Synthesis of Lignin-g-MMA and the Utilization of the Copolymer in PVC/Wood Composites

Lignin with low molecular weight (LA), fractionated from soda lignin by methanol extraction, was grafted with methyl methacrylate (MMA) and used for interfacial modification for poly (vinyl chloride) (PVC)/wood flour composites. By sequential extraction with chloroform and aqueous NaOH solution, the grafting product was separated into three fractions by the different solubility of various components in these solvents. The data of lignin contents in the three fractions indicate that more than 80% of the lignin participated in the copolymerization. As indicated by the contact angle, data the hydrophilic wood surface was transformed into a hydrophobic one by the grafting product treatment. The grafting product exhibited a positive influence on improving the mechanical performances of PVC/wood flour composites. In comparison with untreated ones, the tensile and impact strengths of composites containing 30 phr of wood flour treated with 2 wt% grafting product (MMA/LA = 1:1) were increased by 18.7% and 25.9%, respectively. Furthermore, the optimum ratio of MMA/LA was 2:1, for which the increments in tensile and impact strengths were 20.9% and 35.3%, respectively. A significant increase in storage modulus (E) was observed upon the incorporation of treated wood flour SEM (scanning electron microscope) images showed that the dispersion of treated wood flour in the polymer matrix was improved. It can be inferred that the polymer-wood interfacial bonding was strengthened.