Highly porous bio-based foam made with cellulose nanofiber and citric acid prepared using an environment-friendly and economical process

Due to environmental concerns, replacing conventional synthetic materials with eco-friendly bio-based materials is receiving much attention from academic and industrial research. As the most abundant polymer among several bio-based materials, cellulose is widely used to produce bio-based porous materials that have been used in various applications, including packaging, thermal insulation and sound absorption. Different processing methods have been used to prepare nanocellulosic porous materials but the specific requirement and time consuming process limit the use of these methods for large-scale production. Further, the use of toxic and expensive inorganic or synthetic blowing agents or crosslinking agents limits the applications of these porous materials. Therefore, to overcome these drawbacks, we used an environmentally friendly, time-saving, economical process to produce bio-based cellulose nanofiber (CNF) foam using bio-based nontoxic and inexpensive citric acid as a green crosslinking agent. The foam is prepared by homogenizer followed by freezing, solvent exchange and oven drying. The prepared foam indicates low shrinkage and has a very low density. The foam shows a highly porous structure (more than 98% porosity) and the morphology of the foam is examined by SEM. The FTIR study confirms the covalent crosslinking, and the foam shows high compressive modulus and strength.