Iodine Depletion Analysis of Polyvinylidene Fluoride Bladders for the Potable Water System on Axiom Station

As part of Axiom Space’s ongoing efforts to test and qualify potable water storage containers, the Water Accumulation and Treatment Assembly (WATA) team conducted a bench-top scale test of Polyvinylidene Fluoride (PVDF) by exposing the material to an iodine solution concentration of 4 ppm, which is at the high end of the range specified for the Axiom Station potable water system. Dog-bone shaped specimens of PVDF were submerged in the iodine solution at the same surface area to volume (SA/V) ratio expected to be seen by a 25 L water storage bladder when fully loaded with iodinated water. The samples were then analyzed to determine the resulting chemical and mechanical properties. Chemical effects on the iodine solution were determined by Ultraviolet–Visible spectroscopy (UV/VIS) and Total Organic Carbons (TOC). This assessment is expected to reduce the amount of testing time, necessary resources, and repeated efforts to determine the iodine saturation point of a full-scale water storage bladder. Based on the analysis presented in this paper, PVDF has a steep initial absorption period (T-10 hours) before slowing down. However, a 1-week soak increased the projected lifetime of the solution (i.e. iodine concentration remains above 1 ppm) to at least six months.