We are IntechOpen, the world’s leading publisher of Open Access books Built by scientists, for scientists 4,100 116,000 120M Open access books available International authors and editors Downloads Our authors are among the 154 TOP 1% 12.2% Countries delivered to most cited scientists Contributors from top 500 universities Selection of our books indexed in the Book Citation Index in Web of Science™ Core Collection (BKCI) Interested in publishing with us? Contact [email protected] Numbers displayed above are based on latest data collected. For more information visit www.intechopen.com 4 Antibacterial Modification of Textiles Using Nanotechnology Moustafa M. G. Fouda Petrochemical Research Chair, Department of Chemistry, College of Science, King Saud University, KSA 1. Introduction This chapter is undertaken with a view to survey important scientific research and developmental works pertaining to antibacterial modification of textiles using nanotechnology as a new means to achieve such textiles. Inevitably, conventional antimicrobial agents and their applications to textiles are reported. This is followed by a focus on inorganic nanostructured materials that acquire good antibacterial activity and application of these materials to the textiles. Evaluation of the antibacterial efficacy is described. An outlook which envisions the importance of using nanotechnology in the antibacterial finishing of textiles is also outlined. 2. History 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 1940 s, 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 phenals. 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 ITT.s 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 48 A Search for Antibacterial Agents 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 industrial fabrics [2]. 3. Introduction Clothing and textile materials are good media for growth of microorganisms such as bacteria, fungi. According to recent reports, microorganisms could survive on fabric materials for more than 90 days in a hospital environment. Such a high survival rate of pathogens on medically used textiles may contribute to transmissions of diseases in hospitals. As a means to reduce bacterial population in healthcare settings and possibly to cut pathogenic infections caused by the textile materials, utilization of antimicrobial textiles in healthcare facilities is considered to be a potential solution[3]. Textile surface modification provides a way to impart new and diverse properties to textiles while retaining comfort and mechanical strength. Currently, functional finishes on textile fabrics are of critical importance to improve textile products with multifunctional properties. Textile finishes can be divided into aesthetic and functional finishes. Aesthetic finishes are finishes used to modify the appearance or hand of a fiber or fabric. They can alter the texture, luster, or drape of a textile material. Mechanical and chemical processes may be used to impart an aesthetic finish, this type of finishing with a greater emphasis being placed on mechanical processes. Many different chemicals and processes are used in the finishing of textile materials. Functional Finishes that alter fiber or fabric performance, maintenance, durability, safety, and environmental resistance can be considered as functional finishes. Functional finishes are generally applied specifically to alter properties related to care, comfort, and durability. Most functional fabric properties are imparted by using chemical and wet processing methods [4, 5]. Some common functional finishes are listed below: Antimicrobial, Antistatic, Durable press, Flame resistant/retardant, Soil release/resistant, Water proof/repellent, UV Protection, Self cleaning, Wrinkle recovery. This chapter will focus on the antimicrobial finishes of textiles. The driving force behind the chemical finishing of cotton during the next 10 years is anticipated to comprise several factors. Of these factors, mention is made of the following: (i) chemical finishes which maximize the added value; (ii) chemical finishes which are friendly with the environment; (iii) methods which are convenient for application, and (iv) the need for better quality and minimum use of water and energy [6]. In recent years, antimicrobial finishing of textiles has become extremely important in the production of protective, decorative and technical textile products. This has provided opportunities to expand the use of such textiles to different applications in the textile, pharmaceutical, medical, engineering, agricultural, and food industries [7]. Antimicrobial finishing of textiles protects users from pathogenic or odor-generating microorganisms, which can cause medical and hygienic problems, and protects textiles from undesirable aesthetic changes or damage caused by rotting, which can result in reduced functionality. As a consequence of their importance, the number of different antimicrobial agents suitable for textile application on the market has increased dramatically. These antimicrobial agents differ in their chemical structure, effectiveness, method of application, and influence on Antibacterial Modification of Textiles Using Nanotechnology 49 people and the environment as well as cost [8-12]. In the literature [9, 10, 12], there are several different classifications of antimicrobial agents according to efficiency, mechanism of antimicrobial activity and washing resistance. According to these studies, products can be divided into biocides and biostats, leaching and bound antimicrobials, controlled-release and barrier-forming agents, and agents of poor and of good washing resistance. In general, the activity of antimicrobial finishes can be biocidal or biostatic. While the biocides (bactericides and fungicides) include agents that kill bacteria and fungi, the biostats (bacteriostats and fungistats) inhibit the microorganisms’ growth. The mode of action is directly related to the concentration of the active substance in the textile. The minimum inhibitory concentration (MIC) is required for biostatic activity, but the minimum biocidal concentration (MBC) should be exceeded for biocidal activity. The majority of antimicrobial agents in the textile industry utilize a controlled-release mechanism [12]. These agents, which are also called, leaching antimicrobials [9], are not chemically bound to the textile fibers and their antimicrobial activity is attributed to their gradual and persistent release from the textile into their surroundings in the presence of moisture, where they act as a poison to a wide spectrum of bacteria and fungi. The antimicrobial efficiency depends directly on the concentration, which should not drop below the MIC. Owing to leaching of the agent into its surroundings, the concentration of the active substance in the textile decreases and gradually falls under the limit of effectiveness. This can induce resistance to these substances in microorganisms; in addition, leaching agents do not withstand repeated laundering. A controlled release mechanism can also be found in agents that are chemically incorporated into the fiber surface, but with an active substance that is leachable in water. The important advantage of these agents over other leaching antimicrobials is that they can be regenerated under appropriate conditions. The bound antimicrobials [9] include finishes that are chemically bound to the surface of the textile fibers, where they act as a barrier and control microorganisms which come into contact with the fiber surface. Because these agents do not leach into the surroundings of the textile substrate, the probability of microorganisms developing resistance to them is small. Covalent binding of the agent to the textile surface can be ensured if there are enough reactive groups in the agent and the fibers, and if the application process is carried out under suitable conditions. Accordingly, when using bound antimicrobials, the mechanism of chemical binding to the textile surface and the conditions that initiate or catalyze the reaction should be known. Bound antimicrobials are much more resistant to repeated laundering in comparison to leaching agents. However, washing durability of the agent cannot assure its durability of antimicrobial function. The latter could decrease or even expire with the adsorption of dirt, deadly microorganisms or complex formation between the finish and the anionic detergent during laundering. For antimicrobial finishing in the textile industry, it is not only the antimicrobial efficiencies of the agents that are important, the environmental, health and safety aspects of their use must also be taken into account [7]. It should be stressed that the release of finishes from the textile into the surroundings could have negative impacts on living organisms in water because they can affect susceptible bacteria, thereby potentially selecting resistant bacteria. Fortunately, bound antimicrobials are environmentally friendly finishes with no leaching of toxic products into the surroundings. Taking these facts into account, much research has focused on the synthesis 50 A Search for Antibacterial Agents of novel antimicrobial agents where leaching antimicrobials have been replaced with bound antimicrobials. Some of the most important examples are presented in this chapter. 4. Conventional Antimicrobial Agents for textiles 4.1 Quaternary ammonium compounds Cationic surface active agents (cationic surfactants), including particularly quaternary ammonium salts (QASs), are important biocides that for many years have been known to be effective antiseptic and disinfectant agents [8-10],[12, 13]. As antimicrobial agents for textiles, monoammonium and “gemini’’ or “dimeric’’ ammonium surfactants (Figure 1) with an alkyl, alkylaryl and perfluorinated hydrocarbon group are used [14, 15]. These are active against a broad spectrum of microorganisms such as Gram-positive and Gram-negative bacteria, fungi and certain types of viruses [16]. The antimicrobial activity of QASs depends on the length of the alkyl chain, the presence of the perfluorinated group and the number of cationic ammonium groups in the molecule. The antimicrobial function arises from attractive interactions between the cationic ammonium group of the QAS and the negatively charged cell membrane of the microbe; these interactions consequently result in the formation of a surfactant–microbe complex. This in turn causes the interruption of all essential functions of the cell membrane and thus the interruption of protein activity [17]. QASs also affect bacterial DNA, causing a loss of multiplication ability [18]. If the long hydrocarbon chain is bonded to the cationic ammonium in the structure of the QAS, two types of interactions between the agent and the microorganism can occur: a polar interaction with the cationic nitrogen of the ammonium group and a non-polar interaction with the hydrophobic chain. Penetration of the hydrophobic group into the microorganism consequently occurs, enabling the alkylammonium group to physically interrupt all key cell functions. Fig. 1. Chemical structure of monoquaternary ammonium salt, alkyltrimethylammonium bromide (A), and diquaternary ammonium salt,alkanediyl-α,ω- bis(dimethylalkylammonium bromide) (B). Antibacterial Modification of Textiles Using Nanotechnology 51 Despite many positive properties, QASs have an inherent weakness: leaching from the textile. There are no reactive functional groups in the structure of the QAS to allow its chemical bonding to the fibers. Owing to the lack of physical bonding, leaching of the QAS occurs, resulting in a fast decrease in concentration to below the MIC. In addition, QASs have poor wash durability. To develop new, permanently bonded, non-leaching QAS biocidal groups for textile fibers, contemporary studies have synthesized polymerizable QASs [19-21] with acrylate or methacrylate groups for incorporation in the structure (Figure 2). Such QAS monomers have been named surfactant monomers or “surfmers”. Under appropriate conditions, “surfmers” polymerize into a bulk polymer network with a polycationic structure, including side QAS groups chemically bonded to the main polyacrylate chain. The merit of fixed bonding to the textile surface is that the QAS groups can act as a biobarrier and kill microorganisms by contact. Furthermore, the formation of a polymer network on the surface of the fibers strongly increases the durability and wash resistance of the antimicrobial agent. Fig. 2. Chemical structures of various “surfmers”: alkyl(2-(acryloyloxy) ethyl)dimethyl ammonium bromide (A) benzyl(11- (acryloyloxy)undecyl)dimethyl ammonium bromide (B) , N- (4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11- heptadecafluoroundecyl)-N,Ndiallylmethyl ammonium iodide (C) 52 A Search for Antibacterial Agents 4.2 N-halamines N-halamines are heterocyclic organic compounds containing one or two covalent bonds formed between nitrogen and a halogen (N–X), in which the latter is usually chlorine [22]. N–Cl bonds of different stability can be formed by the chlorination of amine, amide or imide groups in dilute sodium hypochlorite. N-halamines are biocides that are active for a broad spectrum of bacteria, fungi and viruses. Their antimicrobial properties are based on the electrophilic substitution of Cl in the N-Cl bond with H; this reaction can be carried out in the presence of water and results in the transfer of Cl+ ions that can bind to acceptor regions on microorganisms. This hinders enzymatic and metabolic processes, leading to the destruction of the microorganisms. As an N–H bond, which does not have antimicrobial properties, is formed in the substitution reaction, further exposure of the agent to dilute sodium hypochlorite is needed for regeneration of its antimicrobial activity [23, 24] . N-halamines can be applied to various textile surfaces including cellulose [25-27], polyamide [28] and polyester [29] fibers. To increase their effectiveness and the durability of the antimicrobial finish [25], research has been oriented toward synthesis of N-halamide monomers with an incorporated vinyl reactive group (Figure 3) [30, 31] that can polymerize on cellulose fibers under appropriate conditions to form a coating with excellent durability after washing [30]. Fig. 3. Chemical structures of 3-(4'-vinylbenzyl)-5,5-dimethylhydantoin (A) and N-chloro- 2,2,6,6-tetramethyl-4-piperidinyl methacrylate (B). Antibacterial Modification of Textiles Using Nanotechnology 53 4.3 Chitosan Chitosan is a deacetylated derivate of chitin, which is a natural polysaccharide mainly derived from the shells of shrimps and other sea crustaceans. Chemically, it can be designated as poly-β-(1→4)-D-glucosamine or poly-(1,4)- 2-amido-deoxy-β-D-glucose (Figure 4) [32]. In addition to its antimicrobial activity, chitosan has some important advantages such as non-toxicity, biocompatibility and biodegradability. Fig. 4. Chemical structure of chitosan To provide antimicrobial effect for textiles, chitosan can be used as an additive when spinning antimicrobial fibers [33] and also as a finishing agent [32] for surface modification, mainly of cellulose, cellulose/polyester and wool fibers. Chitosan is positively charged and soluble in acidic to neutral solutions because the amino groups in chitosan have a pKa of ~6.5. Its antimicrobial function arises from its polycationic nature, which is caused by protonation of the amino groups at the C-2 atoms of the glucosamine units; such antimicrobial function is very similar to that determined for QAS. Positively charged amino groups can bind to the negatively charged bacterial surface, resulting in the disruption of the cell membrane and an increase in its permeability. Chitosan can also interact with the DNA of microorganisms to prevent protein synthesis. The antimicrobial efficiency of chitosan depends on its average molecular weight, degree of deacetylation and the ratio between protonated and unprotonated amino groups in the structure [32]. It is believed that chitosan of a low molecular weight is more antimicrobially active than chitosan oligomers [32]. The efficiency also increases with increased deacetylation, which can exceed 90%. An important disadvantage of chitosan is its weak adhesion to cellulose fibers, resulting in a gradual leaching from the fiber surface with repetitive washing. To enable chitosan to bind strongly to cellulose fibers, various crosslinking agents are used, including mostly polycarboxylic acids (1,2,3, 4- butantetracarboxylic and citric acids) [32, 34] and derivates of imidazolidinone[35]. In the presence of a crosslinking agent, hydroxyl groups of chitosan and cellulose can form covalent bonds with carboxyl groups of polycarboxylic acid in an esterification reaction or with hydroxyl groups of imidazolidinone in an etherification reaction, thus leading to the formation of a crosslink between chitosan and cellulose. This greatly improves durability and wash resistance. In addition, the reactivity of quaternized chitosan has been improved by introducing functional acrylamidomethyl groups to the primary alcohol groups (C-6), which can form covalent bonds with cellulose in alkaline conditions (Figure 5) [36]. 54 A Search for Antibacterial Agents Fig. 5. Chemical structure of reactive O-acrylamidomethyl-N-[(2-hydroxy-3- trimethylammonium)propyl]Chitosan chloride The chemical binding of chitosan to cellulose fibers can also be achieved by oxidation of cellulose fibers with potassium periodate under acidic conditions to form aldehyde groups, which are allowed to react with the amino groups of chitosan and form a Schiff base (C=N double bond) [37]. Following the model of N-halamine halogenation, some of the amino groups in chitosan have been transformed into an –NHCl structure in the presence of sodium hypochlorite [38]. It has been found that chlorination significantly improves the antimicrobial activity of chitosan. 4.4 Halogenated phenols Among halogenated phenols, triclosan 5-chloro-2-(2.4-dichlorophenoxy) phenol (Figure 6) [39] is the most widely used biocide; it is present in many contemporary consumer and personal health-care products, detergents and household objects, including textiles and plastics. Fig. 6. Chemical structure of triclosan Antibacterial Modification of Textiles Using Nanotechnology 55 At bactericidal concentration, triclosan is very effective against a broad range of microorganisms, including antibiotic- resistant bacteria. As the widespread use of triclosan could represent a potential risk in terms of the development of resistant microorganisms [39], strong binding to solid surfaces with subsequent controlled release is important. Triclosan has therefore been applied to cellulose fibers in combination with polycarboxylic acids as crosslinking agents [40]. The application of polycarboxylic acid to fibers previously finished with triclosan enhances the washing durability of the antimicrobial coating. Novel host–guest complexes including triclosan molecules have been prepared with the use of cationic β-cyclodextrins (Figure 7), which are torus-shaped cyclic oligosaccharides containing six to eight glucose units linked by α-1,4 bonds [41]. Water solubility, stability and antimicrobial activity have been determined for the host–guest complexes. Owing to strong electrostatic attraction, the complexes are adsorbed to the surface of cellulose fibers almost completely. Triclosan has also been encapsulated in biodegradable polylactide as a carrier and used for finishing non-woven textiles [42]. Fig. 7. Schematic presentation of host–guest complexes between cationic β-cyclodextrin and triclosan. 4.5 Polybiguanides Polybiguanides are polymeric polycationic amines that include cationic biguanide repeat units separated by hydrocarbon chain linkers of identical or dissimilar length. One of the