Functionalization of lignin: Fundamental studies on aqueous graft copolymerization with vinyl acetate

The second most abundant natural polymer, lignin, an under-valued co-product from the pulp and paper, and biofuel industry has a great potential to be utilized to engineer value-added, green products. Graft copolymerization of vinyl acetate (VAc) on lignin was performed using potassium persulfate as an initiator and ammonium iron (II) sulfate as a catalyst. Aqueous reaction medium is used for the preparation of graft copolymer as a cost effective and greener route. The effects of reaction conditions were studied to obtain optimal grafting percentage with very low homopolymer formation. The effects of various factors like temperature, initiator concentration, amount of monomers, and volume of catalyst found to have considerable effects on grafting efficiency. Highest grafting of 60% was observed for 1:1.5 ratio of lignin and vinyl acetate at 70 °C in presence of 9.24 × 10−2 mol/L initiator and 5.1 × 10−4 mol/L of catalyst concentration. Graft copolymerization was identified from the new absorption peaks at wavelengths around 1720 cm−1 and 1210 cm−1 (Fourier transform infrared spectroscopy), and the new degradation peak observed at 339 °C (thermogravimetric analysis). Reinforcing or blending of VAc-g-lignin with desirable polymers can yield value-added greener products.

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► Improved utilization of the industrial byproduct – lignin.
► Graft copolymerization of vinyl acetate on lignin.
► Mild reaction conditions and aqueous medium.
► Optimization of grafting reaction and characterization of graft copolymer.