Silver-wool Textiles – Development Pathway and Challenges

J. Johnston
Victoria University of Wellington,
New Zealand

Keywords: silver, textiles, wool

Summary:

This paper presents an overview of the pathway and challenges encountered in the development and use of silver entities to impart antimicrobial activity to woollen textiles. The antimicrobial properties of silver have been known for a very long time, dating back to its early use in food and beverage containers, e.g. silver goblets, vessels and tableware, and in medicine to prevent the spread of infections. Silver is known to be effective against some 650 types of microbes including the common ones Staphyloccus aureus, Escherichia coli, Samonella, Listeria monocytogenes, Campylobacter and other pathogens such as the HIV-1 virus. From about the early 1990s there has been a substantial increase in the interest and research activities relating to the synthesis and use of silver nanoparticles as antimicrobial agents in a variety of substrates and composite materials. Here, the very small size of the nanoparticles enable them to penetrate the cell wall of microbes and through the dissolution of silver ions they disrupt the cell chemistry, thereby destroying the microbe. Also, the very large specific surface area of the silver nanoparticles facilitates the ready dissolution of silver ions from the surface which can then migrate from an external medium into the microbes and similarly cause their demise. A large number of research papers reporting the use of silver nanoparticles as an antimicrobial agent and incorporating them into polymers, fibres, inorganic and mineral substrates have emerged. These nanosilver composites have been variously fabricated into products for use in food packaging and food preparation equipment, surface coatings, medical devices, synthetic polymer and natural cotton, hemp and wool fibres and textiles. From this, a number of commercial products, notably in the packaging, coatings and synthetic textile areas, have emerged and are available in the marketplace. A substantial amount of information is available in the public domain. Wool is a high quality, renewable natural fibre which represents only about 4% of textile products, e.g. apparel, carpet, rugs and upholstery fabrics, worldwide. Wool also has good thermal insulation, moisture absorption and fire retardant properties, which are additionally advantageous. The diameter and nature of the fibres and hence their use is dependent on the breed of sheep. High quality fine merino wool is strongly sought after for high performance and high fashion apparel, which command a premium price. Coarser quality wool with stronger fibres is used in wool carpets and rugs. Mid micron wool is used in apparel and upholstery. Through the use of silver entities, there is the opportunity to impart antimicrobial properties to these various wool types. Although there are some publications relating to the use of silver nanoparticles as antimicrobial agents in wool, it does not appear that any of this work has been progressed beyond the laboratory stage. This probably reflects the smaller and more specialised market share of wool products in the marketplace. Over recent years we have carried out an extensive research and development programme on incorporating silver entities into wool fibres, understanding the chemistry relating to the incorporation and interaction of different silver entities into the various types of wool fibres from different sheep, and characterising the chemistry, structure, optical properties and antimicrobial properties of the silver-wool composites accordingly. We have used loose wool, combed top (sliver) wool, yarn and knitted and woven fabric as substrates, and have progressed our research and development work through the laboratory stage to pilot scale operation and commercial scale trial production of treated yarn and fabric. An overview will be presented here.