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. To accurately determine the relative performance of gaskets and O-rings made from different elastomer formulations, seals should be tested in a way that mimics the expected use conditions. Thankfully there are standardized methods to evaluate performance. For example, ASME BPE-2009 Appendix J discusses a method for evaluating hygienic seal performance after exposure to cyclic steam. This method is particularly helpful for understanding how a gasket would hold up under conditions typically experienced in bioprocess applications. The pictures below shows a James Walker Elast-O-Pure EP75B gasket compared to a typical USP Class VI EDPM gasket after exposure to 250 steam cycles. Excessive intrusion into the pipe lumen is obvious in the photo on the typical seal on the right.
Characterization of material purity and potential effects on production processes and the drug product itself is a much broader topic. Confirming that a material does not affect living cells is of critical importance to a bioprocess application. United States Pharmacopeia (USP) <87> and <88> Class VI (or the equivalent ISO standard) testingis the most common method for confirming biocompatibility. Extractable and other purity characterization methods are less standardized at this point but vital to understanding the potential product impact. Since extractable materials from elastomers either from processing aids or by-products of the curing process, would likely be organic in nature; total organic carbon (TOC) analysis is an effective means to determine the relative purity of an elastomer compound. Should identification and quantification of specific extractable species be needed, a complete extractable study would be required on the particular elastomer compound.
Regardless of the exact methods used to evalute performance and purity of a gasket or O-ring, the important thing to remember is that there is an inherent variation between elastomer compounds even made from the same base polymer. Data on specific elastomer compound/seal combination is necessary in order to truly understand the purity and performance of a gasket or O-ring in a given application.
Continue to the Evaluating Elastomer Purity Section.