Colloidal lignin nanoparticles from acid hydrotropic fractionation for producing tough, biodegradable, and UV blocking PVA nanocomposite

Colloidal lignin nanoparticles (LNPs) from low temperature acid hydrotropic fractionation (AHF) of poplar wood and commercial alkali lignin using p-Toluenesulfonic acid (p-TsOH) were directly mixed with PVA to make PVA/AHF-LNP nanocomposite films. p-TsOH itself acted as a plasticizer for PVA; however the application of p-TsOH alone reduced PVA film tensile strength and therefore toughness. At proper loadings of LNPs and p-TsOH, both the failure strain and tensile strength of PVA/AHF-LNP composites were improved. The formation of hydrogen bonding between the p-TsOH/AHF-LNP aggregates with hydroxyl groups on PVA molecular chains, and the breakage and reforming of p-TsOH/AHF-LNP aggregates, along with the nanophase crazing due to the presence of p-TsOH/AHF-LNP aggregates were identified as the main mechanisms for improving the toughness of PVA/AHF-LNP nanocomposite. The composite also had improved UV shielding performance and biodegradability due to the presence of p-TsOH and LNPs compared with neat PVA. This nanocomposite film could be used as biodegradable anti-ultraviolet packing film.