Rubbery matrix

One way of improving the adhesion between polymer and filler is to improve the level of wetting of the filler by the polymer. One approach, which has been used for many years, is to coat the filler with an additive that may be considered to have two active parts. One part is compatible with the filler, the other with the polymer. Probably the best known example is the coating of calcium carbonate with stearic acid. Such coated or activated whitings have been used particularly with hydrocarbon rubbers. It is generally believed that the polar end attaches itself to the filler particle whilst the aliphatic hydrocarbon end is compatible with the rubbery matrix. In a similar manner clays have been treated with amines. 

The outstanding morphological feature of these rubbers arises from the natural tendency of two polymer species to separate one from another, even when they have similar solubility parameters. In this case, however, this is restrained because the blocks are covalently linked to each other. In a typical commercial triblock the styrene content is about 30% of the total, giving relative block sizes of 14 72 14. At this level the styrene end blocks tend to congregate into spherical or rod-like glassy domains embedded in an amorphous rubbery matrix. These domains have diameters of about 30 nm. 

Visualization of Nano-Filler Dispersion and Morphology in Rubbery Matrix by 3D-TEM... 

TEM is still the most powerful technique to elucidate the dispersion of nano-filler in rubbery matrix. However, the conventional TEM projects three-dimensional (3D) body onto two-dimensional (2D) (x, y) plane, hence the structural information on the thickness direction (z-axis) is only obtained as an accumulated one. This lack of z-axis structure poses tricky problems in estimating 3D structure in the sample to result in more or less misleading interpretations of the structure. How to elucidate the dispersion of nano-fillers in 3D space from 2D images has not been solved until the advent of 3D-TEM technique, which combines TEM and computerized tomography technique to afford 3D structural images, incidentally called electrontomography . 

FIGURE 19.1 Morphology of nano-filler in rubbery matrix Nano-particles are aggregated, and the aggregates also associate to give filler agglomerate in rubber. (From Kohjiya, S., Kato, A., Suda, T., Shimanuki, J., and Ikeda, Y., Polymer, Al, 3298, 2006. With permission.)... 

Polyurethane propellants derive their name from a rubbery matrix which is formed through the reaction of organic, hydroxyl-carrying... 

Kilian 103) has used the van der Waals approach for treating the thermoelastic results on bimodal networks. He came to a conclusion that thermoelasticity of bimodal networks could satisfactorily be described adopting the thermomechanical autonomy of the rubbery matrix and the rigid short segments. The decrease of fu/f was supposed to be related to the dependence of the total thermal expansion coefficient on extension of the rigid short segment component. He has also emphasized that calorimetric energy balance measurements are necessary for a direct proof of the proposed hypothesis. 

The SHG intensity reached a maximum value for all of the films poled at 110°C within 1-2 mins after the field was applied. The dopants were free to orient in response to the applied field (thus increasing the SHG intensity) rapidly due to the high degree of mobility in the rubbery matrix. In all cases, the value of yp) decreased during poling at 110°C. The film maintained at 110°C lost about 20% of its maximum signal and the film quenched from 110°C to 95°C lost about 15% of its maximum signal before the... 

The results obtained for unvulcanised EPDM and NR filled with carbon black provide convincing evidence that the physical network has a bimodal structure [62, 79]. Two types of EPDM chains and/or chain fragments with widely differing densities of EPDM-carbon black adsorption junctions are present in the rubbery matrix outside the EPDM-carbon black interface (tightly bound rubber) (Figure 10.11) [62],... 

By appropriate selection of the markers for stiffness and adhesion, it is possible to differentiate the rubbery matrix (low modulus, high adhesion) and the filler particles (high modulus, low adhesion). As shown in Fig. 3.66, elevations in the height image corresponds well with areas of higher stiffness and lower adhesion. The carbon black particles can be observed in a non-homogeneous distribution at the surface of this microtomed specimen. 

These properties determine how carbon black will be distributed within the blend. These properties are not those of the filler but are the essential properties of the matrix. The matrix thus has strong influence on particle distribution. SEM studies showed that high vinyl polybutadiene and styrene-butadiene copolymers had morphologically identical carbon black distribution. However, their mechanical properties were very different. NMR analysis indicated that the difference in mechanical behavior is related to the interaction and more precisely to the molecular motions in rubbery matrix. 

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