Macromol. Symp. 147, zyxwvuts 167-172 zyxwvu (1999) zyxwv 167 zy MECHANICAL PROPERTIES OF RECYCLED POLYMERS Francesco Paolo La Mantia Dipartimento di Ingegneria Chimica dei Processi e dei Materiali Universita di Palermo, Wale delle Scienze, 90128 Palermo, Italy SUMMARY: Modifications of structure and morphology of the polymers induced by the thermomechanical stress (or by the presence of water for some polymers) during reprocessing can cause a drastic deterioration of mechanical properties of the recycled material. The property zyxwv - reprocessing relationships are an important tool to determine not only the properties of the recycled polymers but also the strategies to use (processing conditions, stabilizers, fillers, compatibilizers, etc) in order to obtain recycled polymers with good mechanical properties. In this zy work, typical behaviour of some mechanical properties as a function of the number of reprocessing operations is discussed and correlated with their structure and morphology. The influences of the type of apparatus and of the processing conditions are also considered. INTRODUCTION Polymers undergo, during recycling operations, changes of the structure and, in some cases, of morphology (Ref. 1). Changes of structure mean a decrease in the chain length as well as formation of chain branching and functional groups while crystallinity can vary depending on the changes in molecular weight. Thermomechanical stress, the presence of oxygen and, for condensation polymers, the presence of water or of other small molecules is responsible for these modifications. Changes of both structure and morphology induce drastic variations of some properties and, in particular, of rheological and mechanical properties, outdoor resistance and thermal stability. Clearly, the level of degradation and then deterioration of the properties depends on the amount of "stress" and on the number of reprocessing operations. The knowledge of variations of properties with the number of reprocessing steps and with the stress level is, therefore, an important tool in the use of these secondary materials. In this work, typical behaviour of some mechanical properties as a function of the number of reprocessing operations will be discussed for some important polymers and correlated with their structure and morphology, with the type of apparatus and with the processing conditions (thermomechanical stress level). Finally, the influence of stabilizers is also considered. PROPERTY - REPROCESSING RELATIONSHIPS The behaviour of properties of the recycled polymers as a function of the number of reprocessing operations depends on: zyxwv 0 WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 CCC 1022-1 360/99/$ 17.50+.50/0