Modification Of Microwave Pretreated Plantation Poplar Wood Performed By Resin-impregnation And Heat-treatment

Poplar is widely cultivated and becomes one of the three species of fast-growing plantations in china, but it has some inherent defects like poor dimensional stability and low strength properties which limit its end-use. Consequently, it is significant to improve performance and expand application fields by modification. Dimensional stability of wood can be improved through heat treatment, which may reduce the mechanical performance of its products. Densification with impregnating resin could increase its strength, however, the low permeability of wood limited the unsteady-state permeation of resin and might affect the impregnation depth and uniformity. Therefore, the feasibility of modification for microwave pretreated wood by resin-impregnation and heat-treatment was studied on this paper, then physical and mechanical properties of modified wood were tested by means of technique, which might provide references and basis for the research on the modification of poplar wood.The main conclusions of this study are as follows:(1) Appropriate microwave pretreatment generated high internal steam pressure, resulting in the rupturing of wood cell pore membranes and ray cells. Therefore, the great increase of permeability in the radial and longitudinal direction can be achieved and created favorable conditions for the impregnation of PF resin. The optimal condition for microwave pretreatment was56%,19kw and89s for initial wood moisture content, radiation intensity and duration time, respectively.(2) The weight gain ratio and density of wood impregnated with low molecular weight PF resin under pressure of1.0MPa for2h was significantly improved, around40%and584.8kg·m-3, respectively. It can be observed that PF resin mainly impregnated into the wood cell cavity and intercellular space, especially in the vessels.(3) Heat treatment significantly reduced hygroscopicity, linear and volume swelling ratio, and surface wettability of PF impregnated wood, thus increasing the dimensional stability. The color of impregnated poplar was darkened by heat treatment. a*, ΔE*, and ΔH*improved with the increasing of heat treatment temperature, while L*decreased, and b*, AC*showed some volatility. The impact of temperature of heat treatment on properties mentioned above was greater than that of time. (4) MOE and MOR of poplar wood was significantly increased by PF resin impregnation, while decreased by heat treatment. The higher the heat treatment temperature, the more obvious MOE and MOR decreased, and200degrees was an inflection point.(5) FTIR spectra showed that with the increasing of heat treatment temperature or the extension of heat treatment time, the absorption peak of hydrophilic hydroxyl and carboxyl group of untreated and impregnated wood decreased obviously. PF resin not only impregnated into the wood cell lumen and intercellular space, but also reacted with some groups in cellulose, hemicellulose and lignin. The variation tendency of relative crystalline of impregnated wood and untreated wood were different by heat treatment under different conditions, and the overall regularity was not remarkable.