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| Fig A15: effect of borate on red wine solution absorbance; evidence of interaction |
Fig A16: comparison of oxidative and non - oxidative bleaches; stain removal performance |
In conjunction with oxidative bleaches such as sodium perborate and hydrogen peroxide, borate addition has been shown to
enhance the total bleaching performance. Data indicate that this is probably due to the enhancement of the non-oxidative
pathway or process rather than the increased levels of peroxoborate anions caused by added borate, but it is likely too
that peroxoborate is more reactive toward some stain components than is hydrogen peroxide giving it a broad band efficacy.
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| Fig A17: comparison of non-oxidative bleaching performance; borax vs. sodium bicarbonate |
Bleaching in liquid laundry detergents, dishwasher powders and surface cleaners
This section has so far dealt exclusively with powders for fabric washing, but perborate bleaching is also relevant to other
cleaning products.
Liquid formulations for fabric laundering
Many advances in the incorporation of peroxygen bleach, including perborate, into main wash liquid detergents have been
described, but not proved fully viable. In aqueous formulations, perborate bleach suffers from loss of available oxygen
and low solubility.
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The catalytic breakdown of available oxygen by trace metal ions - particularly of copper, iron and manganese – is considered
to be the route for this loss. Many effective stabilizers, essentially powerful sequestrants or cocktails of sequestrants
with specific ability to form very strong complexes with the various metal ions, have been described which slow the loss to
practical levels. The most effective in water-based liquids, from Borax studies, appear to be sodium phosphate and sodium
diphenylaminesulfonate (DPAS).
Significant stabilization is achieved at 10ppm and practical stabilization (<5% loss of Avox in one month at 30ºC) occurs
with 1wt.% DPAS.
Several other stabilizing agents have been described which extend the shelf life with respect to available oxygen, but
thus far its loss over time is considered too great.
Bleach-containing non-aqueous detergent formulations, based upon one or more glycol-based compounds or non-ionic surfactants,
an activator such as TAED and appropriate stabilizers, show promise.
In bleach-containing aqueous detergent formulations, the solubility of components such as perborate is clearly critical, as
are their stabilities in storage. Sodium perborate solubilization can be increased tenfold by the addition of borate or other
co-solutes. This property is reviewed in more detail in another section [see Solubilization section].
Liquids based on hydrogen peroxide are currently only used as separate bleaches or stain pre-treatments because of their
lack of stability at the higher pH of detergents. However, the discovery of the so-called borate-polyol pH jump phenomenon
(see pH effects section) in conjunction with a source of available oxygen including perborate, may result in complete liquid
detergents containing bleach.
Automatic dishwasher formulations and household cleaners
The home dishwashing machine and packaged household cleaners have to deal with soils and stains on glazed ceramics,
glass, plastics and metals.
In many cases, bleaching agents are included in automatic dishwasher formulations - until recently as hypochlorite or
other chlorinated compounds.
However with the addition of fragrance and enzymes to the formulations, an activated perborate bleaching route is
favored. Perborate is less agressive towards other formulation ingredients and together with the TAED activator,
provides good stain removal performance.
Tableware such as metals, glass etc. responds well to borate cleaning activity. Specifically it has also been
noted that the use of borates such as sodium perborate, boric acid and boric oxide results in improved tarnish resistance,
and protects ceramic surfaces by preventing glaze damage.
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