木塑层合板的制备工艺及抗弯性能

Processing and bending behavior of wood-plastic laminated timber

为了弥补常规木塑复合材料的力学性能较低的不足,满足木塑复合材料在结构领域中的应用要求,试验以国产速生杨木为研究对象,以聚乙烯和聚丙烯塑料合金为粘结剂,采用平压法制备了结构用木塑层合板。通过研究热压温度、木材塑料质量比和马来酸酐添加量等3个因素对木塑层合板胶合性能的影响,以优化其制备工艺;在此基础上,进一步研究和分析了木塑层合板抗弯性能的影响因素及其作用机理。结果表明,拉伸剪切荷载作用下,偶联剂的介入,木塑层合板的破坏模式由空白试件的界面分层剥离转变为木材拉伸断裂;试验范围内,温度为180℃、木材塑料质量比为3/2、马来酸酐添加量为4%时木塑层合板的胶合性能较优,胶合强度达到0.98MPa,与未添加偶联剂的空白试件相比,胶合强度提高16.7%;采用层积法制备工艺,木塑层合板的抗弯性能能够达到结构用材的要求;密度0.6和0.8 g/cm3时,木塑层合板随着板材密度和木材塑料质量比的提高,静曲强度增大、抗弯弹性模量降低,木材单层板形态完整;密度为1.0 g/cm3时,随着木材塑料质量比的提高,木塑层合板静曲强度降低、抗弯弹性模量提高,当木材塑料质量比为3∶3时,木塑层合板中木材横纹出现大量不连续裂纹,木材的形态完整性下降;热压温度190℃、木材塑料质量比3/2和3/3、马来酸酐添加量为4%、板材密度为0.8 g/cm3时,制备的木塑层合板抗弯性能较优,能够达到100E等级的要求;结果可为木塑层合板在结构领域中的应用提供参考。

The mechanical performance of common wood plastic composites was poor and couldnot be used as structural member. Structural wood-plastic laminated timber was prepared with domestic fast-growing poplar wood veneer and thermoplastic plastic alloy by the flat-pressed method. The plastic alloy was composed with polyethylene and polypropylene film with the weight ratio of 1:1 and acting as adhesive in laminated timber. The hot pressing temperature, ranging from the melting temperature of plastic alloy measured by differential scanning calorimeter to the pyrolysis temperature of wood materials, could be determined preliminarily. Secondly the effects of the hot pressing temperature, the wood-plastic ratio and the concentration of maleic anhydride on the bonding strength of wood-plastic laminated timber were studied. Then the tests on the effects of the above 3 factors on the bending behavior of wood-plastic laminated timber were carried out. The results showed that, the interfacial damage mode of wood-plastic laminated timber with coupling agent under tension and shear forces was wood failure, while that of controlled specimens was interfacial delamination between wood and plastic. Compared with controlled specimens, the bonding strength of wood-plastic laminated timber pretreated with coupling agent was the highest, and increased by 16.7% at 180℃, wood-plastic ratio of 3/2 and maleic anhydride concentration of 4%. Wood-plastic laminated timber exhibited better mechanical properties with the flat pressing preparation method, and could be used as a structural wooden member. Bending strength was negatively correlated with modulus of elasticity for wood-plastic laminated timber. In the experiment, bending strength of wood-plastic laminated timber increased with the increasing of the wood density and the ratio of wood to plastic at the density of 0.6 and 0.8 g/cm3, while modulus of elasticity decreased, and the microstructure of wood kept integrated. Compared with the densities of 0.6 and 0.8 g/cm3, wood-plastic laminated timber was stronger at a density of 1.0 g/cm3. Bending strength decreased with the increasing of wood-plastic ratio at the density of 1.0 g/cm3. The resistance of wood-plastic laminated timber increased with the density and the wood-plastic ratio. There was much discontinuous crack at the direction of cross grain of wood veneer, so the structural integrity of wood decreased at a wood-plastic ratio of 3/3. The bending properties of wood-plastic laminated timber met the demands and reached the 100 E level according to the national standard of China when the hot-pressing temperature was 190℃, the wood-plastic ratio was 3/2 and 3/3, the concentration of maleic anhydride was 4%, and the density was 0.8 g/cm3. The study may provide valuable information for the structural applications of wood-plastic laminated timber.