Abstract Load-bearing structural timber requires durable and reliable adhesive bonding. Hence manufacture is determined by strict regulations for instance regarding wood temperature specifications. This research investigates bonding at significantly lower substrate temperatures providing sufficient time for cure to ascertain whether appropriate bond strength can be achieved. Scarf joints were produced at different wood temperatures with melamine-urea-formaldehyde (MUF). Resin and hardener were applied on separate sides. Adhesive strength was verified by macroscopic testing of the bond strength and microscopic examination of the properties of the adhesive. Resulting tensile shear strength varied marginally for different temperatures even after water immersion. Penetration of the adhesive into the wood in fiber direction was deeper on hardener than on resin application side due to differences in viscosity with no dependence on temperature. Nanoindentation visualized adhesive penetration into the cell wall with increased hardness and reduced modulus of elasticity from unfilled cells to adhesive filled cells independent of temperature. The results indicate least influence of the substrate temperature at the time of adhesive application on the macro- and microscopic level permitting bonding at low temperatures, given that enough time for cure at sufficient temperature is allowed.

中文翻译：

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木材低温粘接强度及微观力学

摘要 承重结构木材需要耐用可靠的胶粘剂。因此，制造由严格的规定决定，例如有关木材温度规范。该研究调查了在显着较低的基材温度下粘合，从而提供足够的固化时间以确定是否可以获得适当的粘合强度。围巾接头是在不同木材温度下用三聚氰胺-脲-甲醛 (MUF) 制成的。树脂和硬化剂分别涂在不同的面上。粘合强度通过粘合强度的宏观测试和粘合剂性能的微观检查来验证。即使在浸水后，不同温度下产生的拉伸剪切强度也略有不同。由于不依赖于温度的粘度差异，粘合剂在纤维方向上对木材的渗透比在树脂应用侧更深。纳米压痕可视化粘合剂渗透到细胞壁中，从未填充的细胞到粘合剂填充的细胞的硬度增加，弹性模量降低，与温度无关。结果表明，如果允许在足够的温度下有足够的固化时间，则在允许在低温下粘合的宏观和微观水平上，施加粘合剂时基材温度的影响最小。纳米压痕可视化粘合剂渗透到细胞壁中，从未填充的细胞到粘合剂填充的细胞的硬度增加，弹性模量降低，与温度无关。结果表明，如果允许在足够的温度下有足够的固化时间，则在允许在低温下粘合的宏观和微观水平上，施加粘合剂时基材温度的影响最小。纳米压痕可视化粘合剂渗透到细胞壁中，从未填充的细胞到粘合剂填充的细胞的硬度增加，弹性模量降低，与温度无关。结果表明，如果允许在足够的温度下有足够的固化时间，则在允许在低温下粘合的宏观和微观水平上，施加粘合剂时基材温度的影响最小。