Protection from Micro-organism

Textile materials and clothing are known to be susceptible to microbial attack, as these provide large surface area and absorb moisture required for microbial growth. Natural fibers have protein (keratin) and cellulose, etc., which provide basic requirements such as moisture, oxygen, nutrients and temperature for bacterial growth and multiplication. This often leads to objectionable odor, dermal infection, product deterioration, allergic responses and other related diseases.

Microorganisms cause problems with textile raw materials and processing chemicals, wet processes in the mills, roll or bulk goods in storage, finished goods in storage and transport, and goods as they are used by the consumer. This can be extremely critical to a clean room operator, a medical facility, or a food processing facility, or it can be an annoyance and aesthetic problem to the athlete or normal consumers.

Antimicrobial finish

The term ‘Antimicrobial’ refers to a broad range of technologies that can provide varying degrees of protection for textile products against microorganisms. Antimicrobials are very different in their chemical nature, mode of action, impact on people and the environment, inplant handling characteristics, durability on various substrates, costs, and how they interact with good and bad microorganisms.

What are microbes?

Microbe type	Description	Causes	Treat with
Bacteria	Simple structure. Fast growing in warmth and moisture	more destructive to cotton fiber. Unpleasant odors (e.g. E. coli), pathogenic and cross infection	Antimicrobial agent
Fungi, molds and mildews	Complex structure, slow growth rate, active at pH level 6.5	Staining and loss of performance. Skin infections (e.g. athletes foot)	Antimycotic agent
Algae, dust mites	Either fungal or bacterial. Active at pH 7-8, require continuous sources water and sunlight to grow	Darker stains. Dust mite occupies the household textiles such as blankets bed linen, pillows, mattresses and carpets. Allergic reactions and respiratory orders.	Antimicrobial and Antimycotic agent

How micro-organism works?

Cotton is biologically degraded by several microorganisms. Micro-organisms do not directly attack the substrate upon which they live. They are able to manufacture very complex non-living molecules called ‘enzymes’ which have the power to break down cellulose. These enzymes are solubilizing biocatalysts, proteinaceous, and highly specific. They enable complicated chemical reactions to occur under mild conditions even though the amount present at any time may be very small, for example, 0.001 to 0.01% on the weight of the substrate. Cellulolytic enzymes are not produced on the cellulose on the absence of cellulose. These enzymes are locally absorbed on the cellulose chains and it is proposed that different steps of degradation may occur.

Figure: How cellulose is broken down under the influence of an enzyme. The diagram illustrates cleavage of a "glycosidic" bond in cellulose (a polymer of glucose) by reaction with a molecule of water. This hydrolysis, the fundamental step in the biodegradation of cellulose, which would otherwise be immeasurably slow, is accelerated by the presence of an "enzyme", or biocatalyst. The insoluble polymer is converted into soluble sugars which can then be metabolized inside the bacterial or fungal cells.

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, defense textiles and technical textiles, such as, geotextiles have therefore all been finished using antimicrobial agents.

• Later, the home textiles, such as, curtains coverings, & 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 non-woven sector especially in medical textiles.

• Textile fibers with built-in antimicrobial properties will also serve the purpose alone or in blends with other fibers. Bioactive fibers are not only used in medicine and health applications but also for manufacturing textile products of daily use and technical textiles. The field of application of the bioactive fibers 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.

Necessity of Antimicrobial Finishes

Antimicrobial treatment for textile materials is necessary to fulfill the following objectives:

1. To avoid cross infection by pathogenic micro-organisms;

2. To control the infestation by microbes;

3. To arrest metabolism in microbes in order to reduce the formation odor; and

4. To safeguard the textile products from staining, discoloration and quality deterioration.

Requirements of Antibacterial finish

1. Effective against a wide range of micro-organisms, particularly bacteria and microfungi.

2. Active during the life of the product.

3. Of low mammalian toxicity and non-toxic to humans at the concentrations used.

4. Colorless and odorless.

5. Effective at low concentrations.

6. Inexpensive and easy to apply.

7. Resistant to sunlight and heat.

8. Not affecting fabric handle or strength.

9. Compatible with water-repellent and flame-retardant agents, dyes, and other textile auxiliaries.

10. Does not sensitize the fabric to damage by light or other influences.

11. Should not produce harmful effects to the manufacturer, user and the environment.

Factors for micro-organism growth

1. Moisture: micro-organism requires moisture for their growth and with the increase in moisture content (MC %) of the material, the microbial growth and attack increases. It has claimed that,

At 10% MC of sample, about 1.4 million organisms per gram of raw cotton

At 50% MC of sample, about 9000 million organisms per gram of raw cotton

2. Temperature: Most of the organisms exhibit a rapid destructive action on cotton fabrics at a temperature from 25-30ºC.

3. pH: the growth of micro-organism is highly affected by the pH and most cellulose destroying bacteria are active at pH 7-8

4. Laundering: laundering also caused little observable surface damage to cotton fiber but it was observed that damage to cotton fiber by microbial attack increases with each laundering. Severe damage was noticed after 10th laundering, suggesting that possible physical breakdown may have made the fibers more accessible to microbial attack.

Mechanism of Antimicrobial Activity

Negative effect on the vitality of the microorganisms 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. The activity which affects the bacteria is known as antibacterial and that of fungi is antimycotic.

Fungi (Bacteriostatic agent)	Fungi (Bactericidal agent)
Non-leaching or ‘biostatic’- provides a textile surface structure unsuitable for microbe growth.	Leaching- diffused out of the fabric and kills any fabric present, inhibiting further growth
Slower acting Work by inhibiting of microbial growth	Faster acting Causes significant destruction of microbes
Good durability Less health and environmental risk Increased microbial development to resistance	Poorer durability Potentially higher health and environmental risk Decreased microbial development to resistance
Example: Silver based compounds, tributyltin maleate – controls bacteria and fungal growth	Example: chloroxynol (both fugicidal and bactericidal)

Methods of Proofing

1. By physical barrier

2. By the addition of toxic substances to the fiber

3. By chemical modification of the cotton fiber

4. by Silicone quaternary ammonium compound

By Physical barrier

The microbial degradation of cotton fibers is localized and it requires direct contact between the organism and the fiber. It should be possible to prevent microbiological attack on cellulose by imposing a continuous, inert physical barrier or film between the attacking agent and the substrate.

Coating materials such as paraffin, chlorinated paraffin, and rubber, have been used with cotton yarns, netting, ropes, canvas etc as a rot proofing agent. It was claimed that a net treated with such materials was found to retain its strength for over 54 months when immersed in water as compared to only 2.5 months for untreated net of the same type.

Proofing by toxic agents

To obtain resistance to microbial attack toxic inhibitors can be applied o fibers, silver, yarn or fabric at sizing, dyeing or other stages of manufacture. Toxic agents that are used for this purpose are

Inorganic inhibitors: The most popular are compound of copper. The copper compounds are normally applied from solution, for example, cuprammonium carbonate, cuprammonium hydroxide, cuprammonium fluoride to give copper concentrations on the fabric of 0.8% to 2%.

The compounds of zirconium, titanium, thorium, cerium, lanthanum and didymium can also be used which has been claimed to have very good mildew resistance together with some degree of water repellency.

Organic inhibitors: Phenolic compounds are one of the most popular mildew proofing agents used in the past including polychlorophenols, the diarylmethanes and the acrylamides. Among many phenolic compounds, chlorinated phenol is more popular as mildew and rot proofing agents. Pentachlorophenol is one of the most widely used and most active chlorinated phenolic compound. They are used in wide range of textiles including cotton, flax, and jute fabrics used as covers, tarpaulins, shop blinds, tents, etc.; also carpet backings, coated fabrics, hospital materials, mattress covers, pressed felts and woollen textiles.

The main drawback of pentachlorophenol is its lack of durability, but permanence can be increased by a resin coating.

Proofing by chemical modification:

Cellulosic fabrics have been made resistant to degradation by cellulolytic micro-organisms by chemical modifications. These modifications includes

• Acetylation

• Cyanoethylation

• Phosphorylation

• Reaction with formaldehyde

Acetylation: Acetylation is the earliest process and the degree of resistance depends on the amount of acetylation as the figure shows

Acetylation (%)	Acetyl per anhydroglucose	% of strength retention (week)
		10	30	50
0	0.0	0	0	0
19	0.9	42	22	0
25	1.2	85	67	48
30	1.4	104	100	91

Cyanoethylation: Cyanoethylation involves introduction of cyanoethyl groups into some of the glucose units of the cellulose by an ether linkage. This occurs by reaction with hydroxyl groups in the cellulose:

cell-OH + CH₂=CHCN cell-OCH₂-CH₂-CN

cellulose acrylonitrile cyanoethyl cellulose

It has mentioned that the blocking of only one hydroxyl group per anhydroglucose unit brings about resistance to microbial degradation, which also brings resistance to heat and resistance to rotting.

Phosphorylation: Chemical modification is also done by treating fabric with an aqueous solution of phosphoric acid followed by drying and curing at temperature at 150 to 200ºC. The phosphate ester of cellulose produced has good flame and mildew resistance properties.

Reaction with formaldehyde: Treatment with formaldehyde can also protect cotton fiber from microbial degradation. The reaction goes:

2cell-OH + HCHO cell-O-CH2-O-cell

cellulose formaldehyde cross linked cellulose

Formaldehyde content synthetic resin finish also protects cotton fiber from bacterial and fungal attack. One important disadvantage of formaldehyde treatment of cotton fabric is the considerable loss in tensile strength.

Silicone quaternary ammonium compound

A significantly different and much more unique antimicrobial technology used in the textile industry does not leach but instead remains permanently affixed to the surface it is applied to.

Applied in a single stage of the wet finish process, the attachment of this technology to surfaces involves two means. First and most important is a very rapid process, which coats the substrate (fabric, fiber, etc.) with the positive ion. This is an ion exchange process by which the cation of the silane quaternary ammonium compound replaces protons from water or chemicals on the surface.

The second mechanism is unique to materials such as silane quaternary ammonium compounds. In this case, the silanol allows for covalent bonding to receptive surfaces to occur.

The technology stays on the substrate it does not cross the skin barrier and does not affect normal skin bacteria, cause rashes or skin irritations.

Commercial Antimicrobial Agents and Fibers

Company	Brand	Properties
Ciba Speciality Chemicals	Tinosan AM 110	Durable antimicrobial agent for textiles made of polyester and polyamide fibers and their blends with cotton, wool or other fibers.
Clariant	Sanitized AG	Both natural and synthetic fibers.
Avecias	Purista-branded based on poly (hexamethylene) biguanide hydrochloride (PHMB)	particularly suitable for cotton and cellulosic textiles and can be applied to blends of cotton with polyester and nylon
Devan	Aegis	Poly cationic, porous and absorbent properties. Fibers finished with these substances bind micro organisms to their cell membrane and disrupt the lipo poly saccharide structure resulting in the breakdown of the cell.

Evaluation of Antimicrobial Activity

Various test procedures have been used to demonstrate the effectiveness of the antibacterial activity. Some of the tests used are:

1. Agar diffusion 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.

2. Challenge test (Quantitative). 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).

3. Soil burial test.

4. Humidity chamber test.

5. Fouling tests.