Compressive deformation of phenol formaldehyde (PF) resin-impregnated wood related to the molecular weight of resin

Abstract

The effects of molecular weight of PF resin on the deformation behaviour of NaClO₂ treated resin-impregnated wood during compression were investigated. Blocks of Japanese cedar were subjected to 2% NaClO₂ aqueous solution. This was repeated up to four times resulting in a weight loss of 28%. Treated and untreated samples were impregnated with PF resin having different molecular weight. With increasing molecular weight, weight gain and volume gain decreased for untreated PF resin-impregnated wood, while NaClO₂ treated wood impregnated with high molecular weight PF resin showed almost double the weight gain compared to untreated condition. NaClO₂ treatment has shown considerable potential for high compression of PF resin-impregnated wood at lower pressing pressure regardless of the molecular weight of the resin. Low to high molecular weight resin was shown to penetrate into NaClO₂ treated wood as estimated by weight gain contributing to the plasticization of cell wall considerably and thus resulting in cell wall collapse at low pressing pressure. The density of NaClO₂ treated wood impregnated with high molecular weight resin attained a value of over 0.8 g/cm³ which is close to the density of untreated wood impregnated with low molecular weight resin. Such compressed wood exhibited high dimensional stability after boiling for 3 h. Thus, the penetration of resin into wood contributes to highly compressed dimensional stable resin-impregnated wood at low pressing pressure.