Abstract
When EPDM discs are in contact with a liquid such as toluene, a mass transfer takes place. The process is controlled by transient diffusion, with a concentration dependent diffusivity and a finite coefficient of convective transfer at the liquid/rubber interface. Moreover, a rather high swelling takes place during the absorption stage, leading to an increase in the dimensions of the flat discs. The increase in the thickness of the discs is approximately ×1 17-1 18 greater than that in the radius, exhibiting anisotropic behaviour. The flat discs have been cured by pressing them in the heated slabs of a press, which leads to a kind of orientation of the molecules. The state of cure of ∼96% was evaluated using a numerical model taking into account heat transfer and the kinetics of heat generated by the cure reaction. The kinetics of the cure reaction were determined using either calorimetry in scanning mode or a moving die rheometer run under isothermal conditions at three temperatures within the 170-190°C temperature window. Various percentages of peroxide (as a vulcanising agent) were used, i.e. 2, 10, and 20%. The diffusivity and its dependence on liquid concentration was of the same order of magnitude for the three samples, while the extent of liquid absorbed decreased considerably with percentage peroxide. A numerical model based on finite differences and taking into account all these facts, was built to describe the process of absorption.
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