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Thermoplastic elastomers: processing features  #11 (93), 2010

Vitaliy Kalinin

Thermoplastic elastomers combining properties of plastics and rubber are conquering the market more and more actively. Equipment manufacturers offer to their customers TPE processing extruders and injection molding machines including those for coextrusion and multicomponent molding. Our expert’s article speaks about advantages of such materials as well as features of TPE processing by various methods.

High performance and elasticity

The market of thermoplastic elastomers (TPE) grows with every passing day. Industrial laboratories permanently conduct researches in creating materials with unique properties, develop formulations for specific articles meeting both processing and customer requirements.
Thermoplastic elastomers combine elasticity of rubber and performance of thermoplastics. Such properties provide the following advantages:
– opportunity of processing with various methods (extrusion, injection molding, vacuum and extrusion blow molding;
– as materials are produced as pellets they are ready to be processed with no additional operations;
– no halogens in formulations allow to keep workability of molding tool and improve environment properties;
– depending on percentage of base elements in a thermoplastic elastomer formulation it is possible to achieve a wide range of hardness (Shore A hardness 10-90, Shore D hardness 35-65), melt flow rate (0.1-100 g/10 min) and also low mass fraction (0.89-1.2 g/cm);
– wide operating temperatures range (-55 to +135°С);
– resistance to UV radiation, ozone, detergents, alkalescences and subacids, oils and petrol.
– adhesion to PP, PS, ABS, PA-6, PA-66, SAN, PC, ABS/PC and other polymer materials allows to apply coextrusion, multicomponent injection molding as well as use TPE as additive in order to increase impact strength and resistance to low temperatures;
– opportunity to produce articles with unique properties (transparent, flame resistant, porous, soft-touch, hygienically compatible, variously colored and odor-free ones).

Styrene-based TPE
Styrene-based thermoplastic elastomers are produced with styrene-butadiene-styrene block copolymers (SBS) or styrene-ethylene-butylene-styrene block copolymers (SBES) and various fillers, masterbatches and stabilizers.
Unsaturated SBS blocks provide blends with higher sensitivity to UV light and significantly decrease upper margin of operating temperatures range. That is why application area of such TPE is limited. Generally they are used in footwear industry and for manufacturing flexible components of home appliances, handles of manual tools, wheels. Also these materials can be added into polyolefin in order to improve their impact strength and resistance to low temperatures.
Unlike SBS, SEBS-based thermoplastic elastomer has stable structure allowing to increase resistance to high temperatures, ozone, UV light and aggressive environments. SEBS-based blends are widely applied in technical components where high physical and mechanical properties and functional characteristics are the key factors.
They are applied in production of such articles as automotive floorings, corrugated tubes, protectors and bushings, air ducts and window sealings, soft interior components, anti-vibration components, drainage and garden hoses and fittings, in-house door and window sealings and refrigerators.

TPE processing equipment
As thermoplastic elastomers processing does not require curing, standard injection molding machines can be used. One may apply general-purpose screw designed for polyolefin processing with L/D 20:1 and 2.5:1-3.5:1 compression rate.
For TPE extrusion it is possible to use standard equipment designed for polyolefin and PVC processing. Long extruders with L/D 20:1 and 2.5:1-4:1 compression rate are preferable. Whereas barrier screws are not essential to achieve complete melt homogenization such screws contribute to improved material quality.
TPE are thermally stable materials allowing not to perform cleaning of cylinder in case of shutdowns.
The leading manufacturers of processing equipment have brought these new materials to notice long ago and now offer extruders and injection molding machines including ones for coextrusion and multicomponent molding designed for TPE processing.
Furthermore the market witnessed some novelties: hybrid extrusion lines producing two or three-component profiles consisting of rubber and TPE (for example solid TPE + foamed TPE + EPDM rubber).

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