Physical ageing evolution of the viscoelastic properties of filler reinforced rubber measured with the torsion pendulum after a temperature change

Abstract

The viscoelastic properties of filler reinforced rubber are measured at small strains with the torsion pendulum after a temperature change and the evolution of the storage and loss modulus is measured against the physical ageing time. Physical ageing refers to the state in which the molecules are out of thermodynamic equilibrium after a temperature change. The time needed to achieve equilibrium is the physical ageing time, during which the material displays shifting mechanical properties. For unfilled rubber, physical ageing occurs only after temperature changes below the glass transition temperature, Tg . However, filler reinforced rubber presents physical ageing after a temperature change at temperatures significantly above Tg . Therefore, the existing models of physical ageing are unsuitable for filler reinforced rubber and further characterization of the evolution of their viscoelastic properties after a temperature change is needed. The torsion pendulum is utilised to measure the material properties since it allows measurements in the rheological simple linear viscoelastic small strains and during long periods of time. The impulse response function obtained from the torsion pendulum measurements is used to calculate the storage and loss modulus at different times after a rapid temperature decrease at room temperatures. The resulting evolution shows a progressive stiffening of the material with an increase of storage modulus and decrease of loss modulus with physical ageing time. This investigation on the evolution of the viscoelastic properties after a temperature change sets the path for a proper characterization of the physical ageing phenomena for filler reinforced rubber and this allows a more reliable constitutive model to be derived.