A detergent may be regarded as a chemical formulation, which essential consists of surface active agents and subsidiary constituents, such as fillers, builders, boosters etc. The detergent may be in the form of solid, liquid, paste or powder. The most important advantages of the synthetic detergents is better wetting and cleaning action and no consumption by hard water because of higher solubility of their Ca2+ and Mg2+ ions.
Detergent
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Many different detergents |
Surfactants are nothing but the surface active agents. These are the most important ingredient of synthetic products. When dissolved in water or dispersed in a liquid it cleans the surface by removing oil, in which dust particles are dispersed. The cleaning action of a surfactant depends upon its surface activity. It is a property which decrease the surface tension at the boundary surface between two phases.
Thus, those substances that lower the surface tension of water are called surfactants. Surfactants are the organic compounds in which two dissimilar groups water soluble and water insoluble are present within the molecule. e.g. sodium lauryl sulphate, sodium stearyl sulphate, sodium aryl sulphonates, linear alk benzene sulphonate, amide sulphonates etc.
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| Detergent |
Meaning of the terms related to detergents:
1) Emulsion and Emulsifying agents:
Emulsion refers to any dispersion of one liquid in another. When two immiscible liquids are shaked together, the oily liquid is dispersed in fine droplets, but the emulsion is nit stable. The liquids separate into two layers because of the coalescence of the fine droplets into bigger ones and then ultimately form a separate layer.
Emulsifying agents are the agents that lower the interfacial surface tension so that the emulsion is easily formed and also stabilise the emulsion by protecting the dispersed fine droplets of oil by forming a layer around them. The layer is formed by solubilizing the non polar part of the emulsifying agent in oil drop, while the polar group remains in water. Foaming is enhanced due to the lowering of water/ air Interfacial surface tension due to adsorption of emulsifying agent at the interface.
2) Wetting and Non-wetting:
Wetting means the spreading of liquid on a surface with ease and this is attributed a very small contact angle between the liquid and the solid surface, so that the liquid spreads over the solid surface easily. The wetting action is generally, accomplished by the use of surfactant additives which lowers the interfacial surface tension.
In case of Non-wetting the contact angle between the liquid and the solid surface is greater than 90°C and hence the liquid tends to ball up and run off the solid surface.
Wetting agents consists of polar- non polar type molecules. The polar porsion of the molecule may be one of the functional groups of organic chemistry containing oxygen, sulphur or even phosphorus, nitrogen or halogens, the groups may or may not be ionic. The non-polar portion is usually hydrocarbon chain.
3) Hydrophobic and hydrophilic nature:
Hydrophobic means water hating or water disliking or water repelling substances, which are insoluble in water and hence repel water. In hydrophobic sols, there is no affinity between the particles and water. These sols are less stable as compared to the hydrophilic sols.
Hydrophilic means 'water-loving' or 'water-liking' substances. In hydrophilic colloids, there is an interaction between the colloidal particles and water. Water combines with particles. The hydrophilic sols are more stable than the hydrophobic sols.
Functional groups which have tendency to bind water are hydrophilic in nature.
4) Amphipathic structures-
If a molecule contains two dissimilar structural groups e.g. water soluble and water insoluble, such a molecule is known to have amphipathic structure.
Ch3-CH2-(CH2)n-CH2-COONa
Here, COONa called as Hydrophilic (water soluble) and other group is Hydrophobic (water insoluble).
5) Micelles:
Micelles are the aggregates of many small molecules or groups of atoms which are held together by secondary valentines. i.e. by cohesive or vander Waal's forces or micelles are spherical with dimensions of the order of 2.5 to 5 nm, depending on the emulsifier used. Many organic colloids, emulsion soaps and detergents generally form such micelles or micelles colloids. Soap in water is colloidal, the particles are composed of a number of small molecules of sodium or potassium salts of fatty acids.
However, the same soap is dissolved in alcohol as single molecules. The micelles are usually less soluble than macro molecules. The soap micelles are split even by dilution or heating of the soap sol.
Cleaning action of detergent:
The cleaning action of detergent consists of -
a) Thoroughly wetting the dirt and the surface of the article being washed.
b) Removing the dirt from the surface.
c) Maintaining the dirt in a stable solution or suspension.
Detergent builders:
Detergent builders are the substances that increase the cleaning or washing activity of surfactants and thus make the synthetic detergent more effective. e.g. Inorganic salts such as sodium sulphate, sodium carbonate, sodium silicate and phosphates are more effective detergent builders. Since the surfactants are very expensive as compared to detergent builders, the addition of these inorganic builders into synthetic detergent lowers the cost of the resulting product without affecting its wetting and detergent activity.
On the other hand, these properties are improved by the addition of the builders. Further, the use of these additives make it possible to obtain a free flowing powder from liquid or low melting surfactants.
Additives:
Additives are the substances added to detergents for several purposes:
1) Bleaching agents:
a) Sodium hydrosulphite or sodium hypichloride are added in some synthetic detergents for removing colouring matters.
b) Sodium carboxy methyl cellulose is extensively used in small quantities with the detergents as an anti-redeposition agent because it has the ability to suspend and prevent redeposition of the soil on the washed germents.
c) Sodium perborate is added to bring about slow bleaching because the compound releases oxygen.
2) Optical brighteners:
Optical brighteners are the derivatives of coumarin or stilbene. These are colourless fluorescent dyes which are absorbed by textile fibres from solution and are not removed on rinsing. Their function is to convert ultraviolet radiation into visible blue light, thus masking the grayness on the washed garments. The amount of optical brighteners added to the detergents varies from 0.001 to 0.1% only. The visible improvement resulting from the brighteners is so striking that all medium to heavy-duty detergent products contain them.
3) Hydrotropes:
These are added to liquid detergents. Their function is to 'drove the detergents and builders into solution, to affect the solubilizing action. The most commonly used hydrotropes are the sodium or potassium salts of benzene, toluene, cumene and xylene-sulphonates. When present at relatively high concentrations, these highly soluble solutes increase the solubility of sulphonate and sulphate surfactant in concentrated aqueous compositions.
sometimes, solvents are also incorporated in detergents to get homogenous concentrations and also function as additives. e.g. ethanol is used to clarity liquid shampoos, deodourised kerosene and pine oil is used in industrial and household detergents.
4) Enzymes:
Certain enzymes are added to the detergents to reduce strains. Enzymes added are generally proteolytic and amylolytic in nature. These are used in about 1000-1300 units, casein units per litre and alpha-amylase units per litre in wash.
5) Soil Redeposition Preveting Agents:
Sodium carboxy methyl cellulose us extensively employed in synthetic detergents to prevent soil redeposition and is most effective with cotton. However, it is not that much effective with synthetic fibres, peculiar hydrophobic properties.
For synthetic fibres, polymers such as polyvinyl pyrrolidone and polyvinyl alcohol are used for preventing soil redeposition.
