| Wood used outdoors is prone to physical, chemical, and biological degradation, especially their susceptibility to fungal decay greatly depends on moisture content (MC). Therefore, efforts have been undertaken to reduce MC and keep it below the critical value. Water repellents applied to wood commercially have been almost exclusively of the simple non-chemically bonded type, mainly based on paraffin waxes. Therefore, in the present study, the influence of paraffin wax emulsion at economical feasible concentrations on solid wood was investigated under stable temperature with various stable relative humidity and sinusoidal changing relative humidity. This work was conducted to observe the effect of paraffin wax emulsion (PWE) on moisture changes and transverse dimensional swelling of wood during moisture sorption processes, in combining with measuring the percent weight gain and SEM analysis. The main results of this study were summarized as follows:(1) The percent weight gain of treated wood with 0.5,1, and 2% PWE were 0.7%,1.5% and 2.8%, respectively. The SEM analysis of 2% PWE treatment confirmed the appearance of PWE in wood after the treatment.(2) Moisture case in static adsorption experiment, the EMC decreased with an increase in PWE concentration, that the highest values of moisture adsorption coefficient (Z) and moisture adsorption slope in the first 24h belonged to control samples. The moisture repellent effectiveness (MRE) varied from 3 to 25%, depending on RH value and degree treatments of PWE. The PWE treatments also had a favorable effect on the moisture sorption rate of wood. In addition, by evaluating some constants in the Hailwood-Horrobin model in order confirm the important role of PWE in wood moisture repellent.(3) The lateral dimensional change in static adsorption experiment, the dimensional swelling was anisotropic in every RH, and the lateral swelling decreased when PWE concentration increased. Additionally, evaluating of humidity expansion coefficients (Y) and moisture expansion coefficient (X) reconfirmed the role of PWE treatment in dimensional stability. The PWE treatments also had a favorable effect on the dimensional swelling rate during adsorption process.(4) In dynamic experiment, the moisture and lateral dimensional change tendency were sinusoidal shape for all wood samples. The moisture amplitude increased as the cyclic period increased for the same thickness, but the amplitude in 10mm thickness was smaller than 4mm thickness in the same cyclic period. In addition, amplitude of moisture and Z value decreased with increasing of PWE concentration treatment, led to MRE value in 10-66% range. The amplitude of dimensional change and humidity expansion coefficient (Y) were lower in the PWE treated wood, reflected in anti-deformation effectiveness of PWE treatment. However, the moisture expansion coefficient (X) was not obviously correlated with treatment.(5) The time point that moisture and dimensional change approached the max values were slower than those in relative humidity, namely phase lag, in which the values of moisture change were the largest, followed by values of radial dimension and tangential dimension. The phase lag decreased when cyclic period increased for one thickness and the phase lag of 10 mm thickness were larger than that in 4 mm thickness. The phase lag tendency of PWE groups was similar to control sample, but this value increased with an increase in PWE concentration treatment. All wood sample groups presented the sorption hysteresis and swelling hysteresis, in which sorption hysteresis also decreased when PWE concentration increased.(6) After comparing some elements in static condition and dynamic condition, it was found that PWE treatment was more effective in dynamic condition. |
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