Ruíz de Azúa Oiane, Agulló Núria, Arbusà Jordi, Borrós Salvador
Grup d'Engineyeria de Materials (GEMAT), Institut Quimic de Sarria (IQS), Universitat Ramon Lull, 08017 Barcelona, Spain.
Sailing Techcnologies, S.L., 08017 Barcelona, Spain.
Polymers (Basel). 2023 Jan 4;15(2):252. doi: 10.3390/polym15020252.
The glass transition temperature (Tg) of room-temperature curing epoxy adhesives is limited by the temperature used during curing. It is already known that the excess of epoxy groups can undergo a homopolymerization reaction initiated by tertiary amines at elevated temperatures, resulting in an increase in Tg. However, there is no evidence of this reaction occurring at room temperature. In the present work, the influence of formulation stoichiometry on Tg and mechanical properties was investigated. Dynamomechanical, rheological and mechanical properties of epoxy adhesives were determined by DSC, DMA, rheometer and tensile and shear strength testing. It has been probed that an excess of epoxy resin combined with a complex curing system composed of a primary amine, a polymercaptan and a tertiary amine leads to an increase in Tg up to 70 °C due to the homopolymerization reaction that takes place at room temperature. However, as the excess of epoxy resin is increased, gel time becomes slower. Regarding mechanical properties, it has been proven that an excess of epoxy resin provides a tighter and tougher material but maintains flexibility of the stoichiometric formulation, which is meant to enhance the resistance to impact-type forces, thermal shock and thermal cycling.
室温固化环氧胶粘剂的玻璃化转变温度（Tg）受固化过程中使用的温度限制。已知过量的环氧基团在高温下可发生由叔胺引发的均聚反应，导致Tg升高。然而，没有证据表明该反应在室温下发生。在本工作中，研究了配方化学计量对Tg和力学性能的影响。通过DSC、DMA、流变仪以及拉伸和剪切强度测试来测定环氧胶粘剂的动态力学、流变和力学性能。已经探究发现，由于在室温下发生的均聚反应，过量的环氧树脂与由伯胺、多硫醇和叔胺组成的复合固化体系相结合会导致Tg升高至70°C。然而，随着环氧树脂过量的增加，凝胶时间变慢。关于力学性能，已证明过量的环氧树脂能提供更紧密、更坚韧的材料，但仍保持化学计量配方的柔韧性，这旨在增强对冲击型力、热冲击和热循环的抗性。
