28 Antimicrobial Finishes

K Kalaiarasi

epgp books

 

 

 

 

    Introduction

 

There is a growing interest all over the world for functionality of textile products such as water proof, wrinkle resistance, UV – protection, flame resistance and resistance to microbial attack. Among the functional finishes, antimicrobial finishes of textiles are considered as the most significant because fabrics are considered as second skin. The intrinsic properties of the textile fibres offer suitable environment for the microbial growth. Microbial infiltration causes cross infection by pathogens, development of odour, staining and loss of performance properties of textile materials. The textile substrates and the products are finished with antimicrobial agents to protect the consumers and the products.

 

Consumers are conscious of health and hygienic life style. They prefer textile materials that have antimicrobial properties. Hence there is a global demand for antimicrobial finished textile materials especially in the field of medical textiles. Numerous antimicrobial agents are available for textile finishing like triclosan, silver nano particles, quaternary ammonium compounds etc. However, due to their synthetic origin, they affect the environment.

 

Hence natural antimicrobial agents are gaining momentum for its excellent therapeutic potential and efficiency in treating infectious diseases. Natural antimicrobial agents like neem, eucalyptus, turmeric, Aloe vera etc., have received greater attention due to their nontoxic and environment friendly nature.

 

Objectives

  • To enable the students to know about the different antimicrobial agents
  • To understand the need, application and uses of antimicrobial finished fabrics To know about the assessment and standards for antimicrobial finish

   Microorganisms

 

Microorganisms such as bacteria, fungi, algae and viruses are the tiniest creatures which cannot be seen with the naked eye. Microbes grow and multiply very rapidly under optimal conditions. Bacteria are subdivided in to Gram positive, Gram negative, spore bearing or non-spore bearing type. Few bacterial species are pathogenic, cause diseases and produce infection. Fungi, moulds or mildew are complex organisms that weaken the fabrics and decrease their performance properties. Fungi are active at slightly acidic pH of 6.5. Algae are typical microorganisms which require water and sunlight to grow. They produce darker stains on the fabrics and are active at neutral pH range.

 

Textiles as carriers of microorganisms

 

Natural fibres are easily attacked by microbes because they retain water readily and microbial enzymes readily hydrolyse their polymer linkages. Cellulosic fibres such as cotton, jute, wool and flax are most susceptible to microbial attack. Microbes, both pathogenic and odour causing adhere to the fibres and leads to subsequent growth and damage to the fibres.

 

In synthetic fibres, the microbial growth is slower as compared to natural fibre because they do not retain much water. These fibres retain the stale perspiration in the interstices resulting in the microbial growth and multiplication. If the synthetic fibres are coated with finishing agents like polyethylene and polysiloxane emulsions, they allow the microorganisms to degrade the polymer. Under conducive conditions, nylon, polypropylene and polyester fibres are also susceptible to microbial attack.

 

Effect of microbial growth on textiles

 

The presence of microorganisms in textile substrate causes health problems, odours and finally fabric deterioration. Microbial attack leads to discolouration and loss of functional properties like elasticity and tensile strength. During the growth of microorganisms, they breakdown nutrients such as sweat and soil and produce odour causing molecules. For example, Gram positive bacteria S.aureus generate 3-methyl 1,2 hexanoic acid which causes unpleasant body odour. Also bacteria convert human perspiration in to foul smelling substances such as carboxylic acid, aldehydes and amines. Proteus vulgaris a Gram negative bacteria, breakdown urea into ammonia and leads to the generation of odour in baby diapers.

 

Garments provide moisture and darkness and thus enhance the microbial infections. Clothing soiled by urine and faeces promote the growth of E.coli and Brevibacterium ammoniagens. Proteus mirabilis enhances diaper rashes and associated infections. Aspergillus species produces lung diseases.

 

Microbial growth increases with increasing moisture at neutral pH (7-8). They grow well in dark except phototropic species. They produce pigments on exposure to light and cause coloured stains on fabric.

 

Need for antimicrobial finish

  • To protect the textile materials from microbial degradation, discolouration and staining
  • To prevent cross infection by pathogenic microorganisms
  • To inhibit the colonisation of odour causing microbes
  • To increase fabric durability
  • Reduce the frequency of laundering and thereby saves water and energy

Classification of Antimicrobial Finish

 

Antimicrobial finish is sub divided into three main groups:

 

1) Rot proofing: Antimicrobial finish is given to textile substrate to provide p r o t e c t i o n either long term or short term against physical deterioration.

 

2) Hygiene finishes: In this method antimicrobial finish is applied to textile substrate to control infection by unwanted microbes.

 

3)Aesthetic finishes: In this method, antimicrobial finish is given to control odour development and staining.

 

Antimicrobials

 

The term ‘antimicrobial’ refers to substances that provide protection to textile materials against microorganisms. Antimicrobials differ in their structure, chemical composition, mechanism of action, durability, interaction with microorganisms and impact on human and environment. Antimicrobial agents that inhibit the growth of microorganisms are known as biostats eg: bacteriostats that inhibit growth of bacteria, fungistats that inhibit the growth of fungi. Antimicrobial agents that destroy or kill the microbes are known as biocides ie: bacteriocides, fungicides.

 

Mode of action

 

Antimicrobial agents act in various ways.

 

The main modes of action are:

 

1.Coagulation of protein

2.Disruption of cell membrane which maintains the integrity of cellular contents

3.Removal of free sulfhydryl groups essential for function of enzymes.

4.Inhibition of key enzymes responsible for the metabolism of the cell

 

Antimicrobial agents function in two different ways.

 

Leaching type: In this type, the antimicrobial substances diffuse into the growth medium and destroy the microbes coming into contact with it. The leaching type anti-microbial agents are not chemically bonded with the fabrics and can be removed by contact with moisture. The major disadvantage in this type of finish is poor durability and it may penetrate the skin and cause skin irritations and rashes.

 

Non-leaching type or biostatic finish: The antimicrobial agents are molecularly bonded with the fabric substrate. They would not diffuse off from the fabric substrate but inhibits the microbes approaching the textile surface. They do not lose their effectiveness by becoming depleted. They do not cause harm to anything other than microorganisms and so may not cause any health problems. These agents do not lose their effectiveness even on repeated laundering and hence exhibits good durability. This type is most suitable for textile materials that are having human contact and durability is considered.

 

The antimicrobial agent adsorb onto the surface of the negatively charged bacterial cell and leads to the disruption of the cytoplasmic membrane thus inhibiting the microorganisms.

 

Based on the activity against microorganisms, the antimicrobial finished textile materials are categorized into two types, namely, active and passive. Active antimicrobial textiles act against microbes and destroy it whereas the surface structure of passive material creates negative influence on the living environments of microorganisms.

 

Characteristics of good antimicrobial agent

 

Must exhibit broad spectrum of activity against bacterial and fungal species It must be non – toxic to consumer and environment Should not cause irritation and allergy Durable to washing, dry-cleaning and hot pressing

 

Should not affect the strength, appearance and handle of the fabric Should not kill the residence flora on the skin of the wearerSelective activity against undesirable micro organisms Must not have any side effects for the producer, consumer and environment. Easily applicable.

 

Types of antimicrobial agents

 

Antimicrobial agents used in textile industry are of two types:Natural and synthetic

 

Natural antimicrobial agents

 

The sources of natural antimicrobial agents are medicinal plants, marine and terrestrial organisms, including fungi and bacteria. Herbs including Aloe Vera, Marigold and Neem extract have antimicrobial activity. Compounds extracted from different parts of plants such as bark, leaves, roots and flowers containing common coloring materials such as tannin, flavonoids and quinonoids exhibit strong antimicrobial properties. These antimicrobials are eco-friendly and non-toxic.

 

Neem extract

 

Neem (Azadirachta indica), belong to the family Meliaceae (mahogany). The bioactive substances of neem are present in all parts of the tree, but for extraction generally the bark, leaves, seed and roots are used. The neem extract has a potential to inhibit the growth of both Gram positive and Gram negative bacteria.

 

Aloe vera

 

Aloe vera (Aloe barbadensis) belongs to the family Liliaceae. It is also called as ‘Lily of the desert’. Aloe vera gelis widely used as a skin care product. Aloe Vera exhibits antimicrobial properties, hence it is utilised for medical textile applications, such as wound dressings, etc.

 

Prickly chaff flower

 

Achyranthus aspera (Prickly Chaff Flower) is the commonly used medicinal plant which possesses antimicrobial activity and act against both Gram-positive and Gram-negative bacteria.

 

Tulsi leaves

 

Tulsi (Osmium basilicum) belongs to Labiacea family. Tulsi leaves are used as antimicrobial, insecticidal and antiprotozoal agent.

 

Turmeric

 

Curcumin, a yellow pigment present in turmeric possess antimicrobial property. It exhibits bactericidal activity.

 

Chitosan

 

Chitin, a poly (β-(1-4)-N-acetyl-D-glucosamine) is a natural polysaccharide. Chitin is found in many naturally occurring creatures such as yeast, fungi, bacteria and it is the prime constituent in the exoskeleton of crustaceans like crab, shrimp and insects. It is the most abundantly found polymer second only to cellulose. When chitin is acetylated to at least about 50%, then it is called chitosan. Chitosan has inherent antibacterial activity, biocompatibility and biodegradability. The positively charged chitosan interacts with negatively charged residues at the cell wall of fungi or bacteria. The interaction changes cell permeability and causes the leakage of intracellular substances.

 

Sericin

 

Sericin is a natural protein derived from silk worm Bombyx mori which comprises 25-30% of silk protein. It wraps the fibroin fibres with successive sticky layers that aid in cocoon formation. During the degumming process, sericin is removed. Sericin has antibacterial, UV resistant, oxidative resistant and moisturizing properties.

 

Natural dyes

 

Natural dyes obtained from various plants possess anti-microbial properties. Pomegranate (Punica granatum) is a potent antimicrobial agent due to the presence of tannins. Tannins possess antimicrobial activity against wide range of bacteria and fungi. Henna rich in naphthoquinones and walnut rich in juglone exhibit antibacterial and antifungal activity. The antimicrobial activity of the textile substrate impregnated with the natural dyes depends on the dye uptake and the presence of functional groups.

 

Synthetic antimicrobial agents

 

Antimicrobial agents that are manufactured by chemical synthesis are called as synthetic antimicrobial agents. Synthetic agents are further classified into organic and inorganic agents.

 

Organic agents

 

Many organic compounds are used as antimicrobial agents including drugs and chemotherapeutic agents.

 

Halogenated phenols

 

Triclosan, a derivative of diphenyl ether reveals broad-spectrum antimicrobial activity. It degrades bacterial cell membrane and inhibits a specific enzyme that the bacterium needs for its survival. It has bacteriostatic activity against a wide range of bacteria.

 

Quaternary Ammonium Compounds (QACs)

 

QAC’s have a silane base at one end of the molecule and a long chain of carbon atoms at the other end. QAC based antimicrobial agent, forms a covalent bond with the fabric. When a microbe approaches the fabric the free end of the QAC molecule reacts with the cell wall and causes leakage of the microbial cell and causes cell death.

 

Polyhexamethylene biguanide (PHMB)

 

The halide form of PHMB i.e., polyhexamethylene biguanide hydrochloride is applied on cellulosic materials. PHMB form hydrogen bonds with cellulosic fibers. When the fabric treated with PHMB comes in contact with a bacterium, the biocide interacts with the surface of the bacteria. This results in the leakage of inner material and causes death of the bacterium.

 

Monomethylol-5,5-dimethylhydantoin (MDMH)

 

MDMH is a hydantoin derivative. It protects cellulosic fabrics from bacterial attack by cleaving the bacterial cell membrane and thereby inhibiting the growth of bacteria. It is covalently bonded with the fabric. It exhibits good antibacterial activityagainst both Gram-positive and Gram-negative bacteria.

 

Inorganic metals and its oxides

 

Silver

 

Silver is an important tbroad-spectrum antimicrobial agent and is widely used in textiles. Silver is generally safe and effective in controlling bacteria. Blending of silver with the polymer during or prior to extrusion of fibre and fibre or fabric coating are the two important methods for incorporating silver in textiles. Silver is inert in metallic form but ionic silver is effective against several different microorganisms including E.coli, Candida and Pseudomonas aeruginosa.

 

Silver in ionic form is commonly applied on fabrics used in wound dressings. Silver ions destroy the bacterial cells by inhibiting the enzymes found in cell membranes. Silver ions interfere with bacterial electron transport and inhibit DNA replication.

 

Nanosilver has gained attention in its application to textiles. The nanosilver particles are effective because of the large surface area to mass ratio and modified surface charge.

 

Copper is an important disinfecting agent that is used from time immemorial. Copper is added during fibre formation or it is applied on the surface of textile materials. It is a safe antimicrobial agent but it is not as efficient as silver.

 

Zinc exhibits antimicrobial activity. Fabric with zinc sulphate exhibited antibacterial activity against S. aureus and E. coli. Zinc nanoparticles (zinc oxide) also acts as effective antimicrobials.

 

Antimicrobial finishing methods

 

Antimicrobial agents are generally applied to textile products as final finishing process whereas in some cases, it is applied in the fiber stage. For synthetic fibers, the antimicrobial agent is incorporated during extraction.

The textile fabrics can be finished with antimicrobial agents by different methods

 

1)By using spun in additives: Antimicrobial agents are added to the dope solution during the manufacturing process of manmade fibres or yarns.

 

2)Padding: This method is simple and easy to perform. But the durability of the finish is poor because of weak linkages between the fibers and antimicrobial agents. In this method the fabric is immersed in aqueous solution containing antimicrobial agents for 5 -10mins and padded through squeeze rolls. The fabrics are then dried and cured at specific temperature and time.

 

3)Exhaust method: The fabric is soaked in solution containing antimicrobial agents and allowed to reach equilibrium. This method enables the movement of finishing agents from the solution on to the fabric until it is completely exhausted.

 

4)Spraying:   Spraying of solution containing antimicrobial agent is not recommended, due to the risk of inhalation. This   method is    particularly suitable for nonwoven fabrics.

 

5)Micro-encapsulation: Microencapsulation is a process in which liquid droplets or smaller particles are coated with continuous film of polymeric material. It is an important technique for imparting functional finishes to textile materials. The capsules formed are applied to fibres by padding, impregnation, exhaust and spraying techniques.

 

6)Polymer modification: Polymer modification is brought about copolymerizing antimicrobial agent with fibre monomers. Durability of the finish is higher when compared to other techniques as the biomaterial form an integral part of the fibre. This method is costly as it requires distinct polymerization units.

 

7)Nanotechnology: cotton fabric finished with nanoparticles prepared from neem extract exhibited excellent antimicrobial activity. Antimicrobial activity was retained even after 25 washes whereas the fabric coated with neem extract retained the antimicrobial activity only upto 10 washes.

 

Methods for improving the durability of the finish

 

cross linking agents are used to link bioactive substances and fibremicro encapsulation of antimicrobial agents on the surface of the fibre covalent bond formation between fibre and antimicrobial agents copolymerization on to the fibre.

   Determination of antimicrobial activity

 

Numerous methods are used to assess the antibacterial activity namely agar diffusion, quantitative analysis, soil burial, humidity chamber and fouling tests respectively.

 

Agar diffusion test is a preliminary test to identify the diffusive antimicrobial finish and is not appropriate for non-diffusive finishes. In quantitative analysis, the difference between the bacterial count of the finished and unfinished material is assessed.

 

Evaluation of anti-fungal activity

 

The anti-fungal activity of the textile material is determined by three methods:

  1. Growth test: A mixture of five different mould or fungi is allowed to grow on the fabric and how far the textile material is supporting the growth of fungi is evaluated.
  2. Zone inhibition test: The inhibition zone formed around the bioactive material is assessed.
  • Wet chamber test: The rate of growth of fungus in wet chamber on the contaminated fabric is assessed visually or by measuring the strength of the fabric.

Applications

 

Anti-bacterial finish is used in apparel and sportswear. The anti-bacterial finished undergarments prevent skin related diseases and urinary tract infection. It is also desirable for baby clothing as their thin skin is permeable and highly sensitive to microbes. Antimicrobial finish is given to industrial fabrics like tents and ropes to protect it from mildew and rotting, to home furnishing textiles such as carpets, shower curtains and upholstery, to textiles used in museums, hospitals, hotels, crowded public places and schools as they have the risk of getting infection.

 

Conclusion

 

Increasing consumer awareness on hygienic products ends in value based textile resource materials. Consumers are looking for resolution to microbial problem and the exclusive benefits afford by antimicrobial finish. Potential antimicrobial agents from nature can minimise the detrimental activities of the antimicrobial products. Textile materials, finished with natural antimicrobial agents are the need of the hour.

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