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

The technique of second time derivative (STD) analysis is developed and app lied to the chemiluminescence (CL) profiles of two polypropylene (PP) formu lations and a 5% w/w blend of polybutadiene (PBD) in PP to assess this nove l method of analysis as a means of reliably determining the oxidative induc tion time (OIT) of polymers. It is proposed that the STD technique, when us ed 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 conv entional extrapolation method. This is particularly so in systems that exhi bit a gradual onset towards autoacceleration and/or convoluted CL profiles. Chemiluminescence profiles of the PBD-PP blend that were obtained at diffe rent temperatures were subjected to STD analysis, and Arrhenius plots of th e data were made. The results are consistent with the notion that the PBD a nd 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 fo r the PBD phase is partly attributed to the greater partitioning of thermal stabilizer in this phase. (C) 2001 John Wiley & Sons, Inc.