Heat Generation and Rubber—Filler Coupling Bonds

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Abstract
It is well known that heat generation is dependent upon the type of polymer, filler, and other components of the compound. In addition, the state of cure has a large effect on heat buildup. With any given vulcanizate system, network constraints can reduce heat generation to a minimum. These network constraints include crosslinks, as well as coupling bonds between filler particles and the polymer chains. Using peroxide crosslinking of natural rubber and organofunctional silanes with a silica filler, network crosslinks, and filler coupling bonds can be independently varied. From equilibrium swelling, it was possible to determine the quantity of each type of constraint. Network crosslinks and coupling bonds respond to equilibrium swelling in approximately the same way, although the peroxide and silane functionality interact chemically to influence the number of each type of constraint. The rate of heat buildup and the maximum temperature generated were obtained from the Goodrich Flexometer (ASTM—D623). Increasing either network bonds or coupling bonds reduced the rate of heat generation and the heat buildup monotonically to a minimum value dependent upon the elastomer system. Both types of network constraint affected these responses about equally. Comparison of silica and carbon black fillers in SBR demonstrated that the insertion of coupling bonds was an efficient method of reducing heat buildup. Other rubber properties (particularly modulus and abrasion resistance) optimized more readily since their response to the coupling bonds and network crosslinks were quite different.

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