Migration of Paraffin Wax to Sulfur Vulcanized Styrene–Butadiene Rubber (SBR) Surface: Effect of Temperature

Abstract

Because of the low molecular weight of some additives (e.g., antiozonants) in the vulcanized styrene–butadiene rubber (SBR) formulation, they are able to migrate and diffuse to the surfac creating a weak boundary layer which is deleterious to adhesion. However, the factors favouring or inhibiting the migration of antiozonants to the vulcanized SBR surface have not been fully understood. This work was conducted to determine the influence of the temperature on the migration of antiozonant paraffin wax to the surface of a commercial sulphur vulcanized styrene–butadiene rubber. The antiozonant migration experiments were performed for 15 hours in an oven at different temperatures ranging from 40° to 90°C. The changes in the vulcanized SBR surface were monitored by ethylene glycol contact angle measurements, ATR–IR spectroscopy and scanning electron microscopy (SEM). Additionally, the weight loss of the vulcanized SBR after each heat treatment was recorded. The heating of vulcanized SBR at different temperatures for 15 hours caused a partial removal of paraffiin wax from the surface. By heating at a temperature close to the paraffin wax melting point, the crystals of paraffin wax on the vulcanized SBR surface were melted, causing a decrease in the thickness of the paraffin wax film on the surface, which became smoother too. Furthermore, some paraffin wax was evaporated during heat treatment, especially for the vulcanized SBR heated at 90°C. However, even after heating at 90°C, a thin film of paraffin wax always remained on the vulcanized SBR surface. Finally, the migration of zinc stearate to the paraffin wax layer on the vulcanized SBR surface occurred by heating at 90°C for 15 h. © Koninklijke Brill NV, Leiden, 2012