Wood modification with thermosetting resins is an increasingly popular method aiming to increase the number of applications for readily available plantation timber. Phenol urea formaldehyde (PUF) resin is impregnated into the timber, which is dried, and subsequently heat cured. This treatment renders the raw material dimensionally stable and imparts the ability to withstand wood destroying fungi and insects. While the type of resin (urea4, phenol5, melamine-based6) and the curing conditions (wet- or dry curing, different curing temperature) have been the subject of several studies, the influence of resin migration in the drying step is less clear. Previous work on polyethylene glycol suggests that the diffusion of a polymeric bulking agent into the cell wall of wood is influenced strongly by the atmospheric conditions in the drying stage.
The current study compared matched test groups with different drying schedules (temperature, relative humidity) that were otherwise treated identically. Cyclic water soaking after the treatment revealed significant differences in the bulking coefficient and dimensional stability achieved in both groups. If it is possible to explain this effect on a nanoscale level, it may become feasible to further optimise resin modification systems. Therefore, liquid- and solid-state NMR spectroscopy were used to study the chemical interactions and nanoscale morphology in the resin impregnated cell wall.
Keywords: wood modification, nuclear magnetic resonance (NMR), anti-swelling efficiency (ASE)
Authors
Carlo Kupfernagel
BioComposites Centre, Bangor University, Bangor, UK
Morwenna Spear
BioComposites Centre, Bangor University, Bangor, UK
Daniel Yelle
Forest Products Laboratory, Madison, USA
Mohammad Rahman
Department of Physics, University of Warwick, Coventry, UK
Steven P. Brown
Department of Physics, University of Warwick, Coventry, UK
Graham Ormondroyd
BioComposites Centre, Bangor University, Bangor, UK,
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