These may range from pure water to mixtures of water, detergents, and other additives that promote the removal of organic and inorganic contaminants from hard surfaces. They may be acidic, alkaline, or neutral. They usually contain several ingredients, whereby each component performs a distinct function and affects the way the contaminant is removed from a substrate. Aqueous cleaners are available in the form of concentrated liquids and as powders. Some benefits of aqueous cleaners are low costs and improved environmental and health safety.
Aqueous cleaners have been used for a long time by metal industry and are capable of removing most contaminants, such as inorganic contaminants, particulates, films, light oils and residues (including solvents or other types of cleaners) left by manufacturing processes, shop dirt, and light scale. Whereas solvents depend largely on their ability to dissolve organic contaminants on a molecular level, aqueous cleaners utilize a combination of physical and chemical properties to remove contaminants from a substrate. Aqueous cleaning is also more effective at higher temperatures. For these reasons, good engineering practices and process controls tend to be more important in aqueous cleaning than in traditional solvent cleaning to achieve optimum and consistent results. But for the same reasons aqueous cleaners also exhibit considerable flexibility in application because their performance is strongly affected by formulation, dilution, and temperature.
Acid and alkaline cleaners may attack metal parts. In many cases, additives are placed in aqueous cleaners to minimize these adverse effects. Other disadvantages could be increased wastewater discharges, and longer drying times.
Ingredients may include:
The primary physically active ingredients are usually organic molecules, where a portion of the molecular structure is hydrophilic (water- loving) and a portion is hydrophobic (water-repelling). Such molecules function in detergents as a bridge between soil and water by promoting the physical cleaning actions through emulsification, penetration, spreading, foaming, and wetting. It is a common practice to blend surfactants to optimize their properties. Ionic surfactants are of two kinds, anionic surfactants, which are negatively charged in water solution and cationic surfactants, which are positively charged. If the charge of the water soluble portion depends upon the pH of the solution, it is termed an amphoteric surfactant. These surfactants behave as cationic surfactants under acid conditions, and as anionic surfactants under alkaline conditions. Ionic surfactants are generally characterized by their high foaming ability. Nonionic surfactants, which do not dissociate when dissolved in water, have the broadest range of properties depending upon the ratio of hydrophilic/ hydrophobic balance. This balance is also affected by temperature. For example, the foaming properties of nonionic detergents is affected by temperature of solution. As temperature increases, the hydrophobic character and solubility decreases. At the cloud point (minimum solubility), these surfactants generally act as defoamers, while below the cloud point they are varied in their foaming properties. However, because of precipitation problems, cationic and anionic surfactants can not be blended.
Water conditioners are used to prevent the build-up of various mineral deposits (water hardness, etc.). These chemicals are usually sequestering agents or chelating agents. Sequestering agents form soluble complexes with calcium and magnesium. Examples are sodium tripolyphosphate, tetra-potassium pyrophosphate, organo-phosphates, and polyelectrolytes. Chelating agents include sodium gluconate and ethylene diamine tetracetic acid (EDTA).
Oxidizing agents used in detergent application are hypochlorite (also a sanitizer) and perborate. Chlorinated detergents are most often used to clean protein residues.
Enzymes are of biological origin and are proteins with a specific chemical function. The important quality of enzymes as cleaning agents, is their ability to specifically attack and degrade organic soil by catalyzing its conversion to smaller solvable entities. Detergents containing enzymes such as amylases and other carbohydrate-degrading enzymes, proteases, and lipases, are finding acceptance in specialized food industry applications. The primary advantages of enzyme detergents are that they are more environmentally friendly and often require less energy input (less hot water in cleaning).
Highly alkaline detergents (or heavy-duty detergents) use caustic soda (sodium hydroxide) or caustic potash (potassium hydroxide). An important property of these highly alkaline detergents is that they saponify fats: forming soap. These cleaners are used in many CIP systems or bottle-washing applications. Moderately alkaline detergents include sodium, potassium, or ammonium salts of phosphates, silicates, or carbonates. Tri-sodium phosphate (TSP) is one of the oldest and most effective. Silicates are most often used as a corrosion inhibitor. Because of interaction with calcium and magnesium and film formation, carbonate-based detergents are of only limited use in food processing cleaning regimes.
Acid detergents include organic and inorganic acids. The most common inorganic acids used include: phosphoric, nitric, sulfamic, sodium acid sulfate, and hydrochloric. Organic acids, such as hydroxyacetic, citric, and gluconic, are also in use.
Fillers add bulk or mass, or dilute dangerous detergent formulations which are difficult to handle. Strong alkalis are often diluted with fillers for ease and safety of handling. Water is used in liquid formulations as a filler. Sodium chloride or sodium sulfate are often fillers in powdered detergent formulations.