Poly(methyl methacrylate) films reinforced with coconut shell lignin fractions to enhance their UV-blocking, antioxidant and thermo-mechanical properties

Lignin is a high added-value product obtained from agrowastes through organosolv process to yield materials for technological applications. Here, coconut shell organosolv lignin was fractionated using green solvents (acetone and ethanol) and incorporated in poly(methyl methacrylate) (PMMA) films. The non-fractionated (WCSAL) and soluble fractions (ACT-F and EtOH-F) were completely characterized regarding their structures. The fractionation process altered lignins molecular weights, decreasing with the increased solvent polarity, although the higher polarity favored the dissolution of acylated and methoxylated fragments. PMMA films incorporated with lignin fractions were analyzed by TGA and DSC, which showed improved thermal and thermo-oxidative stabilities. DMA analyses of the films indicated that lignin soluble fractions had a plasticizer effect, while non-fractionated lignin increased PMMA films glass transition temperature (Tg). The antioxidant capacity of the films was also enhanced with the addition of lignins, in which those incorporated with soluble fractions showed the lowest IC50 values. The optical properties and photo-stability were also considerably improved, especially in the UVA and UVB regions. Therefore, solvent-fractionation represents a potential sustainable process to obtain lignins featuring different chemical structures, which can be applied effectively in the enhancement of PMMA films properties.