Lignin Nanoparticle Stabilized Pickering Emulsion Coating for Fabricating Water- and Oil-Proof, Biodegradable, and Recyclable Paper

Paper derived from plant fibers is considered a highly promising alternative to non-degradable plastic packaging. However, its widespread use in packaging is limited by its poor water- and oil-proof properties. To address this challenge, this study developed a polyvinyl alcohol (PVA)/lignin nanoparticles (LNPs)/stearic acid (SA) (PLS) Pickering emulsion composite coating to fabricate high-performance biodegradable paper. In the emulsion system, the PVA acted as an oil-repellent in the aqueous phase, the SA served as a water-repellent in the oil phase, and the LNPs functioned as emulsifiers that effectively stabilized the emulsion. Owing to the synergistic effect among PVA, SA, and LNPs, the coated paper exhibited good water- and oil-proof properties (with a water contact angle of 111.2°, Cobb 60 value of 17.73 g/m 2 , and Kit rating exceeding 9/12), along with high mechanical strength (including a dry tensile strength of 7.12 kN/m and a wet tensile strength of 0.97 kN/m). While significantly enhancing performance, the PLS emulsion coating retained the environmental benefits of paper, could be easily removed to facilitate fiber recycling, and the coated paper was fully degradable in soil within 120 d. Overall, the PLS emulsion coating effectively enhanced the properties of paper without compromising its eco-friendly characteristics, demonstrating significant potential for promoting the substitution of plastic with paper.