Temperature modulated DSC and DSC studies on the origin of double melting peaks in poly(ether ether ketone)

Crystallization kinetics and melting behavior of poly(ether ether ketone) were studied by differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC). The isothermal crystallization was performed between 290 and 320 degreesC. The Avrami exponents and the level off time were determined from the Avrami analysis. The minimum induction time required for the occurrence of double melting peaks was obtained by increasing the isothermal crystallization time in steps of one minute. It was found that the level off time did not represent the delimitation of single- or double-melting peak behavior. To elucidate the behavior of double melting peaks, the samples were crystallized isothermally between 280 and 320 degreesC for 10 min, and then they were heated to 380 degreesC at 2 degreesC/min. From the TMDSC results, the exothermic behavior in the non-reversing curves supports the mechanism of melting-recrystallization at T-c less than or equal to 310 degreesC. On the other hand, no exothermic flow for T-c at 320 degreesC supports the mechanism of two different morphologies. As the isothermal crystallization temperature increased from 280 to 320 degreesC, the contribution of melting-recrystallization to the upper melting peak gradually decreased, and finally disappeared. (C) 2003 Elsevier Ltd. All rights reserved.