Selective acid precipitation of Kraft lignin: a tool for tailored biobased additives for enhancing PVA films properties for packaging applications

Abstract The use of renewable materials with unique properties has brought new perspectives regarding their use as potential substitutes to the petroleum-based products. The aim of this work was to evaluate the effects caused by the addition of Kraft lignins, selectively precipitated in acid and alkaline medium, on the thermal, thermo-oxidative, UV-blocking, antioxidant, antimicrobial and mechanical properties of polyvinyl alcohol (PVA) films. Kraft lignins (KL) were selectively precipitated in alkaline (KL A) and acid (KL B) media. KL A and KL B were characterized by FTIR, 1H-13C HSQC, 31P NMR and GPC. PVA films were produced through casting method and characterized by TGA, DSC, OOT, UV–Vis, mechanical, antioxidant and antimicrobial properties. The selective precipitation process yielded lignins with different concentration of phenolic and total hydroxyls for KL A and KL B. The addition of KL A and KL B at 1.0% wt. in PVA films produced materials with enhanced thermal, thermo-oxidative, UV-blocking, mechanical, antioxidant and antimicrobial properties. It can be concluded that the selective precipitation of lignin represents an alternative for obtaining fractions with peculiar structural features that can improve their compatibility with thermoplastics, yielding potential bio-based products with suitable features to be used as packaging materials.