Systems, filler carbon black properties

In rubber systems containing carbon black, flocculation may cause substantial changes in mechanical properties. Flocculation in these systems counteracts filler dispersion. Carbon black flocculation occurs in filled rubber stock during storage or during vulcanization in the absence of shear. " Temperature is the important kinetic factor which affects the flocculation rate (Figure 5.19). In addition to temperature and time, flocculation depends on the type of carbon black and its concentration. 

These results, combining the widely known instability (and dissipative structure ) phenomenon of melt fracture with the new non-equilibrium description of multiphase polymer systems, will hopefully stimulate more experimental and theoretical work devoted to these (frozen) dissipative structures. Up to now, it remains open which property of the melt may be responsible for its suddenly occurring capability to disperse fillers (pigments, carbon-black, etc.) or other incompatible polymers above melt fracture conditions. We can only speculate that the creation of microvoids ( = inner surfaces) in particular and a sudden increase of gas solubilisation capability at and above melt fracture allows the polymer melt to wet the surface of the material to become dispersed. This means that a polymer melt might have completely different (supercritical) properties above melt fracture, than we usually observe. 

The study of the mechanical properties of filled elastomer systems is a chaUenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward mle of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fiUers hke sihca and carbon black on the reinforcement of elastomers.In general, the strucmre-property relationships developed for filled elastomers have evolved into the foUowing major areas FiUer structure, hydrodynamic reinforcement, and interactions between fiUers and elastomers. 

On the other hand, the alkoxide system presented several problems in formulation. The system first chosen as a model consisted of a trimethoxymethyl silane crosslinker, 8000 centistoke HEB siloxane, and a catalyst. A number of catalysts were used and each exhibited different cure rates and electrical properties. DuPont tetraalkoxytitante-Tyzor appears to he one of the better catalysts used in this type of curing system. Fillers are usually incorporated into the silicone formulation to improve mechanical properties, promote adhesion, and to serve as light screening and pigment agents. Cab-o-sil, a form of fumed silica, carbon-black, titanium dioxide and calcium carbonate are then used as RTV fillers. 

Adsorption Properties. Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with a higher specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dispersibility to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

Even dynamic measurements have been made on mixtures of carbon black with decane and liquid paraffin [22], carbon black suspensions in ethylene vinylacetate copolymers [23], or on clay/water systems [24,25]. The corresponding results show that the storage modulus decreases with dynamic amplitude in a manner similar to that of conventional rubber (e.g., NR/carbon blacks). This demonstrates the existence and properties of physical carbon black structures in the absence of rubber. Further, these results indicate that structure effects of the filler determine the Payne-effect primarily. The elastomer seems to act merely as a dispersing medium that influences the magnitude of agglomeration and distribution of filler, but does not have visible influence on the overall characteristics of three-dimensional filler networks or filler clusters, respectively. The elastomer matrix allows the filler structure to reform after breakdown with increasing strain amplitude. 

Epoxies are excellent electrical insulators. Electrical properties are reduced on increasing the polarity of the molecules. Addition of metallic fillers, metallic wools and carbon black convert the non-conductive epoxy formulation into an electrically conductive system. Non-conductive fillers increase the arc resistance and to some extent increase the dielectric constant. 

Flow restrictions are also observed in flow of melts. Figure 9.9 shows flow limits of carbon black filled polyolefins. Data show that yield stress appears at low concentrations of carbon black and that the type of the matrix does not affect flow characteristics which are caused by the presence and properties of fillers. The viscosity of these systems are well described by Fedor s equation ... 

The knowledge of the enthalpy of peaks after T gives the automotive chemist knowledge of the cross-linking process. This is an important property for isolators because the impedance of vibrational inputs is dependent on either the mass of a system or the ability of an isolator or mount to absorb vibration. Generally, if a component s hardness is influenced more by cross-linking than by addition of filler (i.e., carbon black, which can be measured by TGA) the ability to absorb NVH inputs is better. 

Carbon black is the most widely used conducting filler in composite industry. Carbon black filled immiscible blends based on polar/polar (65), polar/nonpolar (63,66), nonpolar/nonpolar thermoplastics (67,68), plastic/rubber and rubber/mbber blends (69,70) have already been reported in the literature. The properties of carbon black filled immiscible PP/epoxy were reported recently by Li et al. (60). The blend system was interesting because one of the components is semicrystalline and the other is an amorphous polar material with different percolation thresholds. The volume resistivity of carbon black filled individual polymers is shown in Fig. 21.23. 

This chapter has reviewed both the types and the properties of elastomers, compounding with a range of filler or reinforcement systems such as carbon black, and enhancement of tiller performance by novel use of compounding ingredients such as silane coupling agents. Other issues such as antioxidant systems and vulcanization systems were also discussed. The role of the modern materials scientist in the tire and rubber industry is to use materials to improve current products and develop new products. Four key parameters govern this development process ... 

Other compounds commonly used in vulcanization, in addition to sulfur and accelerators, are zinc oxide and saturated fatty acids such as stearic or lauric acid. These materials are termed activators (as opposed to accelerators). Zinc oxide serves as an activator, and fatty acids are used to solubilize the zinc into the system. Rubber formulations can also include fillers such as fumed silica and carbon black, and compounds such as stabilizers and antioxidants. Further complicating the situation is the engineering practice of blending various elastomers to obtain the desired properties. 

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