Iodine Depletion Analysis of Polyether Urethane Bladders for the Potable Water System on Axiom Station

On the International Space Station (ISS), stored potable water is treated with biocidal iodine to prevent microbial growth over time. However, iodine is absorbed and removed from solution by a variety of wetted materials. One example is a polyether urethane (PEU) air cell bladder used in certain commercial bladder tanks. This bladder material is known to absorb iodine quickly while also leaching out small amounts of total organic carbon (TOC), causing the water to violate the ISS potable water specification and requires loading the resupplied water into the ISS wastewater bus for on-orbit “polishing.” As part of Axiom Space’s ongoing efforts to test and qualify potable water storage containers, the team conducted a bench-top test of a PEU bladder by exposing the material to a high iodine solution concentration. This assessment reduced the amount of testing time, resources, and repeated work necessary when performing full-scale tests on the commercial bladder tank. Dog-bone tensile samples were submerged in high concentration iodine solution at an analogous surface area to volume (SA/V) ratio seen by the PEU bladder in a fully loaded water tank. After various storage times, the chemical properties of the test solution and mechanical properties of the bladder material samples were analyzed. For longer time-period samples, and after the iodine in the initial solution was depleted, the high-concentration iodine solution was refreshed. The goals for this analysis were to determine when the bladder material would achieve iodine saturation, and if the bladder material experienced any deleterious effects from iodine absorption. The study showed that future testing at higher concentrations would be necessary as the 40 ppm pretreatment solution did not reach saturation as the material is highly absorbent. This investigation determined that the mechanical properties of the material were not affected by the exposure to the higher iodine concentration.