Abstract
Wood modification improves the properties of wood as a building material by altering the wood structure on a cellular level. This study investigated how dimensional changes of wood on a macroscopic scale are related to the cellular level chemical changes on the micron level after impregnation modification with melamine formaldehyde (MF) resin under different heat curing conditions. Our results showed that the curing conditions affected the polycondensation reactions and the morphological structure of the MF resin within the cell lumen. The diffusion of the resin into the cell wall was estimated based on the triazine ring vibration of melamine in the Raman spectrum at 950–990 cm−1. Thereby, it was shown that macroscopic changes in wood dimensions do not provide a reliable estimate for the cell wall diffusion of the resin. The removal of cell wall constituents during the modification, which was facilitated by the alkaline pH of the impregnation solution, counterbalanced the cell wall bulking effect of the resin. This was particularly evident for wet cured samples, where diffusion of MF resin into the cell wall was observed by confocal Raman microscopy, despite a reduction in macroscopic wood dimensions.
Highlights
Wood modification improves the properties of wood as a building material by altering the wood structure on a cellular level
The curing conditions did not affect the increase in dry sample mass, but mass changes are insensitive to the location of chemical agents within the hierarchical structure of wood
A gradual increase in relative dry dimensions with increasing solid content of the impregnation solution was only determined after dry curing (Fig. 2b), which indicated the diffusion of the melamine formaldehyde (MF) resin into the cell wall microstructure and a successful cell wall bulking
Summary
Wood modification improves the properties of wood as a building material by altering the wood structure on a cellular level. This structure provides wood with a high strength to weight ratio[3], but the hygroscopic behaviour of wood is associated with dimensional changes[4] and degradation by decay fungi[5] These moisture-related problems can be reduced significantly by impregnation modification using thermosetting resins, such as melamine formaldehyde (MF) resin. Thereby, the uptake of liquid water and water vapour into the cell wall is reduced, which limits the dimensional changes of wood[18] and enhances its decay resistance[20] This cell wall bulking effect is commonly determined at a macroscopic level by the increase in dry sample dimensions. Thereby, thermosetting resins are believed to form macromolecules that are too large to enter the cell wall pores before the diffusion is facilitated by the removal of the solvent from the lumen[23]
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