The so-called elastomer refers to a type of polymeric material with a glass transition temperature (Tg) below room temperature, an elongation at break of more than 50%, and a better recovery after removal of an external force. A polymeric material whose glass transition temperature is above room temperature is ductile; elastomer has an elongation at break of more than 200%, 100% modulus stress is low, and elasticity is better called rubber.
1. TPU thermoplastic elastomer
Thermoplastic polyurethane elastomer (TPU) is a block copolymer consisting of an oligomeric polyol as soft segment and a diisocyanate chain extender as hard segment. TPU can be plasticized and solvent can dissolve polyurethane, its molecular structure is generally linear, but there is also a certain physical crosslinking between molecular structures. The crystallinity and degree of phase separation of polyurethane materials are related to attraction between macromolecules and intramolecules, which is related to types of soft and hard segments that make up polyurethane, that is, type and density of groups.
TPU has high modulus, high strength, high elongation, high elasticity, and excellent comprehensive properties such as wear resistance, oil resistance, low temperature resistance and aging resistance. It is a new environmentally friendly material with a wide range of applications. Materials, adhesives, ink adhesives, films, sheets, melt-blown spandex, automotive interiors, and wires and pipes are widely used.
2. Raw materials and additives for synthesis of polyurethane elastomer (TPU)
There are three main raw materials for synthesis of TPU, namely oligomeric polyols, polyisocyanates (generally bifunctional), and low molecular weight chain extenders. In addition, in order to increase production efficiency, shorten cycle and improve certain technological properties in industrial production, it is necessary to add some other additives.
Table 2.1 Raw materials and additives for TPU
3. Synthetic TPU process
Synthesis of TPU is divided into mass polymerization method and solution polymerization method according to synthesis process.
The bulk polymerization method is divided into prepolymer method and one-step method: prepolymer method is to react diisocyanate and macromolecular diol for a certain period of time, and then add a chain extender to obtain TPU; one-step method is a diisocyanate, a macromolecular diol and a chain extender are mixed and reacted in a reactor to obtain TPU. Among them, in production, one-step method and two-step method have their advantages, see Table 3-1 for details
Table 3-1 Comparison of advantages and disadvantages of synthetic methods
Solution polymerization consists of first dissolving a diisocyanate in a solvent, then slowly adding a macromolecular diol and stirring for a certain period of time, and finally adding a chain extender to obtain TPU.
Fourth, TPU manufacturers
At present, there are many TPU manufacturers, and quality is also uneven. The main products are: polyester TPU, polyester TPU, aliphatic TPU, polycaprolactone TPU, polycarbonate TPU, polyester flame retardant TPU, TPU+GF, TPU+ PC alloy, anti-static conductive TPU etc.
Table 4-1 TPU Manufacturers
In terms of general analysis, there are many TPU giants in foreign countries, while most TPU manufacturers in my country are small and medium-sized enterprises. Few functions, lack of core competitiveness. At same time, as my country's industrial product quality requirements become higher and higher, relevant enterprises can take advantage of relevant opportunities and make new developments for development of enterprises.
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