Water-based Cleaning Chemistry
Aqueous (Water-based) Cleaning Chemistry
Detergents are mixtures containing surfactants, alkaline or other materials, and sometimes solvents. The process of lifting soil from a surface by displacing it with surface active materials that have a greater affinity for the surface than they do for the soil is defined as detergency. With the exception of big-active or enzyme (i.e., protein)-based chemistries, SSL deals with liquid detergents to avoid 'spotting' a substrate or surface with powdered cleaners that may be unevenly dissolved in water. Detergents remove soils by dissolution (water soluble soils), wetting, emulsification, deflocculation, dispersion and/or saponification.
Wetting: The action (by surfactants) of lowering surface and interracial tensions so that a cleaner can penetrate small spaces and get under the soil to help lift it from the substrate.
Emulsification: After wetting, the process of coating oil droplets (soils that do not dissolve in water) with surfactant to keep them from recombining and migrating to the surface of the cleaning bath. This action may make the ultimate phase separation of soil and cleaner difficult under some aqueous cleaning conditions.
Deflocculation: The breaking down of soil into fine particles, with the result that they are dispersed throughout the cleaning media. The soil/liquid matrix is maintained as a dispersion or colloidal suspension, preventing agglomeration.
Saponification: The alkaline hydrolysis of fat, that is, the reaction of insoluble fatty acids contained in some oils and greases with alkalies to form water-soluble soaps. This cleaning method is used for solvent-free defluxing and degreasing.
Water: Tan (i.e.. municipal) or treated with softeners, by deionizing, etc.
Surfactants: Molecules designed to be preferentially absorbed at water-hydrocarbon interfaces. Composed of both hydrophilic (water soluble) and lipophilic (oil soluble) groups, they may be cationic, anionic or nonionic depending on the charge of the hydrophilic end. Cationic surfactants are considered poor cleaners because of their negative charge. Anionic or positively charged surfactants are water-soluble and commonly used in immersion cleaning. Nonionic, that is, surfactants with no charge are also used for surface cleaning when a lower-foaming detergent is required. In addition to wetting, surfactants can enhance the emulsifying and dispersing properties of a cleaner.
Builders: Inorganic salts that provide alkalinity and buffering capacity common to almost all aqueous cleaners (pH may be alkaline, neutral or acidic). Alkalinity may be divided by hydroxides, carbonates, berates, silicates, phosphates or zeolites (crystalline hydrated aluminosilicates). Many builders also soften water or help with saponification or deflocculation.
Saponifiers: Alkalis that react with fatty acids in oils to form soaps. Chemistry may be mineral (sodium or potassium)- or organic (solutions of monoethanol amine)-based.
Solvents: Aqueous or organic chemistries designed to enhance the removal of oily soils by dissolving them, e.g., glycol ethers, ethylene (Butyl Cellosolve) and propylene compounds.
Additives overlap builders in function. They act primarily as contaminant dispersants, water softening agents, anti- foaming agents, detergent fillers and corrosion inhibitors. Examples include ethylene diamine tetraacetic acid (EDTA), amine compounds and various polymers.
Sequestering Agents are produced as powders or liquids to combine with calcium, magnesium and other heavy metals in hard water. They form molecules in which these ions are held securely, or sequestered, so that they can no longer react with other species in solution.
Chelating Agents are employed to solubilize hard water salts so that they remain in solution. Produced in both powdered and liquid forms, they do not degrade or loose their potency at elevated temperatures which make them ideal for aqueous cleaning. However, they can interfere with the ability of other chemicals to remove emulsified oils and dissolved metals from solution which can lead to waste disposal problems. In addition to EDTA, nitrilo tri acetate (NTA) is also used.
Inhibiting Agents are commonly added to aqueous cleaners to minimize their effect on metal substrates. They are used for cleaning non-ferrous products at high pH and as rust inhibitors to prevent the rusting or oxidation of cleaned parts (or cleaning equipment that is not constructed of stainless steel). Inhibitors may be inserted in the wash or rinse cycles of single- or multi-stage cleaning processes and are found in all types of immersion and spray operations.
Emulsifiers: Specialty chemicals used to disperse soils (e.g., oil and grease) that do not dissolve in water. Useful for low soil loading, but the concentration of emulsifiers in a detergent limits bath life. Separation of soil and cleaner may be accomplished by making the emulsion unstable by lowering pH and/or temperature.
The SSL accepts donations of sample cleaning products when accompanied by an MSDS and an agreement by the vendor to take back any unused quantities. A list of cleaner constituents is requested; this list is kept confidential. The SSL does not endorse any particular product; client reports describe the successful cleaners by manufacturer and in generic terms, and list other comparable products and sources where possible. To date, over 500 aqueous and semi-aqueous cleaners are in stock and we have evaluated nearly 600.