The isothermal degradation of some polyetherketones: a comparative kinetic study between long-term and short-term experiments Lorenzo Abate*, Ignazio Blanco, Oriana Motta, Antonino Pollicino, Antonino Recca Dipartimento di Metodologie Fisiche e Chimiche per l’Ingegneria, Universita ` di Catania, Viale A. Doria, 6, 95125 Catania, Italy Received 27 July 2001; accepted 2 October 2001 Abstract The kinetics of the isothermal degradation of three high thermally stable aromatic polyetherketones was studied by both a long- term (about 3 years) experiment at a temperature (270  C) largely lower than the temperatures of fusion, and a set of short-term experiments at temperatures near the temperatures of fusion. An induction period was observed at 270  C, followed by two degradation stages, the first with an exponential increase of the weight loss rate (V) as a function of heating time (t) and the final one showing constant weight loss rate. Short-term experiments showed similar behaviour, but no induction period was observed. The equations V=V o 2 t and V=K at various temperatures were determined for the exponential and linear degradation stages, respectively. The e-folding time  increased with temperature according to Arrhenius-type equations, by which the apparent acti- vation energy values for degradation could be determined. The results are discussed and indicate that the kinetic parameters of degradation change with temperature. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Thermogravimetric analysis; Polyetherketones; Kinetic parameters; Thermal degradation 1. Introduction In recent years the interest of the aerospace industry has been devoted to the development of low density materials to be used in structural applications and, in particular, of high performance composites with poly- mer matrix. Themosetting matrices are widely used for this purpose, but their brittle nature to impact-initiated failure and the high production costs of their compo- sites limit their use and drive the industries to examina- tion of thermoplastics. Since these polymers can be subjected to high temperature not only in manufactur- ing, compounding and processing stages, but also in service or during repair, an important aspect of the development of modern engineering plastics is directed toward producing thermally stable thermoplastics keeping good physical and mechanical properties as well as good resistance to oxidative and chemical breakdown at high temperature. Since the thermal stability of a polymer is connected with the initial degradation tem- perature and the rate of degradation, the study of the kinetics of degradation and the determination of the associated kinetic parameters, particularly the apparent activation energy values, appear to be an interesting topic of research in this field. We have in progress a comparative kinetic study on the degradation, in various environments and experi- mental conditions, of aromatic thermoplastic polyethers containing ketone and sulfone groups [1–6], which are economically accessible polymers showing favourable properties for use as matrices for high performance com- posite materials, because of the presence of fully oxidized and flexibilizing ether and carbonyl groups [7–11]. Short-term isothermal experiments are usually per- formed to determine kinetic parameters associated with the thermal degradation of polymers, but the apparent activation energy values and the corresponding degra- dation curves thus determined might not be suitable to represent the behaviour of polymers in service because they are usually obtained at temperatures near (or, in some cases, above) the melting temperatures. 0141-3910/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(01)00249-X Polymer Degradation and Stability 75 (2002) 465–471 www.elsevier.com/locate/polydegstab * Corresponding author. Tel.: +39-095-7382752; fax: +39-095- 333231. E-mail address: labate@dmfci.unict.it (L. Abate).