Thermoplastic elastomers (TPEs) have the elastic behaviour of rubber and the processability of thermoplastics. TPEs have been one of the most active areas in materials and application development. A market research study by Freedonia Group forecasts the average growth of TPE for 2006-2011 period at 6.3% reaching about 4 mln tons by 2011. Automotive is the largest application of TPEs accounting for 40-50%.
Demand is slowing in developed economies, as most of the easy substitutions for thermoset rubber have been accomplished. There are signs of commoditization in areas like consumer and building/construction, and the overall market is shifting primarily to China, where many products made of TPEs are now being manufactured. These include footwear, housewares, consumer products, appliances, tools, and sports/leisure products. TPE suppliers are responding with higher-performing materials and extended functionality.
The European market for thermoplastic elastomers (TPE-S, TPE-O and TPE-V) will grow from an estimated 499,000 tons in 2007 to 570,000 tons in 2012, according to plastics and rubber industry consultant Patrick Ellis (PE, Mercurey / France). According to a Frost & Sullivan analysis of the European TPE market, the automotive industry is the largest end user for TPEs in Europe. The use of thermoset rubbers such as EPDM, polychloroprene and styrene butadiene rubber (SBR) still appreciably outweighs TPE in automotive applications. However, the industry has continued to replace thermoset rubber with TPE since Frost & Sullivan last researched this market in 2002, and this trend is expected to continue in the future. In 2001, TPE represented around 14% of thermoset rubber (by weight) used in motor vehicles and by 2004, this had increased to 15.2%.
With the commercialisation of several new types of thermoplastic vulcanizate that have been grouped together as super-TPVs, manufacturers of higher-end thermoset rubber and thermoplastics are being challenged to retain their market shares. This has opened up opportunities for TPVs in more demanding applications such as auto under-hood, appliance and industrial parts that are subjected to high temperature requirements. They are also expected to tap niche markets such as communications devices and consumer products that are used in harsh environments. Super-TPVs such as Zeotherm offer higher heat resistance than conventional TPV and co-polyesters. Zeotherm has sustained heat resistance of 150 degree C and a short-term heat resistance of up to 175 degree C. To withstand this kind of heat, other materials such as Santoprene and co-polyesters used in under-hood applications have to be incorporated with a heat shield. Elimination of the heat shield is a major advantage of super-TPVs as this helps in reducing the total cost of the system. Zeotherm also offers better over-mould adhesion onto nylon substrates than conventional TPVs.
Advantages over synthetic rubber such as recyclability, greater ease of processing and design flexibility are likely to ensure its continued penetration in automotive applications, says the analyst of this research service. Thermoplastic polyolefin elastomers have also gained an edge over most thermoset rubbers because they offer faster moulding cycles, lower energy consumption, closer tolerances on fabricated parts and lighter weight. These benefits are expected to increase demand for TPEs.
TPE nowadays is being targeted for applications higher on the performance ladder. SEBS has joined TPO in replacing copolyester elastomer (COPE) TPEs in more highly engineered applications like airbag covers. Similarly, styrenic TPEs are increasingly being used to replace more costly TPUs in abrasion-resistant applications. Specialty TPE grades are emerging with greater transparency, lower hardness, chemical resistance and scratch and mar resistance. Higher-heat materials are also being developed for very small and tightly packaged applications in wire and cable and automotive. Overmold bondability to other thermoplastics, textiles and metals remains a focus of R&D. Regulatory and market demands are also forcing suppliers to develop new materials without halogenated flame retardants and with lower volatile emissions to prevent fogging in.
There are three major types of TPE: block copolymers, rubber/plastic blends and dynamically vulcanised rubber/plastic alloys known as thermoplastic vulcanisates. New types of styrene block copolymers have improved high temperature ageing, fluid resistance, elastic recovery and set. New block copolyester TPEs have better blow moulding processability, softness and high dynamic flexing fatigue performance. One of the advantages of TPEs over thermoset rubbers is that they can be processed by standard plastics processing methods. New material includes bio-based materials with 10-100% renewable content. The nylon 12-based materials, based on castor and canola oil, have properties similar to standard grades and are targeted for sport goods. Some of the latest developments are:
Spain’s Merquinsa introduced the world’s first TPUs derived from bio based materials such as vegetable or fatty acid based polyols.
A biobased TPU from GLS, called OnFlex U, comes from soybean oils. Renewable content is claimed to be 30-45% and hardness ranges from 65-95 Shore A. Performance is similar to traditional grades for sectors like medical, consumer, and industrial.
At K 2007, Arkema introduced first commercial engineering TPE made from renewable resources. Pebax Rnew is a polyether-block-amide (PEBA) made with Arkema’s Rilsan nylon 11, based on castor oil. Grades have 20-90% renewable content and Shore hardness from 25 D to 72 D for electronics, athletic shoes, and automotive uses.
Multibas has introduced new Multiflex TEA alloys that provide improved bondability to engineering thermoplastics. Multibase is working on improved weathering grades (withstanding up to 4000 kJ accelerated exposure) for auto exterior uses. For interior applications, the company is focused on new grades that provide fogging resistance at up to 110 C/230 F, suntan-oil resistance, and improved gas-fading resistance.
Transparent TPEs are in greater demand for enhanced design flexibility in a range of overmolding applications. Kryberg has launched new Thermolast K grades of translucent SEBS-based TPEs that boast a previously unattainable level of adhesion to PC and ABS. They also bond to other styrenics, PBT, acrylic, and PETG. Hardnesses are 50 A to 80 A.
Heat resistance has been extended with new Thermolast V SEBS compounds that have a service temperature of 140 C for industrial and auto underhood parts.
Teknor’s new Elexar EL1402 family of non-halogenated SEBS grades meet UL 94V-0 with hardness starting at 50 A for wire/cable and molding. New value-added SEBS grades include Monprene MP1871R to replace silicone in medical tubing and MP2295 Kuraray has built a pilot plant in Japan for an entirely new all-acrylic TPE. It consists of alternating hard blocks of PMMA and soft blocks of poly-n-butyl-acrylate. It is said to offer weatherability, transparency, softness, and good adhesion to polar resins and paint. Hardness is 30 Shore A to 60 D. It can be injection molded, slush molded, and extruded into sheet and film. Sony has used it in camera grips. Other markets are consumer and sporting goods, automotive, and optical films.
New TPE alloys are finding a place in auto interiors. A Schulman introduced a licensed technology for Inteva Products, which consists of a hybrid TPE for slush molding IP skins to replace slush-molded TPU or sprayed urethane. The styrenic/olefinic alloy has lower density than TPU and is reportedly comparable in scratch and abrasion resistance and weatherability.