Silicas and Carbon Blacks

The analysis is thus relatively exact for heterogeneous surfaces and is especially valuable for analyzing changes in an adsorbent following one or another treatment. An example is shown in Fig. XVII-24 [160]. This type of application has also been made to carbon blacks and silica-alumina catalysts [106a]. House and Jaycock [161] compared the Ross-Olivier [55] and Adamson-Ling... 

Exfoliating layered particles such as the clays, mica, or graphite is being used to provide very effective reinforcement of elastomers at loading levels much smaller than in the case of solid particles such as carbon black and silica [228-231]. Other properties can also be substantially improved, including increased resistance to solvents, and reduced permeability and flammability. 

Van Zijverden, M., et al., Diesel exhaust, carbon black, and silica particles display distinct Thl/Th2 modulating activity, Toxicol. Appl. Pharmacol. 168, 2, 131, 2000. 

Clays. Clay, which is generally considered a mild reinforcing filler, is used sparingly in tires. It is most often used in white sidewalls or in low performance tires. Clay tonnage in tires woddwide is estimated at 36,0001 annually. Clay can also be coupled to rubber with silanes, and this is the more popular version used in tires. Even with silane coupling, days are still a weak reinforcing filler compared to both carbon black and silica. 

Filler, in general, can be defined as finely divided particles that are often used to enhance the performance and various desirable properties of the host matrix, depending on a typical application. A great deal of research endeavors have been dedicated to the development and the use of different fillers with a dimension at the nanometer level. In rubber technology the term nano is not unfamiliar to a rubber specialist. Since the start of the twentieth century, carbon black and silica have been utilized as effective reinforcing agents in various rubber formulations for a variety of applications. The primary particle sizes of these fillers remain in the nanometer range. However, with these conventional fillers the dispersion toward individual... 

A series of six stress-strain cycles with a crosshead rate of 600 mm/min was applied to specimens having a parallel length of 25 mm and a cross-section of 1 x 4 mm2 on a tensile testing machine. The samples were continuously stretched in six hysteresis cycles up to 60% of their elongation at break values, as shown in Fig. 47. This procedure is an established one and widely practiced for elastomeric composites reinforced with fillers such as carbon black and silica, which tend to build a strong filler-filler network [83]. 

This assumption is based on the fact that PTFE agglomerates are soft and deformable particles in comparison to conventional (hard) fillers such as carbon black and silica for which (2) was originally derived. Morphological analysis (shown in Fig. 5) reveals that PTFE agglomerates can be considered as soft deformable particles. 

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... 

Parker [4] end-group functionalized poly(1,3-butadiene) polymers with isopropyl hydroxyl-amines to improve the affinity and interaction with carbon black and silica fillers to extend tire lifetime. 

Halasa [2] reduced hysteresis in tires by anionically copolymerizing functionalized butadiene, (I), and styrene, (II), to enhance elastomer compatibility with carbon black and silica fillers. 

Tire tread rubber formulations were prepared by Parker [4] and consisted of poly(styrene-co-butadiene) rubber terminated with iV-isopropylphenylnitrone, (III), to promote interaction between the polymer end-groups and carbon black and silica fillers to reduce hysteresis. 

For example, sulfur-cured SBR samples that contained no filler, carbon black, silica, or a combination of carbon black and silica were heated with the 2-buta-nol under supercritical conditions. The SBR had an original weight average molecular weight of about 400,000. The weight average molecular weights of the devulcanized SBR samples recovered are reported in Table 2. 

S-SBR grades have excellent balance between wet traction and rolling resistance therefore, they can be used for low fuel consumption tire treads in all-season tires and high-quality rubber goods. In applications of S-SBR, carbon black and silica will often be added to enhance the property. 

When the behavior of carbon black and silica is compared in compounded rubber, it is evident that silica adsorbs less rubber than carbon black. In addition to the differences in the chemical compositions of the surfaces this difference is caused by the differences in the dispersive components of surface energies of each filler. Car-... 

Figure 7.34 shows that the model fits experimental data for carbon black and silica particles. 

Figure 7.35. taiiS of natural rubber filled with carbon black and silica vs. interaggregate distance, 833. [Adapted, by permission, from Wang M-J, Wolff S, Tan E-H, Rubb. Chem. Technol., 66, No.2, 1993, 178-95.]... 

Rubber, due to its elastomeric properties, usually, has a low abrasion resistance. Fillers such as carbon black and silica can be added to impart abrasion resistance. Figure 8.38 shows the extent to which different grades of carbon black are abraded. As interaggregate distance decreases the abrasion loss decreases as well. 

In SBR the compounding ingredients can be (1) reinforcing fillers, such as carbon black and silica, which improve tensile strength or tear strength (2) inert fillers and pigments, such as clay, talc, and calcium carbonate, which make the polymer easier to mold or extrude and also lower the cost (3) plasticizers and extenders, such as mineral oils, fatty acids, and esters (4) antioxidants, basically amines or phenols, which stop the chain propagation in oxidation and (5) curatives, such as sulfur for unsaturated polymers and peroxides for saturated polymers, which are essential to form the network of cross-links that ensure elasticity rather than flow. 

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