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

Methanol-insoluble high-molecular weight (M-w = 26,610g mol(-1)) soft wood kraft lignin was oxypropylated under the mild condition of 40 degrees C and 1 atm for 12h 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 M-w and M-n of the oxypropylated lignin were 46,330 and 17,110g 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 degrees C and 367 degrees C, those of the bio-polyesters prepared with sebacic acid and polybutadiene (dicarboxy terminated) were 380 degrees C and 453 degrees 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.