Understanding the Effects of Processing on the Properties of Perfluoroalkoxy (PFA)

Abstract

The effect of processing on the properties of three transfer moulding grades of perfluoroalkoxy was investigated. There is anecdotal evidence to suggest exposure to high shear rates and residence time at processing temperature detrimentally affect the polymer, however there is a lack of information published in this area. This work set out to provide a better understanding of the material behaviour under various processing conditions. A bespoke capillary rheometer was used to determine flow characteristics at various temperatures between 5-400s-1. The materials were found to be shear thinning, with the virgin grades exhibiting Newtonian behaviour at low shear rates. The viscosity of the carbon black filled PFA was found to have a higher viscosity than the virgin materials, despite it having a higher Melt Flow Rate. Spectroscopy was found to be unsuitable for investigation of polymer containing carbon black due to laser heating. However changes due to residence time at processing temperature in the virgin material could be detected using statistical analysis of Near Infrared spectra. Whether the mechanical properties of the virgin material changed following exposure to high shear rates or residence time varied on manufacturer, with Dyneon 6502TZ appearing to be more process stable than Chemours 350TJ. This information can be used to optimise the transfer moulding process, and assist in meeting the requirements of the Chemical Processing Industry for larger and more complex lined piping components.