Dimensional Stability Measurements of Thin Wood Veneers Using the Wilhelmy Plate Technique
Keywords:hydroxymethylated resorcinol (HMR), water repellent, dimensional stability, perimeter, Wilhelmy plate method
The objective of this study was to investigate the effect of hydroxymethylated resorcinol (HMR) and a commercially available water repellent (WR) treatment on the dimensional stability and water uptake behavior of maple veneers. The Wilhelmy plate technique was used to assess the effects of the chemical treatments on the veneer by comparing the perimeter of the veneers before and after 24 h water immersion and by monitoring the initial water uptake behavior. The veneers were treated with the HMR and WR by dipping treatment at three different loadings: 5, 15, and 30 min of treatment time.
Water uptake into the untreated veneer increased dramatically during the 30 min of immersion time in water, compared with the HMR-treated veneer. Water uptake into the HMR-treated veneer, which was treated at the highest retention level (30 min), was limited during the initial stage of the waterimmersion test.
The initial amount of water uptake into the veneer was lowered by 65% to 75% as a result of the HMR treatment, and the initial amount of water uptake into the water repellent-treated veneers was lower than that of the HMR-treated veneers depending on the HMR/WR treatment retention level. The initial amount of water uptake of the water repellent-treated veneers was lowered by 5 to 10%, compared with the HMR-treated veneers at the treatment time of 15 and 30 min.
HMR treatment improves the dimensional stability of wood as evidenced by the reduced swelling of the HMR-treated samples compared to the untreated samples in the water-immersion test.
The changes of sample perimeters measured by the Wilhelmy plate method were larger than those measured by digital calipers because the Wilhelmy plate method measures the perimeter change on the microscopic (cellular) level. It is hypothesized that the Wilhelmy plate method is a more effective tool than the caliper method for investigating the dimensional stability of small, thin, or nonrectangular samples in aqueous environments.
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