Stabiliser diffusion in long-term pressure tested polypropylene pipes analysed by IR microscopy

The concentrations of Irganox 1010 averaged over the pipe wall as determined by IR microscopy were in excellent agreement with those obtained from High Performance Liquid Chromatography and Oxidation Induction Time (OIT) analysis. Diffusion constants were calculated from the stabiliser concentration profiles based on the Fickian equations using appropriate initial and boundary conditions. A literature value is compared to these experimental results. The developed IR technique allows monitoring the stabiliser migration faster and more reproducibly than the conventional approach by manual abrasion of layers and measurement of the OIT. Additionally, this brings a tremendous improvement with regard to spatial resolution. As a result the impact of hoop stress and extrusion rate on the migration of stabiliser in PP-R pipes can be shown for the first time.