Reinforcement effect and molecular motions in semicrystalline PEEK films: Mechanical and physical modelings. I

Abstract

The influence of the crystalline phase on the viscoelastic behavior of poly (aryl ether ether ketone) (PEEK) films is assessed by dynamic mechanical spectrometry. Prediction of the viscoelastic behavior near T g of semicrystalline films is performed through mechanical and physical modelings. Changes in the a relaxation induced by the crystalline phase are related to both the mechanical coupling between phases and the decrease in the molecular mobility of chains, which is improved for samples showing a broad crystallite size distribution. Crystalline phase also induces some modifications in the characteristics of the β spectrum. The reinforcement effect brought by the crystalline phase in such a temperature range is predicted through a mechanical model. Then, changes in tan δ level in the β 1 region induced by the crystalline phase result from the mechanical coupling between phases. The magnitude of such changes only depends on the crystallinity ratio and it is not controlled by the crystallite size distribution. The crystalline phase also induces changes in the pattern of the β 2 transition, which could be attributed to modifications in the conformations of the chains near the crystalline entities and/or the magnitude of interactions between chains. Such modifications seem to be sensitive to the thermal history of PEEK samples.