Naturally Hydrophobic Foams from Lignocellulosic Fibers Prepared by Oven-Drying

Lignocellulosic sugarcane biomass underwent an alkaline treatment for partial lignin extraction and then foams with very low apparent density (0.09 g/cm3) were easily obtained by oven-drying aqueous dispersions of fibers. The fiber networks were covalently reinforced through cross-linking by heating the dried material in the presence of citric acid. The lignocellulosic foams were naturally hydrophobic (water contact angle = 117°), without requiring any further chemical modification. The hydrophobicity is attributed to the combination of (1) residual lignin, (2) redeposited lignin that has undergone thermal treatment, (3) the fiber and foam surface roughness, and (4) the structure's ability to trap air. The cross-linked fiber networks showed shape-recovery properties under compressive stress, high absorption capacity, and mechanical resistance when immersed in water and oil. This work demonstrates that lignocellulosic foams from sugarcane bagasse, processed following low cost and green methods, are promising for selective removal of hydrophobic compounds in aqueous environments and in a range of insulating and packaging products.