Aircraft deicing and anti-icing operations are crucial to successful flight operations. Icing of aircraft during takeoff can result in severe consequences; even small amounts of ice present on wings or tail components can interfere with the aerodynamic properties necessary for flight. The military specification for aircraft deicing fluids is Society of Automotive Engineers (SAE) Specification 1424. Under this specification, Type I deicers are low viscosity fluids that are shed from the aircraft during takeoff. Type IV deicers are higher viscosity fluids that provide continued protection during extended freezing precipitation. Deicers currently used for aircraft deicing, including ethylene glycol and propylene glycol, pose significant threats to surface waters. Oxidized starch may provide a less toxic deicer with lower biochemical oxygen demand.
The objectives of this research were to 1) evaluate freezing point depression of different starch formulations, 2) determine the biological oxygen demand (BOD) and aquatic toxicity of the most effective formulation, and 3) to provide a preliminary evaluation of the compatibility of oxidized starch solutions with aircraft materials.
Starch solutions were oxidized using hydrogen peroxide and catalysts. The oxidized starch solutions were evaluated for freezing point depression and post-treated to reduce viscosity. The most effective formulation was then evaluated for oxidation products, corrosivity, aquatic toxicity, and biochemical oxygen demand.
Freezing point depression of oxidized starch formulations ranged from 19.7 to 28°C; viscosities similar to those of commercially available deicers were after post-treatment with granular activated carbon. Oxidized starch exerted a BOD up to six times lower than glycol deicers; toxicity was greater than pure propylene glycol but lower than propylene glycol deicer formulations. Corrosion testing indicated compatibility with aerospace materials in most cases. Organic acids were identified by gas chromatography/mass spectrometry as the primary constituents in the oxidized starch solution and their sodium salts are likely responsible for freezing point depression.
This deicing system would provide effective aircraft deicing while exerting minimal environmental effects (e.g., lower toxicity to aquatic organisms and lower biochemical oxygen demand). Furthermore, these deicers could be made from waste starch, promoting sustainability within DoD.