Synthetic polyisoprene rubbers Mooney viscosity

Synthetic high c/.y-polyisoprenes have Mooney viscosities of typically 75-80, although certain producers offer low Mooney grades having viscosities of about 60 which have proved useful in blends with other synthetic rubbers and to adhesive manufacturers. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

The curing and dynamic properties of precipitated nano-silica on NR without and with the sulfur addition (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and SBR was investigated. Silica was treated with bis(3-triethoxysilylpropyl)tetrasulfane (TESPT) to form bonds at interfaces. Cure, Mooney viscosity, glass transition temperature, bound rubber, crosslink density and DMA were measured. The properties of silica-filled SBR and BR correlated with highest rolling resistance and SBR-silica correlated with best skid resistance. A Payne effect was observed in the loss modulus under some experimental conditions. In addition to possible filler de-agglomeration and network disruption, the nanoscale of the filler may have further contributed to the non-linear response typified by the Payne effect. ... 

Synthetic polyisoprene batches exhibit far less viscosity increase on storage due to the slower crystallisation rate of the polymer. This may be illustrated by storing similar batches based on natural rubber and a synthetic polyisoprene and periodically measuring Mooney viscosities (Fig. 6). 

Following the mixing operation polyisoprenes should have higher Mooney viscosities than equivalent natural rubber compounds but, nevertheless, will still exhibit faster flow under high shear. Compounds based on the synthetic polymer may be cold fed to extruders in which the necessary prewarming prior to extrusion is easily achieved or, alternatively, for hot feed extruders premilling should be kept to a minimum to avoid too... 

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