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properties against oxygen. It is melt-blended with a liquid polybutene oil plasticizer in an amount insufficient to render the plasticized elastomer tacky. If made tacky, enough 'de-tackifier' is used to allow the product to be formed into a removable seal. The TPE may be a conventional thermoplastic vulcanizate, or a block copolymer of a vinylaromatic compound (typically styrene) and a conjugated diene (typically butadiene or isoprene) or mixtures of these. The block may be a diblock, triblock or higher block, but the preferred polyblock copolymer is a triblock with styrene endblocks and a butadiene/isoprene mid-block. Preferably the diene mid-block is hydrogenated to provide a poly(lower) monoolefin mid-block. When the TPE is a TPV some, or all, of the mineral oil used to make the TPV processable also may be substituted with the polybutene plasticizer. The elastomeric product is particularly useful for sealing elements for containers in which foodstuffs and medical products must be preserved for a long period.
๐ SIMILAR VOLUMES
Piston ring
Change-over valve mechanisms are often assembled on a manifold base which contains a number of fluid inlet and outlet passages. These supply and discharge pressurised fluids from ports on the mechanism through separate pipes. A gasket is usually provided between the manifold base and the change-over