Mechanisms of Cleaning Organic Films from Solid Substrates using Aqueous and Organic Solvents

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ABSTRACT CTS-9616638 C. Grant/ P. Carbonell NC State The main objective of this work is to obtain fundamental insight into cleaning mechanisms in order to develop environmentally benign cleaning alternatives. Experiments will yield kinetic information about the removal of organic films from rotating disks using aqueous nonionic surfactant solutions in conjunction with organic solvents. Such kinetic information gives insight into the mechanism of cleaning processes. Because of the inherent immiscibility of the aqueous and organic phases, it is possible to partition the contaminant into the organic phase. This enable the aqueous phase to be recycled, reducing the total volume of cleaning waste generated. Both phases can bne analyzed to gain further insight to the stability of the resulting emulsion and the surfactant interactions with the organic sovent. Prior to work by our group has allowed better understanding of the mechanism for abietic acid film removal from rotating disks using micellar and submicellar aqueous nonionic surfactant solutions. From prior work, it was discovered that cleaning occurs by a three stage process. The first state is controlled y the solubilization of the organic phase through surfactant penetration and subsequent mass transfer from the interface to the bulk aqueous solution. During the first stage, the film absorbs water from the aqueous solution reducing its viscosity, until drops start to move on the disk surface under the action of shear forces. These drops aggregate into spiral-shaped continuous rivulets through which the organic phase flows until it comes off the disk edge. Such behavior occurs during the second stage of cleaning, which has a rate of removal appreciably faster than the first stage. The rivulets eventually break, leading to a third stage with lower removal rates, in which the removal mechanism is apparently the roll up of organic phase drops under the action of shear forces. Photographs showing the morphology of the film structure in the different cleaning stages provide experimental evidence that supports the described mechanism. A model was derived that relates the empirical observations of cleaning rates to physical parameters describing solubilizing film hydrodynamics. The proposed research will investigate the combined rates of hydrodynamics, dissolution, and partitioning in the removal of two contaminants: abietic acid and polybutene form different solid substrates(i.e., exopy-glass laminate, copper, nickel). This work will also study the phase separation behavior of the contaminated effluent in an effort to recycle the cleaning solution. Our research will be unique because an organic solvent will be used in conjunction with an aqueous nonionic surfactant solution allowing for reuse of the aqueous cleaning solution. The proposed research will be carried out in collaboration with CORPEX Technologies, Inc. in Research Triangle Park, NC through the NSF GOALI program. CORPEX Technologies manufactures cleaning solutions that are combinations of surfactants and organic solvents. Preliminary experiments conducted at CORPEX Technologies have determined that the addition of an organic solvent to an aqueous solution will increase the rate of cleaning when used with surfactants. In addition, once cleaning is complete the organic solvent can be phase separated from the aqueous solution. The organic contaiminant (i.e.,grease or oil) partitions into the organic phase, leaving a very clean aqueous solution. This minimizes waste water generation and produces only a small amount of organic waste. In prior work exclusively with aqueous based cleaners, the amount of contaminant removed from the rotating disk was continuously measured as a function of time in the bulk cleaning solution using a UV absorbance detector. With the addition of an organic solvent, however, the cleaning solution becomes turbid. As a result, optical techniques such as UV absorbance can not be used. To circumvent t his problem, radioactive tracers will be mixed with the organic contaminant. This contaminant will be spin coated onto the disk to form a uniform film. During cleaning experiments, an on-line liquid scintillation analyzer will be employed to continuously detect the amount of contaminant removed from the disk. The heterogeneous scintillation analyzer created scintillation by passing the sample over solid beads as opposed to mixing with a liquid cocktail. The fundamental cleaning information obtained by this project will assist CORPEX Technologies in its continuing development of environmentally friendly cleaning solutions. The majority of the experimental work will be done at NCSU. However, the close proximity to CORPEX will enhance the technical interaction and enable a rapid transfer of technology from NCSU to CORPEX.