Fabrication and characterization of structurally modified lignin-based hydrophobic films

Plastic waste has emerged as a global environmental crisis, prompting the search for sustainable alternatives to petroleum-based polymers. Within the context of the sustainable bioeconomy, lignin has gained significant attention as a promising biorenewable resource. However, the application of lignin is limited by its complex molecular structure and low compatibility with other polymers. In this study, lignin was structurally modified with palmitic groups to enhance its processability, compatibility, and hydrophobicity for use in film applications. The resulting palmitoylated lignin (p-lignin) was blended with polycaprolactone (PCL) and fabricated into films via solvent casting. Composite films containing up to 50 % p-lignin were successfully produced, with the 40 % p-lignin formulation exhibiting optimal performance. Water contact angles of fabricated films reached 119.4° for palmitoylated hardwood kraft lignin (HK-P) and 124.5° for palmitoylated hardwood organosolv lignin (HO-P), compared to 83.8° for the neat PCL film. In addition to enhanced hydrophobicity, films demonstrated excellent UV blocking performance with an Ultraviolet Protection Factor of 50 or higher. While mechanical strength decreased due to lignin aggregation, the films maintained thermal stability and demonstrated solvent-based reprocessability, preserving their surface morphology and hydrophobic performance after re-casting. These findings highlight the potential of lignin-based hydrophobic films as sustainable materials for UV-protective and water-repellent packaging or coatings applications. • Palmitoylated lignin enhanced hydrophobicity and UV protection in films. • PCL/p-lignin films achieved contact angles up to 124.5° and UPF > 50. • Films maintained hydrophobicity after solvent-based reprocessing. • This work demonstrates lignin’s potential for sustainable water-repellent packaging.