Hydroperoxide titration by DSC in thermally oxidized polypropylene

Unstabilized polypropylene (PP) films and stabilized PP fibres were thermally oxidized at 80 °C under high oxygen pressure (5.0 MPa). Their oxidation was monitored by infrared (IR) spectroscopy, iodometric titration and modulated differential scanning calorimetry (MDSC). This latter technique allows separation of the thermograms into two parts: a reversing signal containing the major part of the melting endotherm and a non-reversing exothermal signal increasing with hydroperoxide amount containing also a minor part of the melting endotherm. Comparisons of the heat of this exotherm with hydroperoxide concentration determined by iodometry, in unstabilized or stabilized samples, led to the conclusion that the exotherm is mainly due to the decomposition of hydroperoxides, which are thermolabile species resulting from oxidation. The heat of this exotherm is −325 kJ mol−1, which agrees with thermochemical data. It appears that DSC can be used for the determination of hydroperoxides in PP, having the main advantages of being faster and more practical than conventional chemical or spectroscopic methods.