Elastomers can be divided into thermosetting elastomers and thermoplastic elastomers according to whether they are plasticized. Thermosetting elastomer is the traditional meaning of rubber, thermoplastic elastomer (TPE) in the 1990s began to gradually be more and more commercial applications. This type of elastomer is processed in two different ways: rubber is processed with thermosetting equipment, and TPE is processed with thermoplastic equipment.
TPE is defined as a polymer material that shows rubber elasticity at room temperature and can be plasticized at high temperatures. These polymers share some of the characteristics of thermoplastic rubber and thermoplastic plastics. The basic structural characteristic of TPE polymer chain is that it is simultaneously connected or grafted with certain plastic segments (hard segments) and rubber segments (soft segments) with different chemical compositions.
There are several types of TPE: styrene thermoplastic elastomers, polyurethane thermoplastic elastomers, polyolefin thermoplastic elastomers, polyamide thermoplastic elastomers.
1, styrene thermoplastic elastomer
Styryl-type
Block copolymer thermoplastic elastomer is the earliest studied thermoplastic elastomer, mainly including SBS, hydrogenated SBS(SEBS), SIS and hydrogenated SIS, etc., is currently the world's largest production, the fastest developing one kind of thermoplastic elastomer. From an application point of view, the most interesting thing about styrene thermoplastic elastomers is that their properties are similar to vulcanized rubber at room temperature, and their elastic modulus is unusually high and does not change with relative molecular mass. Due to its high strength, softness, rubber elasticity and small permanent deformation, styrene thermoplastic elastomers are widely used in footwear industry, plastic modification, asphalt modification, waterproof coatings, liquid sealing materials, wires, cables and so on.
2, polyurethane thermoplastic elastomer
Polyurethane thermoplastic elastomer (TPU) is generally a linear polymer material with an average molecular weight of 600 ~ 4000 long chain polyols (polyether or polyester) and a molecular weight of 61 ~ 400 chain extender and polyisocyanate. In the main chain of TPU macromolecules, the long chain polyols (polyethers or polyesters) constitute 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. Since the ratio of hard and soft segments can be adjusted over a wide range, the resulting TPU can be either a soft elastomer or a brittle, high-modulus plastic. TPU has been widely used in many areas of the national economy such as shoe industry, medical health, clothing fabrics and defense supplies, but its disadvantages are poor aging resistance, low friction coefficient of wet surface, easy to slip.
3. Polyolefin thermoplastic elastomers
Polyolefin thermoplastic elastomers (TPO) mainly include block copolymers, grafted copolymers and blends. Polyolefin thermoplastic elastomers (TPO) synthesized by metallocene catalyst ethylene octene copolymer (POE) and thermoplastic dynamic vulcanization rubber (TPV) prepared by dynamic vulcanization are two main types of polyolefin thermoplastic elastomers.
(1). POE
POE refers to ethylene-octene copolymer (EOC), ethylene-butene copolymer (EBC), ethylene-hexene copolymer, etc., ethylene-α-olefin copolymerization of polyolefin elastomers.
Generally speaking, POE mainly refers to ethylene-octene copolymer elastomers, and the mass fraction of octene is greater than 20%. The particularity of POE molecular structure gives it excellent mechanical properties, rheological properties and aging resistance, can be used as rubber, and can be used as thermoplastic elastomer, can also be used as plastic impact modifier and toughener, low temperature toughness is good, cost-effective, in many occasions is gradually replacing ethylene propylene rubber, is widely used in plastic modification.
The molecular structure of POE is similar to EPDM, so POE will also have excellent properties such as aging resistance, ozone resistance and chemical medium resistance. Through crosslinking POE, the heat resistance temperature of the material is increased, the permanent deformation is reduced, and the main mechanical properties such as tensile strength and tearing strength are greatly improved.
POE main crosslinking methods are: electron beam or gamma-ray radiation crosslinking method, peroxide crosslinking method and silane crosslinking method, in addition, POE can also use optical crosslinking, salt crosslinking and other crosslinking methods. Commonly used peroxide crosslinking agents are: diisopropylbenzene peroxide DCP, 2, 5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane (bis 2,5), bis (tert-butyl peroxy isopropyl) benzene BIPB, benzoyl peroxide (BPO) and so on.
(2). TPV
The thermoplastic elastomer obtained by dynamic vulcanization is called thermoplastic vulcanized rubber (TPV). TPV is a special type of TPE, which is different from block copolymers that are elastic, but is produced by the synergistic action of elastomer/thermoplastic polymer blends and has better properties than simple blends.
EPDM is a ternary copolymer of ethylene, propylene and unconjugated diolefin. The diene double bond is reactive. Under the action of vulcanizing agent, EPDM with high crosslinking degree can be obtained. EPDM has good heat resistance, weather resistance and mechanical properties, but its hardness and processing properties are poor, which limits its development.
The key technology for the preparation of TPV is dynamic vulcanization technology, and one of the advances in this technology is the use of low-cost existing processing methods to prepare new products by blending existing polymers. For example: nylon /EPDM type TPV, PP/EPDM type TPV, nylon/nitrile rubber type TPV and so on.
4. Polyamide thermoplastic elastomers (TPAE)
TPAE consists of a high melting point crystalline hard segment (polyamide) and an amorphous soft segment (polyester or polyether). Its performance depends on the type of hard segment and the length of the two types of blocks. Due to the existence of hard segment polyamide, TPAE has excellent toughness, chemical resistance, wear resistance and noise reduction. By selecting and controlling the types of blocks, their mechanical, thermal and chemical properties can vary over a wide range.
According to the raw materials required for TPAE synthesis, the synthesis methods can be divided into dibasic acid method and isocyanate method. TPAE is prepared by esterification of carboxy-terminated aliphatic polyamide blocks with hydroxy-terminated polyether diols by dibasic acid method. The isocyanate method uses semi-arylamide as the hard segment and aliphatic polyester, polyether or polycarbonate as the soft segment.
