Effect of processing conditions and lignin content on thermal, mechanical and degradative behavior of lignin nanoparticles/polylactic (acid) bionanocomposites prepared by melt extrusion and solvent casting

Polylactic (acid) bionanocomposites filled with 0, 1 and 3 wt.% of lignin nanoparticles (LNPs) were produced by means of two processing techniques, melt extrusion (E-PLA) and solvent casting (C-PLA). The samples were thermally and mechanically characterized by using thermal analyses (TGA and DSC) and tensile tests. Nucleation effect was proved to be remarkably enhanced when homogeneous dispersion of LNPs in PLA matrix was achieved at 1 wt.%, in melt extruded samples, while further increase of the loading of LNPs up to 3 wt.% did not favor the crystallization behavior. Elongation at break in the case of extruded bionanocomposites was positively affected by the presence of LNPs; nonetheless, in the case of solvent cast films, a decreased tendency of tensile parameters was observed, attributed to inhomogeneous dispersion of LNPs. Disintegrability in composting conditions has been also tested and visual observation, chemical, thermal and morphological investigations proved that the incorporation of 1 wt.% of LNPs hindered the disintegration of PLA matrix, due to the hydrophobic nature of the filler. When the nanoparticles content rises up to 3 wt.%, aggregation and rougher film surface structure induced higher degradation rate.