Filled compounds with carbon black

Fig. 3.65 Left TM-AFM images left height, right phase) showing the filler microdispersion in the unvulcanized compounds, (a) unvulcanized EPDM filled with modified silica (Compound 1) (z-scale height, 310 nm, phase, 30°) (b) unvulcanized EPDM filled with carbon black (Compound 2) (z-scale height, 365 nm, phase, 35°). Right (c), (d) filler distributions as determined from the analysis of the phase images (a) and (b) Reproduced with permission from reference [141]. Copyright 1999. American Chemical Society...

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. 

In 50% sulfuric acid at 90 °C butyl rubber shows the best resistance with carbon black loading particularly with channel and lamp blocks. Silica filled compounds lose up to one-third of the strength of the rubber with considerable swelling at 70% concentration of sulfuric acid. 

Rubber is filled with carbon black or calcium silicate which act also as reinforcing agents. For example, the tensile strength of vulcanized SBR can be raised tenfold through compounding with 50% carbon black. Elastomers of... 

The attribution of the Payne effect to the filler network is strongly supported by the fact that carbon black pastes, made with carbon black and low molecular weight oils, present very similar G levels at very low shear strain (Payne, 1965). Obviously, when strain increases, G drops drastically for carbon black pastes and much more slowly for filled rubber compounds, because of the progressive desorption of elastomeric chains. 

Many proposals have been made in wbicb OM (mainly PAni) blends could be used. Some of them are visionary and creative, like roofs coated with photovoltaic cells, wallpaper with electrical heating capability, heated textiles, dust filters, and many more [62]. Often the expectation that such blends would have properties superior to those of carbon black-filled blends, in conductivity or in mechanical or colour aspects, guided the vision. Whereas PAni blends can actually deliver somewhat higher conductivity values (up to 50 S/cm, the best value for laboratory samples, see Ref. [22b] and Ref. [23a], 5 S/cm for technical scale [65]) compared to those of carbon black compounds (best values around 0.5 S/cm), the other presumed advantages are not there. Nor are mechanical or processing properties, electrochemical stability under applied voltage and current (like for heating devices), or the color aspects of PAni blend any better than with carbon black compounds. 

Examination of dispersion with carbon black compounds by optical microscopy and scanning electron microscopy found that the best dispersive mixing condition is created when the fill factor is 0.9. 

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. 

The effects of the presence of carbon black on the dynamic mechanical properties of various types of filled rubber have been reviewed by Medalia [58]. In an early work (1939), Roelig [59] found that hysteresis increases with carbon black loading. Naunton and Waring [60] and later Gehman et al. [61] found that the elastic moduli of tread compounds decrease greatly with increases in strain. Stambaugh [62] attributed the reduction in modulus, with increases in strain, to the strain per se rather than to the increase in... 

The term percolation [8] has been used to describe in particular the discontinuous conductivity behavior of carbon-black-filled compounds. It is a widely known fact that the conductivity of a compound filled with carbon black does not increase in a linear fashion with the concentration of conductive carbon black added. What in fact happens is that there is a sudden increase in conductivity that does not take place until a certain characteristic concentration, the critical volume concentration, is reached, whereas continued addition of carbon black after this point once again brings only a gradual increase. 

Silica particles are commercially available in the same size range as carbon black (i.e., down to 0.01 pm or 10 nm). Silica has been commercial reinforcing filler since the 1940s. The processing of silica-filled rubber compounds is more difficult than with carbon black-filled compounds because polar interparticle forces make it more difficult to break up agglomerates [101]. 

Pico Abrasion Data for Carbon Black Filled NR Compounds with or without QDI... 

FIGURE 26.4 Master curves on smooth, wavy glass, on a sihcon carbide track dusted with magnesium oxide and on a clean silicon carbide track of three acrylate-butadiene rubber (ABR) compounds as gum rubber, filled with 20 pphr carbon black and 50 pphr, respectively. (From Grosch, K.A., Sliding Friction and Abrasion of Rubbers, PhD thesis, University of London, London 1963.)... 

Physical properties of carbon black-filled EPR and EPDM elastomers have been found to be comparable with the suUur-cured analogues [372]. Aromatic oils increase the optimum dose requirement for these compounds due to the reaction of the transient intermediates formed during radiolysis of the polymer with the oil as well as energy transfer which is particularly effective when the oil contains aromatic groups. The performance and oxidative stability of unfilled EPDM as well as its blend with PE [373], and the thermal stabdity and radiation-initiated oxidation of EPR compounds are reported by a number of workers [374,375]. 

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