hard cell

Architect's memo 85: November 2006

Bacteria that is! These oldest of life forms are also the most ubiquitous. They will live, not only in all the most obvious places, but also on top of mountains and in the deepest ocean; in the frozen rocks and ice of Antarctica to near boiling mud pools in Rotorua. They can live with or without oxygen and even thrive in atmospheres toxic to humans. And if life gets a bit too tough, well, they can close down their systems and go dormant for extended periods.

But are they goodies or baddies? Well they really are a mixture. At the dawn of life on earth cyanobacter, such as stromatolites, were able to exist in the nitrogen rich atmosphere of that time and deliver up oxygen in sufficient quantities that would later create a hospitable atmosphere for mammals. So let's hear it for cyanobacter!!

There are many other synergies. There are bacteria that live around the roots of some plants and which are able to convert gaseous nitrogen to the soluble nitrates that the plant can beneficially use; there are benign bacteria that live in the human gut which protect us, by sheer weight of numbers, from other, more malign types; there are other strains which use a fermentation process to produce energy and pee almost pure alcohol - which suggests another, as yet undeveloped, synergy with man.

They are a vital part of the carbon cycle; have been used to help clean up oil spills; are essential to the production of cheese, pickles, wine, sauerkraut, yoghurt and can be used as miniature biotechnology factories for the production of therapeutic drugs such as insulin.

There is a dark, pathogenic side to bacterial society, harbouring such nasties as cause tetanus, typhoid, tuberculosis, cholera et al as well as sepsis and most food-borne illnesses.

Paint chemists have always had an eye on the small world of microbiology and have long protected their waterborne products from bacterial spoilage in the can by the addition of small amounts of bactericides. They have also been aware that paint films can support the development of defacing moulds, fungi, algae and dosed their products with appropriate fungicides and algaecides. These strategies can be looked upon as self-protective measures.

Some years ago a new trait developed, especially in Japan, whereby the paint surface was looked upon as potentially being bacteriostatic and providing an actively hygienic surface. These technologies have progressed to the stage where they are becoming mainstream in Japan, Europe and the United States.

There are several possible technologies for achieving this but the most popular are proving to be based on silver. This 'noble' heavy metal has shown to have bactericidal properties while having no human toxicity.

The supply of biocidal coatings is not without controversy. Some of the considered arguments against it include: - they could give consumers a false sense of security; reduce the level of cleaning; lead to the development of resistant organisms and possibly, by producing a 'too clean' environment, lead to the development of lower childhood antibody production resulting in a greater incidence of, say, asthma. There could also be a legislative backlash if consumers had higher expectations than could be met in practice.

Resene have taken the position that silver is a useful tool in the fight against pathogenic bacteria and can make a positive contribution in rest homes, food processing areas, bathrooms, toilets etc. They are offering a silver containing option in their premium interior wall coating - Resene Spacecote Low Sheen - for these uses as a useful adjuvant to normal hygiene regimes.

Tech talk and Architect's memos
Technical information on a variety of topics relating to paint, finishes and coatings.

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