Thermally insulating materials from renewable and readily available resources are in high demand for ecologically beneficial applications. Cellulose aerogels made from lignocellulosic waste have various advantages. However, they are fragile and breakable when bent or compressed. In addition, cellulose aerogels are flammable and weather-sensitive. Hence, to overcome these problems, this work included the preparation of polyurethane (PU)-based cellulose nanofiber (CNF) aerogels that had flexibility, flame retardancy, and thermal insulation. Methyl trimethoxysilane (MTMS) and water-soluble ammonium polyphosphate (APP) were added to improve the cross-linking, hydrophobicity, and flame-retardant properties of aerogels. The flexibility of chemically cross-linked CNF aerogels is enhanced through the incorporation of polyurethane via the wet coagulating process. The aerogels obtained during this study have exhibited low weight (density: 35.3-91.96 kg/m3) together with enhanced hydrophobic properties, flame retardancy, and decreased thermal conductivity (26.7-36.7 mW/m K at 25 °C). Additionally, the flame-retardant properties were comprehensively examined and the underlying mechanism was deduced. The aerogels prepared in this study are considered unique in the nanocellulose aerogel category due to their integrated structural and performance benefits. The invention is considered to substantially contribute to the large-scale manufacture and use of insulation in construction, automobiles, and aerospace.
Keywords: cellulose nanofiber aerogels; flame-retardant; flexible; lightweight; polyurethane; thermal insulation.