BR rubber

R. Hulst, R. M. Seyger, J. P. M. van Duynhoven, L. van der Does, J. W. M. Noordermeer and A. Bantjes, Vulcanization of butadiene rubber by means of cyclic disulfides. 3. A 2D solid state HRMAS NMR study on accelerated sulfur vulcanizates of BR rubber, Macromolecules, 1999, 32, 7521-7529. 

Several NMR relaxation studies using carbon-black-filled natural rubber (NR), EPDM and butadiene (BR) rubbers have shown that a layer of immobilised, tightly bound rubber is formed on the carbon black surface [20, 62, 79, 87, 89] (Figure 10.9). 

For autohesion to occur, the polymer must he well above its glass transition temperature. It is the primary mechanism operating in the heat sealing of plastics and the coalescence of droplets from emulsions of the film-forming plastics such as S-BR rubber during drying. 

The synthetic rubbers most frequently used for car tyres are emulsion and solution styreen/butadiene random copolymers (ESBR and SSBR) and butadiene rubber (BR). Truck tyres, however, often contain a certain amount of natural rubber (NR) or its synthetic version isoprene rubber (IR). The Tg-value of BR rubber as such can vary, depending on its chemical structure between -100°C and -20°C the Tg-value of SBR can, in principle, vary between -100°C and 100°C. 

Butyllithium-initiated homopolymerisation of butadiene results in a BR polymer containing random distributed cis-1,4, trans-1,4 and 1,2-BR or vinyl-BR units. The concentration of the catalyst modifier and the polymerisation temperature (between 40°C and 75°C) determine the concentrations of the three different components. Thus, BR rubber is in fact nearly always a terpolymer and its Tg-value can be described by means of the Gordon-Taylor relation [7]. This relation is written in its general form as ... 

BR rubbers or high styrene ESBR rubber. Usually, these rubbers are not compatible [9]. Figure 1.5 shows, for example, the DSC thermograms of SSBR/BR (75/25) samples mechanically blended in an internal mixer at 50°C and solution (cyclo-hexane) blended. The Tg-value of the BR phase (-110°C) is unaffected however, the glass-rubber transition of the SSBR phase is influenced on the low temperature side. The two transition effects clearly present are an indication for the non-compatibility of these two polymers. 

Loss factor / temperature relation of SBR BR rubbers at a frequency of 0.94 MHz... 

Fusion curves of BR rubber (trans content 65%) after crystallization at different cooling rates... 

TABLE 10.3 Assignment of the signals in the H-NMR spectra of partially ozonized E-BR and BR rubbers... 

NR/BR rubber blends Influences of preparation mode and elastomer ratio Degradation of the blends takes place in two steps Castro et al. 2007... 

Polybutadiene (BR rubber) and the random styrene/butadiene copolymer (SBR rubber) are the most widely used polymers. Their principal use is in tyres, which are typically blends of natural/synthetic rubber. BR rubber has good resilience, abrasion resistance and low heat build-up. SBR contains 10-25% styrene which is added chiefly to reduce cost but also to improve wearing and blending characteristics compared with BR alone. BR and SBR are polymerized by a free-radical mechanism as a water emulsion at 50-60 °C (hot rubber) or 0°C (cold rubber). Typical compositions are 70% trans-1,4, 15% cis-1,4 and 15% 1,2. Ziegler systems used in solution polymerization yield an SBR which has higher MW, narrower MWD and higher cis-1,4-content than the emulsion free-radical type. 

In the preceding section, the effect of the shape of the rotors on the mixing behavior of BR rubber in a two-dimensional internal mixer was shown, and it is obvious that the void in the mixer affects the mixing behavior. However, there have been a few studies of the void in the mixer. Kim and White (1989) and Kim (1990) investigated the distribution of the rubber in an internal mixer using different types of rotors and various fill factors and explained the effect of void on the flow in terms of the starvation effect. 

In this section, BR rubber was kneaded using the two-dimensional internal mixer equipped with rotor wings of different shapes, and the dependence of void volume on the shape of rotor wings was investigated (Toh et al., 1994). 

In this section, (i) relationship between formation/extinction of voids and incorporation of ion-exchange resin particles into BR rubber and (ii) effect of fill factor and rotor design on mixing behavior were investigated (Toh et al., 1984 Gondoh et al., 1995). 

Fig. 11 Incorporation and dispersion processes of ion-exchange resin particles into BR rubber observed from the front window of the mixer with the (g) type rotor.

In this section, the mixing behavior of BR rubber and rubber particles as a tracer was studied in a three-dimensional internal mixer with the rotor wing having the most effective distribution of rubber. As the mixing behavior of a three-dimensional internal mixer cannot be observed, it was investigated using a vulcanization technique (Gondoh et al., 1995). 

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