Poly aging tests

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. 

So far, the phenomena discussed pertain to isothermal ageing after a quench (rapid cooling) from above to below Tg. Under such circumstances, ageing always runs in the same direction (increasing retardation times). Peculiar phenomena occur, however, when after a period of ageing at temperature T, the material is heated to a final temperature between T and Tg T < Too < Tg). A good example is poly(vinyl chloride) (PVC) with Tg 80 °C. Struik (1978) compared two samples for which the ageing times at T = 20 °C differ by a factor of 18. When tested at 20 °C, their creep properties differed considerably, but all differences disappeared when the tests were done at 50 °C. 

Around 8% bromine content in the final PBT compound is sufficient to achieve the V-0 test rating for all types of brominated flame retardants, but some affect the physical and mechanical properties of the resultant materials more than others. Polymeric brominated styrene additives would be preferred in glass-filled compounds. Brominated polystyrene, such as Saytex HP-7010 from Albemarle Corp. and poly(dibromostyrene) are such materials. They retain excellent properties after heat ageing. High impact strengfti and excellent electrical properties are especially noted for HP-7010 due to the additive s high purity and low aliphatic halogen content. 

If the material becomes unserviceable before blue wool Standard 3 starts to fade visibly, it is placed in Feller s class C (Section 2.7) (Feller, 1978). If the material is more stable than Standard 3 but deteriorates before Standard 6 starts to fade, it is placed in class B. Those materials that survive as well or better than Standard 6 are placed in class A. Feller has suggested some standard polymer materials that can be compared to the material under test when light-ageing these are Paraloid B-72 for class A and poly(n-butyl methacrylate) (Elvacite 2044) for class B. 

Wang, N., Isothermal Physical Aging Characterization and Test Methodology for Neat and Nanotube-Reinforced Poly(Methyl Methacrylate) (PMMA) Near the Glass Transition Temperature, MS Thesis, University of Louisville, 2007... 

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