Cure Characteristics and Vulcanizate Properties of Blends of a Rubber Compound and its Recycled DE-VULC

This investigation is part of an attempt to recycle the rubber powder generated as a waste during sand-polishing of rubber balls and artificial eggs. The rubber powder was devulcanized with a novel chemical mixture called De-Link R to yield DE-VULC. Subsequently, varying concentrations of the product were blended with the original rubber compound and the effects on the cure characteristics and vulcanizate properties of the blends were investigated. Contrary to expectation, the scorch time (t₂) and the cure time (t₉₀) fell drastically at lower concentrations but the values rose with increasing concentration in blends that were predominantly DE-VULC. The very large reduction in t₂ and t₉₀ with the addition of small quantities indicates that DE-VULC catalyses the crosslinking reaction of the control compound. The increasing values of t₂ and t₉₀ in the DE-VULC rich blends have been attributed to delayed action due to the decreased curatives concentration. An identical pattern shown by torque maximum and modulus with increasing concentration suggested that crosslink density increases with increasing DE-VULC content until it peaks at 50%. However, the opposite trend of continuously decreasing mechanical properties prompted the inference that two types of crosslinks may be involved: those inherited from the previous vulcanization, which act as fillers, and those resulting from the current vulcanization. The trend of the mechanical properties indicates that the concentration of the latter decreased continuously. However, with 30 - 50% addition, the physical and mechanical properties range from good to excellent, depending on the property of interest.