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Previous investigations have shown that a combination of processing and thermo-oxidative ageing degrades polymeric materials faster than repeated processing or extended ageing performed separately. Hydroperoxide formation and decomposition into radicals are known to play a key role in polymer auto-oxidation. We hypothesise that hydroperoxides formed during the ageing step, decompose in the subsequent processing step, thereby causing faster degradation of the materials. In this study, an un-stabilised polypropylene (PP) powder was compression moulded into thin films that were then aged in air. The hydroperoxide concentration in the aged samples was determined by iodometry. On second compression moulding, the hydroperoxide concentration decreased, in support of the above theory. FTIR analysis showed that the hydroperoxides formed during ageing are rapidly transformed into carbonyl groups upon compression moulding. [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]

We have investigated oxidative degradation of low density polyethylene (LDPE) by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Replacing 16O2 in the exposure atmosphere by 18O2 makes it possible to identify species originating from the artificial ageing, since oxygen present in the material prior to ageing can then be distinguished from oxygen introduced in the ageing process. The yield of O-ions in TOF-SIMS is very high, making oxygen-18 an excellent tool for following early stages of oxidative degradation. Furthermore, we have identified two 18O-containing ions, CH318O+ and C2H318O+, which can also be used to follow the oxidation processes. [Copyright &y& Elsevier]