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 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:
Surfactants:
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
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
Oxidizing agents used in detergent application are hypochlorite (also a sanitizer)
and perborate. Chlorinated detergents are most often used to clean protein residues.
Enzymes
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).
Alkaline Builders
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 Builders
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
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.