TPU is a polyurethane thermoplastic elastomer, which is a multiphase block copolymer composed of diisocyanates, polyols, and chain extenders. As a high-performance elastomer, TPU has a wide range of downstream product directions and is widely used in daily necessities, sports equipment, toys, decorative materials, and other fields, such as shoe materials, hoses, cables, medical devices, etc.
At present, the main TPU raw material manufacturers include BASF, Covestro, Lubrizol, Huntsman, Wanhua Chemical, Linghua New Materials, and so on. With the layout and capacity expansion of domestic enterprises, the TPU industry is currently highly competitive. However, in the high-end application field, it still relies on imports, which is also an area that China needs to achieve breakthroughs in. Let’s talk about the future market prospects of TPU products.
1. Supercritical foaming E-TPU
In 2012, Adidas and BASF jointly developed the running shoe brand EnergyBoost, which uses foamed TPU (trade name infinergy) as the midsole material. Due to the use of polyether TPU with a Shore A hardness of 80-85 as the substrate, compared to EVA midsoles, foamed TPU midsoles can still maintain good elasticity and softness in environments below 0 ℃, which improves wearing comfort and is widely recognized in the market.
2. Fiber reinforced modified TPU composite material
TPU has good impact resistance, but in some applications, high elastic modulus and very hard materials are required. Glass fiber reinforcement modification is a commonly used technique to increase the elastic modulus of materials. Through modification, thermoplastic composite materials with many advantages such as high elastic modulus, good insulation, strong heat resistance, good elastic recovery performance, good corrosion resistance, impact resistance, low coefficient of expansion, and dimensional stability can be obtained.
BASF has introduced a technology for preparing high modulus fiberglass reinforced TPU using glass short fibers in its patent. A TPU with a Shore D hardness of 83 was synthesized by mixing polytetrafluoroethylene glycol (PTMEG, Mn=1000), MDI, and 1,4-butanediol (BDO) with 1,3-propanediol as raw materials. This TPU was compounded with glass fiber in a mass ratio of 52:48 to obtain a composite material with an elastic modulus of 18.3 GPa and a tensile strength of 244 MPa.
In addition to glass fiber, there are also reports of products using carbon fiber composite TPU, such as Covestro’s Maezio carbon fiber/TPU composite board, which has an elastic modulus of up to 100GPa and a lower density than metals.
3. Halogen free flame retardant TPU
TPU has high strength, high toughness, excellent wear resistance and other properties, making it a very suitable sheath material for wires and cables. But in application fields such as charging stations, higher flame retardancy is required. There are generally two ways to improve the flame retardant performance of TPU. One is reactive flame retardant modification, which involves introducing flame retardant materials such as polyols or isocyanates containing phosphorus, nitrogen, and other elements into the synthesis of TPU through chemical bonding; The second is additive flame retardant modification, which involves using TPU as the substrate and adding flame retardants for melt mixing.
Reactive modification can change the structure of TPU, but when the amount of additive flame retardant is large, the strength of TPU decreases, the processing performance deteriorates, and adding a small amount cannot achieve the required flame retardant level. Currently, there is no commercially available high flame retardant product that can truly meet the application of charging stations.
Former Bayer MaterialScience (now Kostron) once introduced an organic phosphorus containing polyol (IHPO) based on phosphine oxide in a patent. The polyether TPU synthesized from IHPO, PTMEG-1000, 4,4 ‘- MDI, and BDO exhibits excellent flame retardancy and mechanical properties. The extrusion process is smooth, and the surface of the product is smooth.
Adding halogen-free flame retardants is currently the most commonly used technical route for preparing halogen-free flame retardant TPU. Generally, phosphorus based, nitrogen based, silicon based, boron based flame retardants are compounded or metal hydroxides are used as flame retardants. Due to the inherent flammability of TPU, a flame retardant filling amount of more than 30% is often required to form a stable flame retardant layer during combustion. However, when the amount of flame retardant added is large, the flame retardant is unevenly dispersed in the TPU substrate, and the mechanical properties of the flame retardant TPU are not ideal, which also limits its application and promotion in fields such as hoses, films, and cables.
BASF’s patent introduces a flame-retardant TPU technology, which blends melamine polyphosphate and a phosphorus containing derivative of phosphinic acid as flame retardants with TPU with a weight average molecular weight greater than 150kDa. It was found that the flame retardant performance was significantly improved while achieving high tensile strength.
To further enhance the tensile strength of the material, BASF’s patent introduces a method for preparing crosslinking agent masterbatch containing isocyanates. Adding 2% of this type of masterbatch to a composition that meets UL94V-0 flame retardant requirements can increase the tensile strength of the material from 35MPa to 40MPa while maintaining V-0 flame retardant performance.
To improve the heat aging resistance of flame-retardant TPU, the patent of Linghua New Materials Company also introduces a method of using surface coated metal hydroxides as flame retardants. In order to improve the hydrolysis resistance of flame-retardant TPU, Linghua New Materials Company introduced metal carbonate on the basis of adding melamine flame retardant in another patent application.
4. TPU for automotive paint protection film
Car paint protection film is a protective film that isolates the paint surface from the air after installation, prevents acid rain, oxidation, scratches, and provides long-lasting protection for the paint surface. Its main function is to protect the car paint surface after installation. The paint protection film generally consists of three layers, with a self-healing coating on the surface, a polymer film in the middle, and an acrylic pressure-sensitive adhesive on the bottom layer. TPU is one of the main materials for preparing intermediate polymer films.
The performance requirements for TPU used in paint protection film are as follows: scratch resistance, high transparency (light transmittance>95%), low-temperature flexibility, high-temperature resistance, tensile strength>50MPa, elongation>400%, and Shore A hardness range of 87-93; The most important performance is weather resistance, which includes resistance to UV aging, thermal oxidative degradation, and hydrolysis.
The currently mature products are aliphatic TPU prepared from dicyclohexyl diisocyanate (H12MDI) and polycaprolactone diol as raw materials. Ordinary aromatic TPU visibly turns yellow after one day of UV irradiation, while aliphatic TPU used for car wrap film can maintain its yellowing coefficient without significant changes under the same conditions.
Poly (ε – caprolactone) TPU has a more balanced performance compared to polyether and polyester TPU. On the one hand, it can exhibit excellent tear resistance of ordinary polyester TPU, while on the other hand, it also demonstrates outstanding low compression permanent deformation and high rebound performance of polyether TPU, thus being widely used in the market.
Due to different requirements for product cost-effectiveness after market segmentation, with the improvement of surface coating technology and adhesive formula adjustment ability, there is also a chance for polyether or ordinary polyester H12MDI aliphatic TPU to be applied to paint protection films in the future.
5. Biobased TPU
The common method for preparing bio based TPU is to introduce bio based monomers or intermediates during the polymerization process, such as bio based isocyanates (such as MDI, PDI), bio based polyols, etc. Among them, biobased isocyanates are relatively rare in the market, while biobased polyols are more common.
In terms of bio based isocyanates, as early as 2000, BASF, Covestro, and others have invested a lot of effort in PDI research, and the first batch of PDI products were put into the market in 2015-2016. Wanhua Chemical has developed 100% bio based TPU products using bio based PDI made from corn stover.
In terms of bio based polyols, it includes bio based polytetrafluoroethylene (PTMEG), bio based 1,4-butanediol (BDO), bio based 1,3-propanediol (PDO), bio based polyester polyols, bio based polyether polyols, etc.
At present, multiple TPU manufacturers have launched bio based TPU, whose performance is comparable to traditional petrochemical based TPU. The main difference between these bio based TPUs lies in the level of bio based content, generally ranging from 30% to 40%, with some even achieving higher levels. Compared to traditional petrochemical based TPU, bio based TPU has advantages such as reducing carbon emissions, sustainable regeneration of raw materials, green production, and resource conservation. BASF, Covestro, Lubrizol, Wanhua Chemical, and Linghua New Materials have launched their bio based TPU brands, and carbon reduction and sustainability are also key directions for TPU development in the future.
Post time: Aug-09-2024