INTRODUCTION During the last decade, the disposal of large volumes of solid urban waste has represented a concern for many countries. The problems created by plastic wastes became particularly important because of the environmental problems caused by their long life and complicated elimination. 1–3 Since polypropylene (PP) is one of the most widely used commodity polymers with a large number of applications, there is no doubt that the huge quantities that are disposed of comprise a large part of total plastic waste. The recycling of residues generated during the processing of PP is a common procedure in some industries; with the recycled material retaining the main properties of virgin PP. Generally, recycling primary scraps of PP do not cause significant changes in average molecular weight, polymer chain structure and morphology; on the other hand, repeated extrusions could affect the molecular weight as a consequence of the weakness of the tertiary carbon in the PP chain and its possible oxidation. 4 Despite the good properties of the material, the most usual application of recycled PP is for the manufacture of low-cost products. 4,5 The introduction of metallocene technology has allowed the use of new strategies for the polymerisation of olefines used in the synthesis of elastomers. 6 This is the reason for the introduction of a new family of ethylene- /α-olefine co-polymers with a narrow molecular weight distribution, as well as the use of thermoplastic elasto- mers based on blends of ethylene–propylene (EPDM) and PP. The addition of both materials improved some of the mechanical properties of recycled PP, such as impact at low temperatures. Another promising possibility is the use of polyethylene (PE) elastomers, which may compete with EPDM terpolymers for blending with PP in pellets. 7,8 Some work has been carried out on the influence of the blending process on the morphology and final properties of PP/rubber systems. 9–13 The main goal of the current work was the rheological and mechanical characterisation of blends of recycled PP with elastomeric additives. Plastics, Rubber and Composites 2003 Vol. 32 No. 8/9 357 DOI 10.1179/146580103225004126 Processing and properties of recycled polypropylene modified with elastomers A. Jiménez, L. Torre and J. M. Kenny This work presents a study of the processability and the characterisation of blends of recycled polypropylene (PP) with two different elastomers. The aim of the work was to demonstrate that the introduction of an elastomeric phase could improve the properties of recycled PP without changing the processing characteristics of the blends in terms of viscosity and temperature. The study was carried out using thermal analysis, thermomechanical analysis and rheological measurements. The rheological analysis of blends of recycled PP and elastomeric additives showed that, despite the different rheological behaviour of the added elastomers, the properties of the blends were dominated by the thermoplastic (PP) phase. A thermogravimetric analysis of the selected blends allowed the calculation of the parameters related to the thermal degradation of such materials and the main results indicated that there were no significant differences between virgin and recycled PP in terms of behaviour at high temperatures. Furthermore, the blending of recycled PP with elastomers did not result in a significant change in thermal degradation behaviour. Crystallisation studies showed that blending polypropylene with elastomers influenced the rate and amount of crystallisation, which increased at low additive concentrations and then decreased at a higher elastomer content. Thermomechanical analysis showed the immiscible character of the blends. The mechanical properties of the blends were affected by the concentration of elastomer, which also influenced the crystallinity of the material. PCR/2018 Keywords: Processing, recycled polypropylene, elastomers © 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining. A. Jiménez is in the Department of Analytical Chemistry, University of Alicante, PO Box 99, 03080 Alicante, Spain; L. Torre (for correspondence torrel@unipg.it) and J. M. Kenny are in the Department of Civil and Environmental Engineering, University of Perugia, Loc. Pentima Bassa 21, 05100 Terni, Italy. Manuscript received 18 February 2003, accepted in final form 23 October 2003.