Ultra-Accelerated Thermal Ageing Tests

Isothermal testing of polymer ageing requires long-term exposure if realistic results are to be obtained, which means a time-consuming and hence expensive exercise, which may have to be repeated many times over many different conditions. Rates of ageing can be accelerated by increasing the temperature of tests or by using a more aggressive environment, but then results must be extrapolated to working conditions, assuming that the same mechanisms still apply. In this paper, we demonstrate that a slow thermal ramp technique, similar to thermo-gravimetric analysis, allows the qualitative and, in some cases, quantitative assessment of ageing to be made in a relatively short time, 15 to 20 days, compared to up to 2 years for isothermal tests. We will illustrate the method in relation to recent work on the ageing of Kraft electrical insulation paper in insulating oil and compare results from isothermal and thermal ramp experiments. In this case, Degree of Polymerisation (DP) was used as a key indicator of degradation.