Elastomers can be divided into two categories based on whether they can be plasticized: thermosetting elastomers and thermoplastic elastomers. Thermosetting elastomers, also known as rubber in the traditional sense, began to be increasingly commercialized in the 1990s as thermoplastic elastomers (TPE). These two types of elastomers are processed using two different methods: rubber is processed using thermosetting equipment, and TPE is processed using thermoplastic equipment.

TPE is defined as a polymer material that exhibits rubber elasticity at room temperature and can be plasticized at high temperatures. This type of polymer combines certain characteristics of thermoplastic rubber and thermoplastic plastics. The basic structural feature of TPE polymer chains is that they simultaneously connect or graft certain plastic segments (hard segments) and rubber segments (soft segments) with different chemical compositions.

There are several types of TPE: styrene based thermoplastic elastomers, polyurethane based thermoplastic elastomers, polyolefin based thermoplastic elastomers, and polyamide based thermoplastic elastomers.

01 Styrene based thermoplastic elastomer

Styrene block copolymer based thermoplastic elastomers are the earliest studied thermoplastic elastomers, mainly including SBS, hydrogenated SBS (SEBS), SIS, and hydrogenated SIS. They are currently the world's largest production and fastest developing thermoplastic elastomers. From an application perspective, the most interesting aspect of styrene based thermoplastic elastomers is that their performance at room temperature is similar to that of vulcanized rubber, and their elastic modulus is abnormally high and does not change with relative molecular weight. Styrene based thermoplastic elastomers have wide applications in the footwear industry, plastic modification, asphalt modification, waterproof coatings, liquid sealing materials, wires, cables, and other fields due to their high strength, softness, rubber elasticity, and small permanent deformation.

02 Polyurethane thermoplastic elastomer

Polyurethane based thermoplastic elastomers (TPUs) 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 fact that the ratio of hard and soft segments can be adjusted within a large range, the resulting TPU can be either a soft elastomer or a brittle high modulus plastic. 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.

03 Polyolefin based thermoplastic elastomers

Polyolefin thermoplastic elastomers (TPOs) mainly include three types: block copolymers, graft copolymers, and blends. Among them, ethylene octene copolymer (POE) synthesized using metallocene catalysts and thermoplastic dynamic vulcanization adhesive (TPV) prepared by dynamic vulcanization method are the two main types of TPOs.

POE refers to ethylene octene copolymer (EOC), ethylene butene copolymer (EBC), ethylene hexene copolymer, etc α－ Polyolefin elastomers formed by copolymerization of olefins.

The commonly referred to POE mainly refers to ethylene octene copolymer elastomer, and the octene mass fraction is greater than 20%. The unique molecular structure of POE endows it with excellent mechanical properties, rheological properties, and aging resistance. It can be used as both rubber and thermoplastic elastomer, as well as as impact modifier and toughening agent for plastics. It has good low-temperature toughness and high cost-effectiveness, and is gradually replacing ethylene propylene rubber in many occasions, and is widely used for plastic modification.

The molecular structure of POE is similar to that of ethylene propylene diene monomer (EPDM), so POE also has excellent properties such as aging resistance, ozone resistance, and chemical resistance. By crosslinking POE, the heat resistance temperature of the material is increased, permanent deformation is reduced, and the main mechanical properties such as tensile strength and tear strength are greatly improved.

The main crosslinking methods of POE include: electron beam or γ The radiation crosslinking method, peroxide crosslinking method, and silane crosslinking method can also be used for POE. In addition, other crosslinking methods such as photocrosslinking and salt crosslinking can also be used. The commonly used peroxide crosslinking agents include: diisopropyl peroxide DCP, 2,5-dimethyl-2,5-bis (tert butylperoxy) hexane (bis 2,5), bis (tert butylperoxy isopropyl) benzene BIPB, benzoyl peroxide (BPO), etc.

The thermoplastic elastomer obtained by the dynamic vulcanization method of TPV is called thermoplastic vulcanized rubber (TPV). TPV is a special type of 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 commonly used elastomer for preparing TPV is ethylene propylene diene monomer (EPDM), which is a ternary copolymer of ethylene, propylene, and non conjugated dienes. The diene double bond has reactive activity, and under the action of a vulcanizing agent, EPDM with high cross-linking degree can be obtained. EPDM has good heat resistance, weather resistance, and mechanical properties, but its hardness and processing performance are poor, which limits its development.

The key technology for preparing TPV is dynamic vulcanization technology, and one of the advancements 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, etc.

04 Polyamide based thermoplastic elastomer (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 segments. Due to the presence of hard segment polyamide, TPAE has excellent toughness, chemical resistance, wear resistance, and noise reduction. By selecting and controlling the block category, its 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 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.