Gel formation of lignin and biodegradation of the lignin gels by microorganisms

The multifunctional, polyphenolic nature of isolated lignins invites practi cal applications in which lignin serves as the principal component of cross -linked network polymers. Unmodified kraft lignin was first condensated wit h phenols and then further condensated with resorcinol under alkaline condi tions, to give lignin-phenol-resorcinol resin (LPR resin). Lignin gels were prepared from the methanol-diluted LPR resin with the use of organic cross -linking agent glutaraldehyde (GA) via reacting for 3 days at 25 degrees C. The gel formation depended on the amounts of methanol, and not the amounts of GA. The Lignin gel obtained exhibited a reversible expansion-contractio n behavior when it was alternatively immersed in ethanol and in water. Degr adation of cross-linked LPR-GA hydrogels by some microorganisms has been in vestigated. From the experimental results, the following findings were obta ined. The lignin-GA gels are degraded by the four Basidiomycotia fungi exam ined. The most effective degradation of the lignin-GA gels was obtained wit h the fungus Flammulina velutipes. The present biodegradation results by wo od-rotting fungi might give some clues as to future biotechnology of cross- linked lignin and lignin hydrogels. (C) 2000 Elsevier Science S.A. All righ ts reserved.