Crystallization kinetics of a PEEK/LCP blend

Abstract

SYNOPSISThe crystallization kinetics of a polyetheretherketone (PEEK)/liquid crystalline polymer (LCP) blend was studied by using differential scanning calorimetry. Nonisothermal runnings were performed on heating and on cooling at different rates. Isothermal crystallization experiments at 315, 312, 310, and 307"C, from the melt state (380°C) were performed in order to calculate the Avrami parameters n and k and the fold surface free energy, a , . Polarized light optical micrographs were also obtained to confirm the Avrami predictions. It was observed that the LCP retarded the PEEK crystallization process and that the PEEK melting temperature decreased with the amount of LCP, but the LCP melting temperature increased with the amount of PEEK. Probably the PEEK improves the perfection of the LCP crystalline domains. A spherulitic morphology in pure PEEK and its blends was predicted by the Avrami analysis; however this morphology was only observed for pure PEEK and for the 80/20 composition. The other compositions presented a droplet and fibrillar-like morphology. The overall crystallization rate was observed to decrease with the crystallization temperature for all compositions. Finally, u, was found to decrease with the increase of LCP in the blends, having unrealistic negative values. Thus, calculations were made assuming a, constant at all compositions. It was observed that u, the interfacial lateral free energy, decreased but still remained positive. It was concluded that in these blends neither a, nor u could be considered constant.

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