Olefinic-type thermoplastic elastomer

The master rheogram for olefinic-type thermoplastic elastomer (TPE) obtained by the unification [77] of viscosity versus shear rate data from two sources [82,83] is shown in Fig. 4.36. The data covers a number of different grades of TPE over a range of shear rate from 1 to 1000/s but is limited to the two temperatures of 20S C and 230°C. A total of 44 data points have been used in the unification process (Table B2 of Appendix B). 

Thermoplastic elastomers (TPEs) are either block copolymers (SBS, SEES, SEPS, TPU, COPA, COPE) or blends, such as TPO (elastomer/hard thermoplastic, also referred to as thermoplastic olefin) and TPV (fhermoplastic vul-canizafe, blend of a vulcanized elastomer and a hard fhermoplastic). These types represent the majority of fhe TPEs other types are either specialty or small-volume materials. 

The rubbery materials, which are processed as thermoplastics, are usually treated as thermoplastics and identified in the same way. However, they are sometimes referred as TPE (which stands for thermoplastic elastomer) and then, these letters are followed by another letter which identifies the type of TPE. For example, TPE-A means that it is amide based, TPE-U means that is urethane based and, TPE-0 means that it is olefin based. 

TPEs which are prepared by physical blending of an elastomer with a thermoplastic. Such TPEs are categorized into two types depending on rubber vulcanization (i) thermoplastic olefins (TPOs) or thermoplastic elastomer polyolefins (TEOs) (ii) thermoplastic vulcanizates (TPVs). 

Olefinic thermoplastic elastomer (TPO) materials are defined as compounds (mixfures) of various polyolefin polymers, semicrysfalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene-propylene rubber (EPR) [10]. A common rubber of this type is called ethylene-propylene diene monomer (EPDM) rubber, which has a small amount of a third monomer, a diene (two carbon-carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements. 

Thermoplastics are resins that repeatedly soften when heated and harden when cooled (conditions that refer to fusibility ). Most thermoplastics are soluble in specific solvents and can bum to some degree. Softening temperatures vary with the polymer type and grade. Care must be taken in application conditions not to exceed the heat distortion temperature of the plastic, wherein the plastic begins to soften and potentially warp. Typical thermoplastics utilized in the automotive arena include, poly(olefins)—for example, poly(propylene) (PP) and poly(ethyl-ene)—nylon, acrylic, acetal, poly(styiene), poly(vinyl chloride) (PVC), poly-(sulfone), and the like. Also within this group are highly elastic, flexible resins known as thermoplastic elastomers (TPEs). 

Ethylene copolymers are produced i) with vinyl acetate (EVA, EVAC), ii) with vinyl alcohol (EVOH, EVAL), iii) as binary copolymers and terpolymers with acrylics (E/EA, E/MA, E/AA etc.), or iv) as lonomer resins. Olefinic thermoplastic elastomers (TPE) are available, usually PP based with EPM or EPDM rubber additions that may be lightly crosslinked. Polypropylenes are offered in various forms homopolymers, block copolymers, random copolymers and mixtures of types. Polybutylene (PB) and Polymethylpentene (PMP) complete the range. 

Plastic types are variable, ranging from flexible to rigid and from thermoplastic to thermoset. Because of these variations, the type of coating applied to them also varies, depending on cure response, solvent sensitivity, and modulus. The type of coating also depends upon the end use of the coated plastic. For example, topcoats can be applied directly to the plastic without the use of a conductive primer if two-toning or blackout areas are not part of the styling latitude. Adhesion promoters also are often utilized if a particularly difficult-to-adhere-to plastic is encountered (i.e., polypropylenes or thermoplastic polyolefins (TPOs), a blend of elastomer and olefin). 

EPDM is a terpolymer produced from ethylene, propylene, and a diene monomer that is usually 5-ethylidene-2-norbornene (ENB), see Eigure 3.12. Good EPDM properties are attainable because the stereospecific Ziegler-Natta catalysts and the newer metallocene-type catalysts are used in the polymerization of these elastomers. Much proprietary knowledge is applied with the latest catalysts to help the EPDM producers achieve a competitive advantage in the marketplace. Today, about 20% of all EPDM goes into the production of TPOs (thermoplastic olefins) or TPVs (thermoplastic vulcanizates), mainly for nontire automobile uses. (About 13% of EPDM production is used in TPO manufacture while about 7% is consumed in TPV production.)... 

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