Carbon black strength

Commercially produced elastic materials have a number of additives. Fillers, such as carbon black, increase tensile strength and elasticity by forming weak cross links between chains. This also makes a material stilfer and increases toughness. Plasticizers may be added to soften the material. Determining the effect of additives is generally done experimentally, although mesoscale methods have the potential to simulate this. 

Nittile mbber is much like SBR in its physical properties. It can be compounded for physical strength and abrasion resistance using traditional fillers such as carbon black, siUca, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the swell in IRM 903 oil at 70°C is typically 25—30%. Nitrile mbber processes on conventional mbber equipment and can be compression, transfer, or injection molded. It can also be extmded easily. 

The mbber compound usually requires an inert inorganic filler and small particle sise carbon particle for reinforcement. The mbber polymers vary in inherent tensile strength from very high in the case of natural mbber to almost nonexistent for some synthetic polymers, eg, SBR. The fillers most commonly used for mbber compounds include carbon black, clay, calcium carbonate, siUca, talc (qv), and several other inorganic fillers. 

In tires, carbon black is important because of the high flex fatigue and tear strength requirements of this product. Poor dispersion can result in premature cracking in both treads and sidewalls. In off-the-road tires poor dispersion results in excessive chip/chunk causing a significant loss in treadwear in addition to tread lug cracking which can lead to loss of an entire lug (radial tread bar). 

The metal fillers act as a reinforcing material that results in added strength and stiffness (126). They color the plastic gray for nickel, 2inc, stainless steel, and aluminum, and brown for copper. Metal additives are more expensive than carbon black or surface-active agents, but they get extensive use in EMI shielding appHcations. 

The carbon blacks used in plastics are usually different from the carbon blacks used in mbber. The effect of carbon black is detrimental to the physical properties of plastics such as impact strength and melt flow. Electroconductive grades of carbon black have much higher surface areas than conventional carbon blacks. The higher surface areas result in a three-dimensional conductive pathway through the polymer at much lower additive levels of the carbon black. The additive concentrations of electroconductive carbon blacks is usually j to that of a regular carbon black (132). 

The tinting strength of mbber-grade carbon blacks shows a linear relationship with shown in Figure 5. Since performance characteristics are... 

Mamzen Oil Co. has developed various Ziegler-Natta catalysts that can produce poly(butadiene-i //-prop5iene) (PBR) (78). PBR shows tack (self-adhesion) and green (unvulcanized) dynamic properties superior to those of BR and EPDM. Carbon black-loaded vulcanizates can be compounded to give high strength and elongation at break (79,80). PBR can also be covulcanized with SBR, BR, and EPDM. 

Polymerization System. This elastomer is prepared by emulsion polymerisation, similar to that used for SBR, but generally carried out to virtually 100% conversion. As for SBR, the chain irregularity leads to a noncrystallising mbber, so that this polymer requires carbon black reinforcement for strength. 

Since polychloroprene crystallizes under stress, fine particle size carbon black is not ordinarily needed or used to enhance tensile strength. More frequently, mineral fillers, for example clay, can be added to reduce cost. A light process oil, free of polycycHc aromatics, can be used to improve the flexibihty or hand of films. On the other hand, an ester plasticizer can be used to improve low temperature properties (161). 

It is an apparent consequence of the second role that SBS polymers with a molecular mass of about 80 000 behave like carbon-black-reinforced elastomers as illustrated in Table 11.16 in respect of tensile strength. 

Another approach has been adopted by the Du Pont Company with Adiprene C. This is a urethane-type polymer with unsaturated groups in the polymer. Because of the unsaturation the polymer may be vulcanised with sulphur, the standard vulcanising agent of the rubber industry. This is a clear-cut example of a product being modified to suit the processor rather than that of a processor adapting himself to meet new products. Whereas Adiprene C has poor tensile strength when unfilled, the use of carbon black leads to appreciable reinforcement (as is the case with SBR and to some extent natural rubber. 

Reinforcing agents can be added to increase the cohesive strength of NR adhesives. Carbon blacks have been extensively used, but polyfunctional... 

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