Elastomers carbon black , dispersibility

Diamine salts of fatty acids are used as multifunctional additives in natural rubber compounds filled with carbon black.They affect the elastomer-carbon black interface. With an increased concentration of multifunctional additive, the concentration of bound rubber decreases but dispersion of carbon black is improved. In silica filled rubber, multifunctional additive also improves the dispersion of silica, but in addition, it decreases the negative influence of silica filler on vulcanization rate. 

The incorporation of carbon black into 50/50 elastomer preblends shows carbon black affinity decreases in the order BR, SBR, CR, NBR, EPDM, and butyl mbber. Poor carbon black dispersion causes an increase in hysteresis and a decrease in fatigue resistance. The effect ofvolumeloading ofafiBer such as carbon black on the properties of the vulcanizate depends on whether the elastomer is strain-crystallizing or not. 

Figure 4.8 Carbon black dispersion and general trends in elastomer compound properties [1, 17],...

Carbon black is the most extensively used filler in terms of volume in thermoplastic/ thermoset elastomers. One method of quantifying carbon black dispersion is through the reduction in resistivity of insulating polymer matrices that occurs by virtue of the CB s ability to create a conductive three-dimensional particulate network. As the amount of carbon black is increased, the resistivity is decreased. In addition, the efficiency of a fixed amount of carbon black is increased as a result of the increased dispersion offered by the use of titanates. As an example. Table 5.8 shows the effect of increasing amounts of LICA 09 on the resistivity of a CB-filled styrene/butadiene block copolymer. 

The recent work described here was initiated in order to develop an improved understanding of the carbon black dispersion process, including the understanding of factors which affect the kinetics of dispersion. We considered the effects of changes in mixing conditions, carbon black type, elastomer type, and so forth on the kinetics of dispersion. The effects of dispersion quality on the properties of carbon-black-filled rubber were also considered. 

The results obtained showed that acrylate elastomer compounds could be mixed more efficiently at higher rpm. Mixing at the higher rpm improved the processability and carbon black dispersion. It was found that an upside down mix was the best method for improving the quality of the mix and reducing mix time in the laboratory mixer. 11 refs. 

DISPERSION OF CARBON BLACK IN ELASTOMERS 33.2.1 Effect of Morphology on Dispersibility of Carbon Black... 

FIGURE 33.5 Dispersion of carbon black N134 in Cabot Elastomer Composite (CEC) and dry-mixed compounds. 

There have been several attempts at models incorporating breakup and coalescence. Two concepts underlie many of these models binary breakup and a flow subdivision into weak and strong flows. These ideas were first used by Manas-Zloczower, Nir, and Tadmor (1982,1984) in modeling the dispersion of carbon black in an elastomer in a Banbury internal mixer. A similar approach was taken by Janssen and Meijer (1995) to model blending of two polymers in an extruder. In this case the extruder was divided into two types of zones, strong and weak. The strong zones correspond to regions... 

In addition to its role as a pigment, carbon black may be incorporated into polymers as a reinforcement for elastomers, as a UV stabiHser in polyolefins, or as an electrically conducting additive. In each case the physiochemical properties of the filler and its ultimate state of dispersion is critical in order to achieve... 

Elastomers require, in most applications, to be reinforced by fillers in order to improve their mechanical properties. Carbon black and silica have been used for a long time in the rubber industry to prepare composites with greatly improved properties such as strength, stiffness and wear resistance. These conventional fillers must be used at high loading levels to impart to the material the desired properties (1). The state of filler dispersion and orientation... 

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. 

A simple qualitative visual method for rating the dispersion of fillers (50phr carbon black) In Blon elastomer was developed and Is Illustrated In Figure 2. A cross section of cured elastomer Is examined under a binocular microscope to check gross dispersion of fillers. The visual dispersion Is rated against a set of standard photographs of dispersions which had previously been ranked and correlated with certain Important physical properties. For example, In Figure 3, the flex life of a well dispersed elastomer was over 300 million cycles while that of a poorly dispersed one was below one million cycles. The correlation of physical properties to dispersion has been substantiated with other rubbers (14). 

Both the modulus-temperature relationships presented in the preceding sections and the tensile data presented above are strikingly similar to those demonstrated for other rubber-plastic combinations, such as the thermoplastic elastomers (see Chapter 4 and the model system presented in Section 10.13) and the impact-resistant plastics (Chapter 3). The IPN s constitute another example of the simple requirement of needing only a hard or plastic phase sufficiently finely dispersed in an elastomer to yield significant reinforcement. Direct covalent chemical bonds between the phases are few in number in both the model system (Section 10.13) and present IPN materials. Also, as indicated in Chapter 10, finely divided carbon black and silicas greatly toughen elastomers, sometimes without the development of many covalent bonds between the polymer and the filler. 

Elastomers can be reinforced, or made tougher, by the addition of very small particles, typically finely dispersed carbon blacks or silicas. Similar types of reinforcement in elastomers can be brought about by the addition of a plastic polymeric phase (Sections 4.4 and 8.4) or the inclusion of polystyrene latexes. 

Attention is called to the following (1) The size of the carbon black particles is comparable to the size of the dispersed phase in the block-copolymer thermoplastic elastomers, and (2) the physical bonding/grafting combination between the rubber and the filler functionally resembles the... 

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