There are four main classes of detergents, anionic, cationic, nonionic,
amphoteric.
Anionic Detergents
Anionic means a negatively charged molecule. In the early days I always
remembered this by anionic (a
negative).
The detergency of the anionic detergent is vested in the anion. The anion is neutralised
with an alkaline or basic material, to produce full detergency.
Cationic Detergents
Cation means positively charged. The detergency is in the cation, which can be a
substantially sized molecule. Strong acids are used, such as Hydrochloric Acid to produce
the Cl anion as the “neutralising” agent, although in essence, no neutralisation
takes place in the manufacturing process.
nonionic Detergents
As the name implies, no ionic constituents are present. They are
“ionically” inert.
Amphoteric Detergents
These contain both acidic and basic groups in their molecule, and can act as
cationic or anionic detergents, depending on the pH of the solution, or as both cation and
anion.
Anionic Detergents
Dealing with the common anionic detergents, we can place these detergents into
the following main groupings:
Alkyl Aryl Sulphonates
Linear alkyl benzene sulphonate would be the highest quantity used of any
detergent in the world, and the alkyl aryl sulphonates as a group would represent more
than 40% of all detergent used.
They are cheap to manufacture, very efficient, and the petroleum industry is a
starting point for the base raw material. The most important alkyl aryl condensate is DDB
(dodecyl benzene). DDB is sulphonated to DDBSA (dodecyl benzene sulphonic acid), and this
in turn is used as a detergent base, where it is neutralised with a base, such as sodium
hydroxide, monoethanolamine, triethanolamine, potassium hydroxide, etc.
Long Chain (Fatty) Alcohol Sulphates
Made from fatty alcohol’s, and sulphated, these are used extensively in
laundry detergents. They can be produced with varying carbon chain lengths, but a C12 -
C18 alcohol sulphate is a good choice.
Other groups
Are the olefine sulphates and sulphonates, alpha olefine sulphates and
sulphonates, sulphated monoglycerides, sulphated ethers, sulphosuccinates, alkane
sulphonates, phosphate esters, alkyl isethionates, sucrose esters.
The anionic detergents are used extensively in most detergent systems, such as
dishwash liquids, laundry liquid detergents, laundry powdered detergents, car wash
detergents, shampoo’s etc.
Cationic Detergents
These have poor detergency, and are used more for germicides, fabric softeners,
and specialist emulsifiers.
You cannot mix cationic and anionic detergents together, as it causes
precipitation. However, Witco Chemical Corporation does produce a product - Emcol
CC-36 - which can be mixed with an anionic, and these are powerful
anti-static products.
The cationic detergents invariably contain amino compounds. The most widely used
would be the quaternary ammonium salts, such as cetyl trimethylammonium chloride, a well
known germicide.
nonionic Detergents
The vast majority of all nonionic detergents are condensation products or
ethylene oxide with a hydrophobe. This group of detergents is enormous, and the
permutations endless. They would be the single biggest group of all detergents, and I do
not propose going into the endless chemistry of these products.
Amphoterics
These have the characteristics of both anionic detergents and cationic fabric
softeners. They tend to work best at neutral pH, and are found in shampoo’s, skin
cleaners and carpet shampoo. They are very stable in strong acidic conditions and have
found favour for use with hydrofluoric acid.
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