Elastomers and Elastoplasts

Going up somewhat in hard segment content to the 50-60% range affords ( at least in polyurethane or urea-urethane RIM) the elastomers and elastoplastics, or perhaps a better word than elastoplastics would be toughened plastics. 

According to physical behavior and means of processing, plastics or plastics raw materials are classified as thermoplasts, thermosets, elastomers, and elastoplasts. Physical characteristics and processing behavior are determined by molecular architecture and temperature of use (Table 33-1). 

The most important property of elastomers and elastoplasts is their accentuated high, hard or soft rubberlike elasticity. The commercially interesting property values in these cases are generally only reached after formulating or compounding with fillers, plasticizers, etc. The subsequent cross-linking depends on the type of rubber, that is, on the nature of the cross-linkable or vulcanizable groups. 

Paints or lacquers are composites of, in general, three components pigments, binders, and solvents. Depending on application, the nature of the pigment can vary between extremely wide limits (see also Chapter 34). The binders are also known as film formers they are exclusively polymers or prepolymers, that is, thermoplasts, thermosets, elastomers, and elastoplasts. The nature of the solvent can also vary within wide limits according to the type of film former and the desired application. Here, solvents are described as good in the paints industry when they lead to low-viscosity paints or lacquers. Such good solvents are usually poor solvents in the thermodynamic sense (see also Chapters 4 and 6). 

Block copolymers were developed rapidly in the 1960s when living anionic polymerization was first utilized to synthesize triblock thermoplastic elastomers or elastoplastics. At the same time, step or condensation polymerization to produce thermoplastic polyurethanes, urea-urethane spandex fibers, and later more specialized materials, such as the semicrystalline polyester-polyether copolymers were developed [10]. Imide block or segmented copolymers utilizing... 

The microstructure and stereoblock distribution peculiar of polypropenes produced with this class of catalysts imparts thermoplastic elastomeric properties to the polymers. Thermoplastic elastomers or elastoplasts (TPEs) owe their elastomeric properties of resiliency and high tensile strength to physical cross-linking (formation of hard domains in a soft matrix) due to the presence of short, crystallizable... 

The synthesis of ABA blocks from a glassy thermoplastic A and an elastomeric B produces other elastoplastics with attractive properties. Polyester chains can be extended with di-isoeyanate, which is then treated with cumene hydroperoxide to leave a peroxide group at both ends of the chain. By heating this in the presence of styrene, a vinyl polymerization is initiated and an ABA block created. The modulus-temperature curves show how the mechanical properties can be modified in this way (Figure 15.7). These block copolymers are known as thermoplastic elastomers. 

Thermoplasts, thermosets, elastoplasts, and elastomers can occur in variousprocessedforms as three-dimensional working materials, as foil, film, and coatings in two dimensional form, or in one-dimensional form as fibers or yarn. All classes of plastics, that is, thermoplasts, thermosets, elastoplasts, and elastomers, can be fabricated into working materials. Most fibers and yarn are thermoplastics, but they also include thermosets (i.e., phenolic resin fibers), elastoplasts (i.e., Spandex fibers), and elastomers (i.e., rubber thread). Foil, films, and coatings can also consist of all classes of plastics. Conversely, however, not all representatives of a given class are suitable for a given processed form. 

In extrusion, the preheated material is forced through the perforated plate of an extruder by means of a screw or a double screw and allowed to cool in a bath or in the air. Thermoplasts, elastomers, elastoplasts, and thermosets are extruded. The required stability of shape of the extruded material can be... 

Filaments and fibers are one-dimensional forms of thermoplasts, or, less often, of thermosets, elastoplasts, or elastomers. They are classffled as natural or chemical flbers according to origin. 

Three kinds of glues or adhesives can be distinguished melt glues, solution glues, and polymerization glues. Elastomers, elastoplasts, or thermosets may be used in all three kinds. 

The conducted tests leaded to developing grounds for the technology for dynamic vulcanization of materials with thermo-elastoplastic properties, in which a thermoplastic polymer constitutes a continuous phase, whereas the dispersed phase consists of cross-linked elastomer particles. Basic elastomers are polyisoprene with isotactivity level of 85% or higher and copolymer EOE containing over 30% of n-octene. 

Physical PP/elastomer mixtures Polyolefins and polymeric mixtures Synthetics Thermal resistance Thermo-elastoplastic properties... 

This copolymer is really an elastoplast, with properties intermediate between that of a plastic and an elastomer. A suggested surface preparation method is as follows ... 

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