The influence of polymer type, stabilizers and sample geometry on the relationship between chemiluminescence and oxygen uptake

Luminescence is known to be a very sensitive technique for determining the stability of materials. In order to judge the applicability of this method to determining by how much a polymer has already been (pre-)oxidized, the r elationship between oxygen uptake and luminescence results is determined. T o determine the robustness of this possible relationship, the influence of polymer type, stabilizers, sample geometry and degradation temperature is m easured. Several polymers (unstabilized polypropylene (PP) powder, stabiliz ed PP films, unstabilized low-density polyethylene (LDPE) powder, unstabili zed LDPE granules, unstabilized polybutylene terephthalate (PBT) powder, un stabilized polyamide 46 (PA46) powder, and unstabilized polyamide 6 (PA6) g ranules) were degraded at different temperatures, and the oxygen uptake and chemiluminescence in oxygen and nitrogen were measured. The best relations hips between oxygen uptake and luminescence results were found for the tota l light intensity (TLI) measured in a ramp experiment in nitrogen. Especial ly at the beginning of the oxidation, a straight-line relationship could be obtained between the consumption of oxygen and the TLI. However, this rela tionship is polymer-, temperature-, and geometry-dependent. Thus ramp CL ex periments cannot be used to quantify the degradation of a sample without a previous correlation curve under the same ageing conditions being available . Ramp experiments can be used to determine differences in the oxidation st ate of samples of comparable shape and with a comparable degradation histor y. (C) 2001 Elsevier Science Ltd. All rights reserved.