Oxidation of unstabilised polypropylene particles as studied by microcalorimetry and chemiluminescence techniques

Microcalorimetry (MC) and chemiluminescence (CL) measurements have been used to study the oxidation of unstabilised polypropylene (PP) particles. The oxidation profiles obtained by the two techniques were found to be similar although a time shift between the profiles was observed, particularly at low temperatures. The similar shape suggests a close relation between the rate of the overall oxidation process as measured by MC and the rate of the CL emitting reactions. MC revealed that the energy evolved up to the maximum of the MC oxidation profile increased significantly above 110 degreesC indicating a change in the overall oxidation process, possibly associated with a more pronounced secondary oxidation. The results indicate that above 110 degreesC the maximum of an oxidation profiles (as measured either by MC or CL techniques) is not suitable for evaluating the temperature dependency of oxidation. FTIR was used to follow the formation of oxidation products. It was found that the oxidation profiles obtained by either MC or CL measurements did not reflect the carbonyl build-up but more likely the hydroperoxide build-up. (C) 2003 Elsevier Science Ltd. All rights reserved.