Study of a copper-lignin with laccase-mediated polymerization treatment for wood preservation: determination of durability in marine environment using novel technologies

Abstract

Wood durability in marine environments is significantly compromised by harsh conditions and the presence of marine xylophages. Biocide treatments are often employed to extend service life, however, its leaching into the environment has driven the development of alternative treatments due to environmental concerns. This study evaluates a treatment for Scots pine based on copper and Kraft lignin, polymerized via laccase enzyme. In this treatment, Kraft lignin was intended to work as copper adsorbent, while laccase-assisted polymerization ensures fixation onto the wood. In order to distinguish the contribution of each component, a set of samples was prepared with different combinations of the three components, including untreated controls. Wood samples were immersed for one year in the Vigo estuary (NW Spain). Biofouling coverage was monitored throughout the immersion period, and the final accumulated biomass was measured. Marine xylophage attack was quantitatively evaluated using X-ray computerized tomography (CT). Copper retention and spatial distribution were analyzed by ICP-OES and XRF, respectively. Cooper-based treatments reduced biofouling and limited attack by marine xylophages. However, the inclusion of Kraft lignin restricted the impregnation depth, resulting in a lower copper content compared to the samples containing only copper. Nonetheless, XRF analysis showed better copper retention in the areas where Kraft lignin was highly present. Also, the reduced penetrability of lignin solution limited the assessment of the role of laccase in lignin polymerization. Additionally, a set of novel technologies for the study of wood in marine environments was integrated in this study. These included X-ray CT and the Itrax Core Scanner, a device that allows the acquisition of high-quality images, energy dispersive X-ray fluorescence and X-ray radiography.