In 1958, Goodrich Chemical Company (now renamed Lubrizol) registered the TPU brand Estane for the first time. Over the past 40 years, there have been more than 20 brand names around the world, and each brand has several series of products. At present, TPU raw material manufacturers mainly include BASF, Covestro, Lubrizol, Huntsman Corporation, Wanhua Chemical Group, Shanghai Heng’an, Ruihua, Xuchuan Chemical, etc.
1、 Category of TPU
According to the soft segment structure, it can be divided into polyester type, polyether type, and butadiene type, which respectively contain ester group, ether group, or butene group.
According to the hard segment structure, it can be divided into urethane type and urethane urea type, which are respectively obtained from ethylene glycol chain extenders or diamine chain extenders. The common classification is divided into polyester type and polyether type.
According to the presence or absence of cross-linking, it can be divided into pure thermoplastic and semi thermoplastic.
The former has a pure linear structure and no cross-linking bonds; The latter contains a small amount of cross-linked bonds such as Allophanic acid ester.
According to the use of finished products, they can be divided into profiled parts (various Machine element), pipes (sheaths, bar profiles), films (sheets, thin plates), adhesives, coatings, fibers, etc.
2、 Synthesis of TPU
TPU belongs to polyurethane in terms of molecular structure. So, how did it aggregate?
According to different synthesis processes, it is mainly divided into bulk polymerization and solution polymerization.
In bulk polymerization, it can also be divided into pre polymerization method and one-step method based on the presence or absence of pre reaction:
The prepolymerization method involves reacting diisocyanate with macromolecular diols for a certain period of time before adding chain extension to produce TPU;
The one-step method involves simultaneously mixing and reacting macromolecular diols, diisocyanates, and chain extenders to form TPU.
Solution polymerization involves first dissolving diisocyanate in a solvent, then adding macromolecular diols to react for a certain period of time, and finally adding chain extenders to generate TPU.
The type of TPU soft segment, molecular weight, hard or soft segment content, and TPU aggregation state can affect the density of TPU, with a density of approximately 1.10-1.25, and there is no significant difference compared to other rubbers and plastics.
At the same hardness, the density of polyether type TPU is lower than that of polyester type TPU.
3、 Processing of TPU
TPU particles require various processes to form the final product, mainly using melting and solution methods for TPU processing.
Melting processing is a commonly used process in the plastic industry, such as mixing, rolling, extrusion, blow molding, and molding;
Solution processing is the process of preparing a solution by dissolving particles in a solvent or directly polymerizing them in a solvent, and then coating, spinning, and so on.
The final product made from TPU generally does not require vulcanization crosslinking reaction, which can shorten the production cycle and recycle waste materials.
4、 Performance of TPU
TPU has high modulus, high strength, high elongation and elasticity, excellent wear resistance, oil resistance, low temperature resistance, and aging resistance.
High tensile strength, high elongation, and low long-term compression permanent deformation rate are all significant advantages of TPU.
XiaoU will mainly elaborate on the mechanical properties of TPU from aspects such as tensile strength and elongation, resilience, hardness, etc.
High tensile strength and high elongation
TPU has excellent tensile strength and elongation. From the data in the figure below, we can see that the tensile strength and elongation of polyether type TPU are much better than those of polyvinyl chloride plastic and rubber.
In addition, TPU can meet the requirements of the food industry with little or no additives added during the processing, which is also difficult for other materials such as PVC and rubber to achieve.
Resilience is very sensitive to temperature
The resilience of TPU refers to the degree to which it quickly recovers to its original state after the deformation stress is relieved, expressed as recovery energy, which is the ratio of deformation retraction work to the work required to produce deformation. It is a function of the dynamic modulus and internal friction of an elastic body and is very sensitive to temperature.
The rebound decreases with the decrease of temperature until a certain temperature, and the elasticity rapidly increases again. This temperature is the crystallization temperature of the soft segment, which is determined by the structure of the macromolecular diol. Polyether type TPU is lower than polyester type TPU. At temperatures below the crystallization temperature, the elastomer becomes very hard and loses its elasticity. Therefore, resilience is similar to a rebound from the surface of a hard metal.
The hardness range is Shore A60-D80
Hardness is an indicator of a material’s ability to resist deformation, scoring, and scratching.
The hardness of TPU is usually measured using Shore A and Shore D hardness testers, with Shore A used for softer TPUs and Shore D used for harder TPUs.
The hardness of TPU can be adjusted by adjusting the proportion of soft and hard chain segments. Therefore, TPU has a relatively wide hardness range, ranging from Shore A60-D80, spanning the hardness of rubber and plastic, and has high elasticity throughout the entire hardness range.
As the hardness changes, some properties of TPU may change. For example, increasing the hardness of TPU will result in performance changes such as increased tensile modulus and tear strength, increased rigidity and compressive stress (load capacity), decreased elongation, increased density and dynamic heat generation, and increased environmental resistance.
5、 Application of TPU
As an excellent elastomer, TPU has a wide range of downstream product directions and is widely used in daily necessities, sports goods, toys, decorative materials, and other fields.
Shoe materials
TPU is mainly used for shoe materials due to its excellent elasticity and wear resistance. Footwear products containing TPU are much more comfortable to wear than regular footwear products, so they are more widely used in high-end footwear products, especially some sports shoes and casual shoes.
hose
Due to its softness, good tensile strength, impact strength, and resistance to high and low temperatures, TPU hoses are widely used in China as gas and oil hoses for mechanical equipment such as aircraft, tanks, automobiles, motorcycles, and machine tools.
cable
TPU provides tear resistance, wear resistance, and bending characteristics, with high and low temperature resistance being the key to cable performance. So in the Chinese market, advanced cables such as control cables and power cables use TPUs to protect the coating materials of complex cable designs, and their applications are becoming increasingly widespread.
Medical devices
TPU is a safe, stable and high-quality PVC substitute material, which will not contain Phthalate and other chemical harmful substances, and will migrate to the blood or other liquids in the medical catheter or medical bag to cause side effects. It is also a specially developed extrusion grade and injection grade TPU.
film
TPU film is a thin film made from TPU granular material through special processes such as rolling, casting, blowing, and coating. Due to its high strength, wear resistance, good elasticity, and weather resistance, TPU films are widely used in industries, shoe materials, clothing fitting, automotive, chemical, electronic, medical, and other fields.
Post time: Feb-05-2020