Influence of solvent swell and bound rubber on wax solubility of carbon black-reinforced NR composite

Wax in a rubber article migrates to the surface and plays the role of an antidegradant by formation of an impervious barrier on the surface. Wax solubility of a rubber article is important for understanding migration behaviors and film formation of wax as well as for determining the proper content of wax in a rubber compound. Wax solubilities of natural rubber composites reinforced with carbon black were measured using wax solution in toluene. A variation of the wax solubility with the carbon black content was investigated. Raw wax solubility decreased with the increase of carbon black content. Solvent swell-corrected wax solubility also decreased with the carbon black content. The raw wax solubilities were corrected with the rubber fractions, total bound rubber contents, and tightly bound rubber contents as well as the solvent swelling ratio to investigate the influencing parameters on wax solubility. It was found that the unbound and loosely bound rubber fractions as well as the solvent swelling enhanced the wax solubility while the tightly bound rubber fraction reduced it.