Victoria University of Wellington,
Keywords: silver, antimicrobial, polymers, textiles
Summary:This paper presents the development of a new technology and its application to natural fibre and polymer composites, whereby silver entities are chemically bound to the fibre and polymer substrates to impart durable, effective and long lasting antimicrobial properties. The use of silver as an antimicrobial agent in food and beverage preservation and medicine, dates back to early civilisations. Silver is known to be effective against some 650 types of microbes apparently without the risk of the microorganisms developing a resistance to it, which is an increasing concern with currently prescribed antibiotics. Common microbes which silver is highly effective against, include Staphyloccus aureus, Escherichia coli, Samonella, Listeria monocytogenes and pathogens such as the HIV-1 virus. These microorganisms were found to be much more susceptible to silver than mammalian cells and hence silver can be used as an effective antimicrobial agent. The interest in using silver nanoparticles in this way grew rapidly with the advances in nanoscience and nanotechnology from the 1990’s. This led to many silver nanoparticle syntheses being reported and nanoparticles being incorporated into a host of substrate materials, particularly thermoplastic polymers. The resulting nanosilver-polymers were fabricated into consumer items for food processing and packaging, appliances including refrigerators, clothing and medical dressings etc. The major issue and growing concern here is that the silver nanoparticles where not chemically bound to the polymer substrate and were undesirably easily abraded or leached out into the environment. This created a lot of negativity in the use of silver as a very effective antimicrobial agent. The novel approach and technology presented here seeks to challenge this position and promote silver as an effective, environmentally friendly antimicrobial agent in natural fibre or polymer composites. This is important for its continued use in food and beverage packaging, surface coatings, textiles and healthcare applications. This is achieved by forming and chemically binding nanosilver, nanosilver compounds or silver ions themselves directly to particular functional groups in the natural fibre or polymer substrate, and controlling the release of the active Ag+ ions for action against the target microorganisms accordingly. In this way an antimicrobial or bacteriostatic surface can be maintained with a very low leach rate of silver ions, which is both environmentally desirable and provides long term effectiveness. Also, as the silver entities are strongly bound to the substrate they do not rub or wash off, thereby providing robustness to many commercial, industrial and healthcare cleaning processes. In an industrial situation, the water used often contains low levels of dissolved chloride ions from the natural source or the water treatment process. As Ag+ ions readily react with chloride ions to precipitate AgCl which is photoactive, this can be problematic. This is also addressed. The antimicrobial silver technology developed here has been successfully applied to paper fibres and paper sheets, textiles and various polymer materials. Examples of these applications and the pathway from the laboratory scale research and development through pilot and commercial scale development will be presented.