Tetrasodium pyrophosphate, which does not sequester calcium as the higher phos- phates, is very stable above 60ºC in alkaline solutions.
Sodium tripolyphosphate and sodium tetraphosphate have calcium-sequestering power superior to that of tetrasodium pyrophosphate but tend to revert to orthophosphate and pyrophosphate when held above 60ºC or in the alkalinity of pH 10 or higher. Sodium hexametaphosphate (Cal- gon) is an effective calcium sequestrant with limited magnesium-sequestering power. Amorphous phosphates are complex glassy phosphates with excellent calcium-sequester- ing power.
Organic chelating agents, which are used in formulation in water conditioners, are more efficient than are phosphates in seques- tering calcium and magnesium ions and in minimizing scale buildup. Most organic agents are salts of ethylenediaminetetraacetic acid (EDTA). The chelating agents are sta- ble above 60ºC in solution for extended peri- ods of storage. These chelating properties for EDTA salts improve as pH increases. They may be used in conveyor lubricant formulations.
Surfactants
These surface-active agents function to facilitate the transport of cleaning and sani- tizing compounds over the surface to be cleaned. Surfactants are known to “make the water wetter”. Although the major functions of surfactants are wetting and penetrating, detergency characteristics, such as emulsifi- cation, deflocculation, and suspension of particles, contribute to their effectiveness.
Surfactants are classified as synthetic detergents because of their numerous prop- erties. As auxiliaries, they are also classified in the same three groups, according to their wetting properties and active components in solution. These auxiliaries are classified as cationic surfactants, which ionize in solution
to produce active positively charged ions and serve as excellent bactericidal agents and ineffective detergents; anionic surfactants, which ionize in solution to produce active negatively charged ions and are generally excellent detergents and ineffective bacteri- cides; and nonionic surfactants with no pos- itive and negative ions in solution or bactericidal properties but with excellent wetting and penetrating characteristics. In addition, the amphoteric surfactants have a positive or negative charge, depending on the pH of the solution.
The general structure for anionic surfac- tants is Q–X−M+, where Q is the hydropho- bic portion of the molecule, X− is the anionic or hydrophilic portion, and M+ is the coun- terion in solution. The hydrophobic portion of the molecule is normally a hydrocarbon chain of the form CnH2n+1, which is usually
designated as R. Q may represent an alkyl-
substituted aromatic molecule, amide, ether, fatty acid, oxyethylated alcohol, phenol, amine, or olefin. The two most familiar anionic surfactants are soaps and linear alkylbenzene sulfonates.
The hydrophobic group forms a part of the cation dissolved in water in the cationic surfactants, whereas the hydrophobic por- tion of an anionic surfactant forms a part of the anion in aqueous solution. A cationic compound is formed by reacting a tertiary amine with an alkyl halide to form a quater- nary ammonium salt R1 R2 R3 + R4X f R1
R2 R3 R4 N+ + X−. At least one of the R sub-
stituents is a hydrophobic group, such as
dimethylammonium chloride, a germicidal agent.
The hydrophilic portion of nonionic sur- factants often is composed of one or more condensed blocks of ethylene oxide. The hydrophobic portion can be any of several groups, including those named for the anionic types. The bond between the hydrophobe and the hydrophile may be an ether grouping or an amide or ester grouping. Other nonionic
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