Phosphate Recovery
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Phosphates, builders and laundry detegents
The role of detergents
The primary purpose of laundering is
to remove soil and stains from clothes, contributing to health and hygiene
and to the maintenance of fabric life. The washing process combines the
effect of heat (washing temperature), mechanical agitation and detergency
to produce clean clothes with a minimum of fabric damage.
In recent years, washing temperatures
have decreased significantly. The amount of water used and the length of
washing machine cycles have also fallen. All this has put a greater onus
on the detergent to perform rapidly and efficiently in the wash.
Essential requirements of modern laundry
detergents are:
- To wash satisfactorily;
- To cause minimum fabric damage;
- To be affordable by the consumer;
- To achieve these results with minimal impact on the environment.
Detergents and their components
A modern laundry detergent is a complex formulation which may contain numerous ingredients. However, at the heart of most detergents, there are three components:
- Builders whose main role is to create optimum water conditions for the surfactant.
- Surfactants, or surface active agents, which attract the soil away from the clothes and into the wash water.
- Stain removal agents such as oxygen bleaches and enzymes.
Detergents also contain many other ingredients such as alkali, bleach activators, antiredeposition agents, fluorescent whitening agents, perfumes, etc.
What makes a good builder?
Most surfactants can not wash satisfactorily alone. They are formulated with builders which reduce water hardness and overcome the negative effect of calcium and magnesium slats present not only in wash water, but also in the soils and the fabric surface. These salts reduce the surfactant efficiency and can cause incrustation on fabrics.
Other important functions of a builder include:
- Soil dispersion properties;
- Prevention of redeposition of soils;
- Provision of alkalinity and buffering;
- Assistance in the detergent manufacturing process and the maintenance of powder flow properties;
- Surfactant adsorption capacities.
From 1947 until the late 80s, sodium tripolyphosphate was used almost exclusively, due to its multifunctional contribution to the washing process.
In recent years other builders have been introduced including the organic nitrilotriacetic acid (NTA) and synthetic zeolite.
Properties
of the three main builders presently on
STPP NTA Zeolite
the market
Removes hardness
v
v
v
Reduces surfactant use
v
v
Improves emulsification
and dispersion
v
Prevents re deposition
v
Controls alkalinity
v
Methods for testing detergent
efficiency. Tests of comparative washing efficiency of
compact and conventional
detergents, J. Constant, CTTN-IREN, Lyon, 1992.
The use of alternative builders always requires the addition of chemicals to compensate for the performance short-comings exhibited by these alternatives.
Increased efficiency for a decrease in environmental impact
Each detergent ingredient has an associated
environmental impact and it is the responsibility of detergent manufacturers
to produce formulations which achieve the desired washing performance with
the minimum environmental impact.
For similar types of detergents, the
impact of a detergent can be related to the dosage used. In recent years
the thrust of detergent formulation has been to maintain performance at
ever decreasing dosage rates.
This in turn directly influences the
volume of detergent released into the sewer systems and eventually to the
environment.
In 1992, a study on detergents concluded
that in hard water, the same efficiency was obtained with 45% less detergent
when STPP based compact powders were used. For non conventional detergents,
the difference was estimated at 21%.
Detergents and ecolabelling
The Nordic Swan Label is an environmental
label which applies, among other things, to the household laundry detergents
sold in the environmentally conscious Nordic countries. The 1991 version
of the Nordic Swan systematically excluded detergents containing phosphates
responding to popular concerns at the time.
Four years later, in the revision of
the Nordic ecolabelling criteria, this situation was reversed and phosphate
based formulations can now obtain the label. The Nordic Swan criteria became
tougher on most other detergent ingredients
This development follows the decision of the European Union which decided that phosphate-based products could qualify for the European Ecolabel on Household Laundry Detergents.
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