Biopolymer-based eco-friendly coatings reinforced with lignin nanoparticles for surface coating applications of...

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 ∼1.30 g/cm³ to 1.10 g/cm³ 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 μm to 3.4 μm, and water absorption also increased with lignin content. Thermal analysis revealed an increase in T_10% from 349 °C for neat PLA to 353 °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.