Effects of accelerated and natural ageing on plasticized polyvinyl chloride (PVC)

About 50 different cables and sheathings from 3, 24- to 34-year-old houses have been investigated with respect to tensile properties, residual stabili ty, composition and remaining lifetime. One type of PVC material, used as a model and containing equal proportions of the plasticizer has been subject ed to accelerated ageing at 80-110 degrees C in air and in nitrogen atmosph ere using low laminar gas flow. The effects of ageing were detected after f ixed periods of time of up to 2 months of exposure, using measurements of m ass loss, residual stability, and elongation at break. The mass loss, as we ll as the consumption of the stabilizer in the model material, seems to be independent of the presence of oxygen. The activation energies were determi ned to about 98-99 kJ/mol for the mass loss in air and in nitrogen, and abo ut 101-104 kJ/mol for the stabilizer consumption. These results indicate th at the mass loss is the dominant process in ageing of plasticized PVC at lo w temperatures. Ageing in air at 80 and 90 degrees C for up to 8 weeks caus ed no significant changes in elongation at break. At 100 and 110 degrees C, the maximum change in elongation at break was about one third of the origi nal value, which corresponded to the maximum mass loss of about one third o f the original amount of the plasticizer. Cables and sheathings collected f rom old buildings were tested and showed little change in elongation at bre ak even after 34 years of use. In addition, the measurements of residual st ability show high values, indicating good thermal stability of the old mate rials. Some materials were also subjected to accelerated ageing in air at 8 0 degrees C. Accelerated ageing did not significantly affect the tensile pr operties of the insulation materials. The maximum change in the content of extractable matter that was observed after ageing was 1%. The investigation has consequently shown that the technical quality and the remaining lifeti me of the old cables and sheathings that had been collected is very good, m aking them suitable for reuse or mechanical recycling. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.