Immiscible Rubber Blends
Most polymer blends are thermodynamically immiscible, leading to a phase-segregated morphology. Control of this morphology, including the domain sizes and interfacial regions, along with partitioning of compounding ingredients such as filler and curatives
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Abstract Most polymer blends are thermodynamically immiscible, leading to a phase-segregated morphology. Control of this morphology, including the domain sizes and interfacial regions, along with partitioning of compounding ingredients such as filler and curatives between the phases, provides opportunities for achieving properties that are otherwise unattainable. This chapter reviews fundamental aspects of phase-separated rubber blends, with a survey of the important literature on the topic. Due to the vanishingly small entropy gain accompanying the mixing of high polymers, most polymer blends are phase-separated; there is no mixing at the segmental level, and the morphology is heterogeneous. The few thermodynamically miscible rubber blends include those having components exhibiting specific interactions (e.g., chlorinated polymers with epoxidized rubber [1, 2]); trivial blends of copolymers (siloxanes [3], polyolefins [4–6], nitrile rubbers (NBR) [7], ethylenepropylene rubbers [8, 9], butyl and polyisobutylene [10, 11], 1,4-polybutadiene (PBD) and styrene-butadiene rubber (SBR) [12, 13]); and miscellaneous cases such as 1,2-polybutadiene/1,4-polyisoprene (NR) [14], polyisobutylene/head-to-head polypropylene [15], polyepichlorohydrin/poly(vinylmethylether) [16, 17], and acrylate rubber/fluorocarbon copolymers [18]. The focus of this chapter is immiscible blends, in which the components are segregated into spatially distinct domains. These domains can range in size from a few hundred nm to microns, and usually have a very broad size distribution (Fig. 1) [19]. Except at the interface of these phases, the dynamics of the components are essentially the same as for the pure materials. However, immiscible blends can still yield novel and useful properties, provided the components are ‘‘compatible’’, a term loosely defined as a blend that does not undergo macroscopic phase separation and has some advantageous properties. Unlike miscible blends, the properties of which are roughly the average of
C. M. Roland (&) Chemistry Division, Naval Research Lab, Code 6120, Washington DC 20375-5342, USA e-mail: [email protected]
P. M. Visakh et al. (eds.), Advances in Elastomers I, Advanced Structured Materials 11, DOI: 10.1007/978-3-642-20925-3_6, Ó Springer-Verlag Berlin Heidelberg 2013
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Fig. 1 Transmission electron micrograph of a blend of 5 % 1,4-polybutadiene in polychloroprene. The mean diameter of the dispersed particles is 80 nm, with a very broad size distribution. A 100 nm scale bar is shown in the upper left corner. From Ref. [19]
those of the pure component, phase-separated blends can exhibit behavior not otherwise attainable. Some aspects are sensitive to the size of the domains, as well as the composition and interconnectedness of the interfacial regions. An important variable in heterogeneous blends is the spatial distribution of crosslinks, filler, stabilizers, etc. The ability to alter the phase morphology and the distribution of compounding ingredients offers the potential for perf
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