The inherent properties of the textile fibres provide
room for the growth of micro organisms. Besides, the structure of the
substrates and the chemical processes may induce the growth of microbes.
Humid and warm environment still aggravate the problem. Infestation by
microbes cause cross infection by pathogens and development odour where the
fabric is worn next to skin. In addition, the staining and loss of the
performance properties of textile substrates are the results of microbial
attack. Basically, with a view to protect the wearer and the textile
substrate itself antimicrobial finish is applied to textile materials.
During World War II, when cotton fabrics were used extensively for tentage,
tarpaulins and truck covers, these fabrics needed to be protected from
rotting caused by microbial attack. This was particularly a problem in the
South Pacific campaigns, where much of the fighting took place under jungle
like conditions. During the early 1940s, the US army Quartermaster Crops
collected and compiled data on fungi, yeast and algae isolated from textiles
in tropical and subtropical areas throughout the world.
Cotton duck, webbing and other military fabrics were treated with mixtures
of chlorinated waxes, copper and antimony salts that stiffened the fabrics
and gave them a peculiar odour. At the time, potential polluting effects of
the application of, these materials and toxicity-related issue were not a
major consideration. After World War II, and as late as the mid-to-late
1950's fungicides used on cotton fabrics were compounds such as
8-hydroxygiunoline salts, copper naphthenate, copper ammonium fluoride and
chlorinated phenols. As the government and industrial firms became more
aware of the environmental and workplace hazards these compounds caused.
Alternative products were sought.
A considerable amount of work was done by the Southern Regional Research
Laboratory of the US Department of Agriculture, the Institute of Textile
Technology (ITT) and some of the ITTs member mills to chemically modify
cotton to improve its resistance to rotting and improve other properties by
acetylation and cyanoethylation of cotton. These treatments had limited
industry acceptance because of relatively high cost and loss of fabric
strength in processing. In addition, the growing use of man-made fibres such
as nylon, acrylics and polyester, which have inherent resistance to
microbial decomposition, came into wider use to replace cotton in many
What are microbes?
Microbes are the tiniest creatures not seen by the naked eye. They include a
variety of micro organisms like bacteria, fungi, algae and viruses. Bacteria
are unicellular 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), spore bearing or non-spore
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. Algae
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
Some harmful species of the bacteria and fungi are listed in Table 1.
|Gram positive bacteria
||Cloth damaging fungi
|Staphylococcus aurues or Pyogens
Necessity of antimicrobial finishes
Antimicrobial treatment for textile materials is necessary to fulfill the
To avoid cross infection by pathogenic micro
To control the infestation by microbes.
To arrest metabolism in microbes in order to
reduce the formation odour.
To safeguard the textile products from staining,
discolouration and quality deterioration.
Requirements for antimicrobial finish
Textile materials, in particular the garments are more susceptible to
wear and tear. It is important to take into account the impact of stress
strain, thermal and mechanical effects on the finished substrates. The
following requirements need to be satisfied to obtain maximum benefits out
of the finish:
Durability to washing, dry-cleaning and hot
Selective activity to undesirable micro
Should not produce harmful effects to the
manufacturer, user and the environment.
Should comply with the statutory requirements of
Compatibility with the chemical processes.
Easy method of application. No deterioration of
Resistant to body fluids; and resistant to
Antimicrobial finishing methodologies
The antimicrobial agents can be applied to the textile substrates by
exhaust, pad-dry-cure, coating, spray and foam techniques. The substances
can also be applied by directly adding into the fibre spinning dope. It is
claimed that the commercial agents can be applied online during the dyeing
and finishing operations. Various methods for improving the durability of
the finish include:
Insolubilisation of the active substances in/on
Treating the fibre with resin, condensates or
Micro encapsulation of the antimicrobial agents
with the fibre matrix.
Coating the fibre surface.
Chemical modification of the fibre by covalent
Use of graft polymers, homo polymers and/or co-polymerisation
on to the fibre.
Mechanism of antimicrobial activity
Negative effect on the vitality of the micro organisms is generally
referred to as antimicrobial. The degree of activity is differentiated by
the term cidal, which indicates significant destruction of microbes and the
term, static represents inhibition of microbial growth without much
destruction. The differentiation of antimicrobial activity is given in the
diagram (Figure 1).
The activity, which affects the bacteria, is known as antibacterial and that
of fungi is animistic. The antimicrobial substances function in different
ways. In the conventional leaching type of finish, the species diffuse and
poison the microbes to kill. This type of finish shows poor durability and
may cause health problems. The non-leaching type or biostatic finish shows
good durability and may not provoke any health problems. A large number of
textiles with antimicrobial finish function by diffusion type.
The rate of diffusion has a direct effect on the effectiveness of the
finish. For example, in the ion exchange process, the release of the active
substances is at a slower rate compared to direct diffusion ad hence, has a
weaker effect. Similarly, in the case of antimicrobial modifications where
the active substances are not released from the fibre surface and so less
effective. They are active only when they come in contact with micro
organisms. These so-called new technologies have been developed by
considering the medical, toxicological and ecological principles.
The antimicrobial textiles can be classified into two categories, namely,
passive and active based on their activity against micro organisms. Passive
materials do not contain any active substances but their surface structure
(Lotus effect) produces negative effect on the living conditions of micro
organisms (Anti-adhesive effect). Materials containing active antimicrobial
substances act upon either in or on the cell.
Antimicrobial substances and their effect
Many antimicrobial agents used in the textile
industry are known from the food stuff and cosmetics sector. These
substances are incorporated with textile substrates comparatively at lower
concentrations. It must be ensured that these substances are not only
permanently effective but also that they are compatible with skin and the
environment. A wide palette of antimicrobial compounds is now in use but
differ in their mode of action. The following list demonstrates the
polyvalent effect of the various antimicrobial substances:
Materials with active finishes contain specific
active antimicrobial substances, which act upon micro organisms either
on the cell, during the metabolism or within the core substance
(genome). However, due to the very specific nature of their effect, it
is important to make a clear distinction between antibiotics and other
active substances, which have abroad range of uses.
Oxidising agents such as aldehydes, halogens and
proxy compounds attack the cell membrane, get into the cytoplasm and
affect the enzymes of the micro organisms.
Coagulants, primarily alcohols irreversibly
denature the protein structures. Radical formers like halogens,
isothiazones and peroxo compounds are highly reactive due to the
presence of free electrons. These compounds virtually react with all
organic structures in particular oxidising thiols in amino acids. Even
at the lowest level of concentrations, these substances pose particular
risk to nucleic acids by triggering mutations and dimerisation.
One of the most durable types of antimicrobial
products is based on diphenyl ether (bis-phenyl) derivative known as
either 2, 4, 4'-trichloro-2' hydroxy dipenyl ether or 5-chloro-2-(2,
4-dichloro phenoxyl) phenol. Triclosan products have been used for more
than 25 years in hospitals and personal care products such as
antimicrobial soap, toothpaste and deodorants. Triclosan inhibits growth
of micro organisms by using an electro-chemical mode of action to
penetrate and disrupt their cell walls. When the cell walls are
penetrated, leakage of metabolites occurs and other cell functions are
disabled, thereby preventing the organism from functioning or
reproducing. The Triclosan when incorporated within a polymer migrates
to the surface, where it is bound. Because, it is not water-soluble, it
does not leach out, and it continuously inhibits the growth of bacteria
in contact with the surface using barrier or blocking action.
Quaternary ammonium compounds, biguanides, amines
and glucoprotamine show poly cationic, porous and absorbent properties.
Fibres finished with these substances bind micro organisms to their cell
membrane and disrupt the lipo polysaccharide structure resulting in the
breakdown of the cell.
Complexing metallic compounds based on metals
like cadmium, silver, copper and mercury cause inhibition of the active
enzyme centers (inhibition of metabolism). Amongst these, the silver
compounds are very popular and already been used in the preparation of
antimicrobial drinking water.
Chitosan is an effective natural antimicrobial
agent derived from Chitin, a major component in crustacean shells.
Coatings of Chitosan on conventional fibres appear to be the more
realistic prospect since; they do not provoke an immunological response.
Fibres made from Chitosan are also available in the market place.
Natural herbal products can be used for antimicrobial finishes since,
there is a tremendous source of medicinal plants with antimicrobial
composition to be the effective candidates in bringing out herbal
Commercial antimicrobial agents and fibres
Thomsan Research Associates markets a range of antimicrobials under the
trade name Ultrafresh for the textile and polymer industry. Ultra fresh
products were developed to be used in normal textile processes. Most ultra
fresh treatments are non-ionic and are compatible with a wide range of
binders and finishes. To incorporate antibacterial into high temperature
fibres like polyester and nylon, it is necessary to use an inorganic
antimicrobial like Ultrafresh CA-16 or PA-42. These must be added as a
special master batch to the polymer mixture before the extrusion process.
For fibres such as polypropylene, which are extruded at lower temperatures,
it is possible to use organic antimicrobials such as Ultra fresh Nm-100,
Dm-50 or XQ-32. In the case of Rossari.s Fabshield with AEGIS microbe shield
programme, the cell membrane of the bacteria get ruptured when the microbes
come in contact with the treated surface; thus, preventing consumption of
antimicrobial over a period of time and remain functional throughout the
life of the product. The active substance 3-Trimethoxy silyl propyl dimethyl
octadecyl ammonium chloride gets attached to the substrate either through
bond formation on the surface or by micropolymer-sing and forming a layer on
the treated surface; the antimicrobial agent disrupts the cell membrane of
the microbes through physical and ionic phenomena.
Ciba Specialty Chemicals markets Tinosan AM 110 as a durable antimicrobial
agent for textiles made of polyester and polyamide fibres and their blends
with cotton, wool or other fibres. Tinosan contains an active antimicrobial
(2, 4, 4'-Trichloro-2' - hydroxyl-dipenylether) which behaves like a
colourless disperse dye and can be exhausted at a very high exhaustion rate
on to polyester and polyamide fibres when added to the dye bath. Clariant
markets the Sanitised range of Sanitized AG, Switzerland for the hygienic
finish of both natural and synthetic fibres. The branded Sanitised range
function as a highly effective bacteriostatic and fungistatic finishes and
can be applied to textile materials such as ladies hosiery and tights.
Actigard finishes from Clariant are used in carpets to combat action of
bacteria, house dust mites and mould fungi. Avecia.s Purista-branded
products treated with Reputex 20 which is based on poly (hexamethylene)
biguanide hydrochloride (PHMB) claimed to posses a low mammalian toxicity
and broad spectrum of antimicrobial activity. PHMB is particularly suitable
for cotton and cellulosic textiles and can be applied to blends of cotton
with polyester and nylon. In addition to the aforesaid antimicrobial agents,
the fibres derived from synthetic with built-in antimicrobial properties are
listed in Table 2.
Benefits of antimicrobial textiles
A wide range textile product is now available for the benefit of the
consumer. Initially, the primary objective of the finish was to protect
textiles from being affected by microbes particularly fungi. Uniforms,
tents, defence textiles and technical textiles, such as, geo-textiles have
therefore all been finished using antimicrobial agents. Later, the home
textiles, such as, curtains coverings, and bath mats came with antimicrobial
finish. The application of the finish is now extended to textiles used for
outdoor, healthcare sector, sports and leisure.
Novel technologies in antimicrobial finishing are successfully employed
in nonwoven sector especially in medical textiles. Textile fibres with
built-in antimicrobial properties will also serve the purpose alone or in
blends with other fibres. Bioactive fibre is a modified form of the finish,
which includes chemotherapeutics in their structure, ie, synthetic drugs of
bactericidal and fungicidal qualities. These fibres are not only used in
medicine and health prophylaxis applications but also for manufacturing
textile products of daily use and technical textiles.
The field of application of the bioactive fibres includes sanitary
materials, dressing materials, surgical threads, materials for filtration of
gases and liquids, air conditioning and ventilation, constructional
materials, special materials for food industry, pharmaceutical industry,
footwear industry, clothing industry, automotive industry, etc.
Evaluation of antimicrobial activity
Various test procedures have been used to demonstrate the effectiveness
of the antibacterial activity. Some of the tests used are:
Agar diffusion test.
Challenge test (Quantitative).
Soil burial test.
Humidity chamber test.
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. Objective evaluation of
the antimicrobial activity is arrived at by making use of the challenge test
where in which the difference between the actual bacterial count of the
treated and untreated material is accounted for.
A series of test methods are available from AATCC (USA), DIN
(International), JIS (Japan) and SN (Switzerland). The degree of
antimicrobial activity of the active substance is expressed by the terms
specific antimicrobial activity and general antimicrobial activity. The
general activity or the bactericidal effect in the Japanese standard is
based on the difference between the initial bacteria count on the
non-modified material (Ma value) and the bacteria count of the modified
material after 18 h of incubation (Mc value). The specific antimicrobial
activity or bacteriostatic effects is based on the difference between the
bacteria count of the reference value (Mb value) and the sample after 18 h
of incubation (Mc value). Due to the limitations of the existing system, a
new test system ISO/TC/38/WG23 (test methods for antimicrobial finished
textile products) has been evolved by considering the technological,
dermatological and ecological aspects of the finish.
Evaluation of the influence of module and fungi
The influence of mould fungi is evaluated by three practical test methods:
At the growth test with a mixture of five
different mould fungi it is evaluated how far the textile is supporting
the fungus growth. The evaluation is not done only visually, but also
material specific force elongation ratio is measured.
In an inhibition zone test, the question is
answered, if the tested finishing agent is protecting the textile from
mould stains and mould over growth. The evaluation is done by rating the
fungus growth in contact to test material and the viewing of the
inhibition zone around the test sample in consequence of the diffusion
of the antifungal agent.
The third test the so called wet chamber test
answers the question how a mould fungus contaminated textile performs in
the wet chamber the evaluation is done visually by viewing the degree of
growth or through tensile strength test.
With advent of new technologies, the growing needs of the consumer in
the wake of health and hygiene can be fulfilled without compromising the
issues related to safety, human health and environment. Taping new potential
antimicrobial substances, such as, Chitosan from nature can considerably
minimise the undesirable activities of the antimicrobial products.
Scientists all over the globe are working in the area and a few of them
reported to have used antimicrobial finishes and fluoro chemicals to make
the fabric having antimicrobial as well as blood repellant properties.
Chitosan and fluoro polymers are reported to be most suitable finishing
agents for medical wears with barriers against micro organisms and blood. To
carve a niche for textile materials, this kind of value adding finishes are
the need of the hour.
H Mucha, D Hoter and M Swerev: Antimicrobial
Finishes and Modifications, Melliand International, May 2002, Vol 8, pp
I Home: Antimicrobials Impart Durable Finishes,
International Dyer, December 2002, pp 9-11.
S Rajendran and S C Anand: Development of
Versatile Antimicrobial Finish for Textile Materials for Health Care and
Hygiene Applications, Bolton Institute, UK.
D Gupta: Antimicrobial Finishing of Textiles, www.resil.com.
E Menezes: Antimicrobial Finishing of Textiles,
The Textile Industry and Trade Journal, January-February 2002, pp 35-38.
S Zikeli: Bioactive Cellulosic, Textile Asia,
January 2003, pp 35-39.
Ha-Soo Seong, J P Kim and S W Ko: Preparing Chito
Oligosaccharides as Antimicrobial Agents for Cotton, Textile Research
Journal, Vol 69, No 7, pp 483-488.
W Huang and K K Leonas: Evaluating a One-bath
Process for Imparting Antimicrobial Activity and Repellency to Nonwoven
Surgical Gown Fabrics, Textile Research Journal, Vol 70, No 9, pp
B Clemo: Applying Ultra Fresh, The Resilient, pp
Y Yang, et al: Durability of Some Antibacterial
Treatments to Repeated Home Launderings, Textile Chemist and Colorist
and American Dyestuff Reporter, April 2000, Vol 32, No 4, pp 44-49.
K Schatz: All-round Answer to Problem Microbes,
International Dyer, June 2001, pp 17-19.
T Wierzbowska, et al: Nonwoven Fabrics of
Bactericidal and Fungicidal Qualities from Biocidemodified Fibres, Asian
Textile Journal, December 2000, pp 95-98.
The author is a Lecturer with the Department of
Textile Technology, KSR College of Technology, Tiruchengode.