Experimental study of crystallization of PolyEtherEtherKetone (PEEK) over a large temperature range using a nano-calorimeter

The recently developed fast scanning differential calorimetry is used for the first time to determine the crystallization kinetics of Poly(EtherEtherKetone) (PEEK). In our experiments, crystallization is studied in isothermal conditions over a large temperature range from 170 degrees C to 310 degrees C. Two different measurement protocols were employed. Between 200 degrees C and 300 degrees C the heat flow was directly measured during isothermal crystallization. Outside this temperature range we measured the heat of fusion on heating after interrupted isothermal crystallization. We show that data can be analyzed with the Avrami approach incorporating a term describing secondary crystallization. The crystallization half-times are measured. The Avrami kinetic coefficient K-Av associated with primary crystallization is evaluated from isothermal crystallization between 170 degrees C and 310 degrees C where data were not previously available. The kinetics of crystallization of PEEK has only one maximum located around 230 degrees C and its Avrami exponent is close to 3, suggesting instantaneous nucleation with subsequent spherical growth. The whole isothermal crystallization process is modeled in terms of Hillier's model since it takes secondary crystallization kinetics into account. Finally, it is shown that the double melting peak behavior observed after isothermal crystallization (below 260 degrees C) is a consequence of the reorganization process during heating. (C) 2014 Elsevier Ltd. All rights reserved.