Abstract
Impregnation modification of wood with melamine formaldehyde resin reduces the adverse effects caused by moisture uptake, but the underlying modes of action are not fully understood. The present study showed that it is crucial to understand the sorption behavior of the pure resin when interpreting the behavior of resin-modified wood. Furthermore, the applied heat-curing conditions had a significant effect on the moisture uptake of resin-modified wood. At the same resin loads, dry curing conditions were more effective in causing a cell wall bulking effect than wet curing conditions. This reduced the water-accessible cell wall pore volume in dry cured wood and counterbalanced the moisture uptake by the resin. Deuterium exchange measurements suggested that the occupancy of cell wall pores reduced the number of simultaneously active sorption sites. However, there was no evidence that a swelling restraint or reduced mechanical relaxation affected the water sorption of resin-modified wood significantly.
Highlights
Wood has remarkable properties such as a high mechanical strength in relation to its low weight, but its properties are strongly influenced by the uptake and release of water from the surroundings
Changes in the melamine formaldehyde (MF) resin caused by heat curing at different temperatures were analyzed by Raman spectroscopy (Fig. 2c)
Cured MF resin lacked the steep increase in MC at elevated humidity that was evident in unmodified wood, and this affected the course of the moisture content of resin-modified wood in the hygroscopic range
Summary
Wood has remarkable properties such as a high mechanical strength in relation to its low weight, but its properties are strongly influenced by the uptake (absorption) and release (desorption) of water from the surroundings. The absorption of water by dry wood generally results in a decrease in strength and an increase in dimensions (swelling) until reaching the fiber saturation point, which is reverted when the wood is dried again [1]. Repeated dimensional changes by frequent variations in wood moisture content (MC) will eventually lead to checks and other defects. Dimensional changes and moisture uptake of wood can be reduced by impregnation modification with thermosetting resins, which forms a composite of wood and resin [3,4,5].
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