Applications of thermoplastic elastomers

In general, the thermoplastic elastomers have yet to achieve the aim of replacing general purpose vulcanised rubbers. They have replaced mbbers in some specialised oil-resistant applications but their greatest growth has been in developing materials of consistency somewhat between conventional rubbers and hard thermoplastics. A number of uses have also been developed outside the field of conventional rubber and plastics technology. 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaced by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

S-I—S and S—EB—S polymers are widely used in adhesive, sealing and coating formulations as well as being important additives to many asphalt formulations. 

Thermoplastic polyurethane elastomers have now been available for many years (and were described in the first edition of this book). The adipate polyester-based materials have outstanding abrasion and tear resistance as well as very good resistance to oils and oxidative degradation. The polyether-based materials are more noted for their resistance to hydrolysis and fungal attack. Rather specialised polymers based on polycaprolactone (Section 25.11) may be considered as premium grade materials with good all round properties. 

Whilst approximately twice the raw material cost of TPO- and S-B-S-type polymers, thermoplastic polyurethane elastomers find applications where abrasion resistance and toughness are particular requirements. Uses include gears, timing and drive belts, footwear (including ski boots) and tyre chains. Polyether-based materials have also achieved a number of significant medical applications. There is also some minor use as hot melt adhesives, particularly for the footwear industry. 

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Because of increased production and the lower cost of raw material, thermoplastic elastomeric materials are a significant and growing part of the total polymers market. World consumption in 1995 is estimated to approach 1,000,000 metric tons (3). However, because the melt to solid transition is reversible, some properties of thermoplastic elastomers, eg, compression set, solvent resistance, and resistance to deformation at high temperatures, are usually not as good as those of the conventional vulcanized mbbers. Applications of thermoplastic elastomers are, therefore, in areas where these properties are less important, eg, footwear, wire insulation, adhesives, polymer blending, and not in areas such as automobile tires. 

Handlin DL Jr Trenor S, Wright K. Applications of thermoplastic elastomers based on styrenic block copolymers. In Matyjaszewski K, Gnanou Y, Leibler L, editors. Macro-molecular Engineering Precise Synthesis, Materials Properties, Applications. Volume 4. Weinheim, Germany Wiley-VCH 2007. p 2001. 

Handlin, D.L., Trenor, S., Wright, K., 2007. Applications of thermoplastic elastomers based on styrenic block copolymers. In Matyjaszewski, K., Gnanou, Y., Leibler, L. (Eds.), Macromolecular Engineering, vol. 4. Wiley, Weinheim, pp. 2001-2032. 

For a long time, the application of thermoplastic elastomers (TPE-0) together with oils was considered impossible, because conventional TPE-0 generally swells strongly when in contact with oily media or oily vapors for an extended period. This swelling may become so significant that it jeopardizes proper service. Therefore, caution is advised for such applications. 

Applications of thermoplastic elastomers of all types have been extensively described [2,44-46]. Some highlights are as follows. 

Mochizuki A (2000) Application of thermoplastic elastomer to medical device, Seikei Kako 12 770-774 (CA 135 262059). 

Polyesters, such as microbially produced poly[(P)-3-hydroxybutyric acid] [poly(3HB)], other poly[(P)-hydroxyalkanoic acids] [poly(HA)] and related biosynthetic or chemosynthetic polyesters are a class of polymers that have potential applications as thermoplastic elastomers. In contrast to poly(ethylene) and similar polymers with saturated, non-functionalized carbon backbones, poly(HA) can be biodegraded to water, methane, and/or carbon dioxide. This review provides an overview of the microbiology, biochemistry and molecular biology of poly(HA) biodegradation. In particular, the properties of extracellular and intracellular poly(HA) hydrolyzing enzymes [poly(HA) depolymerases] are described. 

Before briefly discussing each type it is necessary to consider the performance of thermoplastic elastomers, and the problem of defining service temperature limits for them. The structural features that convey the ability to be processed as a thermoplastic are also a limiting factor in their use. Since it is the pseudocrosslinks that allow these materials to develop elastomeric behaviour, any factor which interferes with the integrity of the pseudocrosslinks will weaken the material, and allow excessive creep or stress relaxation to occur under the sustained application of stress and strain. Temperature is obviously one such factor. 

Stepwise addition polymerization is used in the preparation of segmented polyurethanes (compare Sect. 4.2.1), e.g., poly(ester ether) urethanes which also find application in thermoplastic elastomers. Here, both blocks are preformed separately and are linked together by reaction with isocyanates ... 

Some of the conditions used in rubber test methods may need modifying for application to thermoplastic elastomers because of their intrinsic thermoplastic nature. If the temperatures generally used in ageing and compression set tests on thermosetting rubbers were applied to thermoplastic materials they could appear to perform extremely badly. Whether this was significant would depend on the service temperature. Data sheets need to be checked as those for thermoplastic elastomers may have used much lower temperatures that would be found for conventional rubbers, and it is only too easy to get a misleading impression of performance. 

The field of metal-catalyzed copolymerization of oxetanes and C02 will continue to flourish, due not only to the versatility of the reaction but also to the aliphatic polycarbonate products being important components of thermoplastic elastomers that, in turn, have huge potential in medical applications such as sutures, drug-delivery systems, body, and dental implants, and tissue engineering. The exploration of other oxetane monomers (Figure 8.17) such as 3,3-dimethyloxetane and 3-methoxymethyl-3-methyloxetane, will surely provide a multitude of applications... 

T nterest in polyether-ester block copolymers that are both thermoplastic - and elastomeric continues at a sustained pace (1-9). Most of the recent communications have dealt with the tetramethylene terephthalate/ poly(tetramethylene ether) terephthalate copolymers which are continuing to find increased use in commercial applications requiring thermoplastic elastomers with superior properties. 

Williams, J.L. Medical Applications for Thermoplastic Elastomers, Proceedings of the 1st International Conference on Thermoplastic Elastomer Markets and Technology Schotland Business Research, Inc. Princeton, NJ, 1988. 

Block copolymers are an important class of polymers used in many applications from thermoplastic elastomers to polymer-blend stabilizers. Their synthesis is most often done by ionic polymerization, which is both costly and sometimes difficult to control. However, block copolymer properties strongly depend, for example, on the exact chemical composition, block molar mass, and block yield. These parameters can be evaluated in a single experiment using copolymer GPC with multiple detection. 

Defined diblocks, triblock or multiblock copolymers find important applications in the areas of thermoplastic elastomers, data storage technology [126], and as compatibilizers (e.g. in polymer blends). In thin films these polymers may display different morphologies than in the bulk, which necessitates an accurate analysis. 

Modification of polymers by incorporating block sequences having low glass transition tenperatures is a means of changing the mechanical properties and is especially useful for the formation of thermoplastic elastomers if the basic pol3nner is semi-crystalline. These rubber-like blocks are usually formed by ionic or transition metal catalyzed reactions. Radical pol3nmeri-zation on the other hand is experimentally simpler and applicable to a wide variety of monomers. 

SYNTHESIS OF THERMOPLASTIC ELASTOMERS AND THEIR APPLICATION IN VIRUCIDAL SURGICAL GLOVES... 

Intense commercial and academic interest in block copolymers developed during the 1960s and continues today. These materials attract the attention of industry because of their potential for application as thermoplastic elastomers, tough plastics, compatibilizing agents for polymer blends, agents for surface and interface mo dification, polymer micelles, etc. Academic interest arises, primarily, from the use of these materials as model copolymer systems where effects of thermodynamic incompatibility of the two (or more) components on properties in bulk and solution can be probed. The synthesis, characterization, and properties of classical linear block copolymers (AB diblocks, ABA triblocks, and segmented (AB)n systems) have been well documented in a number of books and reviews [1-7] and will not be discussed herein except for the sake of comparison. 

The market of PP/EPDM blends has grown dramatically because of its recycling abihty and processability by conventional thermoplastic processing equipment. The unique characteristics of thermoplastic elastomer made it an attractive alternative to conventional elastomers in a variety of markets. Liu et al. showed from the experimental blends (53) that materials cost reduction of between 30% to 50% is possible in comparison to commercial products if one applies the PP/EPDM blends to the construction of a basketball court, a tennis court, and a roller hockey rink, which were estimated around 7000, 14,000, and 40,000, respectively. The cost comparison took into account the percentage of rubber or PP used in experimental blend, the exponential factor for a scale-up process and the overall surface area of the specific applications. Among many possible application of this blend two readily feasible applications are roofing and flooring. 

Various applications of the injection molding system have been developed outside the scope of the cure of rubbers, and a few examples are given, with the substitution of thermoset rubbers by thermoplastic elastomers a range of thermoplastic elastomer compounds were introduced and processed using reaction compounding technology. They are called reaction modified thermoplastic elastomers or ReMoTE [5]. 

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