Copper-lignin with laccase-mediated polymerization fixation for wood preservation: determination of durability in marine environment using novel technologies

In the marine environment, the durability of wood is heavily compromised by harsh conditions and the presence of marine xylophages. Biocide treatments are often employed to prolong the lifetime of wood, however, its leaching into the environment motivates the development of alternative treatments due to environmental concerns. In this study, Scots pine samples were treated with a solution based on copper and polymerized Kraft lignin via laccase enzyme was tested. In this treatment, Kraft lignin was intended to work as adsorbent of copper while laccase-assisted polymerization was intended for fixation to the wood. To discern the contribution of each component, a set of samples were prepared with different combinations of the three components (presence/absence) and compared to untreated controls. The wood samples were immersed for one year in Vigo estuary (Spain). Biofouling coverage was monitored along the immersion time and the final mass accumulated was measured. Copper retention and distribution were studied by ICP-OES and XRF, respectively. Marine xylophage attack was evaluated quantitatively using X-ray computerized tomography analysis. The treatments containing copper were less affected by biofouling and marine xylophages. Treatments containing lignin limited the impregnation depth and consequently the copper content was lower than the samples with just copper. However, XRF analysis showed that in the parts where Kraft lignin was highly present, copper was better retained than parts that not. Unfortunately, due to the previously indicated impregnation limitation, the role of laccase in lignin polymerization could not be assessed properly. Additionally, in this study a set of novel technologies for the study of wood for marine use was used. These techniques included the use of X-ray CT and the Itrax Core Scanner, a device that allows the acquisition of high-quality image, energy dispersive X-ray fluorescence, and X-ray radiography.