Since elastomer (rubber) compounds are proprietary formulations controlled by the supplier, there is considerable variation between formulations even when made from the same base polymer. In order to characterize the differences, each formulation should be tested by a means that will provide good detectability of the potential extractables. Due to the basic composition and processing steps of elastomers, any extractable materials, either from processing aids or by-products of the curing process, would likely be organic in nature. Consequently, quantifying the level of total organic carbon (TOC) would provide an effective means for determining the purity of an EPDM elastomer.
While there is no universally accepted method for evaluating TOC extractables, there are several standardized extraction methods. USP <381> is a good example. This method calls for a 2 hour extraction at 121oC. The resultant extractant can then be analyzed by converting the TOC to carbon dioxide by acidification and chemical oxidation with sodium persulphate. The liberated carbon dioxide can then be measured by infrared.
From the data provided in the table, it is clear that TOC analysis provides an effective means for evaluating the relative purity of an elastomer. A stepwise improvement in purity is evident with the James Walker Elast-O-Pure EP75 Black material. The lower TOC level would also indicate an optimized compounding and moulding process which would lead to better sealing performance. When evaluating purity of various elastomers for bioprocess applications, consider TOC analysis as an effective means for evaluating purity and possibly performance of an elastomer.