Review of Thermoplastic elastomers
THERMOPLASTIC ELASTOMERS (TPE) are the materials which combine the characteristics of thermoplastic processibility and the physical properties of vulcanized rubbers.
At present TPEs on base of nearly all classes of polymeric compounds are known:
THERMOPLASTIC VULKANIZATES (TPV) are produced by mixing of polyolefin (PP/PE) mixtures and ethylene-propylene-diene rubber (EPDM) under conditions of dynamic vulcanization.
TPV is notable for excellent resistance to ozone and UV radiation, resistance to effects of different liquids and solvents and it has wide temperature range of performance (from minus 60 to 150°C), low shrinkage and stability of article sizes, resistance to impact loads, endurance to repeated bend, wide choice of offered materials, good recoverability after deformation.
STYRENE BLOCK COPOLYMERS (TPE-S) are produced by mixing of polyolefins (PE, PP) and styrene-butadiene-styrene (SBS) or styrene-ethylene-butylene-styrene (SEBS).
TPE-S structure on base of SBS is chemically unsaturated which makes it to be not resistant to UV, ozone effects and the upper temperature range of operation. In this connection the application range of TPE-S on base of SBS is limited.
TPE-S on base of SEBS are chemically saturated which increases strength to high temperature, ozone and UV effects.
The main advantage of this group of materials is wide range of operation temperatures, wide range of Shore A hardness, adhesion to hard plastics and availability of clear grades.
THERMOPLASTIC POLYOLEFIN ELASTOMERS (TPO) are the mixtures of polypropylene (PP) and ethylene-propylene-diene rubber (EPDM).
TPO is a little bit inferior to TPV in upper temperature range of operation and has less strength and recoverability after deformation. Thereby this class of material is peculiar for impact strength, higher frost resistance and resistance to effects of different liquid media.
The main normalization index determining the grade of thermoplastic elastomer is hardness which as a rule changes from 25, Shore A to 60, Shore D.
Thermoplastic elastomers are stable in the wide temperature range, are not inferior to natural and synthetic rubbers and in some cases are superior to them and can substitute them in production of industrial rubber articles. Thermoplastic elastomers also show good stability of properties at operation temperatures higher than admissible for rubbers.
Different mineral fillers, stabilizers and plasticizers can be introduced in thermoplastic elastomers, the same way as in usual rubbers. Having changed formulations of thermoplastic elastomers it would be possible to adjust their basic consumption qualities.
Thermoplastic elastomers can have the following set properties:
- High mechanical strength;
- High environment resistance;
- Resistance to UV, ozone and moisture effects;
- High flexibility and impact strength in wide temperature range;
- Higher oil and petrol resistance, excellent chemical stability;
- Excellent resistance at low temperature;
- Excellent wear resistance;
- Resistance to impact and alternating loads;
- Resistance to fatigue deformations, high fatigue strength;
- Small creep;
- Low values of residual compression deformation;
- Depending on the application it also has blushing or excellent gloss of surface as well as ability to be painted and lacquered.
Naturally the cost of thermoplastic elastomers is higher in comparison with rubber, however this is compensated with high capacities of their processing: Injection molding cycle takes much less time than long and labor-consuming stage of vulcanization of industrial rubber articles.
- Economy of raw materials due to secondary processing of production wastes. Possibility for complete automation of production process.
- Reduction of utilities costs during production of articles and some other factors prove the advantage of thermoplastic elastomers.
Moreover the industrial rubber articles are ageing with time losing elasticity and acquiring brittleness and fragility. Thermoplastic elastomers on the contrary keep all their properties of elasticity and acquire better properties of strength. And finally the expire period of thermoplastic elastomers as a raw material as well as articles is much longer in comparison with rubber and the gravity weight of thermoplastic elastomers is lower in comparison with rubber. The advantage of thermoplastics is possibility to perform the operation of butt-jointing, welding and adhesion of articles.
Thermoplastic elastomers can be transformed into articles by all traditional methods of plastics processing: injection molding, extrusion, blow molding, calendering and compacting. Besides thermoplastic elastomers can be processed using the methods characteristic for elastomers: rolling, calendering.