Smart Suds
February 2000

Making detergents work smarter, not harder
If it weren't for the environmental needs to use less energy and less chemicals, getting the laundry really clean would be a breeze. All it would take is a hot wash and lots of detergent.

However, over the last few decades, detergent and washing machine manufacturers have responded to these twin sustainability imperatives with great success. Effective washing temperatures have fallen dramatically, and the detergents themselves have changed radically to go even further.

The consumer's top priority, getting stains and dirt out, is being well met, thanks to the huge strides made in detergent laboratories all over the world.

In fact, one of the first breakthroughs came very early on in the century with the discovery that sodium perborate bleaches stains extremely well by releasing active oxygen (through the intermediary of hydrogen peroxide) into the wash. At the same time, it is gentle and safe. But, alone, it only works in hot washes – about 60 degrees C and above.

The answer to this low-temperature perborate challenge came in the 1970s when it was discovered that its performance under 60 degrees C could be restored by the use of activators. These rejoice in names such as tetraacetylethylenediamine (TAED) and sodium nonanoyloxy-benzenesulfonate (NOBS), which interact with the perborate to release peracids, and are even more effective active oxygen sources than hydrogen peroxide. But even so, perborate activated in this way still had a working 'floor' of about 40 degrees C.

Finding another agent which encourages perborate to bleach stains and 'fugitive' dyes (red sock plus white shirt equals pink shirt) at even lower temperatures came with some difficult conditions attached. Not only did it have to work effectively, but it had to be kind to fabrics and dyes, have a good shelf-life (and also last through the wash cycle), and be both safe and environmentally sound. And it had to be affordable.

Activators or catalysts?
There it is – useful oxygen, but locked away in the perborate molecules. With activators, the active oxygen appears after a number of distinct chemical reactions involving them. But is there another way? Catalysts offer another route. They work in a completely different way to enhance bleaching, and are not used up in the chemical reactions like activators. They do their work on the perborate molecules, and are then available to do it again. So there is less chemical usage.

Chemists know that some of the transition metals like manganese, iron and cobalt form complexes that can enhance perborate bleaching at lower temperatures by catalysis.

A manganese-based system did, in fact, come on to the market in the mid-1990s. It was spectacularly effective as an oxygen bleach catalyst, but sadly was found to damage fabrics and dyes unacceptably. As a household product, it was unsuccessful but was still a big step forward in the understanding of these mechanisms.

Higher performance, lower temperature
At Borax, systems for enhancing perborate-containing detergents with catalysts and more effective activators have been under investigation for a number of years. A new catalytic system has now been developed* – and while its complete chemistry is not yet fully determined, it nevertheless works very well, and most importantly meets all the necessary criteria. Exhaustive washing trials in the laboratory confirm that effective bleaching is achieved well below the 40 degrees C floor, the formulation cares for fabrics and dyes, is stable, environmentally benign, and can be manufactured in a simple 'one-pot' industrial process.

Borax's 'designer' catalyst
Knowledge of the behavior of molecular structures enables today's research chemists to answer many questions – including that challenging task 'find me a chemical, out of the millions possible, which does this'.

Catalyse sodium perborate to release its active oxygen? Well, it wasn't as simple an answer to find as it is to report, but Borax's scientists have come up with a catalyst which fits the bill exactly. Significantly better bleaching occurs below 40 degrees C under a variety of wash conditions, and indeed it acts as well on tea stains by a margin of 10 degrees C as does conventional TAED-activated perborate.

The catalyst is a fine example of so-called 'biomimetic' chemistry so popular today. Essentially, scientists have recognized that nature has over millions of years evolved extremely efficient ways of carrying out chemical reactions. The biomimetic approach is to develop synthetic analogues of nature's chemical toolbox. Borax has applied these principles and the resultant catalyst is not unlike a biological enzyme in the way it behaves, possessing a so-called active site where key reactions in the stain bleaching process occur.

Washing tests have demonstrated the catalyst/perborate's impressive bleaching effectiveness and laundry-care combination – a performance the Borax development team ascribes to its stability – harnessing the inherent reactivity of the active site and putting this to useful effect, while at the same time suppressing any unwanted chemical reactions.

Next steps
In the laboratory, Borax has successfully demonstrated a next step forward in what is possible for the laundry detergent of the future with catalysts. In partnership with the detergent and chemical supply industries, Borax is now working to bring these developments to a washing machine near you.

* Subject to patent protection