Diene rubbers glass transition

Before providing such an explanation it should first be noted that progressive addition of a plasticiser causes a reduction in the glass transition temperature of the polymer-plasticiser blend which eventually will be rubbery at room temperature. This suggests that plasticiser molecules insert themselves between polymer molecules, reducing but not eliminating polymer-polymer contacts and generating additional free volume. With traditional hydrocarbon softeners as used in diene rubbers this is probably almost all that happens. However, in the... 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

Elastomers or rubbers are flexible materials that are mainly used in tires, hoses, and seals as adhesives or as impact modifiers of thermoplastics. They exhibit high resistance to impact, even at low temperatures at which materials increase their rigidity. Eor some of the applications (e.g., tires or hoses), these materials have to be slightly crosslinked once they are formed into the desired shape in order to impart them dimensional stability, since otherwise they tend to slowly flow. Elastomers are polymers that are used above their glass-transition temperature (Tg). Some examples of common elastomers are polybutadiene, which is used as an impact modifier of rigid plastics SBR (copolymer of styrene and butadiene), mainly used in tires EPDM (copolymer of ethylene, propylene, and a diene monomer, usually norbornene) NBR (copolymer of acrylonitrile and butadiene) and so on. 

The diene double bond in equation (9.94) may be either cis or trans. The cis products all have lower glass transition temperatures and/or reduced crystallinity, and they make superior elastomers. A random copolymer of butadiene and styrene is polymerized to form SBR (styrene-butadiene rubber). This copolymer forms the basis for tire rubber (see below). The trans materials, such... 

Das et al., demonstrates, an approach of compatibilization between polychloroprene (CR) and ethylene propylene diene monomer rubber (EPDM) by using nanoclay (NC) as a compatibilizer and, simultaneously, as a very strong reinforcing nano-fiUer. With the incorporation of less than 9 wt.% nanoclay, the dynamic storage modulus above the glass transition region of such a blend increases from 2 MPa to 54 MPa. This tremendous reinforcing as weU as the compatibilization effect of the nanoclay was understood by thermodynamically driven preferential framework-like accumulation of exfoliated nanoclay platelets in the phase... 

DMA has been found to be particularly useful in studying blends of rubbers, particularly those that are structurally similar, and so are difficult to characterise by the use of other techniques such as infi ared spectroscopy. A good example of this is the diene rubbers (polybutadiene, polyisoprene, styrene-butadiene rubber, etc.), which are often blended together to produce a wide range of commonly encountered products, e.g. car and truck tyres, seals and gaskets. The difference in the glass transition temperatures of these rubbers (see Table 6.10 below) is sufficient for them to be resolved from each other in a DMA experiment (see Figures 6.9 and 6.10). 

In addition to the diene rubbers, it is also possible to use DMA to identify blends of the other commercially available rubbers, provided that there is a sufficient difference in their glass transition temperature, and to characterise their properties. For example, Carlberg, Colombini and Maurer [44] mixed ethylene-propylene rubber and silicone rubber in a number of blend ratios and studied their morphology and viscoelastic properties. The results obtained experimentally by DMA and DSC were compared to theoretical data produced from self-consistent models, both indicating that the silicone rubber was the dispersed phase in a continuum of ethylene-propylene rubber. 

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