Study of the natural ageing of PVC insulation for electrical cables

摘要

The characterisation of high voltage cable insulation waste is addressed in an effort to determine their further utilisation either as feed in reprocessing or for the recovery of the energy and material content by pyrolysis. Electrically aged (18 years outdoors at 6-10 kV) polyvinyl chloride (PVC) cables were ground by mechanical or cryogenic procedures. The waste was studied in comparison with a PVC virgin resin and a PVC virgin formulation similar to that of the cables both in quantities of additives and structure of polymer. After successive extractions in acetone and benzene the base polymer and extracts were analysed by elemental analysis, GPC, viscometry, IR and ~1H-NMR spectroscopy, TG, DSC, and several standard methods of plastic analysis (plasticizer absorp- tion, static thermal stability, etc.). From the acetone extracted quantities and the plasticizer absorption measurements it appears that only 1-2 di-2-ethylhexylphthalate (DOP) was lost during the service-life of cables and most of the initial quantity remained in the cable composition so only a small addition is necessary for the reprocessing. The IR spectra of polymer extracted from electrical cable waste exhibit important changes concerning double bonds and carbonyl groups. The T_g value is higher for the waste material indicating that it was rigidized due to the polyene fragments arising from partial dehydrochlorination. This is also sup- ported by the viscometric and GPC measurements, the PVC from waste having a higher molecular weight than virgin PVC. Based on T_g curves and static thermal stability the