One gram of silver nano particles is all that is required to give antibacterial properties to hundreds of square metres of substrate material, asserts Anita A Desai.
Silver is a natural enemy of bacteria. Long before the existence of bacteria was recognised, silver containers were valued for their ability to keep food and drink fresh. It was not until the mid-19th century that metallic silver was identified as an effective antibacterial, and not until 2005 that silver became the key ingredient in a cost-effective and long-lasting antibacterial treatment for textiles. Silver kills over 650 different types of bacteria.
Clothing and textile materials are not only the carriers of microorganisms such as pathogenic bacteria, odour generating bacteria and mould fungi but also good media for growth of microorganisms. On many occasions, under favourable conditions these microorganisms cause problems to wearers/users of the textile materials. The need to protect fabrics against rotting and mildew attack has long been recognised.
Today, in the era of eco-friendly environment, it has become very important for human beings to live in a world of hygiene and freshness. Clothing and textile materials are not only the carriers of microorganisms such as pathogenic bacteria, but also good media for growth of microorganisms. Hence, it becomes very important to finish the garments with speciality chemicals that can restrict the growth of these microorganisms.
Microorganisms multiply rapidly in textiles in the presence of heat, humidity and food sources. Almost all of these organisms are not pathogenic. Some microorganisms, which live around the human body and multiply on textiles, have a high pathogenicity. Even if not highly pathogenic, the multiplication of microorganisms can create staining, discolouration, degradation of fibre and textile materials.
Natural and synthetic fibres vary greatly in their responses to microbial growth. Both may act as willing substrates but the mechanism in the two cases is very different. Natural fibres are easy targets for microbial attack because they retain water readily, and microbial enzymes can readily hydrolyse their polymer linkages. Cotton, wool, jute, and flax are reported to be most susceptible to microbial attack. If 105 colonies in 1 ml water are applied to approximately 0.5 g cotton, after a few hours a logarithmic growth is observed and the population increases from 105 to 109 colonies. The damage caused by the fungus Aspergillus Niger on cotton has been extensively investigated by Cerci and Seventekin. They found that there were differences in the strength of cotton as the time, temperature, pH, and medium conditions changed. Within natural fibres too, the persistence period varied greatly.
Growth of microbes is slower on synthetic fibres as compared to their natural counterparts because their polymer backbone does not retain much water. However, these fibres encourage the holding of state perspiration in the interstices, wherein the microbes multiply rapidly. Foot infection, for example, has been found to be more pronounced with synthetic fibre socks than with natural fibre socks. You and Merry found that the adherence of bacteria to the fabrics increased as the content of polyester in the fabrics increased.
Synthetic fibres also become susceptible to microbial degradation if there are finishing agents such as polyethylene and polysiloxane emulsions on these fibres. These additives allow the microorganisms to degrade the polymer into Chewable bites by utilising the acidic or basic by-products of their metabolism, thus, initiating the cycle of hydrolysis. In this way, even the tough polyurethanes can be broken down. Polypropylene, nylon, and polyester fibres have all been seen to be subject to microbial attack under conducive conditions.
Microbial attack on natur