Characteristics of cellulose nanofibril films prepared by liquid- and gas-phase esterification processes

Cellulose nanofibrils (CNFs) are versatile materials, but their sensitivity to humidity affects performance. Esterification with fatty acids enhances the hydrophobicity of CNF films. This study compared gas- and liquid-phase esterification using three fatty acid chlorides at different dosages. Gas-phase esterification minimally affected cellulose crystallinity, maintaining a crystallinity index exceeding 55.8%, whereas liquid-phase esterification significantly reduced crystallinity. Gas-phase esterification achieved hydrophobicity (water contact angle >100°) with less fatty acid chlorides (0.50 eq/OH) compared to liquid-phase esterification (1.00 eq/OH). Tensile strength significantly dropped in the liquid phase (68.4–6 MPa) and up to an 8-fold decrease in the elastic modulus. Conversely, gas-phase esterification maintained tensile strength over 40 MPa, and elastic modulus increased by a minimum of 2.5 times. However, gas-phase esterification resulted in a 5-fold reduction in elongation at break (%). Thermogravimetric analysis indicated a high T max of 362°C for liquid-phase esterified samples and a substantial 24.9% residual weight for gas-phase esterified samples.