This report is an output from the Weathering of Elastomers and Sealants project, which forms part of the UK government's Department of Trade and Industry's Degradation of Materials in Aggressive Environments Program.
A long-term natural ageing program was started in 1958 when 19 rubber compounds were exposed at 3 locations. The final sets of test pieces were withdrawn in 1998 giving a total of 40 years of natural ageing. The results of the physical tests carried out at intervals over the period were published in 2000 by Rapra in 'Natural Ageing of Rubber-Changes in Physical Properties over 40 Years'.
This report details the results of accelerated heat ageing studies undertaken on re-mixed samples of those materials studied for the natural ageing study and on the 20 new compounds chosen to represent polymers not available in 1958 and to reflect changes in compounding practice.
In addition to those properties studied for the artificial weathering exposures, compression set and dynamic properties were also measured.
The results of all these tests are again presented graphically and tabulated, allowing the rate of deterioration of properties to be followed. As the number of graphs are too voluminous to be reproduced in total, those for hardness, tensile strength, elongation at break and 100% modulus are given.
Extrapolation of the accelerated results to longer times at lower temperatures was attempted by two approaches - the Arrhenius relation and the WLF equation - and compression set results analyzed using a dose rate equation. Predictions are made for change at 23°C and 40°C to equate to long-term natural ageing under temperate and hot dry conditions.
2.1 Original Materials
2.2 New Materials
3. Preparation of Test Pieces
4. Physical Tests
5. Exposure of Test Pieces
6.3 Prediction of Natural Ageing
7.1 Change with Time
7.1.4 Tensile Strength
7.1.5 Elongation at Break
7.1.7 Compression Set
7.2.4 Tensile Strength
7.2.5 Elongation at Break
7.2.7 Compression Set
7.2.8 Choice of Analysis Method
7.2.9 Effectiveness of the Predictions