The effect of physical ageing on the properties of amorphous PEEK

Abstract Physical ageing rates of poly(aryl-ether-ether-ketone) have been measured, and interpreted as a kinetic effect associated with the glass formation process. The extent of ageing achieved at equilibrium as measured by differential scanning calorimetry is equal to the product of the super-cooling from the quenched glass transition, and the heat capacity difference between the glass and liquid at the transition temperature. Heat capacities of amorphous and crystalline PEEK have been measured. The activation energy of physical ageing is similar in magnitude to that observed for temperature dependence of crystallization under conditions of viscosity control. Ageing is accompanied by a change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding and a decrease in impact strength. Fracture surfaces show evidence of mixed modes of fracture.