Water-, Oil-, and Stain-Resistant Lignin-Based Degradable Waterborne Polyurethane for Paper Packaging Coating

Degradable paper-based packaging materials are promising alternatives to plastic packaging. However, the inherent limitations of paper, such as poor water and oil resistance, restrict its broader applications. It is essential to develop green and degradable coatings to compensate for the shortcomings of paper materials. In this study, we prepared a tough, hydrophobic, stain-resistant, and degradable lignin-based waterborne polyurethane (LWPU) for a paper packaging coating. LWPU emulsions with good stability were synthesized using low-molecular-weight lignin (LMWL) and polycaprolactone diol (PCL) as raw materials and poly(dimethylsiloxane) (PDMS) as a modifier. LWPU films exhibited excellent mechanical properties, with the optimal tensile strength of 40.3 MPa and elongation at break of 1148%, hydrophobicity, antiaging properties, and UV shielding. The mechanical properties of the coated papers were significantly affected by the emulsion permeation and the type of paper substrate. The dense LWPU coating enhanced the barrier performance of the paper against water, oil, and gas. Incorporating PDMS segments into the coating further improved the hydrophobicity and stain resistance of the paper, allowing for easy removal of common stains. Moreover, the coating can be completely removed from the paper using solvent-dissolving and chemical degradation methods, which is advantageous for paper recycling. This work provides a reference for the industrial application of LWPU emulsions as green paper coatings.