A general Metal-Ion-Modification route for preparing hydrophobic paper and tableware from lignocellulose fibers

Inherent hydrophilicity and poor water resistance prevent using lignocellulosic materials as green plastic al- ternatives to fossil fuel-based plastics. Here, we report a facile metal-ion-modification (MIM) route, swelling with aqueous metal ion solutions, and drying to convert conventional hydrophilic paper and wood pulp into biode- gradable hydrophobic paper and tableware without the addition of hydrophobic sizing chemicals/materials. Metal ions such as Fe3+ and Zr4+ can coordinate with pulp fibers' polar groups (i.e., OH, C-O, and COOH) that induce self-assembly of their surface fibrillated "hairy" cellulose nanofibrils to form a more compact structure with fewer available OH groups for water sorption. This decreases the surface energy of pulp fibers and increases their hydrophobicity and water resistance. Only similar to 3 mg of metal ions is needed to induce the wettability tran- sition in 1 g of kraft pulp, resulting in hydrophobic paper and tableware with water contact angles (WCAs) of 120-140 degrees. The coordinated Fe3+ and Zr4+ are stable, with negligible metal leaching during use, allowing the hydrophobic paper and tableware to be used for food packaging. This MIM technique can be integrated into the existing paper-making process for the scalable production of hydrophobic papers and tableware, providing an alternative route for developing sustainable and biodegradable plastic counterparts.