Hydroxy-Methylated Lignin for the Preparation of UV Shielding PVA/Lignin Films

Traditional plastic films have caused serious environmental issues due to "white pollution". This study isolates lignin from cottonseed hulls to explore alternatives to plastic films. Using both cottonseed hull lignin and commercially sourced white lignin as raw materials, we performed hydroxy-methylation modification via physical and chemical cross-linking to obtain hydroxy-methylated cottonseed hull lignin and hydroxy-methylated white lignin, resulting in hydroxy-methylated lignin with improved hydrophilicity. Additionally, we prepared a hydroxy-methylated lignin/poly-(vinyl alcohol) composite film loaded with sorbitol and incorporated glycerol as a plasticizer to further enhance the mechanical properties of the composite material. The results indicate that the performances of both cottonseed hull lignin and white lignin are notably improved through hydroxy-methylation. The surface of the hydroxy-methylated lignin/poly-(vinyl alcohol) composite film is smooth and dense, with good compatibility between the hydroxy-methylated lignin and poly-(vinyl alcohol). In comparison with the original composite film, the hydroxy-methylated cottonseed hull lignin/poly-(vinyl alcohol) film exhibits a yield strength increase of 60.7 MPa and a 2887.3% enhancement in elongation at break; the cottonseed hull lignin/poly-(vinyl alcohol) film exhibits a yield strength increase of 17.5 MPa and a 567.7% enhancement in elongation at break; the hydroxy-methylated white lignin/poly-(vinyl alcohol) film exhibits a yield strength increase of 56.8 MPa and a 3139.4% enhancement in elongation at break; the white lignin/poly-(vinyl alcohol) film exhibits a yield strength increase of 16.2 MPa and a 520.7% enhancement in elongation at break. The hydroxy-methylated lignin/poly-(vinyl alcohol) composite film demonstrates remarkable mechanical properties, thermal stability, and optical characteristics. These findings provide new insights into the applications of hydroxy-methylated lignin/poly-(vinyl alcohol) composite materials.