Rubber-thermoplastic elastomer of the third generation.

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What kind of material is a thermoplastic elastomer? Due to differences in definitions of thermoplastic elastomers in various articles, many readers do not understand how these elastomers differ. In fact, they cannot be carefully distinguished. Don't worry. , this article will help you re-understand what thermoplastic elastomers are.

1. Thermoplastic elastomer

Thermoplastic elastomer (thermoplastic elastomer) is a new type of polymer material between rubber and resin, and its hardness range is shown in Figure 1. Because it has a multi-phase structure (soft segment and hard segment), it can not only replace part of rubber, but also modify plastic. It is third generation rubber after natural rubber and synthetic rubber. This material has elasticity of rubber at room temperature, and has properties of high elasticity, aging resistance and oil resistance of traditional crosslinked vulcanized rubber; At same time, it has plasticity of plastic and is easy to mold and process. Thus, thermoplastic elastomer materials have become latest materials to replace traditional rubber.

Figure 1. Hardness range of thermoplastic elastomer

Thermoplastic elastomers can be divided into two categories based on their composition, namely block copolymers (styrene, copolyester, polyurethane, polyamide) and thermoplastic/elastomer blends and alloys (thermoplastic polyolefins and thermoplastic vulcanizates). We generally divide thermoplastic elastomers into 6 types based on price and performance: styrenic block copolymer (TPE), polyolefin blend (TPO), elastomeric alloy (EPDM), thermoplastic polyurethane (TPU), thermoplastic copolyesters and thermoplastic polyamides.

Here we want to reiterate that TPE can be thought of as a general term (big concept) for all thermoplastic elastomers, and TPU is a thermoplastic polyurethane elastomer. From this level, TPU is just one type of TPE thermoplastic elastomer. We usually talk about TPE referring to an elastomer based on mixing and modifying SBR styrene elastomers (mainly SEBS, SBS). Now concept of TPE is clear.

Figure 2. Aggregation state and phase structure of TEP

If TPE is classified according to preparation method, it can be classified according to following table 1-1. According to classification, several commonly used TPEs will be introduced in following section.

Table 1-1 TPE classification

Second classification of thermoplastic elastomers

2.1 Styrene based elastomers (SBC)

Styrene-based SBS thermoplastic elastomer is most productive kind of SBS, is a triblock copolymer synthesized from styrene and butadiene as monomers, is closest in apparent properties to various TPEs at room temperature. SBS grades can be divided into two types: linear type and star type according to molecular shape and structural shape, and can be divided into oil-filled type and non-oil-filled type in terms of use.

In recent years, a number of modified products have appeared, such as SEBS and SEPS, made from SBS and SIS by saturated hydrogenation, among which SEBS (styrene-ethylene-butadiene-styrene). It is a multi-purpose new type of thermoplastic elastomer, performance of which in practical application is much higher than that of conventional linear and star SBS, and working temperature can reach 130°C.

2.2 Polyolefin thermoplastic elastomer

Polyolefin thermoplastic elastomers are typically low molecular weight copolymers such as ethylene and octene. Olefin TPE uses crystalline PE or PP as hard segment and EPDM and EPM as soft segment. Mixing rubber (including partially cross-linked forms) forms TPO. Olefin-based thermoplastic elastomers can be classified into three types based on different production methods: TPO, TPV, and POE.

Table 3-1 TPE Types and Compositions

2.3 Thermoplastic polyurethane elastomer (TPU)

TPU thermoplastic polyurethane elastomer has been described in detail in previous articles. Its processing methods include injection molding, extrusion molding, blow molding and calendering. Its basic structure is shown in figure 3 below.

Fig. 3. Structural diagram of TPU

3. Conclusion

Thermoplastic elastomers have entered a period of rapid development. Currently, industrially produced TPEs (thermoplastic elastomers) in world include: styrene (SBS, SIS, SEBS, SEPS), olefins (TPO, TPV), alkenes. (TPB, TPI); polyurethanes (TPU); esters (TPEE); amides (TPAE); organofluorine compounds (TPF); In near future, thermoplastic elastomers will be applied in all areas of our lives in all areas of resins.

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