Utilization of TGA Flynn-Wall and Arrhenius Analysis for Rapid Prediction of Automotive PVC Cable Performance

Both pellet raw material and resulting extruded insulation samples were obtained from three grades of PVC used to produce automotive insulation and were examined for thermal stability on a Thermogravimetric Analyzer (TGA). The Flynn Wall technique was used to obtain degradation activation energies by plotting ln(heating rate) vs 1/T and using a literature value of 7% weight loss as the point of performance failure. The Arrhenius relationship was used to predict multiple year lifetimes at 100°C from the multiple hour degradation times observed on the TGA at 200°C. The insulation specimens of two of the samples were found to be significantly less thermally stable than the pellets - indicating slight decomposition occurred during extrusion onto the cable core. All cable insulation samples predicted service lifetimes many times the expected auto life. A PVC insulation sample was examined for failure at various oven aging temperatures using ASTM D3032 mandrel wrap testing. The weight loss for failure was calculated by substituting the oven age time and temperature into the Arrhenius relationship and using an activation energy obtained from a plot of activation energy vs. weight loss which was found to be constant at weight losses greater than 1%.