Effect of chemical degradation on the mechanical properties of ethylene–propylene–diene (5-ethylidene-2-norbornene) terpolymer-BaSO4 nano composites

Abstract

Time dependent degradation of the gum vulcanizates of ethylene propylene diene (EPDM) and EPDM-barium sulphate nano composites in sulphuric acid were studied. Impact of degradation on the mechanical properties of these composites was also evaluated. Gum compounds and nanocomposites cured with efficient vulcanisation system were subjected to an aggressive acidic medium containing 60% aqueous solution of sulphuric acid (H2SO4). The changes in functional groups were monitored using Fourier transform infrared spectroscopy (FTIR). The results reveal the formation of several oxygenated species on the EPDM rubber molecule due to acid attack; which is enhanced in the absence of barium sulphate nanofillers. Crosslink densities of acid aged samples were measured by the swelling method. An initial decrease in crosslink density as observed in EPDM gum vulcanizates is an indicative of hydrolytic attack at the crosslink sites, whereas the effect is less pronounced in nano composites. The effects of acid attack on mechanical properties were traced out by evaluating the percentage retention in tensile, elongation at break, compression set and abrasion resistance. For aged EPDM gum vulcanizates the retention in tensile showed a positive sign for a given increase in crosslink density, but on further increase of crosslink density due to combination of species formed during decrosslinking, tensile strength decreases. In the case of nano composites the retention in tensile properties was well around 100%. Scanning electron microscopy was used to monitor the changes in surface topography due to attack of acid and it well supports the degradation phenomenon and stabilisation of mechanical properties in the presence of barium sulphate nanoparticles.