Anisotropic Swelling of EPDM Rubber Discs by Absorption of Toluene

Abstract

Abstract Anisotropic swelling is observed when thin ethylene propylene diene monomer discs are immersed in a liquid such as toluene, whatever the percent peroxide acting as the curing agent ranging from 2 to 20. The process is studied either by experiments or calculation. The process of absorption is controlled by transient radial and longitudinal diffusion, with a concentration-dependent diffusivity and a finite and constant coefficient of convective transfer at the liquid-rubber interface. The problem is thus complex with a moving boundary since a rather high swelling takes place during the stage of absorption, leading to an increase in dimensions of the flat discs. The increase in the thickness of the discs is around 1.17– 1.18 times larger than that in the radius, at every time, while the diffusivity is the same for the radial and longitudinal transport. The extent of the change in the volume resulting from the toluene absorption varies from 1 to 1.5 depending on the value of the percent peroxide, the lower volume being obtained for the higher value of the curing agent The diffusivity is about the same whatever the percent curing agent. The state of cure is around 96 as obtained by calculation taking into account the heat transfer and the kinetics of the cure reaction. The kinetics of the cure reaction has been determined by measurements made either with a moving die rheometer run under isothermal conditions at three temperatures selected within the 170–190 °C temperature window, or a calorimeter in scanning mode. This fact can be explained by an orientation of the polymeric chains obtained during the cure, resulting from the pressure of the slabs of the heating press. Various percent peroxide as a vulcanizing agent have been used, e.g., 2, 10, and 20%.