Rubber blend composites elastomer phase

The transport properties of polymer blends are of interest both for the practical application of blends and for providing insight into the morphology of the blend. Measurement of the effect of blend composition on permeability in various rubbers has been described [49i].The permeability of elastomer blends depends on the concentration of the continuous phase and the morphology of the dispersed phase. Extended disperse phase structures, particularly lying in a stacked or lamellar configuration, can lead to a reduced permeability because of the more tortuous path that must be taken by penetrants [49]]. 

The addition of rubber to polypropylene can lead to improvements in impact resistance. One of the most commonly added elastomers is ethylene-propylene rubber. The elastomer is blended with polypropylene, forming a separate elastomer phase. Rubber can be added in excess of 50 percent to give elastomeric compositions. Compounds with less than 50 percent added rubber are of considerable interest as modified thermoplastics. Impact grades of PP can be formed into films with good puncture resistance. 

The concept of co-continuous polymer blends with carbon black preferentially located in one of the continuous polymer phases or at the polymer-blend interface has been studied for more than a decade with an aim to reduce the percolation threshold. Examples of this kind are the work by Geuskens et al. in as early as 1987 [31], which shows that for the same carbon loading, the resistivity of the co-continuous polymer/rubber blends is several orders of magnitude smaller than that of the single polymer/carbon black composites. Recent works on polymer/elastomer combinations [32,33] and on polymer/polymer systems [34- 1] have also shown that the... 

When the conductive filler locahzes in a minor phase of a blend, that phase must be at least partially continuous for the composite to be globally conductive. Morphology is often adjusted to keep a conductive minor phase volume to a minimum, while maximizing continuity in an attempt to minimize the additional cost incurred for the conductive filler. For example, in a rubber-modified polypropylene, the carbon resides in the minor rubber phase. Figure 30 shows that the minor phase rheology of a conductive TPO. For this, the conductive carbon resides fully in the elastomer phase, which is the dark region. The minor elastomer phase morphology has been adjusted to be somewhat lamellar so that the conductive domains can be continuous within the composite at low-volume fractions. 

Blends of EPDM rubbers with polypropylene in suitable ratios have been marketed as thermoplastic elastomers (TPE), also commercially known as thermoplastic polyolefin elastomers (TPO). These heterophasic polymers, characterized by thermoreversible interaction among the polymeric chains, belong to a broad family of olefinic alloys that can now be produced directly during the polymerization phase, unlike blended TPE and TPO, and various compositions (with various compounding additives) can be formulated which are primarily tailored to meet different requirements of most of car applications. The TPE-based synthetic leather and foam sheets are typical examples. 

The DV process for thermoplastic elastomers can be described as follows After sufficient melt-mixing of plastic and rubber, vulcanizing agents are added. Vulcanization of the rubber phase occurs as mixing continues. After removal from the mixer, the cooled blend can be chopped, extruded, pelletized, injection molded, and so on. Such a composition is described as a dispersion of very small particles of vulcanized rubber in a thermoplastic resin matrix. Such compositions are prepared commercially by a continuous process by using a twin-screw extruder. 

Ternary nanocomposites contain three components therefore, coimtless combinahons of materials and compositions are encountered in the literature and in practice. Polyolefins are almost always encoimtered as a component in nanocomposite blends, being the matrix, the dispersed phase, or both. Generally, semicrystalline thermoplastics such as polypropylene (PP) and polyethylene (PE) are very popular as the matrix component, while the dispersed phase consists of either another thermoplashc [15-17] or an elastomer [5,18-23]. Polyolefin-based thermoplashc elastomers, such as ethylene/propylene rubber, and other ethylene-based... 

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