Ethylene-vinyl acetate copolymer/aluminium trihydroxide composites: A new method to predict the barrier effect during cone calorimeter tests

Abstract : This study presents the use of oedometric compression test in order to evaluate the breakdown of a protective layer acting as a diffusion barrier (''barrier effect'') occurring during cone calorimeter tests for ethylene-vinyl acetate copolymer/aluminium trihydroxide (EVA/ATH) composites. The formation of an alumina layer at the sample surface during burning insulates thermally the underlying material and reduces the heat release rate. The efficiency of this barrier depends on the cohesion of the layer formed. This cohesion depends on the ability of the particles (ATH and synergistic mineral fillers) to self-arrange. During the test, the breakdown of this barrier can lead to an increase in HRR. The oedometric compression test allows assessing the ability of fillers to form a cohesive layer. Results obtained from compression modulus of filler powders are directly related to some aspects of the heat release rate curve of composites measured in cone calorimeter tests. Indeed, the appearance and the intensity of the second pHRR (related to the breakdown of the barrier layer) in cone calorimeter test are related to the slope of oedometric compression curve.