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Two post-consumer polypropylene (PP) materials have been examined and compared using a simulated recycling test procedure consisting of repeated cycles of alternating extrusion and accelerated thermo-oxidative ageing. The materials were also subjected to repeated extrusion and thermo-oxidative ageing separately. The materials were characterized by mechanical and chemical properties, such as elongation-at-break, oxidative induction temperature, carbonyl index and changes in molecular weight distributions. The different batches of recycled PP differed substantially in terms of durability and recycling potential. This illustrates one of the problems involved in handling recycled materials i.e. different batches and material streams may differ quite a lot. Interestingly, the elongation-at-break was significantly different for samples taken after ageing and extrusion, respectively. The elongation decreased upon each ageing step, and increased as a result of the subsequent extrusion. Furthermore, the combination of extrusion and ageing tended to degrade the materials faster compared to ageing or repeated extrusion performed separately. [Copyright &y& Elsevier]

An ABS-material has been subjected to a series of six combined cycles of extrusion and ageing in air at an elevated temperature. Each cycle consisted of conventional extrusion processing followed by ageing in air at 90 °C for 72 h. Large changes in the tensile and flow properties were observed. From the second to the sixth cycle, the elongation at break decreased markedly due to the ageing and increased as a result of the extrusion step. Further analysis showed that the large reductions in elongation at break could be attributed to physical ageing of the SAN-phase and to thermo-oxidative ageing of the polybutadiene phase, as shown by further tensile measurements and infrared spectroscopy. SEM-measurements indicated no significant changes in the size and shape of the polybutadiene particles. No significant changes in the molar mass of the SAN-phase were observed. [Copyright &y& Elsevier]