Search

Here, we report work on developing an enzymatic process to improve the functionalities of industrial lignin. A kraft lignin sample prepared from marine pine was treated with the high-redox-potential laccase from the basidiomycete fungus Pycnoporus cinnabarinus at three different concentrations and pH conditions, and with and without the chemical mediator 1-hydroxybenzotriazole (HBT). Laccase activity was tested in the presence and absence of kraft lignin. The optimum pH of Pci Lac was initially 4.0 in the presence and absence of lignin, but at incubation times over 6 h, higher activities were found at pH 4.5 in the presence of lignin. Structural changes in lignin were investigated by Fourier-transform infrared spectroscopy (FTIR) with differential scanning calorimetry (DSC), and solvent-extractable fractions were analyzed using high-performance size-exclusion chromatography (HPSEC) and gas chromatography-mass spectrometry (GC-MS). The FTIR spectral data were analyzed with two successive multivariate series using principal component analysis (PCA) and ANOVA statistical analysis to identify the best conditions for the largest range of chemical modifications. DSC combined with modulated DSC (MDSC) revealed that the greatest effect on glass transition temperature (Tg) was obtained at 130 U g cm -1 and pH 4.5, with the laccase alone or combined with HBT. HPSEC data suggested that the laccase treatments led to concomitant phenomena of oligomerization and depolymerization, and GC-MS revealed that the reactivity of the extractable phenolic monomers depended on the conditions tested. This study demonstrates that P. cinnabarinus laccase can be used to modify marine pine kraft lignin, and that the set of analytical methods implemented here provides a valuable tool for screening enzymatic treatment conditions., Competing Interests: The authors declare that they have no conflict of interest.

Lignins are by-products from biorefinery and paper industries. Their chemical structures are complex, and they are currently mainly used for energy and heat production generated by their combustion. In a context of higher value applications of lignins, lignin-based composites with lignosulfonate matrix and wood fibers reinforcement were pre-treated with laccase (EC 1.10.3.2) from Pycnoporus cinnabarinus , and laccase/mediator system, to modify, as a proof of concept, their mechanical properties. Composites (120 x 9 x 4 mm) were prepared by compression molding at room temperature. The flexural modulus, the fracture strength, and the fracture energy of obtained agrocomposites were evaluated by three-points bending tests. The best mechanical properties (flexural modulus of 3.51 GPa and a fracture strength of 17.5 MPa) were obtained for a simultaneous enzymatic pre-treatment of both lignosulfonate and wood fibers during 17 h with 13 U of laccase per gram of lignosulfonate. [Display omitted] • Composites made of a lignosulfonate matrix and a wood fibers reinforcement were developed. • Flexural modulus and fracture strength of composites were determined by three-points bending tests. • A laccase pre-treatment of the raw materials allows to significantly modify the mechanical properties of composites. • A simultaneous enzymatic pre-treatment of lignosulfonate and wood fibers improved flexural modulus and fracture strength. [ABSTRACT FROM AUTHOR]