Study of the natural ageing of PVC insulation for electrical cables

The characterisation of high voltage cable insulation waste is addressed in an effort to determine their further utilisation either as feed in reproce ssing or for the recovery of the energy and material content by pyrolysis. Electrically aged (18 years outdoors at 6-10 kV) polyvinyl chloride (PVC) c ables were ground by mechanical or cryogenic procedures. The waste was stud ied in comparison with a PVC virgin resin and a PVC virgin formulation simi lar to that of the cables both in quantities of additives and structure of polymer. After successive extractions in acetone and benzene the base polym er and extracts were analysed by elemental analysis, GPC, viscometry, IR an d H-1-NMR spectroscopy, TC, DSC, and several standard methods of plastic an alysis (plasticizer absorption, static thermal stability, etc.). From the a cetone extracted quantities and the plasticizer absorption measurements it appears that only 1-2% di-2-ethylhexylphthalate (DOP) was lost during the s ervice-life of cables and most of the initial quantity remained in the cabl e composition so only a small addition is necessary for the reprocessing. T he IR spectra of polymer extracted from electrical cable waste exhibit impo rtant 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 su pported 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 t hermal stability the following order of thermal stability has been establis hed: PVC waste jacket <PVC electrical cable waste < virgin PVC < PVC virgin cable formulation. One can conclude that PVC cable wastes have retained mo st of the characteristics required for reprocessing, but a higher level of stabilisers must be used to ensure the stabilisation of the deteriorated st ructure and compensate partial deactivation of the initial stabiliser syste m. (C) 2000 Elsevier Science Ltd. All rights reserved.