Dolphins and sugar beet: a source of coatings technology
Natural sources are commanding more and more attention from scientists looking for more environmentally friendly ways of production, ranging from homoeopathic medicines to surface coatings. Our first example of this development is a study by German scientists on the behaviour of dolphins' skin as a key to making non-toxic marine antifouling paints.
Professor Christof Baum, a biologist from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, said that he and his colleagues had found that a unique combination of the texture of the dolphin skin and a gel secreted from its pores allows the mammals to glide smoothly through the water without the risk of the marine flora and fauna responsible for bio-fouling becoming attached. They have already synthesized their findings in the laboratory, had a patent approved, and arranged with a coatings manufacturer to produce the new antifouling before conventional tributyl tins and other toxic substances are banned at the end of 2003.
To find out how dolphins solved the problem of bio-fouling and kept their skin so smooth, Professor Baum and his colleagues took skin samples from their subjects which they froze at temperatures of 1968C using liquid nitrogen. Looking at these under a scanning electron microscope, they found that the dolphins' first line of defence against biofouling was the skin which was not entirely smooth but slightly rippled every nanometer. He said: "This surface structure leaves hardly any protected niches, meaning little chance for any organisms to grow on the dolphin's skin. At the same time the ripples were so small that they did not affect movement through the water." It is planned to mix tiny inert particles in the new coating resin to achieve a slightly uneven surface that duplicates the effect of the dolphin's skin.
More importantly, the team discovered that the skin was covered by a gel-like substance which was rich in vitamins and enzymes that actively resisted the mucus that the various micro-organisms often used to get their first foothold. Prof. Baum said: "The gel on the pilot whale's skin is far more effective at repelling the organisms that cause biofouling than the organisms themselves are at getting a hold. Bacteria or tiny larvae that try to become attached are repelled and quickly washed off by the sea water." He added that in the unlikely scenario that a living organism managed to attach to the dolphin's skin, a third line of defence came into play with the enzymes in the gel attacking and destroying the foreign bodies, causing them to fall away.
Our second example of surface coatings' development from natural sources is the availability of lactate ester solvents derived from sugar beet. In the UK,SIS Chemicals of Lymington, Hants (website www.sischem.co.uk)says that their range (Purasolv) of beet derived lactate esters are emerging as a serious rival to chlorinated solvents. They are claimed to combine excellent solvency power with major environmental benefits. They are non-toxic,readily biodegradable, partly renewable, and also said to have a favourable toxicological profile.
Purasolv EHL (ethyl hexyl lactate) is a non- VOC, according to European guidelines, is not classified as harmful or flammable, can be used with or without water rinsing, and can clean without redeposition with up to 30 per cent soiling.
John Bean
