Increasingly stringent environmental regulations on volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) demand the development of disruptive technologies for cleaning weapons systems and platforms. Currently employed techniques such as vapor degreasing, solvent, aqueous, or blast cleaning processes suffer from shortcomings in environmental friendliness, personnel health and safety, cleaning efficiency, cost-effectiveness, management of contaminated cleaning media, or in maintaining the integrity of equipment material surfaces.

The overall objective of this project was to develop an environmentally benign technology for cleaning metal and non-metal surfaces. The ability of two super absorbent polymer gel systems for removing oil, grease and particulates from metal and plastic surfaces was evaluated in this proof of principle effort. Further research would be needed to improve gel performance, address the post-cleaning gel removal method, address the use of non-fluorinated compounds in gel synthesis, and evaluate the toxicity and environmental fate-and-effects of the gels.

This research identified two potential gels, a lipophilic polyelectrolyte (EG-18) gel and a neutral (NG-18) polymer gel for surface cleaning applications. These gels were evaluated during this proof of principle study following the ASTM G122-96(2008) and MIL-PRF-680B protocols. Representative contaminants of oil, grease and particulate materials were selected.

In this study, the synthesis and characterization of poly(SA-co-EGDMA) (NG-18) gels were demonstrated. The swelling characteristics of the gels were studied as a function of the solvent polarity and temperature, and the kinetics of swelling were also examined. Volume transition via crystallization of the long alkyl chain was investigated by transmittance at 700 nm light with controlling temperature. Moreover, the reversibility and reproducibility of the transition were studied by both swelling and transmittance with cyclic temperature change. These properties suggested the utility of NG-18 gels as recyclable VOCs absorbent materials.

The gel system uses tetrahydrofuran (THF) for swelling, however, cyclohexane or other benign solvents with similar swelling properties may also be used as a swelling agent. In particular cyclohexane is a good possibility with swelling ratio (Q) of 20. Other solvents such as toluene or other non-polar solvents may also be used.

The results of this project will facilitate the development of environmentally compliant, economically feasible cleaners for a wide range of Department of Defense applications, providing a  promising alternative to traditional vapor degreasing, solvent, aqueous, or blast cleaning processes.

Based on the preliminary cost assessment the gel cleaning process appears to be costing a similar amount. The gel cleaning process has the advantage of avoiding emissions of HAPs and VOCs. Further research to improve the neutral gel systems with increased swelling properties and recyclability are recommended. Optimization of the gel synthesis, cleaning process and kinetics at room temperature is recommended.