DIFFUSION AND EXTRACTABILITY CHARACTERISTICS OF ANTIOXIDANTS IN BLUE POLYETHYLENE WATER PIPE - A DSC AND RADIOLABELING STUDY

The diffusion characteristics of two commercial products, Irganox 1010 and Ethanox® 330 antioxidants, have been investigated in blue polyethylene water pipe on ageing in air and water at different temperatures and on weathering outdoors. Antioxidant loss was studied in both instances using differential scanning calorimetry (DSC) and in the latter case using a radiolabelling technique. Under all ageing conditions pipe containing Irganox 1010 shows a greater percentage loss in oxidation induction time at 200°C (DSC) than that containing Ethanox 330 antioxidant. Monitoring of the latter antioxidant by the technique of scintillation counting shows no loss of antioxidant at the bore of the pipe when in contact with water even after 3 months at 60°C. These results are accounted for on the basis of the differences in the diffusion rate, solubility, migration, volatility, hydrolysis, etc, of the molecules. Ethanox® 330 antioxidant has a negligible degree of extractability and as such is suitable for applications in contact with water especially at temperatures below 120°C. Irganox 1010 can only outperform Ethanox® 330 antioxidant at temperatures well above those seen in normal applications. © 1990.