Alternative Aircraft Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxygen Demand (2010)

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8-1 SECTION 8 SUGGESTED FUTURE RESEARCH TOPICS This section presents issues and activities that were identified during the research as being suitable subjects of future research and development by ACRP or others. Further development of the alternative Type IV formulation could be conducted. The purpose of the Tier 1 and Tier 2 tests was to screen and evaluate candidate components for anti- icing performance (freezing point depression, viscosity, surface tension, foaming), environmental impact (biochemical oxygen demand, chemical oxygen demand, aquatic toxicity), materials compatibility (total immersion and sandwich corrosion on aluminum alloys) and safety properties (flash point). The results of these tests showed that formulations with significantly improved toxicity and lower oxygen demand compared to current products, and acceptable performance properties were developed. Some of these key tests, such as aquatic toxicity and corrosion testing, could be replicated by an independent laboratory to validate these results. The tests conducted in Tier 2 demonstrated that the concentration chosen for the corrosion inhibitor, triethanolamine, in the final formulation was acceptable, but can possibly be reduced and still be acceptable. It is recommended that the sandwich and corrosion tests be replicated at lower corrosion inhibitor concentrations to determine the lowest acceptable concentration. The final formulation could then be subjected to a water spray endurance test (WSET) to verify it has a sufficient holdover time (HOT) to perform as a Type IV anti-icing fluid. If the fluid’s HOT is acceptable an aerodynamic acceptance test should then be conducted to ensure the final formulation’s rheological performance is acceptable. The formulations would then need the addition of a dye and require further testing to achieve certification by the Anti-icing Materials International Laboratory (AMIL), Université du Québec à Chicoutimi (UQAC) (Quebec, Canada) and Scientific Material International (SMI) (Miami. FL) under AMS 1428F. Specifically, the program would need to include tests on fluid stability, anti- icing performance, aerodynamic acceptance, and the effect on aircraft materials (sandwich and total immersion testing on other alloys, low-embrittling cadmium plate, stress-corrosion resistance, hydrogen embrittlement and transparent plastics). Examination of low toxicity formulation components. The formulation’s surfactant, and corrosion inhibitor have lower toxicities than other chemicals in their respective product classes. The use of low toxicity chemicals such as these could be considered as alternative components in other products. A standard metric is needed for expressing the potential oxygen demand loading from PDMs. Specifically, the following conceptual metric is proposed for consideration: Grams of oxygen needed to oxidize the chemicals needed to achieve and maintain one square meter of runway free of ice for one hour. Improved methods are needed to minimize the effect of microorganism acclimation on variability of BOD measurements. BOD—Exploration of microorganism acclimation for FPDs would be needed to better understand potential oxygen demand for several of the candidate FPDs including the final choice of DEG.

ALTERNATIVE AIRCRAFT ANTI-ICING FORMULATIONS 8-2 Investigation of degradation by-products of certain candidate additives is needed. Although certain candidate surfactants, corrosion inhibitors, and thickeners are extensively used in a wide range of products, the increased toxicity of their possible degradation products would warrant further investigation. Specifically, by-products from bio-degradation in waterways receiving airport runoff would need to be identified. Further work would be needed to find suitable anti-caking agents for sodium formate. A more extensive list of anti-caking materials and coatings would need to be formulated, together with extensive testing with mixtures of sodium formate. Alternatively, techniques for pelletizing sodium formate could be investigated for improving handling characteristics. The caking behavior of sodium formate would need to be investigated further. Some operators claim sodium formate’s caking tendency makes it unusable. Others reported that a simple mechanical shock was sufficient to eliminate any caking problems. Variables such as time of storage and humidity during storage would need to be quantified to determine when a caking problem may occur. Once the conditions promoting sodium formate’s caking behavior have been determined and particulate agglomerates repeatedly produced, the microscopic nature of these agglomerates would need to be examined. The theory explained in this report, the formation of salt bridge between particles, can be verified by microscopic examination. The effect anti-caking additives have on the formation and strength of these salt bridges may also be able to be evaluated by microscopic examination. A more scientifically based process for selected anti-caking additives would need to be developed. The solubility of anti-caking additives into the adsorbed sodium formate-water mixture as well as the phase behavior of the resulting ternary solution would provide guidance in the selection process. It is believed that the experimental procedure used to evaluate the effect of anti-caking additives in this research is sound and can produce quantitative results. However, the method for distributing anti-caking additives among the sodium formate particles would need to be modified.