Drying oils as bio-based coatings for cellulose-based packaging

The widespread use of single-use plastic packaging and the accumulation of non-biodegradable waste have driven research into sustainable alternatives based on natural polymers. Although cellulose is the most abundant natural polymer, its high hydrophilicity and poor processability limit its direct use in food packaging. The present research, carried out in collaboration with the Italian company SACMI, addresses these issues by developing bio-based, plastic-free, dry mouldable, recyclable, food-contact safe, and hydrophobic coatings for cellulose substrates, aimed at making water-resistant 3D objects for single-use beverage packaging. Tung oil (TO) was selected as a promising bio-based coating, due to its ability to form hydrophobic and crosslinked films via oxidative polymerization, and was characterized and formulated with different organic solvents, showing high solubility and good application properties. Oil-in-water TO emulsions stabilized with Tween 80 were also developed as a more sustainable alternative. To overcome slow spontaneous TO polymerization, two accelerated crosslinking strategies – thermal curing and plasma treatment – were developed. Thermal curing improved the water resistance of cellulose sheets by over 50% and reduced water absorption in 3D dry-moulded samples by over 90%, while maintaining recyclability and food contact compliance. Plasma-assisted crosslinking reduced process times by 45% compared to heat alone, producing highly hydrophobic coatings compatible with industrial dry moulding. Overall, this work demonstrates that TO-based coatings can offer a completely bio-based, recyclable and food-safe solution for cellulose hydrophobization, enabling the production of water-resistant 3D packaging items through potentially scalable and low environmental impact processes.