It is estimated that 8.5 billion pounds of synthetic polymer adhesives, of which approximately 55 percent are volatile organic compounds (VOC), are used annually by government contractors, Department of Defense (DoD) services, NASA, and the Department of Energy Nuclear Weapons Complex. These adhesives are used to assemble and seal hardware and systems during original manufacture, maintenance, and refurbishment. While the total DoD usage is not known, it is estimated that approximately 173,000 pounds of VOCs are released annually from Air Force aircraft operations alone. VOCs commonly used in applying adhesives include aromatics, ketones, and other compounds which negatively impact worker health and safety, adversely affect environmental standards, are ozone depleting, and result in increased hazardous material management costs.
This project is designed to provide the DoD with an adhesive application spray process that will minimize VOC emissions and reduce the costs associated with the use of organic solvents.
The goals of this project are to adapt six non-structural adhesives to both a continuous and a portable supercritcal fluid spray (UNICARB) process. The following approach will be taken to achieve the goals and deliverables for this project. First, the polymeric material and solvent constituents of the six adhesives will be evaluated for their compatibility to the process. This will be achieved by comparing the chemical similarities of the adhesive to that of the polymeric based paints that have been successfully adapted to the UNICARB process. Next, the identity and proportion of the various high- and low-volatile solvent constituents comprising the present adhesive mixture will be determined. From this, the mixture will be reformulated substituting supercritical carbon dioxide for the high-volatile solvent. The ratio of polymer to low-volatile solvent will be set in a range of three to five. Once the phase behavior is determined, the configuration of the batch will be determined and a continuous process will be established and tested.
Key features of the phase diagrams for acrylics without cross linkers, neoprene, formulated neoprene, styrene-butadiene-styrene, and styrene-isoprene-styrene have been mapped. In addition, the first prototype for a portable spray device has been designed and tested. The phase diagrams for the two systems have been determined under both static and dynamic conditions. Interestingly, the dynamic phase transitions occur at higher pressures than the static for all systems. Since this observation contradicts commonly held beliefs regarding these systems, further analysis will be undertaken.
The advantages of adopting this process include, but are not limited to the following: a reduction in VOC emissions; a reduction in solvent costs; the use of existing and proven adhesives and primers; more evenly distributed coatings; a reduction in labor costs; a reduction in worker health and safety costs; and a reduction in the costs associated with hazardous material management resulting from the need for permits and emission control equipment.