Investigation on viscoelastic behavior of virgin EPDM/ reclaimed rubber blends using Generalized Maxwell Model (GMM)

Abstract

The reclaiming process of ethylene-propylene-diene monomer (EPDM) using a twin-screw extruder was studied and the effect of reclaiming conditions including screw speed (40, 80 and 120 rpm) and reclaiming agent content (0, 1.5 and 3 phr) at 280 °C (barrel temperature) on swelling, curing, mechanical properties as well as stress relaxation of virgin EPDM/40 phr reclaimed rubber blends was evaluated. According to the results of swelling test, the reclaiming process led to both crosslinks breakage and main chain scission. The appropriate reclaiming conditions were determined as the highest screw speed (120 rpm) and reclaiming agent content (3 phr). Compared to virgin EPDM vulcanizates, the curing behavior of prepared blends showed that the addition of reclaimed rubber had no effect on the scorch time but increased the optimum cure time and decreased the cure rate index. The results obtained for mechanical properties demonstrated that the tensile strength, modulus at 100% and 200% elongation and hardness decreased while the elongation at break of the blends showed no particular trend. The analysis of stress relaxation behavior using the Generalized Maxwell Model (GMM) revealed that the initial and final moduli of all blends decreased, and surprisingly the relaxation times were shorter or showed no change compared to the reference sample. Further, the Dynamic Mechanical Thermal Analysis (DMTA) results exhibited that the Tg of blends decreased but the maximum loss tangent presents no change following the addition of 40 phr reclaimed rubber to the virgin EPDM. Finally, the frequency sweep test indicated that the storage modulus of all blends was lower than that of the virgin sample.

Keywords

• Thermo-mechanical reclaiming
• EPDM rubber
• Curing behavior
• Stress relaxation
• Generalized Maxwell model (GMM)