Peroxidase‐catalyzed synthesis of lignin–phenol copolymers

Abstract

SYNOPSISHorseradish peroxidase catalyzes the copolymerization of phenols with kraft lignin in aqueous-organic solvent mixtures. Nearly all of the lignin and over one-third of the phenol (either p-cresol or p-phenylphenol) is incorporated into the copolymer which is highly insoluble in dimethylformamide (DMF) , presumably because of crosslinking of lignin molecules via polyphenol bridges. The copolymer consists of 80% lignin, by weight. In the absence of a phenol, lignin is polymerized into a noncrosslinked, DMF-soluble material. Thermal analysis shows that the copolymerization of phenols with lignin results in a material with markedly lower glass transition temperatures and higher (and more uniform) curing exotherms. The materials appear to act as thermosets and may have application as replacements of conventional phenolic resins. 0 1993 John Wiley & Sons, Inc.

Copolymerization of lignin with cresol catalyzed by peroxidase in reversed micellar systems

“…Thus, copolymerization of lignin with cresol lowers the endothermic glass transition temperature. This is consistent with published reports performed in non-aqueous media (Blinkovsky and Dordick, (1993). Therefore, the incorporation of phenol into lignin does not appear to destroy the native structure of the lignin; albeit bound phenols can radically alter its thermal properties.…”

“…Hence, significant differences between the lignin-cresol copolymer and free lignin are most likely due to the distributions of incorporation of cresol into lignin or/and polycresol segments in the copolymer. Blinkovsky et al (1993) observed that the FTIR spectrum of lignin-cresol is strongly different from that of polycresol obtained in aqueous-organic solvent mixtures, but not in reversed micelles. …”

“…Another possible structure of the copolymers is phenol/polyphenol bridges that form between individual lignin molecules (Blinkovsky and Dordick, 1993). These bridges would provide more rotational freedom to the copolymer as compared to native lignin, or lignin-lignin polymer.…”

Enzyme-catalyzed polymerization: an opportunity for innovation

“…While the crystal structure of HRP has not been determined, the active-site structure is believed to be similar to cytochrome C peroxidase, with the Arg-183 residue in HRP corresponding to Ser-185 in cytochrome C peroxidase [30][31][32]. This enzyme is catalytically active in organic media [33][34][35], has a wide specificity with substrates (phenols) that are highly soluble in organic solvents, is commercially available in the pure protein form, and has a structural 'marker' (i.e. active-site heme group) to aid in the elucidation of solvent-induced structural perturbations in the active site.…”

“…Blinkovsky and Dordick [35] have reported the HRP-catalyzed copolymerization of phenols with kraft lignin in aqueous-organic solvent mixtures. Besides cellulose and hemicellulose, lignin is the most abundant polymer on earth.…”