Evaluating PVC Degradation Using UV and Raman Spectroscopies

While the world growth in PVC consumption continues (currently ~35 million tonnes per annum), its poor thermal stability, remains an issue due to restrictions on the use of stabilizers containing heavy metals such as lead. Monitoring degradation in PVC is important, and this work is concerned with the detection of PVC degradation using UV and Raman spectroscopies. The bands which appear in the Raman spectra of PVC samples after thermal degradation at around 1100 and 1500 cm-1, are the result of a resonance Raman effect. Optimization of the PVC degradation assessment process using laser-Raman is crucial to minimize the effects of additive interference and the fluorescent background. The most important factor is the wavelength of the exciting laser source, as it should fall within the absorption range for polyene sequences in degraded PVC. Laser-Raman spectroscopy has been shown to be an appropriate method for the quantitative determination of the polyene length distribution in lightly degraded PVC samples. The application of this method for various degraded PVC samples is reported. Ageing of compounds containing various heat stabilizers were considered, in order to assess their effectiveness. Additives studied included calcium zinc stabilizers and two commercial grades of hydrotalcite (Sorbacid 911 and Alcamizer P93).