Long-term performance accelerated ageing tests

The accelerated aging test should take into account the associated materials as well as the atmosphere that will be encountered in actual use, since they are also controlling factors. It is helpful to include materials of known performance against which to rate the new material, since this allows a check of controlling factors and further validates the extrapolation. Thus, existing data from long term tests may be of considerable value. 

The long-term performance of fibre reinforced cements is of great significance in the development and evaluation of new composites. An important practical tool for this purpose is accelerated testing in the laboratory, where the properties of the composites are determined before and after exposure to the accelerated ageing conditions. In order to develop an efficient test of this kind, it is necessary first to evaluate the physical and chemical processes that may lead to changes in properties in natural exposure, and then devise the means to accelerate them in laboratory-controlled tests. In view of the variety of processes which may lead to ageing, it is difficult to devise a universal test. An illustration of this problem is presented in Table 5.1 and In [33,43], which show that composites which perform well in one type of accelerated test may do poorly in another, and the critical test is different for the different composites. 

This method of interpreting accelerated ageing tests was also found to be applicable for predicting the improvement in long-term performance when using glass fibres of different composition [71,79]. Therefore, it is a valuable tool for development purposes as wel I as for the assessment of the quality of different commercial products. 

Attractive blends for PEMs with high proton conductivity have been made from sulfonated PES, PSU, polyetherketone (PEK), PEEK or poly(2,6-dimethyl 1,4-phenylene ether) (PPE) blended with polybenzimidazole (PBI) or polyetherimide (PEI). To preserve the desired PEM performance, the blends are often crosslinked by radiation, chemical reaction of ionic interactions. For long-term PEM applications it is important that membranes resistance to mechanical, chemical and thermal degradation is maximized. Accelerated aging tests should follow several membrane functionalities, for example conductivity, membrane integrity and permeability. The tests should also identify a possible cross-correlation of effects, namely stress on thermal and/or chemical degradation. 

Develop time- and geometry-based scaling techniques to relate laboratory tests to the real performance of a structure, and accelerated test methods for simulating long-term ageing. 

Dispersants are used so infrequently in some locations that stockpiles are sometimes in place for as long as 20 years before use. In Great Britain, the government studied the aging of dispersants by testing effectiveness [JJO]. The laboratory performed both long-term tests and short-term accelerated tests in various containers and at 20 and 30 °C. The tests did not show dispersant deterioration as indicated by the effectiveness values. 

The process is adapted for thermoplastics and elastomers. For newly developed materials, sufficient long-term aging experience will not be available. In such cases, accelerated laboratory, exposure, and experimental production tests are performed parallel to development. 

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