Laccase catalyzing copolymerization of modified alkali lignin and p-cresol

Lignin is modified with the phenolation method and inserted with active groups. The influences of various phenolic monomers on the modification of lignin are studied. Then the laccase catalyzing copolymerization reaction between lignin and phenol has been optimized, and the characterization and performance determination on the copolymerization products have been done. The results show that the phenolic hydroxyl content in alkali lignin modified by catechol increases significantly from 6.95 mmol/g to 10.83 mmol/g, an increase of about 55.83%. Moreover, the optimal copolymerization reaction conditions include 80% acetone solution, temperature 30℃, pH 3.5, substrate ratio of 0.5/1 between alkali lignin and p-cresol, enzyme concentration of 300 U/mL and reaction time 16 h. Under these optimum conditions, the yield of copolymer increases significantly, up to 93.6%. If catechol modifying lignin is used to copolymerize with p-cresol, the molecular weight of copolymers increases significantly from 2770 g/mol to 20481 g/mol, an increase of about 10 times. Thermal stability analysis shows that the thermal stability of copolymer has been improved by the modification.