- Synthetic detergents can be made from petrochemicals, fats and oils.
- Synthetic detergent molecules, like soap molecules, generally consist of a hydrophilic head and a hydrophobic tail.
- The hydrophobic, long hydrocarbon chain tail of the detergent molecule is attracted to particles of oil or grease by dispersion forces (Van der Waals or London or Weak Intermolecular Forces).
- The hydrophilic, charged or polar head of the detergent molecule is attracted to water molecules.
- Synthetic detergents are less sensitive to the effects of calcium and magnesium ions in hard water.
- A number of additives are used to enhance the cleaning ability of detergents.
- Branched-chain synthetic detergents are far less biodegradable than continuous-chain synthetic detergents.
Classification of Synthetic Detergents
Detergents are classified as either:
- Anionic: negatively charged head
- Cationic: positively charged head
- Non-ionic or neutral: uncharged head
sodium dodecyl sulfate
|Usually contain either
a sulfate (SO4) head
|widely used due to cost and performance
a sulfonate (SO3) head
|Usually contain a modified ammonium ion as active site which produces a germicidal action.
More expensive than anionic detergents.
-fabric softeners and conditioners
|Contains polar parts, eg, OH groups, to provide water solubility.
No ionic groups so no reaction in hard water.
Low lathering prevents foam build up in dishwashers.
|surfactants, wetting agents
||Small hydrocarbon chain length is a better wetting agent than a long one, but long hydrocarbon chain length is better for dirt removal and dispersion.
A chain length of about C12 is the best compromise for most anionic detergents.
||Forms a protective hydrated adsorbed layer on cleaned fabric preventing redeposition of dirt.
|builders (pyrophosphates, tripolyphosphates, silicates eg, zeolites)
||Form soluble complexes with Ca2+ and Mg2+ in hard water and act as deflocculating agents preventing scum buildup.
||To promote and stabilize foam formation.
|oxidisers, eg, perborates
||To promote the effectiveness of some ingredients.
||To digest proteins, carbohydrates and fats.
|Add brightness to fabrics by absorbing UV light and emitting blue light which masks any yellow tint which may develop in white fabrics.
||Enhance the odour of detergents.
The first detergents in use were highly branched alkylbenzenesulfonates,
Microorganisms in septic tanks and sewage-treatment plants cannot degrade branched chains.
To prevent buildup of detergents in rivers and lakes, modern-day detergents are designed to be biodegradable.
Alkylbenzenesulfonates with a continuous chain, rather than a branched chain are biodegradable.
Continuous chain alkysulfates, eg, CH3(CH2)16CH2OSO3-Na+, are also biodegradable.