Views: 6 Author: Site Editor Publish Time: 2023-11-30 Origin: Site
Thermoplastic elastomer, also known as TPE, is a polymer material that combines rubber and plastic properties. It exhibits rubber elasticity at room temperature and can be plasticized at high temperatures.
The basic structural feature of thermoplastic elastomer polymer chains is that they are simultaneously connected or grafted with certain plastic segments (hard segments) and rubber segments (soft segments) with different chemical compositions.
The force between hard segments is sufficient to condense into micro regions (such as glass transition micro regions or crystalline micro regions), forming physical "cross-linking" between molecules. The soft segment is a high-end chain segment with high inherent rotation ability.
Thermoplastic elastomers are an important component of elastomers. Common types of thermoplastic elastomers include styrene based thermoplastic elastomers, polyurethane based thermoplastic elastomers, polyolefin based thermoplastic elastomers, and polyamide based thermoplastic elastomers.
1. Styrenic thermoplastic elastomer
Styrene block copolymer based thermoplastic elastomers are the earliest studied thermoplastic elastomers and are currently the world's largest and fastest growing type of thermoplastic elastomer. Mainly including SBS, Hydrogenated SBS (SEBS), SIS, and Hydrogenated SIS.
The performance of styrene based thermoplastic elastomers at room temperature is similar to that of vulcanized rubber, with an abnormally high elastic modulus that does not change with relative molecular weight.
Due to its high strength, softness, rubber elasticity, and small permanent deformation, it has been widely used in the footwear industry, plastic modification, asphalt modification, waterproof coatings, liquid sealing materials, wires, cables, automotive components, medical device components, household appliances, office automation, and adhesives.
2.Polyurethane thermoplastic elastomer
Polyurethane based thermoplastic elastomers (TPU) are generally linear polymer materials composed of long-chain polyols (polyethers or polyesters) with an average relative molecular weight of 600-4000, chain extenders with a relative molecular weight of 61-400, and polyisocyanate addition polymerization.
Long chain polyols (polyethers or polyesters) in the main chain of TPU macromolecules form soft segments, mainly controlling their low-temperature performance, solvent resistance, and weather resistance, while chain extenders and polyisocyanates form hard segments. Due to the wide range of adjustments in the ratio of hard and soft segments, the obtained thermoplastic polyurethane can be either a soft elastomer or a brittle high modulus plastic, or can be made into films and fibers, making it the only type of TPE that can be achieved.
TPU has excellent wear resistance, oil resistance, and cold resistance, with sufficient resistance to oxygen, ozone, and radiation. At the same time, as an elastomer, it has high tensile strength and elongation at break, as well as excellent properties such as small compression permanent deformation and large load-bearing capacity.
TPU has been widely used in many fields of the national economy, such as the shoemaking industry, healthcare, clothing fabrics, and defense supplies. However, its disadvantages are poor aging resistance, low wet surface friction coefficient, and easy slipping. Moreover, TPU has strong polarity. During the processing, when the shear action is strong, it is prone to internal heating, leading to degradation. Its melt viscosity is highly temperature dependent, and small temperature changes can cause a sharp change in its viscosity. Therefore, the processing temperature range is narrow, coupled with high cost and high price, further limiting the promotion and application of TPU.
3.Polyolefin based thermoplastic elastomers
Polyolefin based thermoplastic elastomers (TPO) mainly include three types: block copolymers, graft copolymers, and blends. Among them, ethylene octene copolymer (POE) synthesized using metallocene catalysts and thermoplastic dynamic vulcanized rubber prepared by dynamic vulcanization method are the two main types of TPO.
(1) Polyolefin thermoplastic elastomer ethylene octene copolymer (POE)
Metallocene polyolefin elastomer ethylene octene copolymer metallocene catalysts have an ideal single active center compared to traditional Ziegler Natta catalysts, allowing for precise control of relative molecular weight distribution, comonomer content, distribution on the main chain, and crystal structure. The synthesized polymer is a highly structured structured polymer with a narrow relative molecular weight distribution, which can accurately control the physical and mechanical properties and processing properties of the polymer.
The polyolefin thermoplastic elastomer ethylene octene copolymer (POE) synthesized using metallocene catalysts has a narrow molecular weight and short branched chain distribution, resulting in excellent physical and mechanical properties (high elasticity, high strength, high elongation) and good low-temperature performance. Additionally, due to its saturated molecular chain and relatively small number of tertiary carbon atoms, it has excellent heat resistance and UV resistance.
POE has better thermal stability, optical properties, and dry crack resistance than EVA, better weather aging resistance than SBS, and a brittleness temperature below -76 ℃. It still has good toughness and ductility at low temperatures. POE has good shear properties, which is conducive to high-speed extrusion and molding, with little or no need for plasticizers, and has a long service life.
POE can be crosslinked using peroxide, silane, and radiation methods. The physical and mechanical properties, chemical resistance, and ozone resistance of the crosslinked material are similar to those of EPDM; The heat aging and UV aging resistance of POE are better than those of EPDM and EPM, making it more suitable for outdoor use, and the thermal compression permanent deformation of POE is smaller than that of EPDM.
POE, as a modifier, can modify both rubber and plastic.
Due to the lower processing temperature of POE, it is easier to mix with non-polar rubbers, especially EPR, EPDM, NR, SBR, and BR.
The biggest application of POE is still in plastic products. Modifying PP with POE greatly improves its notch impact strength; The use of maleic anhydride grafted POE elastomer to modify PA6 can reduce the moisture absorption of the material and significantly improve its impact strength.
Thermoplastic dynamic vulcanized rubber prepared by dynamic vulcanization method.
Thermoplastic dynamic vulcanized rubber (TPV) is a thermoplastic elastomer obtained by dynamic vulcanization method.
TPV is a special type of thermoplastic elastomer (TPE), which is different from elastic block copolymers and is generated by the synergistic effect of elastomer thermoplastic polymer blends, with better properties than simple blends.
The key technology for preparing thermoplastic vulcanized rubber is dynamic vulcanization technology. One of the advancements in this technology is the use of low-cost existing processing methods to prepare new products by blending existing polymers. Compared with traditional and high investment intensive processes for producing new materials, this process can also meet the environmental requirements for large polymerization plants. Another advantage of TPV technology over block copolymers as a source of thermoplastic elastomers is its high upper limit usage temperature, resistance to hydrocarbon media, and low compression set.
4.Polyamide based thermoplastic elastomers
Polyamide based thermoplastic elastomers (TPEA) are composed of high melting point crystalline polyamide hardness and amorphous polyester or polyether soft satin.
According to the raw materials required for the synthesis of polyamide thermoplastic elastomers, their synthesis methods can be divided into binary acid method and isocyanate method.
Using the binary acid method, TPAE is prepared by esterification reaction between carboxyl terminated aliphatic polyamide blocks and hydroxyl terminated polyether diols. The isocyanate method uses semi aromatic amide as the hard segment and aliphatic polyester, polyether or polycarbonate as the soft segment.
By using the isocyanate method, the hard segment of semi aromatic amide is obtained by the reaction of aromatic diisocyanates with dicarboxylic acids, rather than being prepared by traditional methods such as polymerization of diamines with dicarboxylic acids, ring opening polymerization of cyclic lactams, or reaction of diamines with dicarboxylic chloride. Compared to this, the former avoids problems such as low activity of aromatic diamines, difficulty in obtaining aromatic cyclic lactam monomers, and the release of corrosive hydrogen chloride during reactions.
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