Polyurethane elastomer, also known as polyurethane elastomer, is a polymer synthetic material containing more urethane groups on the main chain. It is generally composed of oligomers such as polyester, polyether and polyolefin. It is formed by the gradual addition and polymerization of polyols, polyisocyanates and diols or diamine chain extenders. It is an elastic material between general rubber and plastic, that is, 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 and load resistance, heat insulation, insulation and other properties. Therefore, the application fields of polyurethane elastomers are very wide. It has become an indispensable and valuable material in the national economy and people's life.
Polyurethane elastomer has a wide range of properties, which is closely related to its structure, and its structure depends on many factors such as reactants, reaction time, reaction temperature, and even small changes in water content can cause polyurethane elastomers Huge difference in mechanical properties.
1. Overview of Polyurethane Elastomers
Polyurethane elastomer, also known as polyurethane rubber, belongs to special synthetic rubber and is a kind of elastic polymer containing more urethane groups (-NHCOO-) in the main chain of the molecule. It is a typical multi-block copolymer material. . Polyurethane elastomers are usually prepared by polyaddition reaction using polymer polyols, isocyanates, chain extenders, cross-linking agents and a small amount of auxiliary agents as raw materials. In terms of molecular structure, polyurethane elastomer (PUE) is a block polymer, and its molecular chain is generally composed of two parts. At normal temperature, one part is in a high elastic state, called soft segment; The crystalline state is called the hard segment. Generally, the soft segment is composed of a long flexible chain of polymer polyol, and the hard segment is composed of isocyanate and chain extender. The soft segment and the hard segment are alternately arranged to form repeating structural units. In addition to the urethane group, the main chain of the polyurethane molecule also contains polar groups such as ether, ester or urea group. Due to the existence of a large number of these polar groups, hydrogen bonds can be formed in the polyurethane molecule and between the molecules, and the soft segment and the hard segment are thermodynamically incompatible, which induces the formation of the hard segment and the soft segment microdomain and produces a microscopic phase separation structure. Linear polyurethanes can also form physical crosslinks through hydrogen bonding. These structural characteristics make polyurethane elastomers have excellent wear resistance and toughness, known as "wear-resistant rubber" [1], and because there are many varieties of polyurethane raw materials, the variety and ratio of raw materials can be adjusted to synthesize products with different performance characteristics. products, making polyurethane elastomers widely used in the field of national economy. Although the output of polyurethane elastomer does not account 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: ①High strength and elasticity, can maintain high elasticity in a wide range of hardness (Shore A10-Shore D75); ②Under the same hardness, it has higher bearing capacity than other elastomers ; ③ Excellent wear resistance, its wear resistance is 2-10 times that of natural rubber; ④ Good fatigue resistance and vibration resistance, suitable for high frequency deflection applications; ⑤ High impact resistance; ⑥ Aromatic polyurethane resistance Excellent radiation, oxygen resistance and ozone resistance; ⑦ Excellent grease and chemical resistance; ⑧ Generally, the required low hardness can be achieved without plasticizer, so there is no problem caused by plasticizer migration; ⑨ Molding and Low processing cost; ⑩Ordinary polyurethane cannot be used above 100℃, but the formula can withstand high temperature of 140℃. Under normal circumstances, compared with metal materials, polyurethane elastomer products have the advantages of light weight, loss resistance, low sound, low processing costs and corrosion resistance; compared with rubber, polyurethane elastomers have wear resistance, cut resistance, resistance Tear, high load-bearing, pourable, pottable, transparent or translucent, ozone resistance, hardness range and other advantages; compared with plastics, polyurethane elastomers have the advantages of no brittleness, elastic memory, wear resistance, etc. 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].
2. Processing 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 auxiliary agents in the formula at one time, and pour it into the mold after high-speed stirring to prepare the polyurethane elastomer product. Although the product obtained by the one-step method has poor performance uniformity and repeatability, and can introduce a large number of air bubbles into the reaction system, so that there are a large number of products in the product, the process of this method is simple, saves energy, and reduces costs, so this method is mainly used in It is used in the foaming industry, but is rarely used in the production of cast polyurethane elastomers [3]. At present, with the emergence of some new molding processes such as reaction injection molding (RIM) technology, the one-step method has also been developed more rapidly.
The polyurethane elastomer prepared by the prepolymer method is divided into two steps, so it is also called the two-step method. First, the oligomer alcohol and excess polyisocyanate are reacted to form a prepolymer with an NCO group at the end group, and then the polymer is reacted with a chain extender during casting to prepare a polyurethane elastomer. This method is mostly used in the production of polyurethane elasticity. The disadvantage is that the prepolymer is sensitive to temperature, requires high equipment during casting, and has a long process. The difference between the semi-prepolymer method and the prepolymer method is that some polyester polyols or polyether polyols, chain extenders, chemical additives, etc. are added to the prepolymer in the form of a mixture. That is to say, the oligomer polyol in the formula is divided into parts, one part is reacted with excess diisocyanate to synthesize prepolymer, and the other part is mixed with chain extender and added during injection. The mass fraction of free NCO in the resulting prepolymer is relatively high, generally 0.12-0.15 (12%-%), so this prepolymer is often called "quasi-prepolymer". The characteristics of the semi-prepolymer method: ① The viscosity of the prepolymer component is low, and it can be adjusted to be similar to the viscosity of the mixed component of the curing agent; ② The ratio is also close (that is, the mixing mass ratio can be 1:1). This not only improves mixing uniformity, but also improves some properties of elasticity. This method is easy to realize industrialization: among the above three methods, generally speaking, the polyurethane elastomer prepared by the prepolymer method has the best performance, and the one-step method has the worst performance. This is because in the one-step method, the polymerization and chain extension reactions are carried out at the same time. In the later stage of the reaction, due to the sharp increase in the viscosity of the system, the activity of the molecular chain is controlled by the diffusion reaction, the reaction is not complete, and the molecular weight of the obtained polyurethane elastomer is relatively small. The structure is not uniform, which affects the performance of the polyurethane elastomer. In the process of the prepolymer method, the reaction of the polyurethane prepolymer and the reaction between the polyurethane prepolymer and the chain extender are carried out step by step, and they are all controllable reactions. The reaction is relatively thorough, and the obtained polyurethane elastic The bulk molecular weight is relatively large and the structure is relatively uniform, which is conducive to the formation of hydrogen bonds between macromolecules, thereby improving the performance of the polyurethane elastomer. The properties of the polyurethane elastomer prepared by the semi-prepolymer method are between the prepolymer method and the one-step method, and the reaction temperature is low, which is suitable for industrial production. This paper discusses the relationship between the structure and properties of polyurethane elastomers, all of which are synthesized by the prepolymer method.
3. Structure and properties of polyurethane elastomers
The mechanical properties of polyurethane elastomers are directly related to the internal structure of polyurethane elastomers, and their microstructure and morphology are strongly affected by the interaction between polar groups, such as the type, structure and morphology of soft and hard segments. Mechanical properties and heat resistance of polyurethane elastomers. In recent years, people have begun to study the relationship between the mechanical properties of polyurethane elastomers and their aggregated structures and microstructures.
a. Microphase separation structure of polyurethane elastomer
The properties of polyurethane are mainly affected by the morphological structure of the macromolecular chain. The unique flexibility and excellent physical properties of polyurethane can be explained by the two-phase morphology. The degree of microphase separation and the two-phase structure of soft and hard segments in polyurethane elastomers are critical to their performance. Moderate phase separation is beneficial to improve the properties of the polymer. The separation process of microphase separation is that the difference in polarity between the hard segment and the soft segment and the crystallinity of the hard segment itself lead to their thermodynamic incompatibility (immiscibility) and a tendency to spontaneous phase separation, so the hard segment is easy to Aggregate together to form domains, which are dispersed in the continuous phase formed by the soft segments. The process of microphase separation is actually the process of separation and aggregation or crystallization of the hard segment in the elastomer from the copolymer system.
The phenomenon of polyurethane micro-phase separation was first proposed by American scholar Cooper. After that, a lot of research work was done on the structure of polyurethane [4]. The research on the aggregate structure of polyurethane also made progress, forming a relatively complete structure. The microphase structure theory of [5] system: in the block polyurethane system, the microphase separation of the hard segment and the soft segment is induced by the thermodynamic incompatibility between the segment and the soft segment. The attractive force of the segments between the hard segments is much greater than that of the segments between the soft segments. The hard segments are insoluble in the soft segment phase, but are distributed in it, forming a discontinuous microphase structure (sea-island structure). It plays a physical linking and reinforcing role in the soft segment. In the process of microphase separation, the increased interaction between hard segments will facilitate the separation of hard segments from the system and aggregate or crystallize, promoting microphase separation. Of course, there is a certain compatibility between the plastic phase and the rubber phase, and the phases between the plastic micro-domains and the rubber micro-domains are mixed to form a flow-through phase. At the same time, other models related to microphase separation have also been proposed, such as Seymour [6] and others proposed that the hard segment and soft segment enriched regions form a continuous cross-linked network with each other. Paik Sung and Schneide [7] proposed a more realistic microphase separation structure model: the degree of microphase separation in urethane is imperfect, not entirely microphase coexistence, but includes mixed soft segment units . There is mixing between segments in the micro-domain, which has a certain degree of influence on the morphology and mechanical properties of the material. The soft segment contains hard segments, which can lead to a change in the glass transition temperature of the soft segment. Brightly improved, narrowing the range of materials used in low temperature environments. The inclusion of soft segments in the hard segment domains can lower the glass transition temperature of the hard segment domains, thereby reducing the heat resistance of the material.
b. Hydrogen Bonding Behavior of Polyurethane Elastomers
Hydrogen bonds exist between groups containing nitrogen atoms and oxygen atoms with strong electronegativity and groups containing hydrogen atoms. The cohesive energy of the groups is related to the size of the cohesive energy of the groups. Strong, hydrogen bonds mostly exist between segments. According to reports, most of the imine groups in the various groups of polyurethane macromolecules can form hydrogen bonds, and most of them are formed by the imine groups and the carbonyl groups in the hard segment, and a small part is formed with the ether oxygen in the soft segment. group or ester carbonyl formed. Compared with the bonding force of intramolecular chemical bonds, the hydrogen bonding force is much smaller. However, the existence of a large number of hydrogen bonds in polar polymers is also one of the important factors affecting the performance. Hydrogen bonds are reversible. At lower temperatures, the close arrangement of the sexual segments promotes the formation of hydrogen bonds: at higher temperatures, the segments receive energy and undergo thermal motion, the distance between segments and molecules increases, and the hydrogen bonds are weakened or even disappear. Hydrogen bonds play the role of physical cross-linking, which can make the polyurethane body have higher strength, abrasion resistance, solvent resistance and smaller tensile permanent deformation. The more hydrogen bonds, the stronger the intermolecular forces and the higher the strength of the material. The amount of hydrogen bonds directly affects the degree of microphase differentiation of the system [8].
c. Crystallinity
The linear polyurethane with regular structure, more polar and rigid groups, more intermolecular hydrogen bonds, and good crystallinity, has improved some properties of the polyurethane material, such as strength and solvent resistance. The hardness, strength and softening point of polyurethane materials increase with the increase of crystallinity, while elongation and solubility decrease accordingly. For some applications, such as one-component thermoplastic polyurethane adhesives, fast crystallization is required to obtain initial tack. Some thermoplastic polyurethane elastomers release faster due to their high crystallinity. Crystalline polymers often become opaque due to the anisotropy of refracted light. If a small amount of branched or pendant groups are introduced into the crystalline linear polyurethane macromolecules, the crystallinity of the material decreases. When the crosslinking density increases to a certain extent, the soft segment loses its crystallinity. When the material is stretched, the tensile stress makes the molecular chain of the soft segment oriented and the regularity is improved, the crystallinity of the polyurethane elastomer is improved, and the strength of the material is correspondingly improved. The stronger the polarity of the hard segment, the more conducive to the improvement of the lattice energy of the polyurethane material after crystallization. For polyether polyurethane, with the increase of the hard segment content, the polar groups increase, the intermolecular force of the hard segment increases, the degree of microphase separation increases, the hard segment microdomain gradually forms crystallization, and the crystallinity increases with the hard segment content. Gradually increase the strength of the material.
d. Influence of soft segment structure on the properties of polyurethane elastomer
Oligomeric polyols such as polyethers and polyesters make up the soft segments. The soft segment accounts for most of the polyurethane, and the properties of the polyurethane prepared from different oligomer polyols and diisocyanates are different. The flexible (soft) segment of polyurethane elastomers mainly affects the elastic properties of the material and contributes significantly to its low temperature and tensile properties. Therefore, the Tg parameter of the soft segment is extremely important, and secondly, the crystallinity, melting point and strain-induced crystallization are also factors that affect its ultimate mechanical properties. Polyurethane elastomers and foams made of polyester with strong polarity as soft segments have better mechanical properties. Because the polyurethane made of polyester polyol contains a large polar ester group, not only hydrogen bonds can be formed between the hard segments, but also the polar groups on the soft segment can partially interact with the hard segments. The polar groups form hydrogen bonds, so that the hard segment phase can be more uniformly distributed in the soft segment phase, which acts as an elastic cross-linking point. Some polyester polyols can form soft segment crystallization at room temperature, which affects the properties of polyurethane. The strength, oil resistance and thermal oxidative aging of polyester polyurethane material are higher than those of PPG polyether polyurethane material, but the hydrolysis resistance is worse than that of polyether type. Polytetrahydrofuran (PTMG) polyurethane is easy to form crystals due to its regular molecular chain structure, and its strength is comparable to that of polyester polyurethane. Generally speaking, the ether group of the soft segment of polyether polyurethane is easy to rotate internally, has good flexibility, and has excellent low temperature performance, and there is no ester group that is relatively easy to hydrolyze in the polyether polyol chain, and its resistance to hydrolysis Better than polyester polyurethane. The α carbon of the ether bond of the polyether soft segment is easily oxidized to form peroxide radicals, resulting in a series of oxidative degradation reactions. The polyurethane with polybutadiene molecular chain as the soft segment has weak polarity, poor compatibility between soft and hard segments, and poor elastomer strength. Due to steric hindrance, the soft segment containing the side chain has weak hydrogen bonds, poor crystallinity, and the strength is worse than that of the same soft segment main chain without side group polyurethane. The molecular weight of the soft segment has an effect on the mechanical properties of the polyurethane. Generally speaking, assuming that the molecular weight of the polyurethane is the same, the strength of the polyurethane material decreases with the increase of the molecular weight of the soft segment; if the soft segment is a polyester chain, the strength of the polymer material decreases slowly with the increase of the molecular weight of the polyester diol; If the soft segment is a polyether chain, the strength of the polymer material decreases with the increase of the molecular weight of the polyether glycol, but the elongation increases. This is due to the high polarity of the ester soft segment and the large intermolecular force, which can partially offset the decrease in the strength of the polyurethane material due to the increase in the molecular weight and the increase in the soft segment content. The soft segment of polyether is weak in polarity. If the molecular weight increases, the content of the hard segment in the corresponding polyurethane decreases, resulting in a decrease in the strength of the material. Zhu Jinhua et al. [9] synthesized a series of polyurethane block copolymers and graft copolymers containing different soft segments, and tested their dynamic mechanical properties. The results showed that the compatibility of polyurethane copolymers and the chain of macromolecules Structure-related, the presence of graft chains has a significant effect on the compatibility and damping properties of polyurethane block copolymers. Generally, the effect of soft segment molecular weight on the resistance and thermal aging properties of polyurethane elastomers is not significant. The crystallinity of the soft segment has a great contribution to the crystallinity of the linear polyurethane. Generally speaking, crystallinity is beneficial to increase the strength of polyurethane. But sometimes crystallization reduces the low temperature flexibility of the material, and crystalline polymers are often opaque. In order to avoid crystallization, the integrity of the molecule can be reduced, such as using copolyester or copolyether polyol, or mixed polyol, mixed chain extender, etc.
e. Influence of hard segment on the properties of polyurethane elastomer
Hard segment structure is one of the main factors affecting the heat resistance of polyurethane elastomers. The structure of the diisocyanate and chain extender that make up the polyurethane elastomer segment is different, which also affects the heat resistance. The hard segment of polyurethane material is composed of polyisocyanate and chain extender. It contains strong polar groups such as urethane group, aryl group and substituted urea group. Usually, the rigid segment formed by aromatic isocyanate is not easy to change, and stretches at room temperature. rod-shaped. Hard segments usually affect the high temperature properties of polyurethane, such as softening, melting temperature. Commonly used diisocyanates are TDI, MDI, IPDI, PPDI, NDI, etc., commonly used alcohols are ethylene glycol, -butanediol, hexanediol, etc., and commonly used amines are MOCA, EDA, DETDA, etc. The type of hard segment is selected according to the desired mechanical properties of the polymer, such as maximum use temperature, weather resistance, solubility, etc., and its economy should also be considered. Different diisocyanate structures can affect the regularity of the hard segment and the formation of hydrogen bonds, thus having a greater impact on the strength of the elastomer. Generally speaking, the isocyanate containing aromatic ring makes the hard segment have greater rigidity and cohesive energy, which generally increases the strength of the elastomer.
The rigid segment containing urea group composed of diisocyanate and diamine chain extender is very easy to form plastic micro-domain due to the large cohesion of urea group, and the polyurethane composed of this rigid segment is prone to micro-phase. separation. Generally speaking, the higher the rigidity of the rigid segment constituting the polyurethane, the easier the microphase separation occurs. In the polyurethane, the higher the content of the rigid segment, the more likely the microphase separation occurs.
The chain extender is related to the hard segment structure of the polyurethane elastomer and has a great influence on the performance of the elastomer. Compared with the chain-extended polyurethane of aliphatic diol, the chain-extended polyurethane containing aromatic ring diamine has higher strength, because the amine chain extender can form a urea bond, and the polarity of the urea bond is higher than that of the urethane bond. Moreover, the difference in solubility parameters between the hard segment of urea bond and the soft segment of polyether is large, so the hard segment of polyurea and the soft segment of polyether have greater thermodynamic incompatibility, which makes polyurethaneurea have better microphase separation. [10], thus diamine chain-extended polyurethane has higher mechanical strength, modulus, viscoelasticity, heat resistance, and better low temperature performance than diol chain-extended polyurethane. Casting polyurethane elastomers mostly use aromatic diamines as chain extenders because the polyurethane elastomers prepared therefrom have good comprehensive properties. Xu Guangjie et al. [11] reported that carboxyl ester polyols were prepared by reacting maleic anhydride with polyols, and then reacting with other monomers such as TDI-80, cross-linking agents and chain extenders to prepare carboxyl-containing polyols. Polyurethane prepolymer was dispersed in an aqueous solution of triethanolamine to make water-based polyurethane, and the influence of the type and amount of chain extender on the performance of the resin was studied, and it was found that the amine chain extender was more effective than the hydroxyl chain extender It is beneficial to improve the mechanical properties of the resin. Using bisphenol A as a chain extender can not only improve the mechanical properties of the resin, but also increase the glass transition temperature of the resin, broaden the width of the internal friction peak, and improve the temperature range of the resin in leather state [12]. The structure of the diamine chain extender used in the polyurethane urea directly affects the hydrogen bonding, crystallization, and microphase structure separation in the material, and largely determines the performance of the material [13]. With the increase of the hard segment content, the tensile strength and hardness of the polyurethane material gradually increased, and the elongation at break decreased. This is because there is microphase separation between the phase with a certain degree of crystallinity formed by the hard segment and the amorphous phase formed by the soft segment, and the crystalline region of the hard segment acts as an effective cross-linking point. It also plays a role similar to filler reinforcement for the amorphous region of the soft segment. When the content increases, the reinforcement effect and effective crosslinking effect of the hard segment in the soft segment are enhanced, which promotes the increase of material strength.
f. Influence of crosslinking on the properties of polyurethane elastomers
Moderate intramolecular crosslinking can increase the hardness, softening temperature and elastic modulus of polyurethane materials, and reduce elongation at break, permanent deformation and swelling in solvents. For polyurethane elastomers, proper crosslinking can produce materials with excellent mechanical strength, high hardness, elasticity, and excellent wear resistance, oil resistance, ozone resistance and heat resistance. However, if the crosslinking is excessive, the properties such as tensile strength and elongation can be reduced. In block polyurethane elastomers, chemical crosslinking can be divided into two categories: (1) the use of trifunctional chain extenders (such as TMP) to form a crosslinking structure; (2) the use of excess isocyanate to react to form dicondensate Urea (via urea groups) or allophanate (via urethane groups) crosslinking. Crosslinking has a significant effect on the degree of hydrogen bonding, and the formation of crosslinks greatly reduces the degree of hydrogen bonding of the material, but chemical crosslinking has better thermal stability than physical crosslinking caused by hydrogen bonding. When the effects of chemical cross-linking network on the morphology, mechanical properties and thermal properties of polyurethane urea elastomers were studied by means of FT-IR and DSC, it was found that polyurethane urea elastomers with different cross-linking networks had different morphologies. As the density increases, the degree of microphase mixing of the elastomer increases, the glass transition temperature of the soft segment increases significantly, and the 300% tensile strength of the elastomer gradually increases, while the elongation at break decreases gradually. When , the mechanical properties (tensile strength and tear strength) of the elastomer reach the highest.
4. Applications of Polyurethane Elastomers
a. Application in coal preparation, mining, metallurgy and other industries
Polyurethane elastomers are the most non-metallic materials that meet the requirements of mines and can replace some metal materials. Polyurethane elastomer products for mountains include sieve plates, elastomer linings, conveyor belts, and the like. Polyurethane rubber sieves include relaxation sieves, tension sieves, slotted sieves, etc. Polyurethane rubber screen plate has the characteristics of excellent wear resistance, water resistance, oil resistance, vibration absorption and noise reduction, high strength, strong bonding with the metal frame, low noise, good self-cleaning effect, lightening the load of the screen machine, saving energy consumption, and prolonging the screen time. Machine life, high screening quality. Many mining equipment such as shakers, special concentrators, flotation machines, concentrators, spiral troughs, pulverizers, concentrators, pipes and elbows, contact materials such as gravel, and require wear-resistant linings; mining monorail cranes The steel core urethane drive wheel, flame retardant and antistatic polyurethane conveyor belt, equipment cable TPU sheath, dust ring, shock absorption, etc., polyurethane elastomer is the preferred material.
b. Polyurethane rubber roller
Polyurethane rubber roller is a kind of polyurethane rubber product with excellent performance, which is generally made of steel or iron covered with a layer of polyurethane elastomer by casting process. According to the use, there are: hulling rubber rollers for grain processing, extrusion rubber rollers and pulping rubber rollers in the paper industry, wire drawing rollers, drafting rollers and cutting rollers in the textile industry, wood, glass and packaging Transmission bearing rubber rollers used in industry, various rubber rollers for printing and dyeing machinery, small rubber rollers for various instruments, transmission rubber rollers for conveying systems, printing rubber rollers, metal cold rolling transmission rubber rollers, metal steel plate color coating rollers, etc. , the rubber layer of these rubber rollers can be made of polyurethane elastomer. Most of the rubber rollers are manufactured by the casting process. Generally, the steel core is placed in the center of the cylindrical mold and the elastomer is cast. Special cots can use centrifugal casting or spin casting. Spin casting eliminates the need for molds and uses room temperature vulcanization to cast elastomer systems, reducing overall processing time.
c. Polyurethane rubber wheels and tires
Polyurethane elastomer has large bearing capacity, wear resistance, oil resistance, and is firmly bonded to the metal frame. It can be used to manufacture rubber rollers widely used in various transmission mechanisms, such as; production line conveyor belts, guide rollers, cable car slides, etc. . In the direction of sports and entertainment, the wheels of high-end roller skates and scooters are all made of polyurethane. The urethane rubber wheel also has the characteristics of oil resistance, good toughness and strong adhesion. Polyurethane is also used in small electronic and precision instrument transmission, various universal wheels, etc. There are also micro-foam tires, PU foam-filled tires, etc.
d. Mechanical accessories
Various sealing rings, shock-absorbing blocks, couplings, automobile snow chains, etc.
e. Shoe material
Polyurethane elastomer has the characteristics of good cushioning performance, light weight, wear resistance, anti-skid, etc., and good processing performance. It has become an important synthetic material for shoes in the shoe industry, making sports shoes such as baseball shoes, golf balls, and football. , soles, heels, toe caps, as well as ski boots, safety shoes, casual shoes, etc. The polyurethane materials used for shoe materials include cast microcellular elastomers and thermoplastic polyurethane elastomers, etc., and the microcellular elastomer soles are the main ones. Polyurethane microcellular elastomer is light in weight and good in abrasion resistance. It is favored by shoe manufacturers. The product has a low density and is much lighter than traditional rubber soles and PVC shoe materials. Microporous polyurethane elastomers are mainly used in the soles and insoles of travel shoes, leather shoes, sports shoes, sandals, etc. in China. They are mainly used in the soles of special sports shoes that require wear resistance and elasticity abroad. The design can be diversified. TPU heel for high abrasion resistance. Thermally decomposable foaming agent can be added in injection molding to make foamed TPU elastic shoe material.
f. Die lining and blanking template for forming sheet metal parts, etc.
When punching thin sheet parts with conventional steel dies, there are often burrs on the fracture surface. The stamping technology of replacing the traditional steel mold with polyurethane rubber is a leap in the metal sheet stamping technology, which can greatly shorten the mold manufacturing cycle, prolong the service life of the mold, reduce the production cost of the molded parts, and improve the surface quality and dimensional accuracy of the parts, especially suitable for It is suitable for trial production of small and medium batches and single-piece products, and is more suitable for thin and complex stamping parts. In tile and ceramic production lines, the use of PU elastomer lining molds can reduce production costs, improve production efficiency and yield. Polyurethane can be used to make concrete molds. Polyurethane molds can be used to reproduce various patterns and produce decorative blocks. In the stamping production of metal molds, polyurethane elastomer rods, tubes and plate pads are used instead of metal springs as buffer components, with high elasticity, flexibility, compression High deformation strength, no damage to the mold.
g. Medical elastomer products
Medical polyurethane elastomers are mainly thermoplastic polyurethanes abroad, and there are also a small amount of cast polyurethane elastomers and microcellular elastomers. Due to its high strength, wear resistance, biocompatibility, and no plasticizers and other small molecule inert additives, polyurethane elastomers occupy an important position in medical polymer materials. Medical polyurethane products include polyurethane gastroscope hoses, medical hoses, artificial and diaphragm and encapsulation materials, polyurethane elastic bandages, tracheal sleeves, etc. [14].
h. Pipes
Utilizing the flexibility, high tensile strength, impact strength, low temperature resistance, high temperature resistance, and high compressive strength of polyurethane elastomers, it can be made into various hoses and hard pipes, such as high-pressure hoses, 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.
