Two-stage crystallization of poly(ether ether ketone) and its blends with poly(ether imide)

Thermal mechanical analysis (TMA) has been used to study the crystallization behavior of poly(ether ether ketone) (PEEK) and its blends with poly(ether imide) (PEI). The two crystallization stages of PEEK are clearly distinguished by measuring the variation of film thickness with time during isothermal crystallization. Upon blending with PEI, the distinction of the two PEEK crystallization stages becomes obscure. This is attributed to the depressions in both nucleation density and spherulite growth rate upon blending with PEI. An Avrami analysis, modified by considering both primary and secondary crystallization, is used to extract the respective kinetic behavior of these two crystallization stages. The results indicate that the secondary crystallization proceeded slower than the primary crystallization in the diffusion-controlled crystallization region. On the other hand, these two crystallization stages proceeded at comparable rate in the thermodynamically-controlled crystallization region. It is also found in the diffusion-controlled crystallization that blending with PEI induced a larger depression in the secondary crystallization rate than in the primary crystallization rate. Explanations for these observations are proposed and discussed.