Polar synthetic rubber blends properties

The susceptibility of NR based polar synthetic rubber blends to preparation methods and protocols makes the use of testing procedures able to detect and monitor the characteristics of these blend structures imperative. Thus, a vast spectrum of test methods is used to measure properties of both the uncured stocks and the vulcanizates. ... 

The thermal properties of NR based polar synthetic rubber blends is expected to affect the application range of these vulcanizates. Degradation, glass transition and crystallization temperatures determine the service conditions of each blend. Additionally, the existence of single or multiple shifted or not glass transition temperatures of each blend supplies evidence for the miscibility of the components involved. " Nevertheless, in many cases further analysis might be required to determine miscibility. 

The miscibility of natural rubber (NR) blends is one of the most important factors when designing NR products. For instance, when the NR is miscible with a dissimilar polymer on a molecular level, we may improve the properties of NR as a function of the composition of the polymer. This is significantly different from the design for immiscible NR blends, whose properties are greatly dependent upon the morphology of the blend but less so on the composition. In most cases, NR is immiscible with non-polar synthetic rubbers, i.e. NR/butadiene rubber (BR) with high c -1,4-butadiene units, NR/styrene-butadiene rubber (SBR), NR/butyl rubber (IIR), NR/silicone rubber (q)13,i4 NR/ethylene-propylene-diene rubber (EPDM). This means it is important to find miscible NR blends and to control the morphology of the immiscible NR blends in a rational way. In this chapter, properties of NR blends are described from the viewpoint of miscibility, i.e. the miscible blend of NR/BR and the immiscible blend of NR/SBR. 

Differences in viscosity values and solubility parameters between NR and polar synthetic rubbers usually produce immiscible blends. Table 9.1 shows the solubility parameters of some relevant rubber types.The morphology of such blends is determined by the mixing procedure followed, the rheological properties and the degree of compatibility of the components involved. Investigating the morphology of the blend delivers significant information... 

The natural rubber does not generally exhibit all the desired properties for use in the rubber industry. Thus, it is possible to obtain better mechanical and physical properties at a lower cost by blending natural rubber with synthetic rubbers. Normally, natural rubber is deteriorated by ozone and thermal attacks due to its highly unsaturated backbone, and it also shows low oil and chemical resistances due to its non-polarity. However, these properties can be achieved by blending it with low unsaturated ethylene propylene diene monomer rubber, styrene butadiene rubber, carboxylate styrene butadiene rubber, nitrile butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, and acrylonitrile butadiene rubber. 

The presence of polar groups in HRs such as polycyclopentadiene results in improved compatibility of these HRs with high molecular weight substances such as rubbers and synthetic resins, with which the HRs are blended in the preparation of compositions and also to enhance properties of HRs, such as pigment dispersion fluidity, and adhesiveness, that the HRs in their modified form do not readily manifest [85]. 

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