Reversibility of the Mullins effect for extending the life of rubber components

ABSTRACT

This paper investigates the recovery of the Mullins effect by heat-treatment of predeformed (300% tensile strain) carbon-black filled ethylene-propylene-diene rubber (EPDM) in an air-circulating oven. The tensile response was measured, and the secant modulus at 100% strain, energy to deform to 300% strain, ultimate tensile strength, strain to failure and permanent deformation were compared to undeformed specimens subjected to the same heat-treatments, 3–24 h at temperatures of 60–80°C. Recovery of properties is dependent on time and temperature of treatment, increasing with longer times and higher temperatures. Recovery of secant modulus follows time-temperature superposition (TTS) with an activation enthalpy of 111 kJ mol⁻¹; TTS is shown to be applicable to the other measures, probably because of additional cure in the rubber resulting from the heat-treatment. Treatments under vacuum led to similar effects as in an air-circulating oven.

KEYWORDS:

• EPDM
• mechanical properties
• Mullins effect
• recovery
• time–temperature superposition

Acknowledgements

The authors wish to acknowledge the contributions of Vanessa Fernandes and Jason Greaves for providing the necessary training to MC, and of J-Flex Rubber Products for supplying the EPDM rubber sheet.

Disclosure statement

No potential conflict of interest was reported by the authors.