| The technology of vacuum-pressure impregnating poplar with low molecular weight urea-formaldehyde of low viscosity was researched in this study, in which Populus deltoides cv.1-69/55was chose as the test specimen and UF with concentration of45%as dipping strengthening material. The optimal impregnation process parameters were obtained from single factor and orthogonal experiments, taking the impregnation pressure and holding time into account. Then the characteristics of test specimens, treated with the optimal impregnation process parameters, were analyzed. After that, the untreated and impregnated specimens treated at160,180,200, and220℃for0.5,1,2and4h, then the untreated, impregnated, heat treated and impregnated-heat treated specimens were characterized by physical properties, mechanical properties and crystallinity, functional groups through modern analytical instruments. The results were shown as follows:1. The weight gain rate and fracture density of poplar that treated with pressure of1.OMPa and dipping time of2h, the optimal impregnation process, reached to36.4%and0.5g/cm3, respectively, which achieves the expectation effect. It can be observed that the UF resin was impregnated into the wood cell cavity and intercellular space by the means of SEM. However, the permeability of resin in the cell wall couldn’t be seen. Through the observation of fluorescent microscope, it can be found that the color area accounts for62.3%of the total area, which means UF resin distributed evenly in the wood.2. The color of the untreated and impregnated poplar was darkened by the process of heat treatment, and the latter was even warmer than the former. The impact of temperature of heat treatment on color was greater than that of time. The heat treatment had an obvious influence on the index of red, green of poplar, a relatively small influence on lightness and the minimum influence on index of yellow, blue.3. The heat treatment significantly reduced the equilibrium moisture content,the bibulous rate, the radial, chordwise and volume expansion rate of the untreated poplar.The untreated poplar and impregnated poplar was decreased obviously by heat treatment. Heat treatment significantly decreased the radial, chordwise and volume expansion rate of untreated poplar and impregnated poplar.4. The surface wettability of untreated poplar and impregnated poplar was reduced by heat treatment, thus increasing the contact angle, from49.1°,48.1°to120.7°106.55°, respectively.5. The bending strength and elastic modulus of untreated poplar and impregnated poplar decreased by heat treatment, and the decline of impregnated poplar was smaller. After impregnation, the bending strength and elastic modulus increased from68N,7025MPa to92N,8292MPa, by the amplitude of35.29%and35.29%, respectively. After heat treatment, the bending strength and elastic modulus of untreated poplar and impregnated poplar declined to20.84N,48.37N and4085MPa and4085MPa, by the amplitude of69.35%,47.42%and69.35%,47.42%, respectively. The wear resistance of impregnated poplar was improved by a little, and that of the heat treated poplar was declined as a whole, especially above the200℃, the decline was obvious. Wear resistance of the untreated poplar and impregnated poplar were at the same level when the process conditions were equal.6. FTIR indicates UF resin not only impregnated into the wood cell lumen and intercellular space, but also reacted with some groups in cellulose, hemicellulose and lignin.XRD indicates, comparing with untreated poplar, the relative crystallinity of impregnated poplar was increased slightly, which means that the regularity and order of microfibril arrangement were improved slowly by the vacuum pressure impregnation of urea-formaldehyde resin,... |
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