The second time derivative analysis of chemiluminescence emission profiles and its application to the accurate determination of oxidative induction times

The technique of second time derivative (STD) analysis is developed and applied to the chemiluminescence (CL) profiles of two polypropylene (PP) formulations and a 5% w/w blend of polybutadiene (PBD) in PP to assess this novel method of analysis as a means of reliably determining the oxidative induction time (OIT) of polymers. It is proposed that the STD technique, when used in conjunction with the integrated CL profile, can enable evaluations of the OIT to be made that are less subjective than those made using the conventional extrapolation method. This is particularly so in systems that exhibit a gradual onset towards autoacceleration and/or convoluted CL profiles. Chemiluminescence profiles of the PBD-PP blend that were obtained at different temperatures were subjected to STD analysis, and Arrhenius plots of the data were made. The results are consistent with the notion that the PBD and PP phases oxidize almost independently. The activation energies for the oxidation of the PBD and PP phases were calculated to be 200 ± 31 kJ mol-1 and 146 ± 9 kJ mol-1, respectively. The higher activation energy for the PBD phase is partly attributed to the greater partitioning of thermal stabilizer in this phase