Hydrophobization of hemicelluloses extracted from fir sawdust: Toward water resistant functional film formulation

The growing demand for sustainable alternatives to petroleum-based plastics has highlighted hemicellulose as promising candidates for film production. Hemicellulose, a major component of lignocellulosic biomass, can form films when combined with polyol plasticizers such as glycerol. However, its high hydrophilicity and poor water resistance limit its practical application in humid environments. In this study, hemicellulose was extracted from fir sawdust using two media, water and 1 M NaOH, and subsequently modified via homogeneous acetylation in a DMF/LiCl system. Compared with previous studies that have mainly focused on the modification of commercially available hemicelluloses using conventional heterogeneous acetylation approaches, this work integrates hemicellulose extraction from lignocellulosic biomass, controlled homogeneous acetylation, and film fabrication within a single approach. This homogeneous modification strategy enables better control of hemicellulose substitution. The modifications were carried out for different durations to investigate the effect of reaction time on substitution. The modified hemicelluloses were characterized in terms of average degree of substitution (DS), reaction yield, surface hydrophobicity (wettability) and thermal properties using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopies, water contact angle measurements and thermogravimetric analysis (TGA). The optimal conditions for acetylation were 8 h for alkaline-extracted hemicellulose and 24 h for water-extracted hemicellulose. Films were prepared from native and modified hemicelluloses. Film blends containing different ratios of native and modified hemicelluloses with plasticizers were prepared. The optimized formulation was evaluated for moisture barrier properties, water solubility, swelling capacity, mechanical integrity and water activity under high humidity conditions (80% RH). The results showed that modified films exhibited enhanced water resistance, with likely reduced water transfer and water activity as well as prolonged structural integrity under humidity exposure.