Green Synthesis for Lignin Plasticization

This study investigated the use of potassium persulfate (KPS) as an initiator for the grafting of methyl methacrylate (MMA) onto softwood kraft lignin. Ammonium iron (II) sulfate hexahydrate was used as a catalyst to overcome the inherent inhibition of lignin to free radical grafting and to make lignin copolymer under mild conditions using an aqueous medium. The influence of temperature, initiator concentration, time of reaction and monomer concentration on percentage of grafting were studied. A maximum of 31% grafting was achieved at 55°C. Graft copolymer was identified from the Fourier transform infrared (FTIR) spectrum by the new absorption peak at 1723 cm^-1and the reduction of intensity of the band around 3350 cm^-1. The reduction of glass transition temperature (T_g), surface morphology and higher decomposition temperature of grafted lignin support the grafting of MMA on lignin. The grafted chains increased the surface area of lignin.