Decay resistance of beech wood and plywood treated with different type of phenol-formaldehyde (PF) resins

IRG/WP 16-40717

V Biziks, S Bicke, H Militz

In this study treatment of beech and poplar wood veneers with (PF) resin industrial scale and screening tests of nine different phenol-formaldehyde (PF) resins were made. Specifically, the effect of different phenol-formaldehyde (PF) resin types on the resistance of beech wood against brown- and white-rot fungi was evaluated. Criteria for selection of optimal (PF) resin were based on minimum WPG requirements to achieve equal durability class (1st durability class according to the EN 350 standard) against fungi. Therefore European beech (Fagus sylvatica) wood blocks (15x20x50 mm³) were vacuum impregnated to various weight percent gains (WPGs) with water-soluble PF resins. Different WPG levels were achieved by using aqueous resin solutions at concentrations of 9, 18 and 27 wt %. Treated wood blocks were exposed to brown-rot fungi (Gloeophyllum trabeum (G.t); Coniophora puteana (C.p)) and white-rot fungi (Trametes versicolor (T.v); Pleurotus ostreatus (P.o)) for 16 weeks. A WPG of approximately 8–14% was necessary for beech wood blocks for a treated with the resin C, D, I and E, but approximately 16% and 27% was necessary when using other resins as B, F, G, H, respectively. Irrespective from resin the required WPG for decay resistance against brown rot fungi was approximately 50-60% lower compared to decay resistance against white rot. No effect of resin on the resistance against (G.t) decay of wood blocks was observed, resulting in resin loadings of 7–8%, whereas the required WPG for (C.p) decay suppression slightly increased from 8 up to 11%, respectively. The results suggest that the magnitude of white fungal deterioration of treated wood is strongly affected by the resin used for treatment. Resin loadings from 7% to 17% against (T.v) and from 12% to 27% against (P.o) were required. This broad range in WPG may be due to varied fungal aggressiveness, filling of the cell wall micropores (bulking) and the stiffness (pliability) of the cell wall matrix. From aforementioned, two resins D and E were selected for treatment of beech and poplar veneers on industrial scale and resistance of treated plywood against white rot fungus (T.v) was evaluated according EN 12038 standard.

Keywords: beech wood, decay resistance, phenol-formaldehyde resin, poplar, plywood

Conference: 16-05-15/19 Lisbon, Portugal

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