Resistance of wood–plastic composites and tannin- and lignosulfonate- based adhesives to xylophagous organisms

Abstract

This study evaluated the biological resistance of wood–plastic composites (WPCs) to deterioration caused by xylophagous fungi (Gloeophyllum trabeum and Trametes versicolor) and drywood termites (Cryptotermes brevis). Eight treatments were applied using different proportions of Eucalyptus sp. particles (50%, 70%, 85% and 95%) and recycled low-density polyethylene plastic (5%, 15%, 30% and 50%), bonded with either 100% tannin-based adhesive or a combination of tannin and lignosulfonate (80%–20%). The samples were hot-pressed under 3.92 MPa pressure at 160 °C for 10 min. To assess fungal resistance, samples measuring 2.5 cm × 2.5 cm × 1.25 cm (length × width × thickness) were exposed for 12 weeks and mass loss was analysed. In the termite tests, samples measuring 5.0 cm × 5.0 cm × 1.25 cm were exposed for 45 days, and both sample mass loss and termite mortality rate were determined. Composites with higher plastic content exhibited less fungal deterioration and lower termite consumption, together with higher insect mortality rates. Adding lignosulfonate contributed to increased biological resistance, especially in formulations containing 30% plastic. In contrast, treatments with a higher proportion of wood and 100% tannin adhesive were more susceptible to deterioration. Formulating WPCs with tannin– lignosulfonate adhesive enhances their durability against xylophagous organisms.