Bookish bacteria
TAKE some silk cotton. Add a dash of the bacteria Rhodospirillum rubrum. Keep aside for a few days. Sieve and dry. This, in essence, is the recipe for a new environment-friendly method of paper manufacture that scientists at the A M M Murugappa Chettiar Research Centre (MCRC) in Madras have developed.
Cellulose, a carbohydrate that is the main constituent of plant cell walls, is also the main constituent of paper. Since the 19th century, forests have been axed the world over to provide the raw material for cellulose-hungry paper and pulp industries. But, hopefully, not for much longer. Says T M Vatsala, deputy director at the MCRC, "The technology we have is different because it uses only the tree products and not the trees."
The floss from the silk cotton tree, Ceiba pentandra, has a fairly high cellulose content -- 64-72 per cent. The rest is primarily hemicellulose, a compound similar to cellulose, which binds the cellulose to lignin, which forms the woody tissue. If this floss is to be used as a raw material for paper manufacture, the cellulose would have to be isolated. In the conventional method of manufacturing paper, mechanical and chemical pulping are used to separate the cellulose from the rest of the material, usually using sulphates or soda, which can lead to effluent problems.
Enter R rubrum, a bacteria that can feed on both cellulose and hemicellulose. When both are present, the bacteria preferentially attacks the latter. The optimum temperature for the growth of the natural strain of the bacteria is 26o C. MCRC scientists have, by selective adaptations, found a strain more suitable for Indian conditions which can grow at temperatures upto 38o C.
The process of manufacture is fairly simple. The fibre length of the silk cotton floss is first reduced using a kitchen mixer, after which it is boiled and cooled. The bacteria is then added to the floss and the mixture left alone for 2-6 days. During this time, the bacteria acts on the hemicellulose, breaking down the bonds between the cellulose and lignin so that the cellulose is freed. After treatment with R rubrum, the mixture is ready to be sieved and compressed into the final product -- a sheet of crisp, white paper.
About 2.5g of silk cotton floss is required to produce 1 sheet of A4-size paper. The waste, which contains the bacteria, can be used to treat fresh batches of silk cotton or fed into a biogas plant. Says C V Seshadri, scientist emeritus at the MCRC, "What we are making is clean, green paper."
The MCRC hopes to completely replace the polluting technology currently used by the paper industry with the new technology. "Right now, the technology is still confined to the laboratory, but we are confident of being able to start large-scale manufacture soon," says Vatsala. Adds Seshadri forcefully, "We are not here to compete with industry. We are here to destroy them."