Elastomer blends, immiscible applications

Multiple notable reviews of elastomer blends exist. The first general treatment of the subject by Hess et al. (1993) reviews the applications, analysis, and the properties of the immiscible elastomer blends. Two related treatments by Roland (1989) and Ngai and Roland (2004) exist and describe the physics of mixing immiscible polymer blends and a more recent account of the analytical methods. Mangaraj (2002) has a more detailed review of elastomer blends. Other reviews by Corish (1978) and McDonel et al. (1978) deal with specific aspects of elastomer blends. A publication by Zhang (2009) on specific EPDM blends with NR/BR for tire sidewall approaches this area from the view of a specific application. Less comprehensive accounts of this area are also described for polyolefin elastomer blends by Slusarski et al. (2003) and Feldman (2005). 

Immiscible Blends. Rubber. Elastomer/elastomer blends are used extensively for commercial applications, particularly in the construction of automobile tires. There is an extensive patent and technological literature on this subject. A recent review (see chapter 19 of Ref. 19 by McDonel, Baranwal, and Andries) summarizes a great deal of this... 

The sampUng of polymer blends in Polymeric Compatibilizers by S. Datta and D. J. Lohse, Hanser-Gardner, 1996, that >93% of polymer blends are combinations of thermoplastic and elastomers. However, automotive tires (5000kt/yr in 1995), a blend of elastomers, are the largest application for any immiscible polymer blend. 

To fulfil this demand, immiscible blend components have traditionally found their synergistic properties utilized in macroscopic blend applications. As an example, for over fifty years polyamides have been blended with a multitude of partners to produce materials with a wide range of highly desirable properties these include improved mechanical properties (with poly(vinyl acetate)), increased hardness and molding stability (with ABS), excellent processability, low permeability and good printability (with polyolefins), and improved toughness (with alkenes or elastomers) [1]. 

The most important commercial use of elastomer blends is in the huge tire market. These blends are generally phase separated and represent one of the largest single applications for immiscible or miscible blends. Ckjmpatibilization is achieved via crosslinking reactions across the interface. The use of SBR/PB (polybutadiene) and NR(natural rubber)/PB for tread, NR/SBR/PB and NR/PB for carcass, NR/PB and NR/SBR for sidewall and NR/SBR/PIB... 

Proton spin-temperature equilibration between the hard- and soft-segment-rich domains of the polyurethane elastomer on the order of 10-100 ms might be considered fast relative to a macroscopically phase-separated blend [26] or copolymer, but slow relative to a strongly interacting mixture [25]. This is reasonable for a microphase-separated material whose solid state morphology has been the subject of considerable theoretical and experimental research. Under fortuitous circumstances, intimate (near-neighbor) contact between dissimilar molecules in a mixture can be studied via direct measurement of proton spin diffusion in a two-dimensional application of the 1H-CRAM PS experiment (Combined Rotation And Multiple Pulse Spectroscopy). Belfiore et al. [17,25,31] have detected intermolecular dipolar communication in a hydrogen-bonded cocrystallized solid solution of poly(ethylene oxide) and resorcinol on the f00-/xs time scale, whereas Ernst and coworkers [26] report the absence of proton spin diffusion on the 100-ms time scale for an immiscible blend of polystyrene and poly(vinyl methyl ether), cast from chloroform. 

The recent proliferation of metallocene-based polyolefins and polyolefin elastomers have gained their popularity owing to their density, cost, and ease of processabUity. PVC/POE blends have therefore been investigated as flexible PVC compounds. However, these blends are thermodynamically immiscible and needed suitable compatibiUzers such as the chlorinated polyethylenes (Eastman and Dadmun 2002). Since they are not miscible, POEs do not lower the PVC modulus sufficiently unless some plasticizer or a compatible elastomer such as EPE is also added. Commercially, some PVC/POE alloys are offered by TeknorApex under Flexalloy trade name with a shore A hardness 40-60 and brittle points down to —50 °C. They are claimed to have excellent low-temperature toughness, flexibility, compression set-resistance, and oil resistance. Suitable applications include automotive hoses, seals, gaskets, wire jacketing, etc. 

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