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Antimicrobial finishes

Two different aspects of antimicrobial protection

INTRODUCTION

Two different aspects of antimicrobial protection provided by chemical finishes

can be distinguished

The first is the protection of the textile user against

pathogenic or odour causing microorganisms (hygiene finishes).

The second aspect is the protection of the textile itself from damage caused by

mould, mildew or rot producing microorganisms.

INTRODUCTION

The growth of microorganisms on textiles can lead to

functional, hygienic and aesthetic difficulties (for example staining).

The most trouble-causing organisms are fungi and bacteria.

Under very moist conditions, algae can also grow on textiles but are troublesome only because

they act as nutrient sources for fungi and

bacteria.

INTRODUCTION

Fungi cause multiple problems to textiles including

discoloration, coloured stains, and fibre damage.

Bacteria are not as damaging to fibres, but can produce

some fibre damage,

unpleasant odours

and a slick, slimy feel.

Often, fungi and bacteria are both present on the fabric in a symbiotic relationship.

INTRODUCTION

Substances added to fibres, such as lubricants, antistats, natural-based auxiliaries (for example size, thickener and hand modifiers) and dirt provide

a food source for microorganisms.

Synthetic fibres are not totally immune to microorganisms, for example

polyurethane fibres and coatings can be damaged

Wool is more likely to suffer bacterial attack than cotton,

and cotton is more likely than wool to be attacked by fungi.

INTRODUCTION

Antimicrobial finishes are particularly important for industrial fabrics that are exposed to weather.

Fabrics used for awnings, screens, tents, tarpaulins, ropes, and the like, need protection from rotting and mildew.

Home furnishings such as carpeting, shower curtains, mattress ticking and upholstery also frequently receive antimicrobial finishes.

Fabrics and protective clothing used in areas where there might be danger of infection from pathogens can benefit from antimicrobial finishing. These include hospitals, nursing homes, schools, hotels, and crowded public areas.

INTRODUCTION

Textiles in museums are often treated with antimicrobial finishes for

preservation reasons.

Sized fabrics that are to be stored or shipped under conditions of high temperature (~ 40 C or 100 F) and humidity

require an antimicrobial finish to retard or prevent microbial growth fuelled by the presence of warp size.

Textiles left wet between processing steps for an extended time often also need an

antimicrobial treatment.

Properties of an effective antimicrobial finish

The growth rate of microbes can be astoundingly rapid.

The bacteria population, for example, will double every 20 to 30 min under ideal conditions (3640 C or 7798 F, pH 59).

At this rate, one single bacteria cell can increase to 1 048 576 cells in just 7 hours.

Therefore, antimicrobial finishes must be quick acting to be effective.

Properties of an effective antimicrobial finish

In addition to being fast acting, a number of other important criteria can be listed for antimicrobial finishes.

The antimicrobial must kill or stop the growth of microbes and must maintain this property through multiple cleaning cycles or outdoor exposure.

The antimicrobial must be safe for the manufacturer to apply and the consumer to wear.

The finish must meet strict government regulations and have a minimal environmental impact.

The antimicrobial finish must be easily applied at the textile mill, should be compatible with other finishing agents, have little if any adverse effects on other fabric properties including wear comfort, and should be of low cost.

Mechanisms of antimicrobial finishes

two types based on the mode of attack on microbes


a variety of chemical finishes have been used to produce textiles with demonstrable antimicrobial properties.

These products can be divided into two types based on the mode of attack on microbes.

One type consists of chemicals that can be considered to operate by a controlled-release mechanism.

The second type of antimicrobial finish consists of molecules that are chemically bound to fibre surfaces.

controlled-release mechanism

The antimicrobial is slowly released from a reservoir either on the fabric surface or in the interior of the fibre.

This leaching type of antimicrobial can be very effective against microbes on the fibre surface or in the surrounding environment.

However, eventually the reservoir will be depleted and the finish will no longer be effective.

In addition, the antimicrobial that is released to the environment may interfere with other desirable microbes, such as those present in

waste treatment facilities.

Molecules that are chemically Antimicrobial finishes bound to fibre surfaces

These products can control only those microbes that are present on the fibre surface, not in the surrounding environment.

Bound antimicrobials, because of their attachment to the fibre, can potentially

be abraded away

or become deactivated

and lose long term durability.


Antimicrobial finishes that control the growth and spread of microbes are moreproperly called biostats, i.e. bacteriostats, fungistats.

Products that actually kill microbes are biocides, i.e. bacteriocides, fungicides.

This distinction is important when dealing with governmental regulations, since biocides are strongly controlled.


The actual mechanisms by which antimicrobial finishes control microbial growth are extremely varied, ranging from

preventing cell reproduction,

Blocking of enzymes,

reaction with the cell membrane (for example with silver ions) to the destruction of the cell walls

and poisoning the cell from within.

An understanding of these mechanisms, although important for microbiologists, is not really a requirement for the textile chemist who applies and evaluates the effectiveness of antimicrobial finishes.

Chemistry of antimicrobial finishes

Antimicrobials for controlled release

Bound antimicrobials


Many antimicrobial products that were formerly used with textiles are now

strictly regulated because of their toxicity and potential for environmental damage.Products such as

copper naphthenate,

copper-8-quinolinate,

and numerous organo mercury compounds fall into this category.

Antimicrobials for controlled release Limited Use materials

Other materials that still have limited use in specialised areas include

tributyl tin oxide (deleted in many countries, Fig. 15.1a),

dichlorophene (Fig. 15.1b)

and 3-iodo-propynyl-butyl carbamate (Fig. 15.1c).

These products typically show a very broad spectrum of activity against bacteria and fungi, but suffer from application and durability problems

Antimicrobials for controlled release General Type

Some more useful products of this same general type include

benzimidazol derivatives,

salicylanilides

and alkylolamide salts of undecylenic acid (particularly effective against fungi).

Application of these materials with resin precondensates can improve durability to laundering, but also deactivation by reaction with the resin may occur.

Antimicrobials for controlled release - Formaldehyde

A widely used biocide and preservation product is formaldehyde.

Solutions of formaldehyde in water, called formalin, were used for disinfection and conservation,

for example, of biological samples for display. Bound formaldehyde is

released in small amounts from common easy-care and durable press finishes

Therefore these finishes include at least until they are washed a small antimicrobial side effect.

This can also be true for some quaternary compounds,

for example wet fastness improvers and softeners.

But for more effective requirements specific antimicrobial finishes are necessary.

Antimicrobials for controlled release-TRICLOSAN

One of the most widely used antimicrobial products today is

2,4,4'-trichloro-2'- hydroxydiphenyl ether, known more commonly as triclosan (Fig. 15.1d).

Triclosan finds extensive use in mouthwashes, toothpastes, liquid hand soaps, deodorant products, and the like.

Although it is effective against most bacteria, it has poor antifungal properties.

Triclosan is also important as a textile finish, but since its water solubility is very low, aqueous application requires use of dispersing agents and binders.

Antimicrobials for controlled release-Quaternary Ammonium Salts

Quaternary ammonium salts have been found to be effective antibacterial agents

in cleaning products

and for disinfecting swimming pools

and hot tubs.

However, their high degree of water solubility limits their use as textile finishes.

Antimicrobials for controlled release-ORGONO SILVER

Research into controlled-release antimicrobials continues with

organo-silver compounds and silver zeolites,

which are promising candidates for textile finishes.

Silver ions, for example, incorporated in glass ceramic, have

a very low toxicity profile

and excellent heat stability.

These principles are also used for fibre modification, an alternative to the antimicrobial finishes with high permanence.

Antimicrobials for controlled release FIBER MODIFICATION

In recent years a variety of antimicrobial modified fibres have been developed,

including polyester,

nylon,

polypropylene

and acrylic types.

An example of these fibre modifications is the incorporation of 0.52 % of organic nitro compounds (for example based on 5-nitrofurfural) before primary wet or dry spinning.

Regenerated cellulosics can be modified with carboxylic or sulfonic acid groups,

followed by immersing in a solution of cationic antimicrobials which are then

fixed to the cellulose by salt bonds.

Antimicrobials for controlled release MICRO-ENCAPSULATION

A novel approach to the controlled release of antimicrobials is

micro-encapsulation.

These capsules are incorporated either in the fibre during

primary spinning

or in coatings on the fabric surface.

Chemistry of antimicrobial finishes




Several antimicrobial finishes that function at fibre surfaces have been commercialised.

One popular product is based on octa-decyl-amino-dimethyl-trimethoxy-silyl-propyl-ammonium chloride (Fig. 15.2a).

This material can be applied by either exhaust or continuous methods.


After application, a curing step is required to form

a siloxane polymer coating on the fibre surface.

This coating immobilises the

antimicrobial part of the molecule (the quaternary nitrogen)

and provides the necessary durability to laundering.


Another bound finish has been developed with

PHMB, poly-hexa-methylene biguanide (Fig. 15.2b).

PHMB can also be

either pad

or exhaust applied.

This chemical has the proper molecular structure to bind tightly to fibre surfaces, yet still be an effective antimicrobial.


The antimicrobial effect of

cationically charged materials is thought to involve interaction of the

Cationic molecule with anionic phospholipids in the microbes cell walls.

This interaction is believed to increase the permeability of the cell walls to the point of cell death.


A new and novel approach to bound antimicrobials was recently introduced.

Cotton reacted with

methylol-5,5-dimethyldyantoin

is then treated with hypochlorite

to form chloramines in the fibre (Fig. 15.3).


These chloramine sites have antibacterial activity

and can function as renewable antimicrobial agents by

continued treatment with hypochlorite through household bleaching and washing after reacting with bacteria (Fig. 15.4).

Problems with using higher concentrations of chloramines include

yellowing with heat (for example ironing)

and cellulose ibre damage

especially significant strength loss,

caused by oxy- and hydrocellulose

(generated by hypochlorous acid

Bound antimicrobials -- CHITOSAN

Another novel approach is the application of chitosan.

This modified biopolymer

is manufactured from inexpensive natural waste.

Chitin from crustacean shells (e.g. from crabs) is converted to chitosan by alkaline treatment.

Chitin is an analogue of cellulose with N-acetyl groups instead of hydroxy groups in position 2 (Fig. 15.5).

Bound antimicrobials -- CHITOSAN

Alkali splits most of them (7595 %), generating free amino groups that provide

Fungistatic

and bacterostatic effects.

This mild antimicrobial activity may be amplified

by methylation of the amino groups

to quaternary trimethylammonium structures.

Chitosan can be applied by

microencapsulation

or by reactive bonding to cellulose

and by crosslinking of chitosan.

The advantages of the antimicrobial finish with chitosan include

high absorbency properties,

moisture control,

promotion of wound healing,

non-allergenic,

non-toxic

and biodegradable properties.

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