Fully bio-based coating for water/oil-resistant food packaging paper: Direct ring-opening grafting of epoxy soybean oil onto chitosan.

Abstract

Given the environmental challenges of petroleum-based water- and oil-resistant food packaging coatings, and the safety risks of fluorine-containing coatings in food contact scenarios, developing alternative coatings with renewability, biodegradability, and safe applicability has become a pivotal direction in this field. This study prepared a fully bio-based paper coating chitosan-grafted epoxy soybean oil (CHI-g-ESO) via ring-opening graft modification of chitosan (CHI) with epoxy soybean oil (ESO). ESO's long-chain alkane segments migrate and accumulate on the coating surface during drying, constructing a low-surface-energy hydrophobic interface that blocks water penetration. CHI's retained polar groups and its electrostatic interactions with paper fibers maintain strong substrate adhesion and serve as a barrier against oil molecules. The ring-opening grafting reaction establishes a 3D cross-linked network between CHI and ESO, which fills paper pores and enhances the coating's structural compactness and mechanical robustness. Response surface methodology optimization showed optimal performance at m(ESO)/m(CHI) = 4.88 and 3.21 wt% CHI, with Cobb 60 value 9.18 g/m2, Kit rating grade 9.0 ± 1.2/12, water vapor permeability 59.7 g·μm/m2·day·Pa, and tensile strength 3.11 ± 0.20 MPa. This fully bio-based coating, which can be applied to paper substrates via a one-step coating process, serves as a substitute for the petroleum-based water- and oil-resistant coatings used in traditional food packaging paper and boasts broad application prospects.