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Influence of high-temperature and high-humidity aging on the material and adhesive properties of addition curing silicone adhesives
International Journal of Adhesion and Adhesives ( IF 3.4 ) Pub Date : 2021-09-01 , DOI: 10.1016/j.ijadhadh.2021.102980
Artur Kochanke 1, 2 , Katharina Krämer 3 , Christoph Üffing 1 , Andreas Hartwig 2, 4
Affiliation  

Silicones are commonly used as sealants when high-performance materials are required due to harsh environmental conditions. To ensure a proper sealing function, the buildup of adhesion to the adherends is a prerequisite that is often addressed by the addition of adhesion promoters. However, the investigation of the fundamental adhesion mechanisms of silicones has been widely neglected. This work focuses on adhesive bond properties with aluminum adherends without the usage of adhesion promoters. The influence of high-temperature and high-humidity aging on the adhesive bond and material properties is examined.

For this purpose, we formulated an addition curing silicone adhesive with a known composition. Aging took place for up to 56 d at different temperatures ranging from room temperature to 150 °C. In addition, we examined the influence of moisture by applying high-humidity conditions (85 °C/85% relative humidity). Changes in bulk material properties were characterized by stress at break, strain at break, Shore A hardness and swelling degree. Moreover, Fourier-transform infrared (FTIR) spectroscopy provided information about the chemical processes. The adhesive properties were determined using lap-shear joints.

At high-temperature aging, the strain at break decreases while the hardness of the bulk material increases. A lower degree of swelling suggests an increasing cross-linking density. At the same time, lap-shear strengths increase and cohesive fracture patterns indicate a substantial buildup of adhesion. The samples aged under high-humidity conditions show a more complicated behavior. The increase in cross-linking density proceeds slower compared to high-temperature conditions (130 °C and 150 °C) but reaches higher values after 56 d. Lap-shear strengths tend to be lower compared to high-temperature storage and are accompanied by a significant amount of adhesive failure. FTIR spectroscopy reveals reactions of the residual hydrosiloxane groups of the cross-linking agent. However, these reactions are insufficient to fully explain the observed behavior. Therefore, reactions of the siloxane backbone are suggested.

Although no specific adhesion promoters were used, high-temperature conditions enabled a substantial adhesion buildup of addition curing silicones on aluminum adherends under dry conditions. In contrast, humid conditions disturb adhesion buildup and are rather unfavorable for adhesion.



中文翻译:

高温高湿老化对加成固化有机硅胶粘剂材料及胶粘性能的影响

当由于恶劣的环境条件需要高性能材料时,有机硅通常用作密封剂。为了确保适当的密封功能,对被粘物的粘附力的积累是一个先决条件,通常通过添加粘附促进剂来解决。然而,对有机硅基本粘附机制的研究却被广泛忽视。这项工作的重点是在不使用粘合促进剂的情况下与铝被粘物的粘合粘合性能。检查了高温和高湿老化对粘合剂粘合和材料性能的影响。

为此,我们配制了一种具有已知成分的加成固化有机硅粘合剂。在从室温到 150 °C 的不同温度下,老化时间长达 56 天。此外,我们通过应用高湿度条件(85 °C/85% 相对湿度)检查了水分的影响。散装材料特性的变化以断裂应力、断裂应变、肖氏 A 硬度和溶胀度为特征。此外,傅里叶变换红外 (FTIR) 光谱提供了有关化学过程的信息。使用搭接剪切接头确定粘合性能。

在高温时效下,断裂应变降低,而块状材料的硬度增加。较低的溶胀程度表明交联密度增加。与此同时,搭接剪切强度增加,内聚断裂模式表明粘附力的大量积累。在高湿度条件下老化的样品表现出更复杂的行为。与高温条件(130 °C 和 150 °C)相比,交联密度的增加进行得更慢,但在 56 天后达到更高的值。与高温储存相比,搭接剪切强度往往较低,并且伴随着大量的粘合剂失效。FTIR 光谱揭示了交联剂的残留氢硅氧烷基团的反应。然而,这些反应不足以完全解释观察到的行为。

虽然没有使用特定的粘合促进剂,但高温条件能够在干燥条件下使加成固化有机硅在铝被粘物上产生大量的粘合力。相比之下,潮湿条件会干扰粘附力的形成并且对粘附力相当不利。

更新日期:2021-09-07
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