Renewable Biopolymers and Chemicals from Kraft Lignin using Fungal Treatment

Immobilized medical fungi were used for lignin bio-modification in this study. Five fungal strains were used to modify Kraft lignin into chemical building blocks for polymers and composites production. All strains showed the ability to modify lignin without additional nutrients. Lignin solubility was increased with the addition of organic solvents to ensure high lignin concetrations during experiments. The effects of organic solvents on fungi growth were also investigated. A comprehensive chemical characterization of bio-modified lignin derivatives was done using thermal carbon analysis (TCA), thermodesorption-pyrolysis-GC-MS (TD-Pyr-GC-MS), and GC-MS analysis, together with liquid chromatography (LC), gel permeation chromatography (GPC), and ¹H-NMR.

The results showed 75% increase of lignin solubility can be achieved by the addition of 2% organic solvent. Furthermore, the fungal enzymatic activities (laccase, MnP and LiP) were increased by the addition of organic solvents. TD-Pyr-GC-MS and GC-MS analyses of bio-modified lignin samples provided evidence of phenolic monomers and/or their immediate precursor removal. TCA and ¹H NMR showed significant cross-linking within the reaction products, and LC results showed an increase in polarity and decrease in polydispersity of the modified lignin products compared to original lignin. GPC showed that molecular weight of modified lignin increased during the bio-treatment. One interesting property observed is that the modified lignin has very low solubility in aqueous media with pH ranging from 2 to 12 and almost no solubility in concentrated organic solvents, while the original lignin can be dissolved in a 2% organic solvent. This new biomaterial has great potential in many industries where stable materials are needed.