English 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, raw material purity, new technology and new application. Thermoplastic polyurethane elastomer (TPU) is an elastomer that can be plasticized by heating and dissolved in solvent. It has excellent comprehensive properties such as high strength, high toughness, wear resistance, oil resistance and good processability, and is widely used in national defense. Thermoplastic polyurethane elastomer has become one of the important thermoplastic elastomer materials because of its excellent performance and wide application, and its molecules are basically linear with little or no chemical crosslinking. There are many physical crosslinks composed of hydrogen bonds between linear polyurethane molecular chains, and hydrogen bonds strengthen its morphology, thus giving it many excellent properties, such as high modulus, high strength, excellent wear resistance, chemical resistance, hydrolysis resistance, high temperature resistance, mildew resistance and so on. These good properties make thermoplastic polyurethane widely used in many fields, such as shoes, cables, clothing, automobiles, medicine and health, pipes, films and sheets. Generally, the final product does not need vulcanization and crosslinking, which can shorten the reaction period and reduce energy consumption. Because it is basically a polymer with linear structure, it can be processed by the same technology and equipment as thermoplastics, such as injection molding, extrusion, blow molding, calendering and so on. It is especially suitable for large-scale production of small and medium-sized parts. Waste can be recycled, and different additives or fillers can be used to improve some physical properties and reduce the cost in production or processing. TPU particles and powder: particle classification Polyurethane thermoplastic elastomers are polyester and polyether, with white irregular spherical or columnar particles, and the relative density is 1. 10~ 1.25. The relative density of polyether type is less than that of polyester type. The glass transition temperature of polyether type is100.6 ~106.1℃, and that of polyester type is 108.9~ 122.8℃. The brittleness temperature of polyether and polyester is lower than -62℃, and the low temperature resistance of polyether is better than that of polyester. Characteristics Polyurethane thermoplastic elastomer has outstanding characteristics such as excellent wear resistance, excellent ozone resistance, high hardness, high strength, good elasticity, low temperature resistance, good oil resistance, chemical resistance and environmental resistance. The hydrolytic stability of polyether ester in humid environment is much higher than that of polyester ester. Synthesis methods The synthesis methods of TPU can be divided into two types according to whether there is solvent or not: solvent-free bulk polymerization and solvent-based solution polymerization. Bulk polymerization can be divided into one-step method and prepolymer method according to reaction steps. One-step method is to mix oligomer diol, diisocyanate and chain extender simultaneously. The one-step process is simple and easy to operate, but its reaction heat is difficult to eliminate and side reactions are easy to occur. Fan Li et al. synthesized polyester thermoplastic polyurethane elastomer by one-step method. Firstly, polyester polyol and chain extender butanediol were weighed in a reactor, and the temperature was raised to 65438 020℃ for vacuum dehydration. Quickly add the preheated polyurethane, stir it evenly, pour it into the preheated container, bake it in vacuum at 120℃, then cool it to 100℃ to obtain a yellowish translucent polyurethane product, and then press it into a test piece on a flat press. The prepared TPU has high mechanical properties and damping properties. Chemical equation of TPU synthesis TPU synthesis process prepolymer method is to react oligomer diol and diisocyanate first, and then synthesize it with dry chain extender under the condition of a small amount of catalyst. Prepolymer method has complex process, high energy consumption and high viscosity of prepolymer, which increases the difficulty of process operation. However, the side reaction of prepolymer is less, and the product performance is better than that of one-step method. According to the continuity of the reaction process, it can be divided into batch method and continuous method. Production equipment commonly used in batch process includes automatic pouring equipment, curing furnace, breaking hammer, extruder and so on. The production efficiency is low and the product quality is uneven, which is not suitable for mass production. Therefore, continuous production technology and equipment have been studied at home and abroad. The continuous process equipment is reactive extrusion production line, and the main equipment includes raw material storage tank, pouring machine, parallel twin-screw extruder, underwater granulator, separation and drying equipment and packaging equipment. Twin-screw continuous reactive extrusion is the mainstream technology in production at present, with high production efficiency and stable product quality, which is suitable for mass production. Its products can be used in coatings, elastomers and adhesives. TPU molecular structure TPU is a kind of (ab) n-type block linear polymer, which consists of flexible soft segment and rigid hard segment. TPU with different segment structure has different properties, and the type of segment structure is mainly determined by the type of raw materials. The introduction of side groups in the molecular structure will reduce the orientation crystallinity between macromolecules, resulting in the decline of mechanical properties and poor swelling properties. However, certain chemical crosslinking can improve the tensile stress and solvent resistance of elastomer and reduce permanent deformation. Hard segment content Hard segment content refers to the mass percentage of hard segments in the formula and is an important parameter in formula design. Hydrogen bonds, microphase separation and crystallinity directly affected by hard segment content are the main factors that determine its morphology. Generally speaking, with the increase of hard segment content, the hardness, modulus and tear strength of TPU increase, while the elongation at break decreases. Isocyanate index Because the synthesis mechanism of TPU is a step-by-step addition polymerization reaction between functional groups, the isocyanate index r 0 (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 reached the maximum, and then with the increase of r 0 value, the molecular weight began to decrease. When r 0 is between 0.95 ~ 1, the modulus, tensile strength and tear strength of TPU increase with r 0. Molecular weight and molecular weight distribution The molecular weight of TPU has obvious influence on its mechanical properties. With the increase of the molecular weight of TPU, the tensile strength, modulus and wear resistance all increase, and these properties tend to be stable when the molecular weight reaches a certain level. The tear strength and flexural strength of TPU decrease with the increase of molecular weight. On the one hand, due to physical crosslinking, the free volume of TPU decreases; On the other hand, the high entanglement of TPU molecular chain and the increase of physical crosslinking reduce its internal fluidity. When subjected to external force, molecular chain rearrangement is difficult to realize and the applied stress cannot be effectively reduced. When the proportion of low molecular weight components is large, it is extremely harmful to the heat resistance and mechanical properties of elastomers, while when the proportion of high molecular weight components is too large, it will bring inconvenience to processing and molding. Therefore, the appropriate molecular weight and molecular weight distribution should be adjusted according to the specific processing requirements of TPU for different purposes. The chain extender 1, 4- butanediol (MDI) commonly used in raw material purity TPU is very easy to absorb water, and its purity and moisture content directly affect the actual production value and have a great influence on the molecular weight of the final product. MDI is easy to self-aggregate, and it is easy to generate dimer if it is not well preserved. The moisture content, acid value and hydroxyl value of polymeric polyols vary from batch to batch, which greatly affects the stability of TPU performance. The moisture and free carboxyl contained in raw materials, on the one hand, react with MDI and consume part of MDI, which leads to inaccurate formula design; On the other hand, the bubbles produced by the reaction play a plasticizing role, which ultimately reduces the performance of the product. Therefore, the raw materials used to synthesize TPU need to be strictly dehydrated before use. New technology and new use TPU is a rapidly developing industry, and related new technologies, new products and new uses are constantly emerging. The use range of TPU extends to almost all industries, and it has been widely used in many fields, such as shoemaking, clothing, pipes, film sheets, cables, automobiles, construction, medicine and health, national defense, sports and leisure. TPU is recognized as a new polymer material with environmental protection and excellent performance. At present, low-end consumption is the main consumption of TPU, and its high-end consumption field is basically dominated by some multinational companies, including Bayer, BASF, Lubrizol, Huntsman and so on. , are increasing the research and development of new products. TPU products with high added value have been continuously developed and put into the market, and TPU materials have become one of the fastest growing thermoplastic materials. A. Footwear: sports shoes Logo, sports shoes air cushion, hiking shoes, snow shoes, golf shoes, roller skates, fabrics and internal bonding materials. B. Clothing: snow clothes, raincoats, windbreakers, winter jackets, field suits, diapers, trousers and other fabric composites (waterproof and moisture permeable). C. Medicines: surgical gowns, hats, shoes, hospital mattresses, ice packs, bandages, plasma bags, surgical dressing belts, masks and other fabrics and lining materials, operating bed airbags. D defense supplies: fabrics and lining fabrics of aircraft fuel tanks and airbags, weapon sealing films, tent windows, military water bags, life jackets, inflatable boats, etc. E. Sporting goods: football surface and liner, inflatable bed, drinking bag, ski gloves (waterproof bag), diving suit, snow suit, swimsuit, snowboard, trademark, airbag, sweatshirt, slimming suit and other fabrics and lining materials. F Industrial supplies: rubber edges of trumpet drum paper, waterproof strips, sound insulation materials and other fabrics, fireproof materials, fireproof clothing, fireproof clothing, fireproof cloth, inner composite materials and outer sheath materials of wires and cables. G other uses: mobile phone keys, plastic inflatable toys, bed sheets, tablecloths, shower curtains, furniture cloths, aprons, pianos, computer keyboards, film-coated fabrics and lining materials.