Vulcanization, accelerated-sulfur recipes

Curing-System Recipes for Accelerated-Sulfur Vulcanization. Recipes for only the curing-system part of formulations are given in Table 4.6. 

TABLE 7.4 Recipes for Accelerated-Sulfur Vulcanization Systems ... 

Ic. Cross-Linking of Polymer Chains.—Formation of chemical bonds between linear polymer molecules, commonly referred to as cross-linking, also may lead to the formation of infinite networks. Vulcanization of rubber is the most prominent example of a process of this sort. Through the action of sulfur, accelerators, and other ingredients present in the vulcanization recipe, sulfide cross-linkages are created by a mechanism not fully understood (see Chap. XI). Vulcanized rubbers, being typical network structures, are insoluble in all solvents which do not disrupt the chemical structure, and they do not undergo appreciable plastic, or viscous, flow. 

The vulcanization recipe wasi EPDM 100, stearic acid 1.0, zinc oxide 5 0, accelerator M 0.5, TMTD 1.5, HAF 50, sulfur 1.5 phr. Peroxide-curing of E-P copolymers was carried out with a modified procedure of (6) EPR 100, dicumyl peroxide 3, zinc oxide 3, TMTD 0.5, HAF 50, sulfur 0.2 phr, the mixture being masticated for 20 minutes at 0-50°C and cured at lb0°G. 

Typically a recipe for the vulcanization system for one of these elastomers contains 2-10 phr of zinc oxide, l phr of fatty acid (e.g., stearic), 0.5-4 phr of sulfur, and 0.5-2 phr of accelerator. Zinc oxide and the fatty acid are vulcanization-system activators. The fatty acid with zinc oxide forms a salt, which can form complexes with accelerators and reaction products, formed between accelerators and sulfur. Accelerators are classified and illustrated in Table 7.1. 

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