Industry demands high-purity cleaning agents and high-purity solvents.
All process fluids must have attributes appropriate to the process. A coolant, lubricant, polishing compound, carrier, buffer, fermentation fluid, or coating that compromises the product integrity, the product surface, or which leaves undesirable residue must obviously be excluded. Inevitably, surfaces are involved whether the product itself has surfaces or whether vessels or equipment are involved.
Process fluids must be removed with a precision cleaning process. Since cleaning is the removal of undesired material, it is important that the cleaning agents are sufficiently pure so that they are not contributing to contamination that would compromise product performance or, in the case of medical devices or pharmaceuticals, compromise the recipient or host. This holds true whether the cleaning agent is water, a discrete organic solvent, a solvent blend, or an aqueous cleaning agent containing organic and inorganic components.
HOW PURE IS PURE ENOUGH?
The required purity of a process fluid depends on when it is being employedand how clean the final product needs to be.
Typically, the degree of purity required increases as the product moves through the manufacturing flow. Early stages of construction usually do not require as high a level of cleanliness as do the final steps. For cleaning agents that are very costly, filtered and/or redistilled solvents are sometimes used for initial assembly and processing steps. Within a given cleaning process, reverse cascade rinsing is often employed. In reverse cascade, the deionized water used for the last process step, the final rinse, is reused as an initial rinse and the initial rinse water is reused in the wash step.
As the final assembler, you require cleaning agents of a particular level of purity and with specific certifications. We have encountered too many suppliers and even a few final fabricators who use commercial or consumer-oriented cleaning agents and assume that they are suited for cleaning their industrial components. Compositions may change without notice and the MSDS does nottell the whole story. The products are frequently complex blends, with many components present at less than the 1% threshold for listing in the MSDS. Some are formulated to suspend removed soils in an emulsion, leading to high soil loading of the cleaning agent and the potential for redeposition of residue. With some exceptions, the consumer-oriented cleaning products are not supported forindustrial use.
Residue from early stages of manufacturing or from processing adjuncts is of concern because soils that are dried-on become adherent and difficult to remove. If you are manufacturing a high-value, critical product, it is important to be aware of all contamination sources, including contamination from process fluids, organic solvents, and blended cleaning agents. For example, if the product contains components fabricated by an out-sourced machine shop, it is in your best interest to know how or if that product is cleaned before it is shipped to you. The shop may not remove the soils, or cleaning may be accomplished with less than optimal cleaning agents, making final fabrication more difficult. It is also important to elucidate details about the fabrication, cleaning processes, and contamination control for vessels, transfer equipment, and packaging.
SOURCES OF PROCESS FLUID CONTAMINATION
In addition to contamination from uncharacterized chemicals, the handling and storage of all process fluids is a potential contamination source. Certifications and receiving inspection cannot guarantee that a product will remain pure during storage, transfer, and use. Plasticizers from lids, closures, and transfer lines can contaminate cleaning agents and destroy critical product. Particles may be introduced from storage drums. Care must be given in the selection and maintenance of storage containers, both for long-term reserve storage (e.g., drums) and short-term, in-use storage (e.g., benchtop squeeze bottles and dispensers). As a general rule, it is recommended that containers be dedicated to one material. If a squeeze bottle is to be re-filled, it should be flushed with a small amount of solvent or cleaning agent before being re-filled. Plastic containers can age and release plasticizers into the solvent, so containers should be replaced on an established schedule. Also, determine that the material being stored is compatible with the bench-top dispenser or storage vessel and does not become contaminated by plasticizersor other material being leached from the container. For critical applications, establish a testing schedule for the stored chemical to assure that it stillmeets incoming specifications.
ARE CERTIFICATIONS ENOUGH?
For critical applications, even certifications from the supplier are not sufficient. Receiving inspection and point-of-use observations may reveal material changesthat occur after shipment from the vendor. We have encountered several situations in which a supposedly water-clear fluid, with appropriate certifications, had a distinctive color. This unexpected, undesirable coloration was detectedand reported by observant, concerned, and educated employees.
First, the requirements for your application must be determined. Second, the correct grade of chemical must be specified. Third, it must be determined if that grade of chemical is available, or if the manufacturer can make the needed process modifications to supply the chemical. If not, or the chemical can be provided only at prohibitively high cost, in-house purification may be the only practical approach. For example, point-of-use filtration or redistillation might be needed where the manufactured chemical meets general industry specifications but is not pure enough for the specific application. Additionally, filtration or re-distillation may be a suitable method to prolong the useful lifetime of a process fluid. In any in-house purification, it is important to assure that the reprocessed fluid indeed meets your requirements.
Next, we shall discuss actual, desirable, and achievable requirements for contamination levels in cleaning agents and solvents, assessing newer solvents and blends.
Barbara Kanegsberg and Ed Kanegsberg are independent consultants in critical and precision cleaning, surface preparation, and contamination control. They are the editors of The Handbook for Critical Cleaning, CRC Press. Contact them at BFK Solutions LLC., 310-459-3614; firstname.lastname@example.org; www.bfksolutions.com.