Biopolymer-based eco-friendly coatings reinforced with lignin nanoparticles for surface coating applications of engineered wood-based panels

Abstract

This study investigated the effects of the addition of lignin at various loadings on the physical, morphological, structural, thermal, and wear properties of the polylactic acid (PLA)-based coatings. The test samples were first produced using a twin-screw and then shaped by compression molding with a hydraulic plastic film machine. The results showed that adding lignin decreased density from similar to 1.30 g/cm(3) to 1.10 g/cm(3) and reduced gloss from 39.2 to 0.8. Air permeability increased from <10 mL/min for neat PLA to 50 mL/min at a lignin content of 5%. Surface roughness (R-a) increased from 1.8 mu m to 3.4 mu m, and water absorption also increased with lignin content. Thermal analysis revealed an increase in T-10% from 349 degrees C for neat PLA to 353 degrees C for coatings containing 7 wt% lignin, as well as a decrease in total mass loss from 96.8% to 94.5%, which was due to char formation. SEM analysis revealed greater agglomeration and microporosity at higher lignin ratios. The wear resistance of the coatings decreased with increasing nano-lignin content. Neat PLA and PLA-g-MA exhibited the highest wear resistance, whereas the coatings containing 7 wt% lignin demonstrated the poorest performance due to increased surface roughness and micro-voids that facilitate material removal during abrasion. In general, the addition of nano-lignin to PLA-g-MA improved thermal stability and promoted the use of bio-based waste materials in coatings, but it slightly reduced mechanical performance and alter optical properties.