Elastomer blends compatibilization

Since most polymers, including elastomers, are immiscible with each other, their blends undergo phase separation with poor adhesion between the matrix and dispersed phase. The properties of such blends are often poorer than the individual components. At the same time, it is often desired to combine the process and performance characteristics of two or more polymers, to develop industrially useful products. This is accomplished by compatibilizing the blend, either by adding a third component, called compatibilizer, or by chemically or mechanically enhancing the interaction of the two-component polymers. The ultimate objective is to develop a morphology that will allow smooth stress transfer from one phase to the other and allow the product to resist failure under multiple stresses. In case of elastomer blends, compatibilization is especially useful to aid uniform distribution of fillers, curatives, and plasticizers to obtain a morphologically and mechanically sound product. Compatibilization of elastomeric blends is accomplished in two ways, mechanically and chemically. 

Navarro Cassu S and Felisberti M I (2002) Polystyrene and polyether polyurethane elastomer blends compatibilized by SMA Morphology and mechanical properties, J Appl Polym Sci 83 830-837. 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

Source Aijunan, P., Technological Compatibilization of Dissimilar Elastomer Blends Part 1. ... 

Aijunan, P. Technological Compatibilization of Dissimilar Elastomer Blends Part 1. Neoprene and Ethylene o-Propylene Rubber Blends for Power Transmission Belt Application. Rubber Division, Proceedings of the American Chemical Society, Nashville, TN, Sept. 29-Oct. 2, 1998, Paper No. 52, 1-28. 

Moreover, commercially available triblock copolymers designed to be thermoplastic elastomers, not compatibilizers, are often used in lieu of the more appealing diblock materials. Since the mid-1980s, the generation of block or graft copolymers in situ during blend preparation (158,168—176), called reactive compatibilization, has emerged as an alternative approach and has received considerable commercial attention. 

There are several other routes to compatibil-izing polyamide/elastomer blends for the purpose of impact modification such as through the use of anhydride modified ABS rubbers [Baer, 1988], anhydride modified S-EB-S block [Gelles et al.,... 

The outstanding impact toughness of the commercial impact modified polyamides is attributed to the small particle size of rubber dispersion and their good degree of adhesion to the polyamide matrix. Typical morphologies of compatibilized polyamide/elastomer blends are shown in Figure... 

Sometimes, the compatibilization of PP/EPDM blends has been the key issue to improve the properties of the blends. Lopez-Manchado s group (7) studied the effect of grafted PP on the compatibihty and properties of PP-EPDM thermoplastic elastomer blends. They functionalized the isotactic PP (iPP) through grafting in Brabender plasticorder with two itaconate. The functionalization of iPP was performed by melt blending through grafting with two itaconic acid derivatives, monomethyl itaconate and dimethyl itaconate (MMI and DMI, respectively). 

Intensive properties of the blend components that dominate vulcanizate properties of the elastomer are improved if the compatibilizer is the predominant fraction of the elastomer blend. Davison et al. (1982) describe the formation of... 

TEM image of a 80/20 PP/ethylene-octene elastomer blend containing 5 wt% silica. A maleated PP compatibilizer has been added to the composite. 

Setua, D. K. and White, J. L., Flow visualization of the influence of compatibilizing agents on the mixing of elastomer blends and the effect on phase morphology, Polym. Eng. Sci. i/ 1742 (1991). 

Basically all conventional sulfur (or peroxide) crosslinked unsaturated elastomer blends could be classified as co-crosslinked compatibilized blend examples. Various ercamples of these combinations are discussed in Section 4.2. Other crosslinking chemistry has been noted in several references with examples discussed in the following. 

The majority of elastomer blends are phase separated, but of interest, as crosslinking can achieve mechanical compatibilization due to crosslinking between the phases as noted in Chapter 3. This compatibilization method can lead to unique and useful blends with a compromise in properties, offering useful commercial products as well illustrated by the applications in tire construction. The unsaturated hydrocarbon elastomers without polar functional groups are rarely miscible with each other, because no specific interactions are present to achieve the necessary thermodynamic driving force for miscibility. The few miscible examples noted generally exhibit matched solubility parameters. 

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