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Understanding Elastomers and Their Effect on Seal Performance & Purity

Understanding the performance and purity of components used in the manufacture of biopharmaceutical products is of critical importance.  This is particularly true for elastomeric (rubber) components like sanitary gaskets and O-rings.  Unlike metals that are produced to a specific composition standard (e.g. 316L), elastomers are typically proprietary formulations controlled by the supplier.  The compounds are referred to by their base polymer (i.e. EPDM, Silicone, etc) however the polymer may only represent a minor component of the overall mixture and indicates nothing about the cure method or processing conditions.  In order to truly understand the properties of elastomers and how they affect gasket or O-ring performance, a basic understaning of elastomer composition is helpful.

Elastomer Composition

Elastomer compounds are a complex mixture of polymer, curatives and various fillers. The polymer is the backbone of any elastomeric compound.  Polymers often used by the industry include ethylene-propylene-diene (EPDM), silicone and fluoroelastomers (FKM, Viton®).  A common filler is carbon black which gives most elastomers their black color but is also used to impart good mechanical properties.  Clays and talc can also be used but usually as a cost reduction exercise and generally do not improve the material properties.  Elastomers require a curing (cross-linking) process in order to give the desired properties.  Silicone curing methods include peroxide and platinum curing processes.  EPDM, FKM and other organic rubbers employ either a peroxide or sulphur method.  In Biopharmaceutical applications, sulphur cured materials should be avoided due to purity reasons.  Other additives such as waxes and plasticizers are often added to improve the processing characteristics and mouldability of the elastomer compound.  These materials are prone to migration and leaching out of the material with time and are often referred to as ‘bloom.’  Once all the ingredients are mixed (compounded) into the final elastomer formulation, the compound is then formed into gaskets or O-rings by a compression, transfer or injection moulding process.  Obviously since there is such latitude in composition and processing, performance can vary considerably between gaskets and O-rings made from different formulations of the same polymer type. 

Continue to the Evaluating Gasket and O-ring Performance Section.