Rubber intrinsic defects

The values determined for the inherent flaws only represent effective sizes, corresponding to a given degree of stress concentration [289]. This stress concentration also depends on the shape of a crack (e.g., bluntness), as well as the dissipative capacity of the material itself [290]. While compounding variables such as crosslink density strongly affect the failure properties of rubber, their influence on the intrinsic defect size is more modest [287,288,291].The measured flaw size is unaffected by temperature [281], although it can vary with carbon black type... 

Rubber and Plastics News 27, No.ll, 12th Jan.1998, p.14-5 INTRINSIC DEFECT EFFECTS ON NR PERMEABILITY... 

Polymer matrix selection determines minimum membrane performance while molecular sieve addition can only improve membrane selectivity in the absence of defects. Intrinsically, the matrix polymer selected must provide industrially acceptable performance. For example, a mixed matrix membrane using silicone rubber could exhibit properties similar to intrinsic silicone rubber properties, O2 permeability of 933 Baiters and O2/N2 permselectivity of 2.1 (8). The resulting mixed matrix membrane properties would lie substantially below the upper boimd trade-off curve for gas permeability and selectivity. In contrast, a polymer exhibiting economically acceptable permeability and selectivity is a likely candidate for a successful polymer matrix. A glassy polymer such as Matrimid polyimide (PI) is an example of such a material because it exhibits acceptable properties and current technology exists for formation of asymmetric hollow fibers for gas separation (10). 

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