According to Wikipedia, Elastomers are usually thermosets (TPV) but may also be thermoplastic (SEBS). TPV polymer chains cross-link during curing while SEBS forms physical cross-linking sites at room temperature. The molecular structure of elastomers can be imagined as a 'spaghetti and meatball' structure, with the meatballs signifying cross-links. The elasticity comes from their ability to return to their original shape after being deformed from an applied stress. Without cross-linking the applied stress would result in a permanent deformation.
(TPE-S) SBS is based on two-phase block copolymers with hard styrene segments and soft Butadiene mid-blocks. Commonly used in footwear, adhesives, bitumen modification and lower- specification seals and grips, where resistance to chemicals and aging a lower priority. When hydrogenated, SBS becomes SEBS, as the elimination of the C=C bonds in the butadiene component generated ethylene and butylenes mid-block. SEBS is exhibits much improved heat resistance, mechanical properties, chemical resistance, and weatherability. Learn more about SEBS
These materials are blends of polypropylene (PP) and un-cross-linked EPDM rubber, in some cases a low degree of cross-linking is present to boost heat resistance and compression set properties. Popular in applications where increased toughness is required. The most successful applications are found in the high end of the hardness scale, typically >80 Shore A and with limited elastomeric properties.
With new catalyst technology it is now possible to blend the EPDM and PP in a reactor making these types of TPEs available from major polymer manufacturers (see section on Vistamaxx). While becoming increasingly popular, there is still a market for custom mechanical blended TPE-O
Compounds of PP and EPDM rubber that have been dynamically vulcanized during the compounding step. The provide an improved properties over the TPE-O category. They have seen strong growth in EPDM-replacement for automotive seals, pipe seals, and other applications where a heat resistance of up to 120˚C is required. Shore hardness values range typically from 45A to 45D. New TPE-Vs now hitting the market are based on engineering plastics blended with high performance elastomers, and can offer greatly improved heat and chemical resistance.
These materials can be based on polyester or polyether urethane types and are used in applications where a product requires excellent tear strength, abrasion resistance, and flex fatigue resistance. Examples include shoe soles, industrial belting, ski boots, and wire and cable. Hardness is restricted to the high end of the Shore A scale, typically >80 Shore A.
Used where increased chemical resistance and heat resistance up to 140˚C are needed thermoplastic copolyesters also exhibit good fatigue resistance and tear strength and so are used in automotive applications such as blow moulded boots and bellows, wire and cable, and industrial hose applications. Again hardness is restricted to the high end and is typically between 85A to 75D.
These products offer the good heat resistance, have good chemical resistance and bonding to polyamide engineering plastics. Their applications include cable jacketing and aerospace components.