Chemical Modification of Methanol-Insoluble Kraft Lignin Using Oxypropylation Under Mild Conditions for the Preparation of Bio-Polyester

Abstract

Methanol-insoluble high-molecular weight (Mw = 26,610 g mol−1) soft wood kraft lignin was oxypropylated under the mild condition of 40°C and 1 atm for 12 h in the presence of NaOH catalyst for the production of bio-polyester. Fourier transform infrared spectra showed that polyether chains were extended due to the oxypropylation reaction. The Mw and Mn of the oxypropylated lignin were 46,330 and 17,110 g mol−1, respectively. The high-molecular weight oxypropylated lignin was reacted with sebacic acid or polybutadiene (dicarboxy terminated) for bio-polyester synthesis. While the decomposition temperatures of the oxypropylated lignin were 217°C and 367°C, those of the bio-polyesters prepared with sebacic acid and polybutadiene (dicarboxy terminated) were 380°C and 453°C, respectively, indicating that the bio-polyesters possessed enhanced thermal properties. The oxypropylation of methanol-insoluble high-molecular weight lignin under mild conditions is one of the promising approaches for preparing bio-plastics with an enhanced thermal property.