Analysis of several differences of commonly used thermoplastic elastomer TPE
Source：德创化工Time：2021-05-27Hits：1878
TPE thermoplastic elastomer (TPE) is a polymer material with rubber and plastic properties, which shows rubber elasticity at normal temperature and can be plasticized at high temperature.
The basic structural feature of thermoplastic elastomer polymer chain is that it is connected in series or grafted with some plastic segments (hard segments) and rubber segments (soft segments) with different chemical compositions.
The force between the hard segments is enough to condense into micro-regions (such as vitrified micro-regions or crystallized micro-regions) and form physical "cross-linking" between molecules. The soft segment is a high-end segment with its own rotation ability.
Thermoplastic elastomers are an important part of elastomers. Common thermoplastic elastomers are as follows: styrene thermoplastic elastomers, polyurethane thermoplastic elastomers, polyolefin thermoplastic elastomers and polyamide thermoplastic elastomers.
1 styrene thermoplastic elastomer
Styrene block copolymer thermoplastic elastomer is the earliest thermoplastic elastomer studied, and it is a kind of thermoplastic elastomer with the largest output and the fastest development in the world at present. Mainly include SBS, hydrogenated SBS(SEBS), SIS and hydrogenated SIS, etc.
The properties of styrene thermoplastic elastomer at room temperature are similar to those of vulcanized rubber, and the elastic modulus is abnormally high and does not change with the relative molecular weight.
With the characteristics of high strength, softness, rubber elasticity and small permanent deformation, it is widely used in footwear industry, plastic modification, asphalt modification, waterproof coatings, liquid sealing materials, wires, cables, automobile parts, medical equipment parts, household appliances, office automation and adhesives.
2 polyurethane thermoplastic elastomer
Polyurethane thermoplastic elastomer (TPU) is generally a linear polymer material prepared by addition polymerization of long chain polyol (polyether or polyester) with average relative molecular weight of 600 ~ 4000, chain extender with relative molecular weight of 61 ~ 400 and polyisocyanate.
The long-chain polyol (polyether or polyester) in the main chain of TPU macromolecule constitutes the soft segment, which mainly controls its low temperature performance, solvent resistance and weather resistance, while the chain extender and polyisocyanate constitute the hard segment. Because the ratio of hard segment to soft segment can be adjusted in a wide range, the thermoplastic polyurethane obtained can be soft elastomer, brittle high modulus plastic, film and fiber, which is the only kind of TPE.
TPU has excellent wear resistance, oil resistance and cold resistance, and has enough resistance to oxygen, ozone and radiation. As an elastomer, TPU has high tensile strength and elongation at break, and also has excellent properties such as small compression set and large bearing capacity.
TPU has been widely used in many fields of national economy, such as shoemaking industry, medical and health care, clothing fabrics and national defense products, but its disadvantages are poor aging resistance, low friction coefficient on wet surface and easy slippage. In addition, TPU has strong polarity, and in the process of processing, when the shearing action is strong, the interior is easy to generate heat, which leads to degradation. Its melt viscosity is strongly dependent on temperature, and a small change in temperature can cause a sharp change in its viscosity, so the processing temperature range is narrow, and in addition, the cost is high and the price is expensive, which further limits the popularization and application of TPU.
3 polyolefin thermoplastic elastomer
Polyolefin thermoplastic elastomer (TPO) mainly includes three types: block copolymer, graft copolymer and blend, among which polyolefin thermoplastic elastomer ethylene-octene copolymer (POE) synthesized by metallocene catalyst and thermoplastic dynamic vulcanizate prepared by dynamic vulcanization method are two main polyolefin thermoplastic elastomers.
Compared with the traditional Ziegler-Natta catalyst, the metallocene catalyst of metallocene polyolefin elastomer ethylene-octene copolymer has an ideal single active center, so it can precisely control the relative molecular mass distribution, comonomer content, its distribution in the main chain and crystal structure. The synthesized polymer is a highly stereoregular polymer with narrow molecular mass distribution, which can accurately control the physical and mechanical properties and processability of the polymer.
On the one hand, polyolefin thermoplastic elastomer ethylene-octene copolymer (POE) synthesized by metallocene catalyst has very narrow molecular weight and short branch chain distribution, so it has excellent physical and mechanical properties (high elasticity, high strength and high elongation) and good low temperature performance; on the other hand, it has excellent heat resistance and ultraviolet resistance because its molecular chain is saturated and contains relatively few tertiary carbon.
POE is superior to EVA in thermal stability, optical properties and dry crack resistance, and its weather aging resistance is superior to SBS. The brittle temperature is lower than-76℃, and it still has good toughness and ductility at low temperature. POE has good shear property, which is beneficial to high-speed extrusion and molding, and has little or no plasticizer and long service life.
POE can be crosslinked by peroxide, silane and radiation, and the physical and mechanical properties, chemical reagent resistance and ozone resistance of the crosslinked material are close to those of EPDM Heat aging resistance and ultraviolet aging resistance are better than EPDM and EPM, so POE is more suitable for outdoor use, and the hot compression set of POE is smaller than that of EPDM.
POE can be used as modifier to modify both rubber and plastic.
Because the processing temperature of POE is low, it is easy to mix with nonpolar rubber, especially EPR, EPDM, NR, SBR and BR.
The biggest application of POE is in plastic products. The notched impact strength of PP modified by POE is greatly improved. When the elastomer grafted with maleic anhydride and POE is used to modify PA6, the hygroscopicity of the material is reduced and the impact strength is greatly improved.
2 thermoplastic dynamic vulcanizate prepared by dynamic vulcanization method
Thermoplastic dynamic vulcanized rubber The thermoplastic elastomer prepared by dynamic vulcanization is called thermoplastic vulcanized rubber (TPV).
TPV is a special type of thermoplastic elastomer (TPE), which is different from elastic block copolymer, but is produced by the synergistic effect of elastomer-thermoplastic polymer blend, and has better properties than simple blend.
The key technology for preparing thermoplastic vulcanizate is dynamic vulcanization technology. One of the advances of this technology is to prepare new products by blending existing polymers with low cost. Compared with the traditional process of producing new materials with high capital investment intensity, this process can also meet the environmental protection requirements of large-scale polymerization units. Other advantages of TPV technology over block copolymer as the source of thermoplastic elastomer are high upper limit service temperature, resistance to hydrocarbon medium and small compression set.
4 polyamide thermoplastic elastomer
Polyamide thermoplastic elastomer (TPEA) is composed of high melting point crystalline polyamide hardness and amorphous polyester or polyether satin.
According to the raw materials needed for the synthesis of polyamide thermoplastic elastomer, its synthesis methods can be divided into dibasic acid method and isocyanate method.
TPAE was prepared by esterification reaction of carboxyl-terminated aliphatic polyamide block and hydroxyl-terminated polyether glycol by dibasic acid method. Isocyanate method uses semi-aromatic amide as hard segment and aliphatic polyester, polyether or polycarbonate as soft segment.
By isocyanate method, the semi-aromatic amide hard segment is prepared by the reaction of aromatic diisocyanate and dicarboxylic acid, instead of the traditional polymerization of diamine and dicarboxylic acid, ring-opening polymerization of cyclic lactam or reaction of diamine and dicarboxylic acid chloride. In contrast, the former avoids the problems of low activity of aromatic diamine, difficulty in obtaining aromatic cyclic lactam monomer and corrosive hydrogen chloride released by reaction.
