Fungal decay resistance, formaldehyde emission and weathering resistance of plywood modified with phenol-formaldehyde resin with partial substitution of phenol by pyrolysis cleavage products of softwood kraft lignin

Abstract

Wood modification by impregnation with phenol-formaldehyde (PF) resins is a promising method to improve the woods’ fungal decay resistance, weathering resistance, and dimensional stability. Recent research indicates that 30% of the non-renewable phenol may be substituted by renewable softwood kraft lignin cleavage products obtained through microwave-assisted pyrolysis. Pinus sylvestris sapwood modified with this resin has good fungal decay resistance but slightly enhanced formaldehyde emission. While these results on solid wood indicate a high potential of the method, the properties of modified plywood may differ, and the weathering resistance has not been studied. In this study, formaldehyde emission, weathering resistance and fungal decay resistance against three basidiomycetes (Trametes versicolor, Rhodonia placenta, and Gloeophyllum trabeum) of plywood modified with pure PF resin and PF resin with 30% substitution of the phenol by lignin cleavage products were analysed. The 30% lignin cleavage product substitution didn’t affect the plywood’s fungal decay resistance, with less than 1% initial mass loss in all modified specimens. While the decay resistance improved significantly for all modified samples compared to reference samples, weathering resistance slightly declined with phenol substitution compared to pure PF resin modification. The formaldehyde emissions of the plywood modified with both resins were in similar ranges to that of unmodified reference plywood. Overall, plywood with good properties for exterior applications may be produced even with the substitution of 30% of the phenol by lignin cleavage products, allowing for increased use of renewable resources.