Effect of physical and chemical ageing on barrier properties of epoxy coating

This work describes the change of gas permeability of epoxy coatings thermally aged at different temperatures from 50 to 200 degrees C in order to address their barrier properties for protecting concrete in civil engineering industry. Argon permeability characterization tests were carried out on samples either coated on concrete or aged as free standing films. With the increase of time and ageing temperature, epoxy becomes more and more permeable and its barrier properties are lost. For better understanding those results, possible ageing mechanisms were investigated. Plasticizer loss was studied by gravimetric analysis and by differential scanning calorimetry. It seems to induce only moderate consequences on barrier and mechanical properties. Reversely, thermal oxidation was shown to severely damage the barrier and mechanical properties due to the existence of chain scissions. Last, structural relaxation ageing is shown to play a negligible role on the investigated time scale but its consequences at longer time remain to be fully understood.