Polybutadiene carbon-black-filled

When CIIR is blended with butadiene-styrene copolymer (SBR), as the concentrations of CIIR are increased, elastic rebound values are decreased linearly and traction is increased [48]. When CIIR is blended into natural rubber/polybutadiene carbon black-filled compounds, the compound shows a lower hysteresis and equal or better wet traction [49]. 

SBR is the most widely used synthetic elastomer. It is an amorphous random copolymer consisting of a mixture of l.2, cis and trans isomers. Cold SBR produced at —20 C consists of 17% 1,2. 6% cis and 77% trans isomers of polybutadiene. This commercial product has a Tt of -60 C, an index of refraction of 1.534S, and a coefficient of linear expansion of 66 X 10 s cm/ cm C. Because of the high percentage of the trans isomer, it is less flexible and has a higher heat buildup, when flexed, than Hevea rubber. Although carbon black-filled or amorphous silica-filled SBR has useful physical and mechanical properties, the SBR gum rubber is inferior to Hevea rubber. 

Figure 5.21. Excess storage modulus of carbon black filled polybutadiene vs. annealing time. [Adapted, by permission, from Boehm G G A, Nguyen M N, J Appl. Polym. Sci, 55, No.7, 1995, 1041-50.]...

Applications . NMR has found the following applications in filled systems carbon black adsorption of SBR, the effect of carbon black loading on cure rate of natural rubber, gel-like behavior of polybutadiene/carbon black mixtures, structure and dynamics of carbon black filled rubber vulcanizalcs, " interaction of... 

Proton spin resonance measurements on carbon black filled rubbers confirm the relatively small effect of the black on local segmental mobility. Waldrop and Kraus (107) were unable to find evidence for two spin-lattice relaxation times (one for surface rubber and one for bulk rubber) and found very little effect of carbon blacks on the position of the minimum in the spin-lattice relaxation time (7j) vs. temperature curve. The shape of the curve was also substantially unaffected (107). Extraction of free rubber from an uncross-linked SBR-HAF black mix did not accentuate the effect of the carbon black. More recently Kaufmann, Slichter and Davis (108) reported the observation of two spin-spin relaxation times (T2) in the bound rubber phases of polybutadiene and ethylene-propylene rubber, each reinforced with 50 phr of an SAF black (155 m2/g surface area). The amount of fully immobilized polymer was only 4% of the total, but the remainder of the bound rubber displayed... 

Fig. 38. Applications of the NMR-MOUSE to elastomer materials, (a) Values of T2 for a curing series of carbon-black filled NR. The measurements made with NMR-MOUSE are compared with the values obtained at 300 MHz in high homogeneous field, (b) T2 of a cross-link series of unfilled SBR with different sulfur contents, (c) T2 versus glass-transition temperature Tg of unfilled SBR by the CPMG and steady-state CPMG methods, (d) Normalized Hahn-echo decays for polybutadiene latex samples for small, medium, and large cross-link densities. Reproduced from Refs. 189 and 190, with permission from Rapra Technology.

Polybutadienes with vinyl contents of 10 7 and 72.4% have been selected for further fatigue-to-failure analysis. Fatigue life measurements have been performed on a large number of specimens by means of the Fatigue-to-Failure Tester (Monsanto). Carbon-black-filled compounds with 50 phr N330 carbon black were cured with conventional curing system at 145°C. Curative levels have been chosen to obtain vulcaniza-tes at several levels of 300% modulus. Fatigue tests were performed on un-notched specimens at room temperature and at several deformation amplitudes. Data discussed here were obtained at 136% strain amplitude. 

Figure 5 shows steady shear viscosity data for a carbon black filled high cis-1.4 polybutadiene compound, as obtained using various rheometers. The Carreau-Yasuda equation was used to yield fit parameters given in the lower right inset the shear viscosity function q = f(y) is drawn in the left graph. As can be seen, a... 

Fig. 5 Experimental data and fitted shear viscosity function of a carbon black filled polybutadiene compound at 100 °C, as obtained in the author s laboratory...

Table 12.2 summarizes the mechanical properties of polybutadiene rubber-clay nanocomposites. The hardness, tensile strength, elongation at break, and permanent set all improved with increasing the clay content (5—40 phr)." " The mechanical properties of polybutadiene rubber-clay nanocomposite with 20 pin-clay content have been compared to those of the polybutadiene composites filled with 20 phr carbon black (SFR and N330), as presented in Table 12.3. This data shows that the organically-modified layered silicate was as effective a reinforcing filler, as carbon black. Some of the mechanical properties of polybutadiene nanocomposite such as hardness, tear strength, and tensile strength even exceeded those of the carbon black filled compounds." " These excellent mechanical properties of the nanocomposites resulted from the uniformly dispersed layered silicate in the elastomer matrix, and the strong interaction between the nanoclay layers and rubber chains. Thus layered silicates could be used in the polybutadiene industry as a promising reinforcing filler, if the layers...

The effects of HAF black on the stress relaxation of natural rubber vulcanizates was studied by Gent (178). In unfilled networks the relaxation rate was independent of strain up to 200% extension and then increased with the development of strain induced crystallinity. In the filled rubber the relaxation rate was greatly increased, corresponding to rates attained in the gum at much higher extensions. The results can be explained qualitatively in terms of the strain amplification effect In SBR, which does not crystallize under strain and in cis-polybutadiene, vulcanizates of which crystallize only at very high strains, the large increase in relaxation rate due to carbon black is not found (150). 

In view of the long history of research efforts on filled rubbers, it is not surprising that the initial works on filled polymer blends appeared in publications authored by rubber compounders and carbon black vendors [17, 18]. For instance, Walters and Keyte [17] observed that the compound ingredients, such as CB and zinc oxide, were not homogenously dispersed in rubber blends. Hess et al. [18] also reported a series of fundamental observations. First, they observed that filler particles tend to remain in the lower viscosity phase, in the absence of significant filler-matrix interactions. However, in the presence of strong polar-polar interactions between the filler particles and one of the phases, the particles were found to be selectively dispersed in the more polar phase and the viscosity became less important. More recently. Portal et al. [19] also presented similar observations about selective localization of CB particles in the natural rubber (NR) phase in NR/ polybutadiene blends. 

Tbe PTC amplitude depends on crystallinity. Meyer (136) showed that crystalline raA s-polybutadiene filled with carbon black has low room temperature resistivity and a significant anomaly, whereas the amorphous cfs-polybutadiene filled with the same amoimt of carbon black has much higher resistivity and no... 

Adhesion between the propellant and the case in solid rocket fuel propellants was studied. The adhesion mechanisms between an inert propellant (a highly filled PU, based on hydroxy-terminated polybutadiene prepolymer, diisocyanate and inert loadings) and a liner of the same nature of prepolymer, diisocyanate, chain extenders and carbon black were investigated. The interfacial properties were found to be influenced by the properties of the prepolymer used. The adhesion of the assembly was only slightly affected by the state of cure of the liner before propellant coating. In peel tests, cohesive failure occurred in the propellant near the interface, IR spectrometry of the propellant surface after separation showed the formation of an interphase in the propellant, dependant on the prepolymer. 3 refs. 

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