Tensile strength carbon black pigments

A fast-curing polymercaptan-epoxy adhesive formulation is shown in Table 11.11. The gel time for the mixed adhesive is about 8 min at room temperature. Tensile shear strength on aluminum is reported to be 2270 psi at 23°C. Note that the different color pigments used in parts A (carbon black) and B (titanium dioxide) are to assist by visually indicating when the two components are well mixed. 

Fillers are materials that modify rubber characteristics (e.g., hardness) and improve its physical characteristics (e.g., tensile strength), in addition to reducing costs. Rubber is sometimes compounded without the use of fillers the resultant product is called gum rubber. Typical fillers are calcined and hydrated clays, magnesium silicate (talc), magnesium oxide, and silicas. Carbon black, a common filler used to increase the heat resistance in industrial components such as tires, is not used as a filler in pharmaceutical components but it is used in smaller amounts as a black pigment. Polynuclear aromatic (PNA) hydrocarbons are a concern with carbon blacks but the grades used by manufacturers of pharmaceutical components contain very low concentrations. 

Reinforcing fillers such as finely divided carbon black increase the tensile and tear strength of the mix. Finely divided coloured pigments can also be added instead of carbon black. 

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. 

Carbon blacks, precipitated pigments, and organic vulcanization accelerators are added to increase tensile strength and resistance to abrasion. 

Most rubber compounds that are intended to develop a reasonable tensile strength, abrasion, and tear resistance will contain up to 50 phr (parts per hundred parts rubber by weight) or more of a reinforcing filler, nearly always a carbon black (thus the color of car tires). The use of carbon black in rubbers is quite different than in plastics, where it is strictly a pigment and limited to much lower loadings. 

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