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Alkalis and alkaline salts
Sodium hydroxide (caustic soda) is a common ingredient in detergents for the food industry. It is a powerful detergent and is used to suspend protein and to convert fats to soap, and it is cheap. However it corrodes aluminium and galvanized iron, strips paints, and presents a hazard to personnel using it. It is available in most geographical areas.
Sodium carbonate (soda ash) is not as efficient a cleaning agent as sodium hydroxide, but it is a cheap source of alkalinity and is used as a detergent filler. It is corrosive to aluminium and galvanized iron, and forms a scale of calcium carbonate and other insoluble salts in hard water. It is available in all geographical areas.
Sodium metasilicate is an effective detergent for many purposes. It is an excellent emulsifying and suspending agent and has reasonable wetting and rinsing properties. It possesses anticorrosive properties but will deposit on stainless steel. It may also deposit with soil as a grey-white coating if used in water above 70°C.
Surface active agent
This kind of agent is employed in a variety of cleaning applications such as wetting, emulsifying and penetrating agents. The main function is to lower the surface tension.
Anionic surface active agents dissociate in solution to give a negatively charged surface active ion and a small inactive action. Most commercial surface active detergents belong to this group. Several agents of this type are available but the alkyl aryl sulphonates are the most common surface active agents.
Nonionic surface active agents do not yield ions in aqueous solutions and are compatible with either cationic or anionic materials. Mixtures of anionic and nonionic surface active agents in a ration of 2:1 in detergent formulations appear to be suitable for the food industry. It is not common to use nonionic surface active agents alone because they are more expensive than anionic surface active agents.
Cationic surface active agents dissociate in a solution to yield a positively charged surface active ion and a small inactive anion.
Their performance as detergents is only fair but they exhibit anti-microbial activity and can be used as disinfectants or in mixed detergent-disinfecting agent mixtures.
Sequestering agents
Sequestering agents are used to bind calcium and magnesium and prevent the formation of insoluble calcium and magnesium salts by the interaction of hard water or dirt with the detergent. The amount of sequestering agents needed depends on the hardness of the water, the composition of the detergent and the composition of the soil.
Different chemicals have the ability to be effective as sequestering agents. Common in use are EDTA (ethylenediamintetraacetate), NTA (nitrilotriacetic acid) and different phosphates.
Sodium tripolyphosphate, sodium tetraphosphate and sodium hexametaphosphate are phosphates mainly used in detergent formulations. In addition to removing the minerals causing water hardness, they have varying functions in emulsification, protein peptization and dispersion.
Inhibitors
Inhibitors neutralize the corrosive effect of some chemicals. The use of inhibitors is dependent on the composition of the detergent and the materials which will be cleaned.
Silicates may be used as anti-corrosive agents in alkaline detergents but will deposit on stainless steel and it is therefore important to know on which materials they will be used.
Acids
Acids are used to remove mineral deposits but they have reduced cleaning effects and are corrosive to different materials (especially galvanized iron and aluminium). The inorganic acids are principally more corrosive than the organic acids.
Acidic detergents are mixtures of one or more acids and surface active agents, and may be inhibitors too. These detergents have a reasonable cleaning effect. If the mineral deposits are removed by acids alone, the cleaning effect will be minimal and it may be necessary to remove fat and protein with an alkaline detergent before removing the deposits with acid.
The inorganic acids used are phosphoric acid, nitric acid, sulphuric acid and hydrochloric acid.
The organic acids used are gluconic acid, tartaric acid, citric acid, acetic acid and sulphamic acid.
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