PHYSICAL AGING OF HIGH-PERFORMANCE THERMOPLASTICS - ENTHALPY RELAXATION IN PEK-C AND PES-C

The developments of physical aging in phenolphthalein poly(aryl-ether- ketone) (PEK-C) and poly(aryl-ether-sulfone) (PES-C) with time at two aging temperatures up to 20 K below their respective glass transition temperatures (T-g = 495 and 520 K) have been studied using differentia l scanning calorimetry (DSC). Substantial relaxation within the aging course of several hours were observed by detecting T-g decreasing duri ng physical aging process at the two aging temperatures. The relaxatio n processes of both polymers are extremely nonlinear and self-retardin g. The time dependencies of their enthalpies during the initial stages of annealing were approximately modeled using the Narayanaswamy-Tool model. The structure relaxation parameters obtained from this fitting were used to predict the possibility of physical aging occurring at th eir respective using temperatures. (C) 1995 John Wiley and Sons, Inc.