Weak boundary layers on wood surfaces
Weak boundary layers on wood surfaces
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木材表面的弱边界层
DOI：
10.1163/156856100742168
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发表时间：
2000
影响因子：
2.3
通讯作者：
I. Johansson
中科院分区：
文献类型：
--
作者：
M. Stehr;I. Johansson
本文提出了弱边界层概念在木材粘附科学中的应用，并对这一概念作了一般性的推广。对化学弱边界层（CWBL）和机械弱边界层（MWBL）进行了区分。提出了CWBL和MWBL的定义。在木材上，CWBL主要是由机加工后迁移到木材表面的提取物引起的，而MWBL主要是由机加工操作本身或由表面处的纤维降解引起的，实际上主要是由自然（UV）光照射引起的。用扫描电镜（SEM）和环境扫描电镜（ESEM）研究了软木锯开的端纹和刨平的侧纹表面。锯开和刨平的木材表面都变形到0.1-0.2 mm的深度，以至于人们不能期望在表面上具有与完整木材相同的强度。当胶层（尤其是端纹接头）或涂层暴露于应力时，压碎和损坏的表面可能包含失效起始点。此外，这种压碎和损坏的表面可以预期为粘合剂和涂料渗透到材料中并锚到完整木材的屏障。显微切片和锯切的端纹表面之间的比较表明，损坏的纤维似乎在某种程度上，以改善胶接性能，使用传统的胶水。对此原因进行了讨论。
Adoption of the weak boundary layer (WBL) concept in wood adhesion science and a general extension of the concept are suggested. A distinction is made between a chemical weak boundary layer (CWBL) and a mechanical weak boundary layer (MWBL). Definitions of both CWBL and MWBL are proposed. On wood, a CWBL is caused mainly by extractives migrating to the wood surface after machining, whereas an MWBL is caused mainly by the machining operation itself or by degradation of the fibres at the surface, in practice mainly by natural (UV) light irradiation. Sawn endgrain and planed side-grain surfaces of softwoods have been studied by scanning electron microscopy [SEM and environmental SEM (ESEM)]. Both sawn and planed wood surfaces are deformed to a depth of 0.1-0.2 mm to such an extent that one cannot expect the same strength at the surface as in the intact wood material. The crushed and damaged surface can be expected to contain failure initiation sites when the glueline, especially in an end-grain joint, or a coating is exposed to stresses. Furthermore, this crushed and damaged surface can be expected to be a barrier for adhesives and coatings to penetrate into the material and anchor to intact wood material. A comparison between microtomed and sawn end-grain surfaces has shown that the damaged fibres seem, to some extent, to improve the glue joint performance, using a conventional glue. Reasons for this are discussed.