Rubber blends loss modulus

The B-series of silica samples were also blended with rubber and the compound formulation is shown in Table 17.6. The uncured gums were then tested according to ISO 5794-2 1998. The uncured samples were tested using a Mooney viscometer and an RPA, which measures the dynamic mechanical properties as the samples cure. Figure 17.7 shows the results of these two tests for the Mooney viscosity at 100°C, storage modulus, loss modulus, and tan 8. 

One could be tempted to overcome the modulus loss in PBT-rubber blends by adding glass or mineral to the rubber-modified blends. While this works to some extent, the effect of the filler or reinforcement is to limit the ductility of the blend. 

Figure 7. Shear modulus G and loss modulus G" of [nitrile-butadiene rubber (NBR)]-[styrene-acrylonitrile (SAN)] copolymer blends. Data from Ref. 4. NBR (vol %), 36 and 51 respectively...

A series of PP/C2C3 rubber blends was measured, subsequently, to investigate the relation between the loss modulus areas of the rubber relaxation effects and the rubber concentration. 

In the case of rubber blend clay composites good state of exfoliation of the clay, sufficiendy strong filler-rubber interactions as well as the compatibility between different rubber phases are playing major role. The presence of intercalated organoclays restricts the mobility of the rubber chains due to their confinement between the layers. As the concentration of nano filler increases the loss modulus increased. This can be explained in terms of the friction between the filler particles and the rubber matrix when the filler particles are uniformly dispersed in the mbber matrix. The damping values are found to decrease with the amount of filler due to the restricted mobility of the polymer chains owing to the intercalation of polymer chains into the layers of silicates. 

De Sarkar et al. [52] have reported a series of new TPEs from the blends of hydrogenated SBR and PE. These binary blends are prepared by melt mixing of the components in an internal mixer, such as Brabender Plasticorder. The tensile strength, elongation at break, modulus, set, and hysteresis loss of such TPEs are comparable to conventional rubbers and are excellent. At intermediate blend ratio, the set values show similarity to those typical of TPEs (Table 5.5). 

Figure 4.2 shows the DMA results of a PP/talc (85/15) system represented in the standard way i.e. the log G and log G plotted as a function of the temperature. The loss shear modulus curve shows relaxation maxima at about 60°C (the crystalline phase [a] relaxation) and at about 0°C the amorphous phase glass-rubber [S] relaxation). Blending such a PP sample with a C2C3 rubber results in an extra (rubber) relaxation maximum at about -50°C. 

Because of its inherent brittleness, polystyrene homopolymer itself has limited application in blends. However, its impact-modified version, viz., HIPS, is more widely used. HIPS itself is a reactor-made multiphase system with 5-13 % polybutadiene ( cis -rich) dispersed as discrete particles in the polystyrene phase, with an optimum particle size of mean diameter of 2.5 pm. The rubber in HIPS is chemically grafted to some extent to the polystyrene. The effective volume of the rubber dispersion is actually increased through the occlusion of some polystyrene. To optimize the impact strength, the rubber particle size (>2.5 pm) and the distribution is normally controlled by the agitation and the proper choice of other process conditions during the polymerization. The property improvements in HIPS, viz., increased impact strength and ductility, are accompanied by the loss in clarity and a decrease in the tensile strength and modulus compared to the unmodified polystyrene. 

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