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 °C. 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 °C for 10 min, and then they were heated to 380 °C at 2 °C/min. From the TMDSC results, the exothermic behavior in the non-reversing curves supports the mechanism of melting–recrystallization at T_c≤310 °C. On the other hand, no exothermic flow for T_c at 320 °C supports the mechanism of two different morphologies. As the isothermal crystallization temperature increased from 280 to 320 °C, the contribution of melting–recrystallization to the upper melting peak gradually decreased, and finally disappeared.