Enzymatic grafting of kraft lignin as a wood bio-protection strategy. Part 1: factors affecting the process

Kraft lignin (KL) isolated from the black liquor of pulping has some antifungal potential. For investigation of this effect, KL was treated with laccase to form covalent bonds to green wood and the critical parameters for enzymatic grafting have been evaluated. The biocidal properties of KL could be confirmed. Growth inhibition of over 50% was found with lignin concentrations equal to or higher than 10 g l-1. The change of wood color was evaluated based on the CIEL*a*b* color system and the data served for evaluation of the effectiveness of the KL binding to wood. The grafting reaction time was the most important variable in the impregnation process. Significant degrees of grafting were achieved in 10 min when samples were left to air dry after impregnation. The color loss was 30% after wood extraction with acetone. Higher temperatures and enzymatic pre-activation did not have a significant effect. As a conclusion, the most suitable procedure for enzymatic grafting of KL onto wood is by air-drying of the impregnated materials.