Catalyst residue effects on the heterogeneous oxidation of polypropylene

Abstract

The chemiluminescence (CL) curves in oxygen from polypropylene with a residual Ziegler-Natta catalyst Titanium concentration ranging from 0.2 to 4.1 ppm were measured from 100 to 150 degrees Celsius and it was found that the intensity of CL increased and the time taken to reach the maximum CL intensity decreased with [Ti]. The temperature dependence of the time to maximum CL intensity showed an apparent activation energy, Ea, of 88.1±0.6 kJ/mol that was independent of [Ti] but the pre-exponential factor, A′, decreased with increasing [Ti] according to a power law: A′=4.7×10−8[Ti]−0.3. This has been interpreted as reflecting the power law dependence of [Ti]−0.33 for the distance between residual particles of catalyst as sites for the initiation of heterogeneous oxidation. This has been tested by stochastic modelling of the spreading of oxidation for a range of volume fractions, p0, of infectious sites. This modelling allows pseudo-CL profiles to be constructed over the temperature range 100–150 degrees Celsius. The modelling has been restricted to p0 values equivalent to higher initial [Ti] but the results show that Ea is independent of [Ti] and A′ shows a power-law dependence of [Ti]−0.29 consistent with the experimental data.