Facile Fabrication of Robust and Stretchable Cellulose Nanofibers/Polyurethane Hybrid Aerogels

Nanocellulose-based aerogels of low density and high porosity have attracted considerable attention. However, the weak mechanical property restricted their practical applications. Herein, flexible, robust, and stretchable cellulose nanofibers/polyurethane (CNF/PU) hybrid aerogels were prepared by incorporating PU into chemically cross-linked CNF aerogels using the wet coagulating method. The resultant CNF/PU hybrid aerogels were lightweight (<0.12 g/cm³) and highly porous (>89.72%), yet had greatly enhanced mechanical properties showing compressive stress of 510 KPa at 80% strain and tensile strength of 247 KPa. The hybrid aerogels were also shown to be capable of bearing tensile weights of over 11 000 times their own weight (the stress is about 251 KPa) without getting fractured. The hybrid aerogels could quickly restore to their original shapes from being bent and twisted, showing great flexibility. Furthermore, the combination of organic phase change materials (PCMs) and aerogels resulted in shape-stabilized PCMs prevent the leakage without compromising the energy utilization efficiency. The CNF/PU hybrid aerogels were shown to be an excellent supporting material for stabilizing liquid PCMs such as octadecane. CNF/PU/octadecane composites exhibited latent heat of up to 223.3 J/g and good shape and thermal stability. Moreover, these composites demonstrated shape memory properties, in which they could be fixed in various shapes at 20 °C or below, and quickly recover to the original shape above the melting point of octadecane.