Hardness polymers

TPE hard polymer pLASTOTffiRS SYNTHETIC - TTiERMOPLASTIC ELASTOTffiRS] (Vol 9) -WVTHof PARRIERPOLYTffiRS] (Vol 3)... 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestmctive method is the measurement of torsional modulus. A number of instmments are available (13—18). More details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

Mechanical and Thermal Properties. The first member of the acrylate series, poly(methyl acrylate), has fltde or no tack at room temperature it is a tough, mbbery, and moderately hard polymer. Poly(ethyl acrylate) is more mbberflke, considerably softer, and more extensible. Poly(butyl acrylate) is softer stiU, and much tackier. This information is quantitatively summarized in Table 2 (41). In the alkyl acrylate series, the softness increases through n-octy acrylate. As the chain length is increased beyond n-octy side-chain crystallization occurs and the materials become brittle (42) poly( -hexadecyl acrylate) is hard and waxlike at room temperature but is soft and tacky above its softening point. 

Products are granular, free-flowing, and dust-free by nature, since no flow conditioner dust is used as with sulfur-coated fertilizers. They possess excellent abrasion resistance and handling integrity. Since the outer coating is a hard polymer, the products do not leave waxy residues on material handling and apphcation equipment. 

Fig. 4. Phase arrangement in hard polymer/elastomer combinations in which the elastomer phase has been dynamically vulcanised.

Other thermoplastic elastomer combiaations, ia which the elastomer phase may or may not be cross-linked, include blends of polypropylene with nitrile (30,31), butyl (33), and natural (34) mbbers, blends of PVC with nitrile mbber (35,36), and blends of halogenated polyolefins with ethylene interpolymers (29). Collectively, thermoplastic elastomers of this type ate referred to herein as hard polymer/elastomer combinations. Some of the more important examples of the various types are shown in Table 3. 

In the hard polymer/elastomer combinations, the elastomer is often chosen to be a polar mbber or it is cross-linked in some cases it is both. Either of these features improves the resistance to oils and solvents (44). 

In thermoplastic polyurethanes, polyesters, and polyamides, the crystalline end segments, together with the polar center segments, impart good oil resistance and high upper service temperatures. The hard component in most hard polymer/elastomer combinations is crystalline and imparts resistance to solvents and oils, as well as providing the products with relatively high upper service temperatures. 

Thermoplastic elastomers that are hard polymer/elastomer combinations are often not truly synthesized. Instead, the two polymers that form the hard and soft phases are intimately mixed on high shear equipment. 

The production of the hard polymer/elastomer combinations is more simple. The two components are mixed together under conditions of intensive shear. In some cases, grafting may occur. In a variation of this technique, the elastomer can be cross-linked while the mixing is taking place, a process described as dynamic vulcanization (32). 

A large number of hard polymer/elastomer combinations made by the last technique have been investigated (30). In some cases, the components are technologically compatibilized by use of a grafting reaction, but usually a fine dispersion of the two phases is formed that is sufficient to give the product the properties of a thermoplastic elastomer. 

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. 

Table 7. Some Trade Names of Thermoplastic Elastomers Based on Hard Polymer/Elastomer Combinations...

Table 15. Properties of Hard Polymer/Elastomer Combinations Based on Polar Elastomers...

Colour formation reactions of this type are utilised in carbonless copy paper, which is based on the principle of colour formation on the copy as a result of pressure of writing or typing in the master sheet. In such systems, the underside of the master sheet contains the colour former, for example compound 243, encased in microcapsules, which are tiny spheres with a hard polymer outer shell. Pressure on the master sheet breaks the microcapsules and allows the colour former to come into contact with an acidic reagent coated on the copy sheet, thus causing an irreversible colour formation reaction. 

An interesting way to prepare shock-resistant coatings [381] follows the synthesis of the ABS-terpolymers, e.g. shock-resistant polystyrene, where a soft, elastomeric phase is incorporated in a hard polymer matrix via covalent bonds. Because organic coatings solidify in situ, elastomeric microgels have been synthesized and mixed to a binder which forms the hard matrix phase before the application of this mixture as a coating material. 

The liquid or low-melting solid monomers can be cured to the solid state by incorporating a curing catalyst and heating the mixtures below the decomposition temperature. Moreover, the cured solids are transparent and hard polymers formed of three-dimensional networks with moderate thermostability. 

Hard oils, in toilet soap making, 22 734 Hard polymer-elastomer combinations, 24 700, 708... 

Thermoplastic elastomers (TPE), 9 565-566, 24 695-720 applications for, 24 709-717 based on block copolymers, 24 697t based on graft copolymers, ionomers, and structures with core-shell morphologies, 24 699 based on hard polymer/elastomer combinations, 24 699t based on silicone rubber blends, 24 700 commercial production of, 24 705-708 economic aspects of, 24 708-709 elastomer phase in, 24 703 glass-transition and crystal melting temperatures of, 24 702t hard phase in, 24 703-704 health and safety factors related to, 24 717-718... 

Among the aliphatic polyhydrocarbons, polyisobutylene with a molecular weight between 1000 and 30,000 was suggested for hard polymers like chlorinated rubber, polystyrene, and PVC by I.G. Farbenindustrie in 1932. 

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