Safe operation of aircraft during freezing conditions necessitates the removal of ice deposits from critical surfaces prior to takeoff. Large quantities of deicing and anti-icing fluids are required to effectively remove ice from critical aircraft surfaces and to prevent its reformation. For the past 50 years, solutions containing ethylene glycol or propylene glycol freezing point depressants have been used for deicing and anti-icing aircraft. These glycol-based fluids have several undesirable characteristics that make them a threat to the environment when released untreated. A consistent, high-priority need for the U.S. Air Force and Department of Defense continues to be alternative deicing solutions for aircraft.
The objective of this project was to develop a high performance, environmentally benign, aircraft anti-icing fluid that could be safely released to the environment without capture, control, and post-treatment of the runoff.
The strategy to develop environmentally advantaged aircraft ice control materials via substitution involved identifying a wide range of candidate formulations and ranking them based on their predicted performance, environmental impact, and cost, using computer model-aided screening, multi-tiered testing, and expert advice from aircraft deicing fluid manufacturers. In the source reduction strategy, the project sought to develop high performance anti-icing fluids that require less material to protect the aircraft from icing. Critical to this approach was the development of a high performance, environmentally benign thixotrope. NonNewtonian thixotropic agents were identified, and a model that predicts non-Newtonian viscosity of a compound based on its chemical structure was developed. This model was used to identify candidate thixotropic agents and synthesize new thixotropes with enhanced performance compared to currently available materials.
The major accomplishments of this project include (1) formulation of environmentally advantaged anti-icing and deicing fluids with low human and aquatic toxicity, enhanced biodegradability, and biological oxygen demand that was 50 percent less than that of a propylene glycol-based fluid (i.e., 5 days), without sacrificing performance and materials compatibility requirements; (2) demonstration of computer-based water quality impact modeling to predict dissolved oxygen concentrations in receiving waters under two different model airport scenarios with various fluid formulations; (3) development of structure/property relationships for the nonNewtonian behavior of polysaccharide thickeners, and (4) identification of a nontoxic, biodegradable, thermally stable polysaccharide thickening agent with rheological properties similar to the commercially available Type IV anti-icing fluids. This project was completed in FY 2002.
The benefits of this project include (1) a drop-in, fully characterized, environmentally advantaged replacement for ethylene and propylene glycol-based aircraft deicing materials; (2) elimination of the cost of capture/treatment of effluent from aircraft deicing processes; (3) reduction of material cost for aircraft deicing processes (since high efficiency fluids require less material usage); and (4) increased flight safety and mission readiness. Additionally, models for predicting nonNewtonian viscosity based on the chemical structure of compounds and the impact of changes in ice control material formulation on runoff water quality at actual airfields were provided.