Agriculture Reference
In-Depth Information
allowing the soil particles to be rinsed freely away without
re-deposition, involves coating the particles with electric
charges that mutually repel. Dispersion is particularly
important in circulating cleaning systems where sludge
can build up, unless dispersed, in slower-moving parts of
the system.
in the matrix of the deposit itself. Alternatively, they may
be a problem in hard water, which undergoes heating or
evaporation. Chelating agents, also known as chelants or
sequestrants, bind the metal ions in water-soluble cages,
removing scale or preventing it. In mixed scale/soil depos-
its, the chelates can have a very pronounced effect on the
break-up of the deposit. These typical chelating agents, for
example, ethylenediaminetetraacetic acid (EDTA) and
gluconate, are restricted in their economy by the fact that
they must be present in ratio to the metal ions needing to
be chelated. In very hard water, or in large volumes of
water, this may be prohibitively expensive. In recent years,
these conventional chelants have been supplemented by
what are known as substoichiometric chelants, usually
water-soluble charged polymers. These act in two ways:
(1) They inhibit the growth of scale microcrystals by
blocking the corners of the crystals where growth occurs,
forcing the crystals to become spherical. Any scale that
does form is thus made soft and powdery and non-adher-
ent to surfaces. (2) They act as dispersants, stringing
microcrystals like pearls on a necklace and preventing
them from sticking together and precipitating. Whatever
the mode of action, these polymeric chelating agents do
not need to be present in a fixed ratio to the metal ions,
but instead function at only several parts per million
(ppm), even in very hard water. Their main action takes
place at low alkalinity, for example, during the rinse stage.
They normally do not actively remove previously formed
hard scales.
Solubilisation
This process is simply the taking up of
soil components into a true solution, rather than an
emulsion or a dispersion. While some soil components
are naturally water-soluble under the right conditions,
others need the assistance of solvents in the detergent
solution. These solvents must be taint-free and of low
toxicity and are usually based on alcohols, glycols or gly-
col ethers. They assist most where greasy soils are too
hard to emulsify easily. Here, the solvents penetrate the
grease and soften or liquefy it.
Chemical reactions
The most important chemical reactions include the
following:
Hydrolysis of proteins and carbohydrates
These
large molecules are made up of smaller subunits, for
example, peptides and amino acids in the case of pro-
teins. Hydrolysis involves splitting the molecules at the
joints of the subunits, thereby releasing smaller water-
soluble molecules. Hydrolysis takes place most rapidly at
extreme pH and is the main reason why alkalis and acids
are used in detergents. While alkaline hydrolysis is usu-
ally more effective, bile proteins in evisceration areas
respond very well to acid hydrolysis. In some cases, the
acid and alkaline hydrolyses may snip the larger mole-
cule in different locations, neither of which alone is
enough to produce small enough molecules. In such cir-
cumstances, for example, old blood stains, alternation of
alkaline and acid detergents may help dramatically.
Oxidation
Oxidation of coloured materials, starches,
etc. Some soil components respond well to chlorine, in
the form of alkaline sodium hypochlorite. Coloured
deposits may be bleached and some protein or fat depos-
its may be readily broken down. The main function of
chlorine in an alkaline detergent solution is as an oxidis-
ing agent. For example, in an alkaline chlorine foam
detergent, the alkalinity and the soluble chlorine mole-
cules like the hypochlorite ion are
both
required to
remove complex soiling made up of protein and fat.
Periodic use of nitric acid-based detergents is common
in some CIP applications. The treatment is primarily to
achieve removal of inorganic scales, but it also has an
oxidising effect on residual protein molecules not
removed by the routine cleaning cycle.
Saponification of fats, oils and greases
This is a
particular form of hydrolysis in which an alkali reacts
with triglyceride fat molecules, cutting the molecule in
three places to give glycerol and soap, both water-soluble.
In practice, the formation of the soap can be either help-
ful, because it acts as a wetting and emulsification agent
in its own right, or harmful, because it produces unwanted
foam in machine or circulation cleaning. In hard water,
the foam is less of a problem, but formation of scum, that
is, calcium soaps, may make the clean less efficient.
Corrosion inhibition
Certain chemical components
may inhibit the corrosion which normally takes place
when aluminium and to a lesser degree zinc come into
contact with detergents at very high or low pH. Silicates,
for example, in the presence of caustic soda, can render
the latter practically non-corrosive on aluminium
although this is usually associated with a less effective
Chelation
Chelation of insoluble metal ions such as
calcium, magnesium and iron. These ions may be present
in scale already formed on a surface, where they provide
anchorage for soil deposits and may become incorporated
