Enzymatic plasticising of lignin and styrene with adipic acid to synthesize a biopolymer with high antioxidant and thermostability

Abstract

Green synthesis of biopolymeric material based on renewable resources and can replace the present conventional plastic materials are today's urgent need. For that lignin was first depolymerised into its macromonomeric units using laccase. And through lipase mediated trans-esterification reaction, monolignol/oligolignols are plasticized with adipic acid at one end and further at another end of adipic acid, styrene molecules was plasticized by atomic transfer radical polymerization (ATRP). FTIR spectroscopy shows a disappearance of hydroxyl band (3437.75 cm−1) and appearance of ether band (1300-1000 cm−1) in the biopolymeric product which revealed that the polymerization occurs due to the formation of ether bonds in between the [-lignin-adipic acid-styrene-] monomeric units. Thermogravimatric analysis (TGA) and Dynamic mechanical analysis (DMA) shows that the polymeric film synthesised is highly thermostable with a glass transition temperature (Tg) of 99.7 °C. On XRD analysis it was observed that the degree of crystallinity increases on adding adipic acid moiety into the polymer and was calculated about 21.88% using DSC. SEM analysis shows lignin was properly dispersed within the styrene resulting into the homogeneous surface. Average molecular weight of the lignin–styrene based polymer was obtained 748063.2 g/mol using GPC and elemental analysis. Biological characterization of the polymeric film has shown strong antioxidant activity with least cytotoxicity on peripheral blood mononuclear cells (PBMCs) which enhanced its biocompatibility. The polymer synthesised can be a potential candidate for renewable and sustainable polymeric material and biomaterial.