Closed-Loop Recycling of Postused Garden Chairs Based on PP Using the Restabilization Technique. I. Evaluation of Processing Parameters C. N. Kartalis, 1 C. D. Papaspyrides, 1 R. Pfaendner 2 1 Laboratory of Polymer Technology, Department of Chemical Engineering, National Technical University of Athens, Zographou, Athens 157 80, Greece 2 Ciba Spezialitaetenchemie Lampertheim GmbH, Chemiestrae, D-68623 Lampertheim, Germany Received 15 June 2001; accepted 7 January 2002 Published online 19 September 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.11014 ABSTRACT: A remelting–restabilization technique was applied to evaluate the closed-loop recycling of postused, white pigmented, garden chairs made from CaCO 3 -filled polypropylene (PP). Analysis of the randomly collected pos- tused chairs showed only an insufficient quantity of residual active stabilizers. Different stabilization systems in selected concentrations were employed to investigate the optimum restabilization recipe for eliminating degradation effects during reprocessing. For monitoring the processing stability of the restabilized and nonrestabilized material a multiple extrusion procedure at two different reprocessing tempera- tures was performed. Furthermore, a repigmentation step was applied to investigate the role of the additional pig- ment on the processing stability of the recycled product. Finally, mechanical tests were carried out, for studying further the effect of restabilization on the mechanical performance of the recycled material. The results lead to the conclusion that restabilization for quality improve- ment of postused filled PP chair material during repro- cessing is permitting its reuse in the original application. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2472–2485, 2002 INTRODUCTION In terms of economics, the success of mechanical re- cycling strongly depends on whether virgin material can be substituted by recyclate fulfilling the same properties as the virgin plastic. In the past few years, the prerequisite of upgrading recyclates has become the key issue for market acceptance. 1–4 Usually, postused plastics, even from well-defined applications, cannot be reused in the form they were collected because physical predamage, structural in- homogeneities, and residual impurities are present, strongly affecting the recyclates’ quality. Already dur- ing their previous processing steps and service life plastics are subjected to undesirable chemical reac- tions, mainly caused by oxidation and photooxidation, which lead to irreversible changes in the polymer structure, negatively affecting the physical and me- chanical properties of the polymer and the corre- sponding recyclate. In addition, predamaged struc- tures of recyclates are much more sensitive to further oxidation than the corresponding virgin materials, be- cause they contain groups that can enhance or initiate thermo- or photo-oxidation. In other words, repro- cessing of recyclates would lead to further degrada- tion of the quality of the recycled material, unless appropriate protection is applied. 2–6 In the case of polypropylene (PP), the recycled poly- mer suffers from severe molecular weight degradation in course of reprocessing. This behavior is correlated with the well-known chain scission mechanism occur- ring during reprocessing of polymers with branched alkanes. 7–10 In particular, during reprocessing the polymer melt is exposed to high shear forces and high temperatures that result in COC chain scission phe- nomena along the polymer structure. The latter leads to chain length reduction, to molecular weight degra- dation and consequently to negative modifications in the basic material properties of the reprocessed grade. 9,10 In practice, oxidative degradation during reprocessing negatively affects the rheological proper- ties of the recycled material as well as typical mechan- ical properties, such as elongation at break, tensile strength, and flexibility. 11,12 Restabilization, probably the most effective ap- proach to improving the quality of recyclates, can compensate or at least reduce the aforementioned de- ficiencies to such an extent that the required process- ing and long-term stability is ensured. As a result, the economical and the ecological value of the recycled end product is increased. 2– 6,13–16 Correspondence to: C. D. Papaspyrides (kp@softlab.ece. ntua.gr). Journal of Applied Polymer Science, Vol. 86, 2472–2485 (2002) © 2002 Wiley Periodicals, Inc.