Enhancing UV-shielding and mechanical properties of polylactic acid nanocomposites by adding lignin coated cellulose nanocrystals

From a perspective of sustainable development, it is desired to develop biodegradable ultra-violet (UV)-resistant and mechanically robust materials. Lignin nanofillers (LNP) are renewable and commercially available nano fillers with promising UV-shielding characteristics. However, the addition of LNP can deteriorate the mechanical properties of lignin-based composites. On the other hand, cellulose nanocrystals containing lignin can serve as a UV-shielding and reinforcing nanofiller without sacrificing the mechanical properties of nanocomposites. In this work, the UV-shielding performance, mechanical properties, and biodegradability of PLA nanocomposites containing lignin-coated cellulose nanocrystals (LCNC) were compared with PLA nanocomposites reinforced with lignin nanofillers (LNP). Nanocomposites with different content of nanofillers (i.e., 3%, and 5%) were prepared via a masterbatch approach followed by extrusion and injection molding. The morphologies of PLA nano composites studied by scanning electron microscopy, confirmed smooth fracture surfaces with micro sized LCNCs aggregates. However, rough fracture surfaces and uniform nanoparticle dispersion were observed in PLA nanocomposites reinforced by LNP. The UV-Vis characterization revealed a synergic effect of incorporating either LNP or LCNCs nanostructures in terms of UV light blocking ability. The addition of low content (3 wt%) LCNCs into the PLA matrix, blocked the highest amount of UV radiation, 75.3% of UV-A and 45.81% of UV-B. Degradation tests of PLA and its nanocomposites showed that the maximum weight loss of PLA nano composites after being hydrolytically degraded for 30 days increased from 8% for PLA to 14% for PLA-5 wt% LCNCs, and 16.7% for PLA-5%LNP. The study provides insights into PLA nanocomposite reinforced with LCNCs or LNP regarding UV protection, biodegradability, and mechanical properties.