Effects of repeated extrusion on the properties and durability of rigid PVC scrap

Determining retained properties and durability are among the most important tasks when evaluating the possibility of mechanical recycling of plastic w aste. In this investigation, profiles made of rigid PVC have been studied a fter various numbers of repeated extrusions to gain knowledge about the cha nges of properties and durability after conventional processing. New indoor profiles of PVC were re-extruded, from one to five times without adding ne w additives. The material was characterised after each extrusion using meas urements of colour, degree of gelation, stress-strain at break and UV-Vis-N IR spectroscopy. The durability of the material was evaluated by accelerate d ageing in ventilated heat ovens with low laminar airflow, at various temp eratures. Changes in elongation at break, colour and chemical characteristi cs, depending on degradation, were measured and compared for the material a fter each extraction and various periods of ageing time. The material showe d an improvement of mechanical properties after the second extrusion. This is explained by an increase in the degree of gelation of the PVC material. The main colour change due to repeated extrusion was yellowing (Deltab). In accelerated heat ageing, the main colour change was towards red (Deltaa) a nd a change in greyness (DeltaL) as a result of thermal dehydrochlorination . The activation energies of the degradation were also determined for the m aterial after each re-extrusion and were found to decrease with an increasi ng number of extrusions. The estimated lifetime for indoor use at room temp erature for the material after five extrusions was one-third of the lifetim e of the material extruded only once. Despite this finding, a long lifetime can be expected even for the material subjected to five consecutive extrus ions, making the material suitable for mechanical recycling. (C) 2001 Elsev ier Science Ltd. All rights reserved.