摘要
胶合板是一种重要的木质工程材料,其纵横交错的组坯方式有效地降低了木质材料的各向异性,因此,胶合板常用于室外环境以代替实木作为结构材使用。由于木材固有的易吸湿性,吸水可改变胶合板的物理力学性能。为探索胶合板层间水分迁移规律,使用X射线断层扫描仪检测吸水前后2种杨木胶合板和杨木试件内水分迁移行为,分析了影响胶合板内水分迁移行为的原因,剖析了吸水过程中胶层和单板结构变化对胶合板吸水行为的影响。研究结果表明,水分在胶合板层间迁移可分为吸湿后木材单板发生润胀、单板间胶层不再连续和完整、水分在板层间孔隙聚集和水分穿过胶层并进入下一板层4个步骤。水分更易在木质单板内高密度区域聚集以及沿结构存在缺陷区域迁移。本研究动态可视化了吸水过程中胶合板内水分分布及胶层形态变化,揭示了胶合板内水分穿过胶层的发生机制,这一研究成果可为优化人造板生产工艺和指导人造板的合理使用提供理论基础。
As a panel raw material,wood has the advantages of low energy consumption and CO2 emission as well as high strength/weight ratio.Plywood is an important engineered wood product manufactured by bonding veneers together.The grain of alternate veneers is arranged to cross at right angles,minimizing the effect of strength anisotropy in the panel.These advantages contribute to a wide application of plywood in outdoor environment.Considering wood is prone to water sorption,water sorption can result in structural instability,strength decrease and decay risk of plywood.Increasing water resistance is crucial for enlarging the application fields and increasing service life of plywood.Glue line between veneers is a typical characteristic of plywood differentiated from solid wood,which has a great influence on water transport behavior in plywood.It is,therefore,necessary to explore the interaction between the water transport behavior and glue line changes.Water distribution and glue line changes in two types of plywood and poplar solid wood were continuously monitored using a gantry?based X?ray computed tomography scanner.Two types of plywood were glued with phenol formaldehyde(PF)and melamine modified urea?formaldehyde(MUF)resins,respectively.The results showed that the water transportation in poplar was mainly along the fiber direction and water could hardly transport along the other directions.Water penetrated glue line between veneers was consisted of four steps that could occur sequentially or simultaneously,which were that,resulted from water adsorption the wood swelled,gaps between veneers appeared in glue line,water accumulated in gaps,and water penetrated to the next layer.The water favored to transport in the regions with high density and structural ruptures of a veneer.These structural ruptures could be induced during peeling veneers.MUF glue line kept consecutive even after the 24 h water sorption.For PF resin,the glue line became non?consecutive after the 4 h water sorption.The different structural stabilities of the glue lines resulted in the different water resists.Specifically,the MUF glue was more water resist than the PF glue.The water distribution and structural deformation of the glue lines were dynamically visualized in this study.Finally,the mechanisms of water transportation between veneers were revealed.The results obtained from this study could be used in optimizing the processing technology and application approaches of wood?based panels.
作者
李万兆
陈玉瑜
梅长彤
LI Wanzhao;CHEN Yuyu;MEI Changtong(College of Materials Science and Engineering,Nanjing Forestry University,Nanjing 210037,China;Changzhou Vocational Institute of Textile and Garment,Changzhou 213164,Jiangsu,China)
出处
《林业工程学报》
CSCD
北大核心
2019年第5期29-33,共5页
Journal of Forestry Engineering
基金
江苏省自然科学基金(BK20170923)
江苏省高等学校自然科学研究项目(17KJB220003)
关键词
胶合板
胶层
结构变化
水分迁移
X射线断层扫描仪
plywood
glue line
structural change
water transport
X-ray computed tomography
作者简介
李万兆,男,副教授,研究方向为木质复合材料;通信作者:梅长彤,男,教授。E-mail:mei@njfu.edu.cn。
