Thermal and thermo-oxidative ageing of an epoxy adhesive

The thermal and thermo-oxidative degradation of a structural epoxy adhesive based on TGDDM and cured with DDA and DDS has been studied using thermogravimetric techniques. Both dynamic, or non-isothermal, and isothermal heating modes have been used and ageing has been undertaken in air at atmospheric pressure, primary vacuum and low pressure nitrogen. Degradation and weight loss of the material occur in two principal stages. In the first stage, weight loss occurs independently of the environment used. In addition, the activation energies calculated by three methods are very close for ageing in the various media. We conclude that this stage corresponds to thermolysis. The second stage exists only in the presence of oxygen, the material remaining relatively stable in nitrogen. This thermo-oxidative process leads to virtually total disappearance of the material with time, leaving only fillers behind. (C) 2000 Elsevier Science Ltd. All rights reserved.