Hydrophobic molded pulp based on partially grafted fibers dispersible in water. Part 1: comparison of the physical properties of recycled paper produced from hydrophobized paper treated by gas grafting with palmitoyl chloride or by internal AKD addit

Abstract Conventional sizing agents often suffer from limitations such as pH dependency, insufficient hydrophobicity, and delayed development of water repellency. To overcome these drawbacks, this study applied a gas grafting treatment with palmitoyl chloride at 200 °C, forming ester bonds with cellulose hydroxyl groups and thereby imparting immediate and stable hydrophobicity. This approach enabled the fibers to retain a portion of hydrophilic surface area, ensuring both water resistance and fiber dispersibility during recycling. Water absorption and recycling performance were compared between gas-grafted handsheets and AKD-sized handsheets under different pulping temperatures. Even with minimal reagent dosage, gas-grafted sheets exhibited markedly lower Cobb values and maintained hydrophobicity after repulping at 50 °C, although with some reduction in tensile strength. In contrast, AKD-sized sheets retained mechanical integrity but showed a significant decline in water resistance when exposed to hot conditions, due to the melting and partial dissolution of AKD. Overall, these findings demonstrate that gas grafting with palmitoyl chloride provides a promising strategy for producing recyclable, water-resistant paper or molded pulp, particularly suitable for applications requiring thermal stability such as food packaging and disposable containers.