Classification And Analysis of Thermoplastic Elastomers

Thermoplastic elastomer is an environmentally friendly low-carbon composite material that possesses the characteristics of rubber (high elasticity, compression permanent deformation, etc.), as well as the processing characteristics of plastic (simple process). In most regions, the abbreviation TPE is commonly used to refer to thermoplastic elastomers. Another theory is that TPE is the general term for thermoplastic elastomers, TPU is thermoplastic polyurethane, TPV vulcanized thermoplastic elastomers, and TPR is generally considered as shoe sole material in China.

 

TPE has environmental, non-toxic, and safe properties, as well as excellent coloring, soft touch, weather resistance, fatigue resistance, and temperature resistance. Its processing performance is superior, and it can be recycled to reduce costs. It can be used for secondary injection molding, coated and bonded with matrix materials such as PP, PE, PC, PS, ABS, or formed separately. TPE (Thermoplastic Elastomers) that have been industrialized in the world include styrene (SBS, SIS, SEBS, SEPS), olefins, dienes, vinyl chloride, aminoesters (TPU), esters (TPEE), amides, organofluorine, organosilicon, and ethylene, covering almost all fields of synthetic rubber and resin today. Today, Xiaou will first introduce some commonly used "TPE" materials.

Thermoplastic Elastomer (TPE)

Generally referred to as "TPE" material in China, it belongs to the category of styrene based thermoplastic elastomers. Styrene TPE (also known as TPS abroad) is a block copolymer of butadiene or isoprene with styrene, with properties similar to SBR rubber.

Its advantages are high elasticity of rubber and the ability to be processed through injection molding; Environmentally friendly, non-toxic and safe, with excellent coloring properties, soft touch, weather resistance, fatigue resistance and temperature resistance, superior processing performance, no need for vulcanization, can be recycled to reduce costs, can be used for secondary injection molding, and can be coated and bonded with matrix materials such as PP, PE, PC, PS, ABS, or formed separately.

The biggest problem with SBS and SIS is poor heat resistance, and the operating temperature should not be too high. Meanwhile, its strength, weather resistance, oil resistance, and wear resistance cannot be compared to rubber.

Countries such as the United States and Europe have made a series of performance improvements to it, including SBS and SIS saturated hydrogenated SEBS and SEPS. SEBS (using BR hydrogenation as the soft chain segment) and SEPS (using IR hydrogenation as the soft chain segment) can significantly improve the impact strength, weather resistance, and heat aging resistance.

Polyurethane thermoplastic elastomer (TPU)

Polyurethane TPE is a thermoplastic polyurethane rubber, abbreviated as TPU, which is a combination of polyurethane hard chain segments reacting with isocyanates and polyester or polyether soft chain segments.

Advantages: TPU has excellent mechanical strength, wear resistance, oil resistance, and flexural flexibility, especially the most outstanding wear resistance; Temperature resistance: -30-120 ℃.

Disadvantages: Poor heat resistance, hot water resistance, and compression resistance, easy yellowing of appearance, easy adhesion to molds, precise processing technology requirements, and high processing costs.

Thermoplastic elastomer dynamic vulcanized rubber (TPV)

Dynamic full vulcanization: refers to the process in which the rubber phase undergoes chemical crosslinking under the action of a crosslinking agent during the melt blending of thermoplastic resin and rubber, and is sheared and broken into a large number of micrometer sized crosslinked rubber particles through strong mechanical shear, which are dispersed in the continuous phase of thermoplastic resin.

When PP is used as the hard chain segment and EPDM is used as the soft chain segment for melt blending, a crosslinking agent is added to vulcanize it. The fully vulcanized EPDM crosslinked rubber particles are fully dispersed in the PP matrix at micrometer scale (less than 1 micrometer) using mechanical high shear forces such as internal mixers and screw machines.

The characteristics of TPV

TPV has the heat resistance and low compression deformation properties of vulcanized rubber;

Excellent processing performance: It can be processed using thermoplastic processing methods such as injection and extrusion, which is efficient, simple and easy to operate, without the need for additional equipment, with high fluidity and low shrinkage rate.

The easy processing properties of TPV without vulcanization shorten the rubber industry production process by 1/4, save energy consumption by 25% to 40%, and improve efficiency by 10-20 times.

Lightweight (0.90-0.97), uniform appearance quality, high surface grade, and good hand feel.

TPV can be used normally from -60 ℃ to+135 ℃; When not under load, it can withstand high temperatures up to+150 ℃.

Wide range of soft and hard applications, ranging from 25A to 70D;

The advantage of easy dyeing greatly increases the degree of freedom in product design.

Green and environmentally friendly, recyclable, with no significant performance degradation after six repeated uses

TPV has excellent ozone and weather resistance;

TPV has dynamic fatigue resistance, excellent weather resistance, and good wear resistance;

Good elasticity and resistance to compression deformation, with environmental and aging resistance equivalent to EPDM rubber.

Polyester thermoplastic elastomer (TPEE)

Thermoplastic polyester elastomer, abbreviated as TPEE, is a type of linear block copolymer containing PBT (polybutylene terephthalate) polyester hard segment (crystalline phase) and aliphatic polyester or polyether (amorphous phase) soft segment. TPEE belongs to high-performance engineering grade elastomers, which have advantages such as high mechanical strength, good elasticity, impact resistance, creep resistance, cold resistance, bending fatigue resistance, oil resistance, chemical resistance, and solvent corrosion. It has good processability and can be filled, reinforced, and alloyed for modification. It has been widely used in automotive components, hydraulic hoses, cables and wires, electronic appliances, industrial products, cultural and sports products, biological materials, and other fields.

Physical and chemical properties of TPEE

By adjusting the ratio of soft and hard segments, the hardness of TPEE can vary from Shore D32 to D80, and its elasticity and strength are between rubber and plastic. Compared with other thermoplastic elastomers (TPEs), TPEE has a higher modulus under low strain conditions than other TPEs with the same hardness. When modulus is an important design condition, using TPEE can reduce the cross-sectional area of the product and reduce material usage.

Compared with polyurethane elastomers (TPU), TPEE has much higher compression modulus and tensile modulus. When TPEE and TPU with the same hardness are used to make the same part, the former can withstand larger loads. Above room temperature, TPEE has a high bending modulus, making it suitable for making cantilever beams or torque type components, especially suitable for making high-temperature components. TPEE has low tenderness and good smoothness, and its low-temperature notch impact strength is superior to other TPEs. Its wear resistance is comparable to TPU. TPEE has excellent fatigue resistance, combined with high elasticity, making it an ideal material for multiple cyclic load conditions, suitable for making gears, rubber rollers, flexible couplings, belts, etc.

TPEE has excellent heat resistance, with higher hardness indicating better heat resistance. The usage temperature of TPEE is very high, which can adapt to the baking temperature of automotive production lines (150-160 ℃), and it has minimal mechanical performance loss at high temperatures. When used above 120 ℃, the tensile strength of TPEE is much higher than that of TPU. In addition, TPEE also has excellent low-temperature resistance performance. The brittleness point of TPEE is below -70 ℃, and the lower the hardness, the better the cold resistance. Most TPEE can be used for a long time at -40 ℃. Due to its balanced performance at high and low temperatures, TPEE has a very wide operating temperature range and can be used at -70-200 ℃.

TPEE has excellent oil resistance and can withstand most polar liquid chemical media (such as acids, bases, amines, and diol compounds) at room temperature. Its resistance to chemicals increases with the increase of its hardness. TPEE has good anti swelling and anti permeation properties for most organic solvents, fuels, and gases, and its permeability to fuel is only 1/3-1/300 of that of oil resistant rubbers such as chloroprene rubber, chlorosulfonated polyethylene, and nitrile rubber.

Conclusion

At present, there is no unified name for thermoplastic elastomers, and it is customary to use English acronyms. For the sake of uniformity, TPE or thermoplastic elastomers are referred to.

(1) TPE=TPR, is a general term for all thermoplastic elastomers and thermoplastic rubbers, representing styrene based elastomers in China;

(2) The styrene elastomer TPE (SBS, SEBS, SIS matrix) and dynamic vulcanized rubber TPV (EPDM+PP-X) in the United States, Taiwan, China and other regions are not classified, and are collectively referred to as TPR.

(3) Differences in TPV/TPO of polyolefin elastomers:

a. Common point: TPO and TPV are both made of EPDM (polyolefin elastomer)+PP.

b. Differences: TPO polyolefin thermoplastic elastomer; TPV - dynamically vulcanized thermoplastic elastomer rubber; TPO belongs to simple physical blends (partially vulcanized, low degree of crosslinking), while TPV is completely vulcanized (dynamic micron level segmented complete vulcanization, very high degree of crosslinking).

(4) TPU: Wear resistant, with high tensile strength; Poor elasticity, not resistant to acid, alkali, and oil.

TPV: resistant to acid, alkali, oil, climate, high temperature, UV, and has the best elasticity; Poor stretching.

TPE/TPR: All kinds of performance are mediocre, and the unit price is the cheapest.

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