To improve the permeability of dye solution in wood, poplar was pretreated by freeze-thaw cycle. The effects of three parameters, such as freezing time, thawing time and circulation times on the dyeing effect of pretreated poplar were investigated by single factor method. On this basis, pretreatment conditions were optimized by response surface methodology. The optimum conditions of this treatment were freezing time of 11.9 h, thawing time of 7.2 h and two cycles. Under these conditions, the dye uptake and chromatic aberration of the treated wood were 25.77% and 21.14%, respectively, which were close to the theoretical predicted values. The results showed that freeze-thaw cycle pretreatment could effectively improve the permeability of poplar and enhance the dyeing effect of wood.
The correspondence of natural and laboratory-accelerated aging of WPC has long been a highly important problem discussed by many scholars. In this work, the changes in moisture content (MC), modulus of rupture (MOR), modulus of elasticity (MOE), screw holding force and creep recovery rates of two groups of wood-plastic composites (WPC) after natural and accelerated aging (high-low temperature cycles and freeze-thaw cycles) were studied to provide guidance for the use of WPC in outdoor applications. The results showed that, after the natural aging and freeze-thaw cycles treatments, MC increased significantly with both 167% of the untreated value of wood-HDPE composites with 30% wood fiber content and a thickness of 25 mm (W25), while 67% and 133% of the wood-HDPE composites with 30% wood fiber content and a thickness of 20 mm (W20), but is almost unchanged after the treatment with high-low temperature cycles. The mechanical strength, including MOR, MOE, screw holding force and creep recovery rate, decreased after natural and accelerated aging. The greatest decreases of MOR, MOE, screw holding force and creep recovery rate were 14%, 13%, 21%, and 7% for W25, while 5%, 8%, 8%, and 14% for W20 respectively. Environmental aging can reduce the strength of WPC, but the bending strength retention rate is more than 85%, showing that performance of WPC is relatively stable compared to wood materials, which is one of the reasons for the widely use of WPC in outdoor applications.