Novel Composite Aerogels Fabricated from Coconut Peat and Chitosan for Heat Insulation

The global need for sustainable and environmentally friendly products made from natural resources has paved the way for significant study into the possible applications of advanced materials, especially bio-based aerogels. To maximize the use of agricultural waste, abundant coconut peat is turned into nanocellulose (average size of 200–400 nm) by sequential alkali pretreatment and ball milling before aerogel fabrication. In this study, chitosan is utilized as an effective crosslinking agent to connect the coconut peat-based nanocellulose by direct blending them and cost-effective freeze-drying for the formation of super-porous unified aerogels. The obtained aerogels exhibit ultra-low density (below 16.5 mg.cm−3), high porosity (above 98.8%), and high specific surface area (149.0 m2.g−1). Additionally, the as-fabricated aerogels have extremely low thermal conductivity (36.3 mW.m−1.K−1) that is much lower than coconut coir aerogels (40–41 mW.m−1.K−1) in the previous work and comparable to commercial heat insulation products such as glass wool (31–43 mW.m−1.K−1) and cellular glass (38–43 mW.m−1.K−1). The effects of chitosan molecular weight and chitosan content (20–80 wt.% of nanocellulose) on the morphology, density, porosity, and thermal conductivity of the synthesized aerogels are comprehensively investigated. It is demonstrated that the higher the molecular weight of chitosan, the better the heat stability, and the heat conductivity can be reduced by adding more chitosan. With ultra-lightweight features and thermal resistance, our aerogels derived from coconut peat-based nanocellulose crosslinked by chitosan are considered promising candidates for heat insulation in practice.