Review of polyurethane elasticity

Polyurethane elastomer, also known as polyurethane elastomer, is a polymer synthetic material containing a large number of urethane groups in the main chain. It is generally made of polyester, polyether and polyolefin. It is formed by the gradual addition and polymerization of oligomer polyol, polyisocyanate and diol or diamine chain extender. It is an elastic material between general rubber and plastic. It has the high elasticity of rubber and the high strength of plastic. It has a large elongation and a wide range of hardness; its wear resistance, biocompatibility and blood compatibility are particularly outstanding. At the same time, it also has excellent oil resistance, impact resistance, low temperature resistance, radiation resistance, load-bearing, heat insulation, insulation and other properties. Therefore, polyurethane elastomers have a wide range of applications. It has become an indispensable precious material in the national economy and people’s lives.
Polyurethane elastomer has a wide range of performance, which is closely related to its structure, and its structure depends on many factors such as reactants, reaction time, reaction temperature, etc. Even small changes in water content can cause polyurethane elastomer Huge difference in mechanical properties.
Keywords: polyurethane elastomer structure and properties application

1Overview of polyurethane elastomer
Polyurethane elastomer, also known as polyurethane rubber, is a special synthetic rubber. It is a type of elastic polymer containing more urethane groups (-NHCOO-) in the main chain of the molecule. It is a typical multi-block copolymer material. . Polyurethane elastomer is usually made by addition polymerization reaction using polymer polyol, isocyanate, chain extender, cross-linking agent and a small amount of additives as raw materials. From a molecular structure point of view, polyurethane elastomer (PUE) is a block polymer whose molecular chain is generally composed of two parts. At normal temperature, one part is in a highly elastic state, called the soft segment; the other part is in a glassy state or Crystalline state, called hard segment. Generally, the soft segment is composed of long flexible chains of polymer polyol, and the hard segment is composed of isocyanate and chain extender. The soft segments and hard segments are alternately arranged to form repeating structural units. In addition to urethane groups, the main chain of polyurethane molecules also contains polar groups such as ether, ester or urea groups. Due to the presence of a large number of these polar groups, hydrogen bonds can be formed within and between polyurethane molecules. The thermodynamic incompatibility between the soft and hard segments induces the formation of hard and soft segment microdomains and produces a microscopic phase separation structure, even if Linear polyurethanes can also form physical cross-links through hydrogen bonding. These structural characteristics make polyurethane elastomers have excellent wear resistance and toughness, and are known as “wear-resistant rubber” [1]. Since there are many types of raw materials for polyurethane, the variety and ratio of raw materials can be adjusted to synthesize elastomers with different performance characteristics. products, making polyurethane elastomers widely used in the national economy. Although the output of polyurethane elastomers accounts for a small proportion of polyurethane products, its variety and wide range of applications are unmatched by other materials. Polyurethane elastomer has excellent comprehensive properties, and its modulus is between that of general rubber and plastic. It has the following characteristics: ① High strength and elasticity, and can maintain high elasticity in a wide hardness range (Shore A10-Shore D75); ② At the same hardness, it has a higher load-bearing capacity than other elastomers ; ③Excellent wear resistance, its wear resistance is 2-10 times that of natural rubber; ④Good fatigue resistance and vibration resistance, suitable for high-frequency flexural applications; ⑤High impact resistance; ⑥Aromatic polyurethane resistance Excellent radiation, oxygen resistance and ozone resistance; ⑦ Excellent resistance to grease and chemicals; ⑧ Generally no plasticizer is needed to achieve the required low hardness, so there is no problem caused by plasticizer migration; ⑨ Molding and The processing cost is low; ⑩ Ordinary polyurethane cannot be used above 100℃, but the formula can withstand high temperatures of 140℃. Under normal circumstances, compared with metal materials, polyurethane elastomer products have the advantages of light weight, loss resistance, low sound, low processing cost, and corrosion resistance; compared with rubber, polyurethane elastomer products have the advantages of wear resistance, cut resistance, and corrosion resistance. It has the advantages of tearing, high load-bearing capacity, pourable, potting, transparent or translucent, ozone resistance, hardness range, etc. Compared with plastic, polyurethane elastomer has the advantages of non-brittleness, elastic memory, and wear resistance. There are various processing methods for polyester elastomers, new technologies and new varieties are constantly emerging, and the application prospects will be very broad [2].
2Processing technology of polyurethane elastomer
In the laboratory, polyurethane elastomers are generally synthesized by hand-casting prepolymer methods, including one-step method, prepolymer method and semi-prepolymer method.
The one-step method is to add the diisocyanate, polyol, catalyst and other additives in the formula at one time, stir it at high speed and then pour it into the mold to prepare polyurethane elastomer products. Although the performance uniformity and repeatability of the products produced by the one-step method are poor, and a large number of bubbles can be introduced into the reaction system, resulting in a large number of bubbles in the product, the process flow of this method isIt’s also good. It is favored by shoe manufacturers. The product has a low density and is much lighter than traditional rubber soles and PVC shoe materials. In China, microporous polyurethane elastomers are mainly used for soles and insoles of travel shoes, leather shoes, sports shoes, sandals, etc. Overseas, they are mainly used for the soles of special sports shoes that require wear resistance and elasticity, and the design can be diversified. TPU heel has high wear resistance. A thermally decomposable foaming agent can be added during injection molding to produce foamed TPU elastic shoe materials.
(6) Mold linings and blanking templates for sheet metal parts forming, etc.
When thin parts are punched out with conventional steel dies, there are often burrs on the fracture surface. The stamping technology of using polyurethane rubber to replace traditional steel molds is a leap forward in metal sheet stamping technology. It can greatly shorten the mold manufacturing cycle, extend the service life of the mold, reduce the production cost of molded parts, and improve the surface quality and dimensional accuracy of the parts. It is especially suitable for It is suitable for trial production of small and medium-sized batches and single-piece products, and is more suitable for thin and complex stamping parts. In ceramic tile and ceramic production lines, the use of PU elastomer lined molds can reduce production costs and improve production efficiency and yield. Polyurethane can be used to make concrete molds. Polyurethane molds can be used to copy various patterns and produce decorative blocks. In the stamping production of hardware molds, polyurethane elastomer rods, tubes and plate pads are used instead of metal springs as buffer components, which have high elasticity, flexibility and compression. High deformation strength and no damage to the mold.
(7)Medical elastomer products
Medical polyurethane elastomers are mainly thermoplastic polyurethane abroad, and there are also a small amount of cast polyurethane elastomers and microporous elastomers. Due to its high strength, wear resistance, biocompatibility, and absence of plasticizers and other small molecule inert additives, polyurethane elastomer occupies an important position among medical polymer materials. Medical polyurethane products include polyurethane gastroscope hoses, medical hoses, artificial and diaphragm and capsule materials, polyurethane elastic bandages, tracheal cuffs, etc. [14].
(8)Pipes
Utilizing the flexibility, high tensile strength, impact strength, low temperature resistance, high temperature resistance, and high compressive strength of polyurethane elastomer, it can be made into various hoses and hard pipes, such as high-pressure hoses and medical catheters. , oil pipes, air delivery pipes, fuel delivery pipes, paint hoses, fire hoses, gas material delivery pipes, etc. Urethane pipes are mostly extruded from thermoplastic polyurethane.