More About Antimicrobial Finishes

Anti microbial finishes have increased its importance in the recent years for several reasons. They serve the consumer by offering protection from the harmful effects (such as infectious diseases) of certain microbes. More commonly, the finish is designed to inhibit odors that may have been generated by the body, soils, contaminants, or personal care products. Some of these finishes are designed to reduce the deterioration of the fabric from biological activity. The use of synthetic fibers and blends in items such as shirts, hosiery, blouses, and underwear has accelerated the need for bacteriostatic finishes on clothing.

The moisture transport characteristics of such blends tend to cause a greater degree of “perspiration wetness” than occurs with fibers of wholly natural fibers. Additionally, there is a growing volume of literature demonstrating the survival and growth of micro organisms in textiles and their disseminations as a potential health risk. It has been recognised that microorganisms, particularly bacteria thrive on textile materials. Natural fibres, such as cotton, are more susceptible than synthetics because, their porous hydrophilic structure retains water, oxygen and nutrients, providing a perfect environment for bacterial growth. This growth can have a variety of serious consequences, especially with hospitals and schools, which have been recognized to control the environment and health of the people. However, the use of antimicrobials to inhibit odour development resulting from microbial growth on textiles exposed to perspiration has become a wide subject of research. The microbial attack on textiles results in. Odour formation, Contamination risk, Strength reduction and Quality loss.

The inherent properties of the textile fibers provide room for the growth of micro organisms. The structure of the substrate and the chemical processes also induce the growth of microbes. Humid and warm environment aggravate the growth of microbes. Infestation by microbes cause cross infection by pathogens and development of odour, when the fabric is worn next to the skin. In addition, the staining and loss of the performance properties of textile substrates are the results of microbial attack. Anti microbial finishes are applied with a view to protect both, the wearer and the textile substrate.

Microbes: what are they?

Microbes are the tiniest creatures which cannot be seen with the naked eye. They include a variety of micro-organisms like bacteria, fungi, algae and viruses. Bacteria are uni-cellular organisms which grow very rapidly under warmth and moisture .Further, sub divisions in the bacteria family are Gram positive (Staphylococcus aureus), Gram negative (E-Coli), sporebearing or non spore bearing types. Some specific types of bacteria are pathogenic and cause cross infection. Fungi, molds or mildew are complex organisms with slow growth rate. They stain the fabric and deteriorate the performance properties of the fabrics. Fungi are active at a pH level of 6.5.Algae are typical micro organisms which are either fungal or bacterial. Algae require continuous sources of water and sunlight to grow and develop darker stains on the fabrics. are active in the PH range of 7.0-8.0. Dust mites are eight legged creatures and occupy the household textiles such as blankets bed linen, pillows, mattresses and carpets. The dust mites feed on human skin cells and liberated waste products can cause allergic reactions and respiratory disorders.

The antimicrobial agent works either by the slow release of the active ingredient or by surface contact with the microbes. The antimicrobial agent inhibits the activity of microbes by interfering with the necessary mechanism of the microbe’s cell. Microorganisms are in the air, human bodies, the soil and on all surfaces with which we come in contact. When certain conditions exist, these organisms grow and multiply. The conditions necessary for growth are nutrient source (organic matters, C, O, N, S), warm temperature and moisture.

The general name antimicrobial finish is given to all types of finishing agents that kill off fungi and bacteria or inhibit growth and thus have disinfecting properties.

The following terms are used in this connection :

•Fungicide : A substance that destroys fungi
•Bactericide – Germicide: A substance that destroys bacteria
•Microbicide : Includes fungicide and Bactericide
•Bacteriostatic: A substance that inhibits bacterial growth

Methods of anti microbial finish can be classified in to two categories. Addition of an anti microbial agent in the polymer before extrusion and post treatment of the fiber or the fabric during the finishing stage.The efficacy of a antimicrobial finish will depend on various factors, such as its chemical nature,method of application, and durability. The selection of the appropriate antimicrobial system used will thus depend on a number of considerations. The first determination is the type of antimicrobial activity desired. Second is the way the system is applied (by padding, exhausting, or incorporating a synthetic fiber containing the antimicrobial agent).

Other important considerations include skin sensitivity of the agent to the consumer, environmental impact of any effluent and the discarded textile effect on other desirable properties of the fabric, durability, and cost. Antimicrobial finishes are produced in general with products based phenol derivatives, organic or inorganic heavy metals compounds that split off formaldehyde and quaternary compounds. Cationic surfactants function as effective anti microbial finishes. With the restriction of formaldehyde and heavy metals, newer compounds have been replaced. Several durable antimicrobial agents show promise for selected end-uses Polyhexamethylene biquanide hydrochloride (PHMB) has a broad spectrum of activity against bacteria and fungi with a long history of safe use. Application may be by pad, spray, foam, or exhaust methods. Upon drying, it becomes quite durable. Metallic silver combined with zeolite and dispersed in the polymer before extrusion spinning provides a polyester fiber that can be intimately blended with cotton to produce a durable antimicrobial composite. The blend is reported to have excellent anti-bacterial and anti-fungal properties.

Alkoxysilanes have been widely used by a variety of industries as coupling agents to bind and reinforce substrates. purposes. The bacteriostatic action of quaternary ammonium compounds on textiles is well known. The latter compounds exert their influence external to the microorganisms by disruption of the delicate cell membranes and therefore do not need to be absorbed in solution to produce their bacterial killing. The combination of these technologies (that is, the bonding power of alkoxy silanes and the bactericidal power of “quats” on a substrate such as textiles) results in a durable, safe, antibacterial treatment and the Antimicrobial compounds are (3-trimethoxysilyl proply-loctadecyl ammonium chloride).

An unexpected benefit to the binding of this organo silicon quaternary to a wide variety of substrates is the great increase in spectrum of both antibacterial and fungal killing power. Quaternary silicones like 3-trimethoxy-silylpropyldimethyloctadecyl ammonium chloride have been used for a number of years as a durable odor preventive on socks. However, it is less than 90% effective on bacteria and have limited activity against fungi. A renewable antimicrobial agent is based on the reaction of monomethylol-5,5-dimethylhydantoin (MDMH) with cotton and subsequent reaction with hypochlorite bleach. The activity is derived from the slow release of chlorine that can be renewed when subjected to hypochlorite bleach again. This application requires that the fabric be white or dyed with pigments or vat dyes due to the reduction of most dyes by chlorine.

Trichloro-orthophenylphenol (Triclosan) can be added to the spinning solution of acrylic or acetate fibers for blending with cotton. Triclosan may also be exhausted or thermo fixed to cotton blends containing polyester to impart antimicrobial properties. Chitosan made insoluble by cross linking is effective in neutralizing some odors. Although it is environmentally friendly, the level of the finish required to be effective imparts excessive stiffness to the fabric.Chitosan is a non toxic, bio degradable natural polysaccharide. The only difference between chitosan and Cellulose is the amine group in the position C-2 of chitosan instead of the hydroxyl group in cellulose.

Magnesium hydroperoxy acetate is another environmentally friendly compound, which can be fixed to cotton to impart some antimicrobial properties.

Plasma treatments are gaining popularity in the textile industry due to their numerous advantages over conventional wet processing techniques. Plasma containing fluorocarbon gas changes both the physical and functional characteristics. The plasma treatment fabric does not alter the weight, thickness, stiffness, air permeability, and breaking strength and elongation. Plasma-treated fabric show higher blood and water resistance compared to other treatments and also show a zone of inhibition for Staphylococcus aureus, thus providing a barrier against microbes.

Antimicrobial Activity Tests

There are various methods to demonstrate the efficacy of an anti microbial activity. Tests normally conducted are

•Agar diffusion test
•Challenge test (Quantitative).
•Soil burial test
•Humidity chamber test
•Fouling tests

Agar diffusion testing is a method of testing chemical agents anti-microbial effectiveness by measuring and determining the agents zone of inhibition. In the agar diffusion method, one species of bacteria is uniformly swabbed onto a nutrient agar plate. Chemicals are placed on paper disks. These discs are added to the surface of the agar. During incubation, the chemical diffuses from the disk containing the agent into the surrounding agar. An effective agent will inhibit bacterial growth, and measurements can be made to quantify the size of the zones of inhibition around the disks.

The relative effectiveness of a compound is determined by comparing the diameter of the zone of inhibition with values in a standard table. Agar diffusion test is a preliminary test to detect the diffusive antimicrobial finish. It is not suitable for non diffusive finishes and textile materials other than fabrics. AATCC test 30 -1993, 147 -1993, 174 -1993 and 90 -1982 {Agar diffusion tests – semi quantitative} In the case of Challenge test, AATCC test is 100 -1993. For Fouling and Soil burial tests, ISO 11721-1 – 2001 is being followed.