Semi-crystalline materials elastomers

The ionomer which was isolated from the neutralization of sample SBD-2 was a brown-colored elastic network of moderate strength. Ionomer samples SBD-1 and SBD-2, neutralized to the stoichiometric end point using KOH, were compression molded at 140°C and examined for tensile properties. The results, as shown in Figure 16, illustrate the profound influence of crystallinity on the elastomeric inner block. The semi-crystalline material (SBD-1) behaves much like a rigid plastic, while the amorphous sample (SBD-2) is an elastomer of moderate strength. 

Like other semi-crystalline materials, PP imdergoes significant creep. Elastomer-... 

In order to make the best use of DMA data, it is useful to relate representative plots to the structural characteristics of different polymer families. Since this initial version of the database is devoted to rigid and semi-rigid thermoplastics, this discussion will focus on the two most important polymer families within this category - amorphous and semi-crystalline materials. Thermoplastic elastomer and a rigid crosslinked systems show significant contrast. 

At room temperature, PE is a semi-crystalline plastomer (a plastic which on stretching shows elongation like an elastomer), but on heating crystallites melt and the polymer passes through an elastomeric phase. Similarly, by hindering the crystallisation of PE (that is, by incorporating new chain elements), amorphous curable rubbery materials like ethylene propylene copolymer (EPM), ethylene propylene diene terpolymer (EPDM), ethylene-vinyl acetate copolymer (EVA), chlorinated polyethylene (CM), and chlorosulphonated polyethylene (CSM) can be prepared. 

Copoly(ester ester)s belong to the family of thermoplastic elastomers (TPEs) and consist in general of thermo-reversible hard and elastic soft domains [11]. The copoly(ester ester) used here consists of 60% poly(butylene terephthalate), 35% poly(butylene adipate) and 5% 4,4 -methylenebis(phenyl isocyanate), and shows domain sizes of about 20 nm [12]. The material possesses a rubber plateau between the glass transition temperature of the mixed amorphous PBA/PBT phase (the PBT phase is semi-crystalline) at about -30°C and the melting point of the PBT at about 220°C. Due to the vulnerability of the amorphous PBA/PBT soft domains towards water attack [13] the PBT/PBA copoly(ester ester) is used here to study the existence of ESC of a chemical rather than a physical nature. For the sake of clarity it should be emphasized that no additives have been used in the copoly(ester ester) described here. 

The tensile stress-strain curves, for the four microstructural types, cover the range from elastomers to typical semi-crystalline thermoplastics (Fig. 3.23). The lowest crystallinity material is a competitor with thermoplastic elastomers . 

It is apparent from considerations of the structure in Section 4.2 that semi-crystalline polymers are essentially two-phase materials and that the increase in modulus is due to the presence of the crystals. Traditional ideas of the stiffening effect due to the presence of crystals were based upon the statistical theory of elastomer deformation (Section 5.3.2). It was thought that the crystals in the amorphous rubber behaved like crosslinks and produced the stiffening through an increase in crosslink density rather than through their own inherent stiffness. Although this mechanism may be relevant at very low degrees of crystallinity it is clear that most semi-... 

PVC, and its copolymers, are most often converted to TPE-type materials by melt mixing them with plasticizers (plastici ers) which are compatible with the plastics material. Both polymeric and low molecular weight plasticizers are used with PVC to give elastomeric compounds. With the semi-crystalline, thermoplastics materials, it is necessary to mfac them with rubbers/elastomers, with which they are not molecularly compatible, so as to form the required softer, elastomeric materials. This is because plasticizers are not compatible with a semi-crystalline, thermoplastics material. 

Chapter 1 introduced the various materials which go into the making of filled poljnner systems. The pol)maer could be a thermoplastic, thermoset or elastomer. Further, it could be linear, branched, amorphous, crystalline or semi-crystaUine. At the same time, it may fall into the category of a homoplo3m er, copolymer, or liquid crystalline polymer. Any type of such a pol)mfter could be compovmded with fillers to form filled polymer systems. 

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