CRYSTALLIZATION AND MELTING BEHAVIORS OF POLY(ARYLETHERETHERKETONE)(PEEK) ON ORIGIN OF DOUBLE MELTING PEAKS

The crystallization and melting behaviors of poly(aryletheretherketone) (PEEK) films were investigated, using differential scanning calorimetry and metallurgy concepts. The shape of the time-temperature-transformation (TTT) diagram, established for PEEK, results from both nucleation and growth phenomena. The double melting behavior exhibited by isothermally crystallized PEEK samples are discussed through the TTT diagram and the influence of the thermal history in the molten state. The upper melting peak arises first and the lower melting peak is developed later. The location of such a second endotherm is shifted toward the higher temperature with increasing either the crystallization temperature or the annealing time while the location of the upper melting peak seems to be unchanged. The double melting behavior is related to a bimodal distribution in size and/or perfection of lamellae developed in a two-step crystallization. With increasing temperature and/or annealing time in the molten state, the pattern of the endothermic curves is modified. The observed changes are discussed through two origins: the progressive disappearance of remnants of the former crystals and a thermal degradation leading to a cross-linking of the polymer. (C) 1994 John Wiley and Sons, Inc.