Thermoplastic polyurethane elastomer, also known as thermoplastic polyurethane rubber, or TPU for short, is an (AB) n-type block linear polymer. A is a high molecular weight (1000~6000) polyester or polyether. B is a diol containing 2 to 12 linear carbon atoms, and the chemical structure between AB segments is diisocyanate. Thermoplastic polyurethane rubber is cross-linked by hydrogen bonds between molecules or light cross-linking between macromolecular chains. As the temperature increases or decreases, these two cross-linked structures are reversible. In the molten state or solution state, the intermolecular forces weaken, but after cooling or the solvent evaporates, strong intermolecular forces connect together to restore the original solid properties. Typical TPU such as spandex, etc. Basic introduction Chinese name: Thermoplastic polyurethane elastomer Color:: Transparent, translucent, transparent yellow background, natural color. Introduction, classification, characteristics, synthesis method, TPU molecular structure, segment structure, hard segment content, isocyanate index, molecular weight and molecular weight distribution, purity of raw materials, new technologies and new uses, Introduction Thermoplastic polyurethane elastomer (TPU) is a type of heated Elastomers that can be plasticized and solvent-soluble have excellent comprehensive properties such as high strength, high toughness, wear resistance, and oil resistance. They have good processing performance and are widely used in national defense, medical, food and other industries. Thermoplastic polyurethane elastomer, with its excellent performance and wide application, has become one of the important thermoplastic elastomer materials. Its molecules are basically linear and have no or little chemical cross-linking. There are many physical cross-links composed of hydrogen bonds between linear polyurethane molecular chains. The hydrogen bonds strengthen its morphology, thus giving many excellent properties, such as high modulus, high strength, excellent wear resistance, and Chemical, hydrolysis, high temperature and mold resistance. These good properties make thermoplastic polyurethane widely used in many fields such as shoes, cables, clothing, automobiles, medicine and health, pipes, films and sheets. The final product generally does not require vulcanization and cross-linking, which can shorten the reaction cycle and reduce energy consumption. Since it is basically a linear structure polymer, it can be processed using the same technologies and equipment as thermoplastic plastics, such as injection molding, extrusion, blow molding, calendering, etc. It is especially suitable for mass production of small and medium-sized parts. Waste materials can be recycled and reused, and different additives or fillers can be used during production or processing to improve certain physical properties and reduce costs. TPU particles and powder: Particle classification Polyurethane thermoplastic elastomers are divided into two types: polyester type and polyether type. They are white irregular spherical or columnar particles with a relative density of 1.10~1.25. The relative density of polyether type is smaller than that of polyester type. The glass transition temperature of polyether type is 100.6~106.1℃, and the glass transition temperature of polyester type is 108.9~122.8℃. The brittleness temperature of polyether type and polyester type is lower than -62℃, and the low temperature resistance of polyether type is better than that of polyester type. Characteristics The outstanding characteristics of polyurethane thermoplastic elastomer are excellent wear resistance, excellent ozone resistance, high hardness, high strength, good elasticity, low temperature resistance, good oil resistance, chemical resistance and environmental resistance, and can be polymerized in humid environments. The hydrolysis stability of ether type ester is much higher than that of polyester type. Synthesis method The synthesis method of TPU can be divided into two categories according to the presence or absence of solvent: solvent-free bulk polymerization method and solvent-based solution polymerization method. Bulk polymerization can be divided into one-step method and prepolymer method according to the reaction steps. The one-step method is produced by mixing oligomer diol, diisocyanate and chain extender at the same time. The one-step process is simple and easy to operate, but the heat of reaction is difficult to remove and side reactions are easy to occur. Li Fan et al. synthesized polyester thermoplastic polyurethane elastomer using a one-step method. First, the formula amount of polyester polyol and chain extender, butylene glycol, were weighed in the reactor, and the temperature was raised to 120°C for vacuum dehydration. Quickly add the preheated polyurethane and stir evenly, pour it into a preheated container, vacuum bake at 120°C, and then lower the temperature to 100°C to bake a light yellow translucent polyurethane product, which is then pressed into a test piece on a flat press. , the prepared TPU has high mechanical properties and damping properties. TPU synthesis chemical equation TPU synthesis process The prepolymer method is to react the oligomer diol and diisocyanate first, and then synthesize it with a dry chain extender under a small amount of catalyst. The production process of the prepolymer method is complex, consumes high energy, and the viscosity of the prepolymer produced is high, which increases the difficulty of process operation. However, the prepolymer has fewer side reactions, and the product performance is better than the one-step method. According to the continuity of the reaction process, it can be divided into batch method and continuous method.
Commonly used production equipment for the batch method include automated pouring equipment, curing ovens, breakers, extruders, etc. Its production efficiency is low, product quality is uneven, and it is not suitable for large-scale production. Therefore, continuous production processes and equipment have been carried out at home and abroad. research. The continuous method equipment is a reaction extrusion production line. Its main equipment includes raw material storage tanks, pouring machines, parallel twin-screw extruders, underwater pelletizers, separation drying equipment and packaging equipment. The twin-screw continuous reaction extrusion method is the mainstream production process at present. It has high production efficiency and stable product quality, and is suitable for large-scale production. It produces products that can be used in coatings, elastomers and adhesives. TPU molecular structure segment structure TPU is an (AB) n-type block linear polymer, composed of flexible soft segments and rigid hard segments. TPUs with different segment structures have different properties, and the type of segment structure is mainly determined by the type of raw materials. The introduction of side groups into the molecular structure will reduce the orientation crystallinity between macromolecules, resulting in a decrease in mechanical properties and poor swelling performance; while certain chemical cross-linking can improve the elongation stress and solvent resistance of the elastomer, and reduce permanent deformation. Hard segment content Hard segment content refers to the mass percentage of hard segments in the product and is an important parameter in formula design. The hydrogen bonding, degree of microphase separation and crystallization properties directly affected by the hard segment content are the main factors that determine its morphology. Generally speaking, as the hard segment content increases, the hardness, modulus and tear strength of TPU increase, while the elongation at break decreases. Isocyanate index Since the synthesis mechanism of TPU is a stepwise addition polymerization reaction between functional groups, the isocyanate index r 0 (the molar ratio of diisocyanate to oligomer diol) directly affects the molecular weight. When r 0 ≤1, the molecular weight of TPU increases with the increase of r 0 . When r 0 =1, the molecular weight reaches the maximum. If the r 0 value continues to increase, the molecular weight begins to decrease again. When r 0 is between 0.95 and 1, TPU modulus, tensile strength, tear strength, etc. increase as r 0 increases. Molecular weight and molecular weight distribution The molecular weight of TPU has a significant impact on its mechanical properties. As the molecular weight of TPU increases, the tensile strength, modulus and wear resistance increase. When the molecular weight reaches a certain level, these properties tend to stabilize. The tear strength and flexural resistance of TPU decrease as the molecular weight increases. On the one hand, the physical cross-linking of TPU reduces the free volume; on the other hand, the high degree of entanglement of TPU molecular chains and the increase in physical cross-linking reduce the Due to their internal mobility, when subjected to external forces, molecular chain rearrangement is not easy to achieve and cannot effectively alleviate the applied stress. When the proportion of low molecular weight components is large, it is extremely harmful to the heat resistance and mechanical properties of the elastomer, while when the proportion of high molecular weight components is too large, it will cause inconvenience to processing and molding. Therefore, the appropriate molecular weight and molecular weight distribution of TPU for different uses should be adjusted according to its specific processing requirements. Purity of raw materials: 1,4-butanediol (MDI), a commonly used chain extender for TPU, is very easy to absorb water. Its purity and moisture content directly affect the actual production value, and have a great impact on the molecular weight of the final product. MDI is prone to self-aggregation and can easily form dimers if not stored well. The moisture content, acid value, hydroxyl value, etc. of polymerized polyols vary from batch to batch, which greatly affects the stability of TPU performance. The moisture and free carboxyl groups contained in the raw materials react with MDI on the one hand, consuming part of the MDI and causing inaccurate formula design; on the other hand, the bubbles generated by the reaction act as plasticizers, ultimately reducing the performance of the product. Therefore, the raw materials used to synthesize TPU need to be strictly dehydrated before use. New technologies and new uses TPU is a rapidly developing industry, and related new technologies, new products and new uses are constantly emerging. The uses of TPU extend to almost every industry. It has been widely used in shoes, clothing, pipes, and films. And many fields such as sheets, cables, automobiles, construction, medicine and health, national defense, sports and leisure. TPU is recognized as a new polymer material that is green, environmentally friendly, and has excellent performance. At present, TPU is mainly used for low-end consumption, and its high-end consumption field is basically dominated by some multinational companies, including Germany's Bayer and BASF, and the United States' Lubrizol and Huntsman, etc. are increasing the research and development of new products with high added value. TPU products are constantly being developed and put into the market, and TPU materials have become one of the fastest growing thermoplastic materials.
A. Footwear: Sports shoe logos, sports shoe air cushions, mountaineering shoes, snowshoes, golf shoes, skates, fabrics and lining materials. B． Ready-made clothing: snowcoats, raincoats, windbreakers, cold-proof jackets, field clothes, diapers, menstrual pants, and other fabric composite materials (waterproof and breathable). C. Medical products: surgical gowns, caps, shoes, hospital mattresses, ice packs, bandages, plasma bags, surgical dressing strips, masks, and other fabrics and lining materials, operating bed airbags. D. National defense supplies: aircraft fuel tanks, weapons storage coatings, tent windows, military water bags, life jackets, fabrics and inner fabrics for inflatable boats, etc., airbags. E. Sports goods: football surface and liner, inflatable beds, drinking bags, ski gloves (waterproof bags), wetsuits, snowsuits, swimsuits, snowboards, trademarks, airbags, sweatshirts, slimming clothes and other fabrics and lining materials. F. Industrial supplies: trumpet drum paper, rubber edges, waterproof strips, sound insulation materials, fireproof materials, fireproof clothing, firefighting suits, fireproof cloth and other fabrics and inner and lining composite materials, and outer sheath materials for wires and cables. G. Other uses: mobile phone buttons, plastic inflatable toys, bed sheets, tablecloths, shower curtains, furniture fabrics, aprons, pianos, computer keyboards, lamination and other fabrics and lining materials.