杉木层状压缩的形成及其密度分布特征

Sandwich Compression Formation and Density Distribution in Chinese Fir(Cunninghamia lanceolata)Wood

实木层状压缩技术是以实体木材的定向定位压缩为目标,以最小的材积损耗,最大限度地提高木材力学性能的一种新型木材压缩方法。通过水热分布调控以及外力加载的协同作用,在调控压缩层的形成位置、厚度和多层压缩的基础上,分析压缩木材密度分布特征,研究层状压缩技术对于人工林杉木(Cunninghamia lanceolata)的适用性及其层状压缩形成的特点。结果表明:预热时间控制在0.5~30 min之间时,获得压缩层位置不同的层状压缩杉木。随着预热时间的增加,压缩层由表层逐渐向中心(厚度方向)移动,压缩层密度达到0.583 g/cm^(3)及以上;通过调控压缩量,获得压缩层厚度为3.00~8.07 mm的4种厚度的表层压缩杉木,压缩层密度提高率比木材整体密度提高率平均高28.7%;将表层压缩和中心层压缩工艺并用,实现形成3个压缩层的多层压缩。扫描电镜观察结果表明,无论压缩层形成于表层还是中心层,压缩层与未压缩层界线出现在早材区域或早晚材交界处,压缩层的早材细胞发生细胞壁屈曲变形,至细胞腔几乎完全消失,而晚材细胞壁及细胞腔仅发生微变形或不变形。依据压缩前后木材密度分布曲线及特征值计算结果,杉木压缩层部位的早材密度提高率最大值可以达到210.6%。

Wood sandwich compression is an advanced technology of compressing wood layers through controlling the position,thickness,and the number of the compressed layers to achieve mechanical property enhancement.By regulating the distribution of temperature and moisture in Chinese fir wood under the desired pressure,the positions and thickness of compressed layers were managed in this study.Furthermore, density distribution in the compressed Chinese fir wood was analyzed to investigate thefeasibility of sandwich compression technology to plantation Chinese fir wood and to clearly understandthe formation mechanism. The results indicated that when the preheating time ranged from 0.5 to 30minutes, Chinese fir wood was sandwich compressed with various positions of compressed layers. As thepreheating time extended, compressed layers moved from wood surfaces into center and the compressedlayer's density exceeded 0.583 g/cm^(3). By changing the compressing rate and thickness of wood specimen,four types of surface compressed wood with a compression layer thicknesses' range between 3.00~8.07 mm were obtained. The average density of the compressed layer was 28.7% higher than that of theoriginal wood. Combining the technologies for surface compression and centre compression, threedistinct compressed layers were formed in the sandwich compressed wood. It was also found that theboundary between the compressed layers and uncompressed layers appeared in the earlywood and theboundary between earlywood and latewood, regardless that compression occurred on wood surface orinside wood. Remarkably, the earlywood cells in the compressed layer underwent significant distortion,leading to the disappearance of almost all cell cavities. On the other hand, latewood cells exhibited littledeformation or even remained intact. Based on the density profiles and the calculated characteristicvalues before and after compression, the maximum density of the compressed earlywood was 210.6%higher than that of the corresponding uncompressed earlywood.