Composites carbon black filled rubber

If the estimated fitting parameters are compared to the predicted values of percolation theory, one finds that all three exponents are much larger than expected. The value of the conductivity exponent ji=7A is in line with the data obtained in Sect. 3.3.2, confirming the non-universal percolation behavior of the conductivity of carbon black filled rubber composites. However, the values of the critical exponents q=m= 10.1 also seem to be influenced by the same mechanism, i.e., the superimposed kinetic aggregation process considered above (Eq. 16). This is not surprising, since both characteristic time scales of the system depend on the diffusion of the charge carriers characterized by the conductivity. 

Carbon-black-filled rubber compounds are usually produced on Banbury-type mixers, while conductive thermoplastics are preferably produced on twin-screw extruders. Unlike other filled compounds or polymer blends it is essential to adhere very precisely to the carbon-black concentration and the production parameters, since a very delicate balancing act is usually required to stay on the tight-rope of optimum composition and avoid falling into the pits of insufficient conductivity, inadequate mechanical properties or sharply increased viscosity. 

Even this definition needs to be classified [7, 8]. To some researchers it is still too broad because it includes many materials that are not usually thought of as composites such as concrete, copolymers and blends, reinforced plastics, and carbon-black-filled rubber. On the other hand, some of the more recent composites are excluded from the category of composites if this definition is strictly applied. For example, many particulate-type composites such as dispersion-hardened alloys and cermets have composite structures that are microscopic rather than macroscopic [2,8]. In some cases, the composite structures are nano-scopic, with the physical constraint of several nanometers as the minimum size of the components [9-16]. The terms... 

The standard phenomenology of carbon black-filled rubber will be presented and the influence on the constitutive response of temperature and filler concentration will be discussed. Although the focus is on traditional vulcanized rubber, other thermoplastic elastomers show similar mechanical properties even if their chemical composition is quite different. Moreover, from a macroscopic point of view, the behavior of such materials is very close to the behavior of some biological soft tissues, such as ligaments and tendons, for what concerns both their static and dynamic responses. 

Table 2.4) or proprietary test methods. Forrest [38] has listed 94 international rubber analysis standards (ISO) and 20 ISO standards in preparation referring to latices, carbon-black-filled compositions, raw and compounded rubbers. 

The Payne effect of carbon black reinforced rubbers has also been investigated intensively by a number of different researchers [36-39]. In most cases, standard diene rubbers widely used in the tire industry, bke SBR, NR, and BR, have been appbed, but also carbon black filled bromobutyl rubbers [40-42] or functional rubbers containing tin end-modified polymers [43] were used. The Payne effect was described in the framework of various experimental procedures, including pre-conditioning-, recovery- and dynamic stress-softening studies [44]. The typically almost reversible, non-linear response found for carbon black composites has also been observed for silica filled rubbers [44-46]. 

Fig. 34 Results of bound rubber estimates at room temperature for various carbon black filled S-SBR composites, as indicated...

Carbon black filled, vulcanised rubber is still difficult to analyse with standard analysis techniques like FTIR and NMR. Application of the thermal analysis techniques TGA and DSC offers the possibility to obtain a reasonable impression of the composition of such a rubber sample. This is illustrated below by the results of TGA and DSC measurements on a rubber sample from a Michelin MXT 185/65-R14 cartyre. 

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. 

Ding, T. Wang, L. Wang, P., Changes in Electrical Resistance of Carbon-Black-Filled Silicone Rubber Composite During Compressions. J. Polym. Sci., Part B Polym. Phys. 2007,45,2700-2706. 

Volnme resistivities have been reported on phenol-formaldehyde [37], carbon fibre reinforced ABS terpolymer [35], natural rubber [38], polystyrene (PS) [35], HDPE-natnral fibre composites [34], carbon black filled PP-epoxy-glass fibre composites [5], XLPE [32], nanoclay reinforced EPDM-g-TMEVS [31] and epoxy resin/PANI blends [33]. 

Wang L, Ding T H and Wang P (2009), Influence of carbon black concentration on piezoresistivity for carbon black-filled silicon rubber composite. Carbon 47 3151-3157. 

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