Preparation and Performance of a Green, Fluorine-Free Chitosan-Stearic Acid Waterproof Agent for Molded Pulp

Abstract

To develop a green, efficient, fluorine-free waterproof pulp molding material, this study incorporated chitosan-stearic acid graft copolymer (CS-SA) into the pulp fiber system via the conventional internal pulp addition method used in the papermaking industry. Compared with post-treatment surface techniques such as spraying and coating, adding the waterproofing agent directly into the pulp ensures its uniform distribution throughout the three-dimensional fiber network—from the pulp to the final product—while balancing the operational feasibility of paper manufacturing with the integrated waterproofing performance of the finished product. The research results demonstrated that CS-SA significantly enhanced the waterproof performance of the product (water contact angle 131°, Cobb value 12.9 g/m², no leakage or permeation at 100 °C water for 30 minutes). Systematic characterization revealed that CS-SA forms a dense hydrophobic film on the fiber surface and between fibers, which is the key to its high-efficiency waterproofing. In addition, the modified material exhibits low cytotoxicity and excellent antibacterial properties, ensuring safety for applications in food packaging. Its superior thermal stability guarantees effectiveness during processing steps such as pulp molding and hot pressing.