten salt hydrate is an aqueous solution with a high salt concentration where the molar ratio of water to salt is near to the coordination number of the salt cation. Because of the similar properties of molten salt hydrates and ionic liquids, molten salt hydrates showed their capabilities to dissolve cellulose. Zinc chloride is a well-known cellulose swelling and dissolving agent with inexpensive price and low toxicity. Dissolved cellulose in zinc chloride salt hydrate has been reported to form hydrogel and films, while cross-linking is necessary to provide sufficient strength.

Waste biomass (i.e., end-of-life paper products) is a good resource for cellulose-based aerogel synthesis in terms of economic benefits. Waste fines and food packaging paperboards are typical unrecyclable biomass. Waste fines are rejected fibers in the paper recycling process because the short fibers are unable to provide sufficient strength for paper. Food packages have the issue as they contain different food residues. Hence, waste biomass is mostly landfilled or combusted. Also, calcium carbonate in these wastes can generate calcium ions, which are also well known as cross-linking agents for hydrogel formation, in the proposed salt hydrate system.

Herein, we report a facile route to fabricate cellulose aerogel directly from waste biomass using zinc chloride salt hydrate, where the role of calcium carbonate changes from impurities to cross-linkers to provide strength. The process is simple and under mild conditions. The fabricated aerogels were characterized using dynamic mechanical analysis (DMA), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). The aerogels showed high mechanical strength and lightweight with good thermal insulation performance. This study could pave a new way to valorize the waste biomass.