Direct esterification of reinforced papers by immersion method and evaluation of their properties

Today, the use of biodegradable packaging materials is very noteworthy. They are one of the most used materials in the packaging industries. These materials require proper barrier and mechanical strength properties. Cellulose nanofibril (CNF) can improve the mechanical strength and air resistance of paper, but it is not able to improve its water barrier property. In this study, modification of the water barrier property of CNF-reinforced papers was evaluated using the esterification process. Handsheets were made by adding CNF to the pulp fibers. After drying, the handsheets were esterified using the liquid-phase acetylation process without any catalyst for different reaction times (0.5, 1, and 3 h). Infrared spectroscopy confirmed a successful chemical modification. The mechanical properties and air resistance of the paper sheet were significantly increased by adding CNF to the pulp. The esterification led to a decrease in the water absorption of the unmixed and mixed papers of about 24.5 and 48%, respectively. Therefore, the addition of CNF to the pulp and surface esterification of the mixed paper caused simultaneous improvement in the barrier and mechanical strength properties of paper.