Thermal curing of Tung oil for hydrophobic and recyclable cellulose-based packaging

Abstract

The extensive use of synthetic plastic-based materials in packaging raises serious environmental and health concerns, driving the search for sustainable alternatives. Cellulose, as a renewable bio-based polymer, presents a promising solution; however, its hydrophilicity restricts its application in moisture-sensitive environments. The incorporation of bio-based coatings can enhance water resistance, yet scalable and efficient strategies remain a challenge in the food and beverage packaging sector. In this study, we present a fully bio-based coating system based on thermally polymerized Tung oil for producing functional cellulose-based materials with enhanced hydrophobicity. The influence of coating thickness, curing temperature, and curing time was investigated through ATR-FTIR, DSC, and TGA analyses, identifying 170 °C for 20 min as the optimal condition to achieve total crosslinking. After dispersion in dimethyl carbonate, Tung oil was applied to cellulose sheets and thermally cured, resulting in significantly improved water repellence while complying with European food contact regulations, as demonstrated by migration tests. Notably, the system was successfully integrated into commercial cellulose substrates, enabling the thermo-forming of 3D structures. Even at only 1 w/w % Tung oil loading, the water absorption of cellulose cups decreased by over 90 % compared to uncoated samples. Furthermore, recyclability tests confirmed that the thermo-formed cellulose objects treated with Tung oil remain completely recyclable into the paper stream. This study proposes a sustainable and potentially scalable strategy for the production of fully bio-based, recyclable, food compliant, and hydrophobic cellulose-based materials, offering a promising alternative to conventional plastic-based materials.