Thermoplastic Polyurethane Elastomer Types

Desmocoll 176, 400 and 420 are primarily linear thermoplastic polyurethane elastomer resins of medium, medium-high and high crystallization rates, respectively. They are supplied as small, light brown, talc-covered, pieces. The polymers have a density of 1 2-1-23 g cm . This density, and their stabilization by the hydrolysis stabilizer Staboxal PCD, imply that they are poly(ester-urethanes). They show outstanding adhesion to numerous materials including plastics, rubber, leather, fabrics, wood, metals, etc. 

The following solvents dissolve some if not all of the foregoing Desmocoll adhesive polymers methyl, ethyl and butyl acetates, acetone, methyl ethyl ketone, methylene chloride, propylene dichloride, trichlor-ethylene, the monomethyl ether acetates of ethylene glycol and 1,3-butylene glycol, etc. Toluene may be used as a dilution solvent. 

Desmocoll 176 is compatible with such plasticizers as benzyl butyl phthalate, diphenyl cresyl phosphate and trichlorethyl phosphate. It has slight or no compatibility with dibutyl phthalate, dioctyl phthalate, triphenyl phosphate, tricresyl phosphate, dibutyl adipate, benzyl octyl adipate, phenyl and cresyl alkyl sulphonates. 

The Desmocoll polymers show compatibility with some or all of the following polymers to the extent that they give clear solutions and films phthalic resins, xylene-formaldehyde resin, cyclohexanone-formaldehyde resin, highly chlorinated terphenyl, terpene-phenolic resin, acetyl cellulose, nitrocellulose, nitrile rubber, chlorinated PVC, vinyl chloride-vinyl acetate copolymer, rosin esters and coumarone resin. 

In bonding strong substrates, and if solvent and greater heat resistance are required in the adhesive bond, then the Desmocolls may be mixed with appropriate amounts of isocyanates such as TDI,4,4, 4 -triphenylmethane triisocyanate (Desmodur R) or Desmodur RF (Fig. 8.7), which is thiophosphoric acid (p-isocyanatophenyl ester) used as a 20% solution in methylene chloride. 

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One partieular form of thermoplastic polyurethane elastomers is the elastic fibre known as spandex fibre. Like the usual thermoplastic rubbers these materials consist of hard and soft segments but to qualify for the term spandex by the US Federal Trade Commission the polymer used should contain at least 85% of segmented polyurethane. The first commercial material of this type was introduced by Du Pont in 1958 (Lycra). Several other similar materials have since been introduced including Dorlastan (Bayer), Spanzelle (Courtaulds) and Vyrene (US Rubber). 

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. 

In the present study we utilized Plasticorder torque values (polymer viscosity) on a relative basis, principally to follow the course of thermoplastic polyurethane elastomer polymerization, and the effect of several relevant variables on this polymerization. These torque data, expressed in meter-grams, served our purposes well, and we have not attempted to translate them to absolute rheological units. Such translation, which is a rather complex problem, has been addressed by others using a different rotor type and other polymers in the Plasticorder.14 That study concluded that the shear rate, y, of the Brabender Plasticorder with a somewhat different rotor configuration (roller blade) is in the range of 23 - 228 sec 1 over the rotor speed range of 30 - 200 rpm. 

One particular form of thermoplastic polyurethane elastomer is the elastic fiber known as Spandex. Several commercial materials of this type have been introduced, which include Lycra (Du Pont), Dorlastan (Bayer) Spanzelle (Courtaulds), and Vyrene (U.S. Rubber). Spandex fibers have higher modulus, tensile strength, and resistance to oxidation, and are able to produce finer deniers than natural rubber. They have enabled lighter-weight garments to be produced. Staple fiber blends of Spandex fiber with non-elastic fibers have also been introduced. 

Of the available polyurethane types, the crosslinked thermoplastic polyurethane elastomers seem to be best for use in powdered form. 

As the substrate sheet, a thin plastic film or tightly packed nonwoven cloth, such as polyester spanbond nonwoven cloth of approximately 0.15 mm, is used. A synthetic rubber, such as styrene-butadiene rubber or thermoplastic polyurethane elastomer, is used as a binder. In addition, a surfactant for hydrophilicity, an antioxidant for prevention of thermodeformation, and a silica-type inorganic filler for prevention of tackiness are used. For the superabsorbent polymer particles, various synthetic polymers, for example, polyacrylate and polyvinyl-type superabsorbent polymers, can be used. For this apphcation, the particle sizes are an important parameter, because they polymer is required to be within the coating layer, and as the absorption rate is no retarded, quickly protrude from the layer when swelling. 

Method D appears to be possibly the most important type of isocyanate-based adhesive system. It is similar to Method B in that a preformed, fully reacted, high molecular weight polymer is employed as a vehicle in the adhesive formulation. The strength of the vehicle holds adherend members in exact position after assembly until the full bond has formed. Method D differs from Method B in that its vehicle polymer is a polyurethane. A further difference is that the inherent adhesive character and strength of the polyurethane vehicle frequently enables its use without added di- or poiyisocyanate. This strength may be realized in essentially amorphous compositions such as the thermoplastic polyurethane elastomers or millable gums. Or it may be achieved with crystallizing urethane adhesive polymers. 

Various polyurethane types can be fabricated as elastomeric film and sheet. The B.F. Goodrich Chemical Company supplies a family of thermoplastic polyurethane elastomers ( Estane ) suitable for making such products, and formerly marketed Tuftane film and sheet made from these polymers. Currently, the Lord Corporation continues the manufacture and marketing of Tuftane film and sheet. Stevens Molded Products has... 

Of the available polyurethane types, the virtually crosslinked thermoplastic polyurethane elastomers would seem to be best and ideally suited for supply and use in powdered form. Their uses include adhesive applications which exploit the advantages of the powder form. 

Two types of thermoplastic polyurethane elastomers have been developed polyester-based and polyether-based. At similar hardness, polyester-based urethane will exhibit better toughness, oil resistance, physical characteristics, and outstanding abrasion resistance. The polyether type has better hydrolytic stability... 

The thermoplastic polyurethane elastomers (Chen et al 1992) exhibit very similar morphologies to that of the SBS or SIS and, similarly to them, allow the characteristics of both phases, crystalline and glassy, to be combined. Polyurethane adhesives can also be classified in the Adhesives implemented by Chemical Process category that can induce certain confusion. To be consistent with our classification one must consider that two types of polyurethane-based adhesives can be commercially available the ones that exhibit semicrystalline properties that can be implemented via a physical process, and the seconds with dormant reactive functions that can react via a chemical process to lead to a network. 

Global consumption of thermoplastic mbbers of all types is estimated at about 600,000 t/yr (51). Of this, 42% was estimated to be consumed in the United States, 39% in Western Europe, and 19% in Japan. At present, the woddwide market is estimated to be divided as follows styrenic block copolymers, 48% hard polymer/elastomer combinations, 26% thermoplastic polyurethanes, 12% thermoplastic polyesters, 4% and others, 9%. The three largest end uses were transportation, 23% footwear, 18% and adhesives, coatings, etc, 16%. The ranges of the hardness values, prices, and specific gravities of commercially available materials are given in Table 4. 

Thermoplastic polyurethane (TPU) is a type of synthetic polymer that has properties between the characteristics of plastics and rubber. It belongs to the thermoplastic elastomer group. The typical procedure of vulcanization in rubber processing generally is not needed for TPU instead, the processing procedure for normal plastics is used. With a similar hardness to other elastomers, TPU has better elasticity, resistance to oil, and resistance to impact at low temperatures. TPU is a rapidly developing polymeric material. 

Polyurethane elastomers are exceptionally tough, abrasion resistant, and resist attack by oil. The polyester types (AU) are susceptible to hydrolytic attack at above ambient temperatures, and certain polyester thermoplastic polyurethanes have been known to stress crack in cable jacketing applications when in contact with water at ambient temperatures this latter effect has sometimes, incorrectly, been ascribed to fungal attack. Polyether types (EU) are far more resistant to hydrolytic attack. Certain polyurethanes can be attacked by UV light, the resistance to this agency primarily being determined by the isocyanate used. 

Solid polyurethane elastomers are of three types, cast, mailable and thermoplastic. They are used in types, bearings, shoe heels, etc. 

Polyurethane multiblock copolymers of the type described by Eqs. 2-197 and 2-198 constitute an important segment of the commercial polyurethane market. The annual global production is about 250 million pounds. These polyurethanes are referred to as thermoplastic polyurethanes (TPUs) (trade names Estane, Texin). They are among a broader group of elastomeric block copolymers referred to as thermoplastic elastomers (TPEs). Crosslinking is a requirement to obtain the resilience associated with a rubber. The presence of a crosslinked network prevents polymer chains from irreversibly slipping past one another on deformation and allows for rapid and complete recovery from deformation. 

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