From the Global Layout of Chemical Giants, Key Future Development Directions for TPU

From the Global Layout of Chemical Giants, Key Future Development Directions for TPU

TPU (Thermoplastic Polyurethane) is a type of thermoplastic elastomer belonging to the polyurethane class. It is a multiphase block copolymer composed of diisocyanate, polyol, and chain extender. As an elastomer with excellent properties, TPU has a very wide range of downstream product applications, being extensively used in daily necessities, sporting goods, toys, decorative materials, and other fields, such as footwear materials, hoses, wires and cables, medical devices, etc.

Current major producers of TPU raw materials include BASF, Covestro, Lubrizol, Huntsman, Wanhua Chemical, Huafon Chemical, Shanghai Heng'an, Ruihua, Xuchuan Chemical, and others. With the layout and capacity expansion of domestic enterprises, the TPU industry has become highly competitive. However, high-end application fields still rely on imports, which is an area where domestic breakthroughs are needed. Let's discuss the promising application fields for TPU products in the future.

1. Supercritical Foamed E-TPU
In 2012, German company Adidas and BASF jointly developed the running shoe brand Energy Boost, which used foamed TPU (brand name Infinergy) as the midsole material. Because it uses ether-type TPU with a Shore A hardness of 80-85 as the base material, compared to EVA midsoles, the foamed TPU midsole maintains good elasticity and softness even in environments below 0°C, improving wearing comfort and gaining wide market acceptance.

2. Fiber-Reinforced Modified TPU Composites
TPU has good impact resistance, but in some applications, materials with high elastic modulus and very high stiffness are required. Glass fiber reinforcement is a common technical means to improve the elastic modulus of materials. Through modification, thermoplastic composites with numerous advantages can be obtained, such as high elastic modulus, good insulation, strong heat resistance, excellent elastic recovery performance, good corrosion resistance, impact resistance, low expansion coefficient, and dimensional stability. BASF introduced a technology in a patent for preparing high-modulus glass fiber reinforced TPU using short glass fibers. Using polytetramethylene ether glycol (PTMEG, Mn=1000), MDI, 1,4-butanediol (BDO) mixed with 1,3-propanediol as raw materials to synthesize TPU with a Shore D hardness of 83, and compounding this TPU with glass fiber at a mass ratio of 52:48, a composite material with an elastic modulus of 18.3 GPa and a tensile strength reaching 244 MPa can be obtained.
Besides glass fiber, products using carbon fiber compounded with TPU have also been reported, such as Lanxess's Tepex Dynalite product and Covestro's Maezio carbon fiber/TPU composite board, whose elastic modulus can reach 100 GPa with a density lower than metal.

3. Halogen-Free Flame Retardant TPU
TPU has high strength, high toughness, and excellent wear resistance, making it very suitable for sheathing materials for wires and cables. However, higher flame retardant performance is required in application fields such as charging piles. There are generally two ways to improve the flame retardancy of TPU: one is reactive flame retardant modification, which involves introducing raw materials with flame retardant functions, such as polyols or isocyanates containing phosphorus, nitrogen and other elements, through chemical bonding during TPU synthesis, the other is additive flame retardant modification, which involves melt blending TPU as the base material with flame retardants.
Reactive modification changes the structure of TPU, but when the amount of additive flame retardant is large, the strength of TPU decreases and processing performance deteriorates, adding a small amount cannot achieve the required flame retardancy rating. Currently, no such commercialized high flame retardancy products that truly meet the requirements of charging pile applications have been seen.
Former Bayer MaterialScience (now Covestro) once introduced an organic phosphorus-containing polyol (IHPO) based on phosphine oxide in a patent. Ether-type TPU synthesized from IHPO, PTMEG-1000, 4,4'-MDI, and BDO exhibited good flame retardancy and excellent mechanical properties, with a stable extrusion process and smooth product surface.
Adding halogen-free flame retardants is currently the most common technical route for preparing halogen-free flame retardant TPU, generally using phosphorus-based, nitrogen-based, silicon-based, boron-based flame retardants in combination or metal hydroxides as flame retardants. Because TPU itself is flammable, the filler amount of flame retardant often needs to be greater than 30% to form a stable flame retardant layer during combustion. However, when the amount of flame retardant added is large, the uneven dispersion of the flame retardant in the TPU matrix leads to unsatisfactory mechanical properties of the flame retardant TPU, which also limits its application promotion in fields such as hoses, films, and cables.
A patent from BASF introduces a flame retardant TPU technology that uses a combination of melamine polyphosphate and a phosphorus-containing phosphinate derivative as flame retardants, blended with TPU having a weight-average molecular weight greater than 150 kDa. It was found that this significantly improves its flame retardant performance while achieving higher tensile strength.
To further enhance the tensile strength of the material, a BASF patent describes a preparation method for a masterbatch containing an isocyanate crosslinking agent. Adding 2% of this masterbatch to a composition that meets the UL94 V-0 flame retardancy requirement can increase the material's tensile strength from 35 MPa to 40 MPa while maintaining V-0 level flame retardancy.
To improve the heat aging resistance of flame retardant TPU, another BASF patent describes a method using surface-coated metal hydroxide as the flame retardant. To improve the hydrolysis resistance of flame retardant TPU, BASF, in another patent application, introduces metal carbonate in addition to melamine flame retardant.

4. TPU for Automotive Paint Protection Film
Automotive paint protection film is a film applied to isolate the paint surface from air, protecting against acid rain, oxidation, scratches, and providing lasting protection for the paint surface. Its main function is to protect the car's paint after installation. Paint protection film generally consists of three layers: the surface is a self-healing coating, the middle is a polymer film, and the bottom layer is an acrylic pressure-sensitive adhesive. TPU is one of the main materials for preparing the middle polymer film.
The performance requirements for TPU used in paint protection films are as follows: scratch resistance, high transparency (light transmittance > 95%), low-temperature flexibility, high temperature resistance, tensile strength > 50 MPa, elongation > 400%, and Shore A hardness range of 87-93, the most important performance is weather resistance, namely resistance to UV aging, thermo-oxidative degradation, and hydrolysis.
Currently, mature products are aliphatic TPUs prepared using dicyclohexylmethane diisocyanate (H12MDI) and polycaprolactone diol as raw materials. Ordinary aromatic TPU turns明显 yellow after just one day of UV irradiation, while aliphatic TPU for PPF can maintain a yellowness index with little change under the same conditions.

Polycaprolactone-type TPU has more balanced properties compared to polyether-type and polyester-type TPUs, on one hand, it exhibits the excellent tear resistance of ordinary polyester-type TPU, while simultaneously showing the outstanding low compression set and high rebound resilience of polyether-type TPU, thus finding widespread application in the market.
Due to different requirements for cost-performance ratios after market segmentation, and with improvements in surface coating technology and adhesive layer formulation adjustment capabilities, polyether-type or ordinary polyester-type H12MDI-based aliphatic TPUs may also have opportunities for application in paint protection films in the future.

5. Bio-based TPU
Common methods for preparing bio-based TPU involve introducing bio-based monomers or intermediates during polymerization, such as bio-based isocyanates (e.g., MDI, PDI), bio-based polyols, etc. Among them, bio-based isocyanates are less common on the market, while bio-based polyols are relatively common.
Regarding bio-based isocyanates, as early as 2000, BASF, Covestro, Mitsui Chemicals, etc., invested significant effort in PDI research, with the first PDI products launched on the market in 2015-2016. Wanhua Chemical used bio-based PDI produced from corn stalks to develop a 100% bio-based raw material TPU product. Recently, Gansu Yinguang Group successfully trial-produced the first tonnage batch of qualified PDI product with purity above 99.5%, achieving the localization of PDI products.
Regarding bio-based polyols, these include bio-sourced bio-based polytetrahydrofuran (also known as polytetramethylene ether glycol, PTMEG), bio-based 1,4-butanediol (BDO), bio-based 1,3-propanediol (PDO), bio-based polyester polyols, and bio-based polyether polyols.
Currently, several TPU manufacturers have launched bio-based TPUs whose performance can already compete with traditional petroleum-based TPUs. The main difference among these bio-based TPUs lies in the level of bio-based content, generally between 30%-40%, with some able to achieve higher levels. Compared to traditional petroleum-based TPU, bio-based TPU has advantages such as reduced carbon emissions, sustainable and renewable raw materials, green production, and resource conservation. BASF, Covestro, Lubrizol, Wanhua Chemical, Miracll Chemical, etc., have launched their bio-based TPU brands. Carbon reduction and sustainability are also key future development directions for TPU.

In summary, in the high-performance TPU R&D focused on by global chemical giants, halogen-free flame retardancy remains a key and challenging area to overcome, especially in demanding application fields like charging pile cables. Yinsu's phosphorus-based flame retardant WADP-10 is targeted solutions developed in response to these industry challenges. Through efficient synergistic compounding, they aim to achieve excellent flame retardant effects (such as UL94 V-0 rating) with relatively low addition levels, while maximizing the retention of the TPU matrix's inherent high strength, high toughness, and good processing performance. They provide important material support for developing halogen-free flame retardant TPUs that meet the needs of high-end applications.