Simultaneous Application of Silver Nanoparticles with ... - Springer Link

Fibers and Polymers 2011, Vol.12, No.5, 635-641

DOI 10.1007/s12221-011-0635-x

Simultaneous Application of Silver Nanoparticles with Different Crease Resistant Finishes Akbar Khoddami*, Shima S Shokohi, Mohammad Morshed, and Dariush Abedi1

Department of Textile Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran 1 Department of Pharmacology, Isfahan University of Medical Science, Isfahan, Iran

(Received August 31, 2010; Revised January 12, 2011; Accepted March 14, 2011)

Abstract: Textiles, especially those made of natural fibers, are suitable medium for the growth of microorganisms which

causes disease transmission, stink, colorful spots, and reduction in fabric strength. This research focuses on the antimicrobial finishing of cotton fabrics using colloidal solution of silver nanoparticles. Due to the difficulties of adding a new step to the finishing process of cotton textiles, efforts have been made to combine the antimicrobial treatment with the conventional finishing processes. For this purpose two chemical finishes of Fixapret ECO as a crosslinking agent and Cellofix ME as a resin former have been used in anti crease finishing of cotton fabric and their effects were evaluated. The properties of the samples have been investigated by measuring the resistant of samples against bacteria, crease recovery angle, abrasion, and washing fastness. The results showed that treated samples by pad-dry method have the best antibacterial effect with a direct relation between the increase in drying temperature and antibacterial properties. However, the washing and abrasion fastness were not at the acceptable level. Co-application of the colloidal solution of silver nanoparticles with the crease resistant materials improved both fastness properties while at the same time limited the direct contact between the nanoparticles and the bacteria so the antibacterial efficiency was reduced. Subsequently, it was concluded that the antibacterial finishing method should be selected according to the end uses. In addition, antibacterial treatment could be one of the multi-purpose finishes for cotton fabric. Keywords: Cotton fabric, Nanotechnology, Silver nanoparticle, Antibacterial, Crease resistant finishes

antibacterial finishing process [1-4]. The wave of nanotechnology has shown a huge potential in the textile and clothing industry and has provided a new area for futuristic research in science and technology. Using nanotechnology to improve existing material performances and developing unrivaled functions on textile materials are flourishing. Commercial textiles containing chemical antibacterial agents are sorely poison and irritant for human body; hence the new types of safe and commodious biocidal materials need to be replaced with these chemical agents [5]. Subsequently, the new antibacterial finishing agents by taking advantages of nanotechnology have been developed. The development of new clothing products based on the immobilization of nanoparticles on textile fibers has recently received a growing interest from both the academic and industrial sectors [6,7]. Silver nanoparticles [8], titanium dioxide [9,10], and zinc oxide [11] are used to impart antimicrobial properties. Metallic ions and compounds show certain degrees of disinfecting effects. In cooperation of catalysis and metallic ion causes part of oxygen in the air or water to be turned into active oxygen, thereby dissolving the organic substance in order to create antimicrobial effect [11]. The number of particles per unit area is increased by applying nano-sized particles, so the antimicrobial effects can be maximized. Since ancient times, silver has been most extensively studied to fight infections and prohibit spoilage. It is found that silver is non-toxic to humans in minute concentrations. Silver attacks a wide range of targets in microbes, so the

Introduction

Invisible wastes from the human body such as sweat and sebum cause microorganisms to adhere to cloths and grow easily and cause nasty odor along with altering the shade and lowering the strength of the fabric. Applying antimicrobial finish decreases the growth of microorganisms and prevents the above mentioned problems. Due to the control of microorganisms, textile fabrics can be used in different areas from hospital environment to everyday household. In consequence, various antimicrobial finishes and sterilization methods have been developed for different textiles. Generally, the antibacterial 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 fiber spinning melt or dope. A number of methods for incorporating antibacterial agents into textile materials have been developed elsewhere; these methods such as insolubilization of the active substances in/on the fiber, micro encapsulation of the antibacterial agents into the fiber matrix, use of graft polymers, homo polymers and/or copolymerization on to the fiber (e.g. graft polymerization of N-halamide monomers onto cellulosic substrates), and chemical modification of the fiber by covalent bond formation (e.g. application of quaternary ammonium salts onto cotton fabrics or covalent attachment of a chloromelamine derivatives) have been developed for improving the durability of the chemical *Corresponding author: [email protected] 635

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microorganisms are unlikely to develop resistance against silver as compared to antibiotics [12]. The silver nanoparticles with their unique chemical and physical properties are proving as an alternative for the development of new antibacterial agents. Large surface area of silver nanoparticles increases their contact with bacteria or fungi and improves the germicidal and bactericidal efficacy. Silver nanoparticles have high reactivity with proteins. They adversely affect cellular metabolism of bacteria and fungus, and restrain cell growth, along with decrease in respiration, basal metabolism of the electron transfer and the transport of the substrate into the microbial cell membrane. Additionally, it prevents the growth of bacteria which cause odor, infection and sores, so it can be widely used in socks, and other healthcare products such as dressings for burns, scald, skin donor and recipient sites [13]. Recently, new techniques for the modification of textile fibers using antibacterial nanosized silver particles were introduced [7,13-18]. Ki . [15] imparted antibacterial properties to the wool fabrics using sulfur nano-silver ethanol based colloid with the particle size of average 4.2 nm. The fibers were treated with nano-silver colloid by a conventional pad-dry-cure method. Lee and Jeong [18] manifested the method in which the polyester nonwovens were incorporated with colloidal silver nanoparticles. In this method, typically the polyester nonwovens were immersed in a colloidal silver nanoparticles bath for 1 min and squeezed to 100 % wet pick-up with a laboratory pad at a constant pressure. Subsequently the treated polyester nonwovens were dried at 120 oC for 5 min. Dubas . [13] disclosed the new procedure in which antimicrobial silver nanoparticles were immobilized on nylon or silk fibers by following the layer-by-layer deposition method. Potiyaraj . [14] synthesized silver chloride nanocrystals on silk fiber. The growth of the nanocrystal was achieved by sequential dipping of the silk fibers in alternating solution of either silver nitrate or sodium chloride followed by a rinsing step. In other study, Lee [7] produced antibacterial woven cotton and polyester fabrics using colloidal silver nanoparticles. Woven cotton and polyester fabrics were padded through a certain concentration of silver colloids and squeezed to 83 % wet pick-up with a laboratory pad at a constant pressure. They demonstrated that antibacterial efficacy on textile fabrics can be easily achieved with using nanosized silver colloidal solution through padding process. It can be seen that in all previous researches, having a separate step for antibacterial finishing of the textiles was crucial which makes this so difficult for textile industries to use a new procedure in industrial scale. Therefore, this study is focused on simultaneous co-application of colloidal solution of silver nanoparticles and different finishing agents in one step. In this paper, multifunctional finishing of the cotton fabrics with crease resistant finishes and colloidal et al

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Akbar Khoddami et al.

solution of silver nanoparticles along with assessing the effects of the processes and their interaction on the properties of cotton fabric is described.

Experimental Desized, scoured, bleached, and mercerized cotton fabric (plain weave, 98 g/m2) was supplied by Broojerd Textile Co., Iran.

Chemicals

The chemicals used in this study were colloidal solution of silver nanoparticles at the concentration of 2000 ppm (Pars Nano Nasb Co., Iran), nonionic detergent of Sera wet C-NR (DyStar Co., Germany), sodium carbonate, acetic acid, magnesium chloride (Merck, Germany), modified dimethyloldihydroxyethylene urea [DMDHEU (Fixapret ECO, BASF, Switzerland)], anti-crease resin of Cellofix ME (Lamberti Co., Italy), Nutrient broth, and Nutrient agar (Becton Dickinson and Company Sparks, MD).

Treatment of Fabrics

All samples prior to any treatments were washed to remove any possible impurities which could adversely affect the fabric performance. Washing was performed using a Roaches Dyeing machine (Pyrotec S). The samples were washed at pH 8-9 (sodium carbonate) with 0.5 g/ non-ionic detergent at 100 ºC for 30 min. Fabrics were then washed off at 35-40 ºC for 45 min and cooled gradually, and finally rinsed with cold water and air dried without any tension. The liquor ratio was 40:1. To obtain the optimum concentration of silver nanoparticles, the cotton fabrics were treated by the conventional pad-drycure process. Padding was performed at the constant pressure after wet pickup of 80 % thorough colloid bath with different nanoparticles concentrations of 25, 50, 100, 150, 200, 250, and 300 ppm, using a padder (HVF 53800, Werner Mathis, Switzerland). The optimum concentrations of 100 ppm for gram-positive bacterium and 300 ppm for gram-negative bacterium were accomplished. Silver nanoparticles were applied using three different methods. In the first method, samples were pad-dried with optimum concentrations of 100 and 300 ppm of silver nanoparticles and dried at different temperatures of 80, 100, 120, and 140 oC. To achieve a simple and facile method to apply the antimicrobial agent to textiles, the optimum concentrations of silver nanoparticles were added to the solution containing anti-crease resin, acetic acid, and magnesium chloride. The solution was pad dried and cured on the fabric according to the recommended conditions by manufacturer. The crosslinking agent, Fixapret ECO, with two different concentrations of 40 and 60 g/ was applied and the fabric was treated with 50 g/ of the resin former agent, Cellofix ME. l

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Co-application of Silver Nanoparticles

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Tests and Analysis

Bacterial Activity Test The antibacterial properties were quantitatively evaluated using two different concentrations of 10 and 10 cfu/ml with the gram-positive bacterium, Staphylococcus aureus (S. aureus), AATCC 1337, gram-negative bacterium of Escherichia coli (E. coli), AATCC 1330, and Pseudomonas aeruginosa (P. aeruginosa), AATCC 1074, according to AATCC test method 100. The bacteriostatic ratio (%) was calculated using the equation (1): R (%) = (A B)/A × 100 (1) where R is the reduction rate, A is the number of bacterial colonies from untreated fabrics and B is the numbers of bacterial colonies from treated fabrics. Laundering Durability Test The laundering durability was measured according to the ISO 105-Col: 1989 test method. Different samples were washed in detergent solution of 5 g/l with L:R of 50:1 and pH of 7 at 40 C, using Polymath (Ahiba, Data color, Switzerland). Abrasion Durability Test The abrasion resistance was measured on a Martindale Wear & Abrasion Tester according to BS 12947-2: 1999 with 3000 rubs and 9 kPa pressure. Wrinkle Recovery Angle The samples crease recovery was tested according to the BS 13938-1:1999 test method by a Shirley crease recovery tester with a sample dimension of 40 mm long and 15 mm wide, time of loading of 5 min, time of relaxation of 5 min, and 10 tests for each direction. 4

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Bacterial reduction against silver nanoparticles concentration at bacterial concentration of 104 cfu/ml. Figure

1.

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Results and Discussion

Bacterial reduction against silver nanoparticles concentration at bacterial concentration of 105 cfu/ml. Figure

2.

silver nanoparticles and dried at different temperatures of 80 to 140 C. Table 1 shows the effects of different drying temperatures on the bacterial reduction with the best results were obtained at 140 C. In other words, the results demonstrated that the higher the drying temperature, the better antibacterial properties with 100 % bacteria reduction. This effect could possibly be due to the higher thermal energy that each particle received during drying at higher temperature causing deeper penetration of silver nanoparticles inside the cotton fiber with better durability. In addition, it is possible that, at higher temperatures, the chemical structure of the dispersing agent used in colloidal solution of silver nanoparticles was decomposed in which the dispersing agent acted as a surfactant that could help washing off the deposited nanoparticles. Also, due to the removal of the dispersing agent, this could possibly cause better contact between the nanoparticles and the bacteria with subsequent higher antibacterial efficiency, because these particles are only effective when they come into contact with the microorganisms [2]. However, more investigation in this respect is necessary. Studying the results of durability indicated that laundering o

The results of antimicrobial tests indicate the direct relation between antimicrobial properties and silver nanoparticles concentration. Figures 1 and 2 show the bacterial reduction of specimens treated with different silver nanoparticles concentration, against S. aureus, E. coli and P. aeruginosa. The results verify the optimum nanoparticle concentrations of 100 to 150 ppm for gram-positive bacterium (S. aureus) and 300 ppm for gram negative bacteria (E. coli and P. aeruginosa) for both applied concentration of bacterium. The differences between gram-positive and gram-negative bacteria essentially rest in the structure of their respective cell walls. Gram-negative bacterium has an outer layer, lipopolysaccharide, preventing silver nanoparticles penetration through the cell wall; hence, higher concentrations of silver nanoparticles are needed to destroy gram-negative bacterium [5]. To facilitate the industrial application, different procedures were tested to apply silver nanoparticles. One of the applying methods was the pad-dry process. In this method the samples were padded with optimum concentrations of

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The effect of different drying temperatures on the bacterial reduction Bacteria type E. coli Concentration 100 ppm 300 ppm Before rinsing 84.3 89.0 Bacterial reduction After rinsing 77.5 72.0 80 oC percentage After abrasion 70.3 67.5 Before rinsing 94.2 95.2 Bacterial reduction After rinsing 81.0 80.7 100 oC percentage After abrasion 75.6 76.7 Before rinsing 98.6 98.5 Bacterial reduction After rinsing 90.3 90.3 120 oC percentage After abrasion 86.5 87.5 99.3 100 Before rinsing Bacterial reduction After rinsing 92.4 92.4 140 oC percentage After abrasion 85.0 89.0

Table 1.

and abrasion decreased the samples antimicrobial properties. During pad-dry process, the silver nanoparticles are just being physically absorbed and kept among fibers; therefore, the durability is not high enough against laundering and abrasion. The results also showed that wash fastness was better than abrasion fastness due to the sensitivity of the deposited nanoparticles on the fibers surface to high level of mechanical action. Poor wash and abrasion fastness led the authors to find another procedure having long lasting antibacterial effect. Subsequently, durable press treatment as a popular finishing process was considered. The goal of durable finishing is to produce clothing that may be washed with minimal creasing and shrinkage depending on the fabric construction, then requiring no or very little ironing to restore a pristine appearance. Two types of general anti-crease finishes of Fixapret ECO and Cellofix ME have been investigated as a crosslinking agent and resin former, respectively. These agents react directly with the hydroxyl groups on the cellulose and cross link the cellulose chains and lock the structure together conferring an improved degree of elasticity to the fiber structure. Subsequently, the fabric resists shrinkage and deformation. Accordingly, it seemed that coapplication of these finishing agents could help improving the durability and fastness properties of the antibacterial finish with the silver nanoparticles. Fixapret ECO should not be termed resin, since it does not polymerize [19]. It is a bifunctional and, therefore unable to form the three dimensional structure typical of the urea and melamine formaldehyde true resin, Cellofix ME. The resin former finishing agents introduce a resin which is thermoset into the cellulose fiber that auto condensed to produce a network within the fiber [19]. For industrial applications, it must be ensured that the silver nanoparticles are not only permanently effective but also they are compatible with the finishing agent. Con-

S. aureus

100 ppm 84.3 67.5 64.3 91.2 79.0 75.6 98.6 90.3 86.5 97.0 92.4 85.0

300 ppm 87.0 70.8 65.2 96.6 79.6 74.5 89.9 86.8 80.0 100 92.5 87.3

P. aeruginosa

100 ppm 80.3 62.7 59.6 87.5 74.0 71.2 91.2 80.7 76.5 96.0 88.5 83.2

300 ppm 89.6 74.3 62.6 94.5 84.0 74.2 98.2 90.2 87.9 100 95.0 92.3

The effect of silver nanoparticles concentration on the crease recovery angle. Figure 3.

sequently, the effects of adding the nanoparticles to the formulation of the crease resist finishes as well as the finish durability were evaluated. The results of the crease recovery tests, Figure 3, indicate that the behavior of the fabric before and after finishing with different concentration of the silver nanoparticles is practically identical. Therefore, it can be concluded that the addition of silver nanoparticles does not have any adverse effect on wrinkle recovery angle. The reason for this phenomenon is that some of the performance properties like strength, recovery power, easy care properties, are not directly affected by fiber properties alone but they are related to several fiber properties and also to the yarn and fabric construction. It is noteworthy that the examples of performance properties that are directly related to the fiber properties are light fastness, thermal properties, tendency to generate static charges, etc [20]. The assessment of antibacterial effect of the suggested finishing method, co-application of anti-crease finishes and optimum concentrations of silver nanoparticles, are shown in Tables 2, 3, and 4. It was found that applying merely anticrease finishes causes release of formaldehyde during the process and an enhancement in the antimicrobial effect.



The effect of different anti-crease agent on the E. coil bacterial reduction Silver nanoparticles concentration Before rinsing Bacterial reduction After rinsing 40 g/l Fixapret ECO percentage After abrasion Before rinsing Bacterial reduction After rinsing 60 g/l Fixapret ECO percentage After abrasion Before rinsing Bacterial reduction After rinsing 50 g/l Cellofix MF percentage After abrasion

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Table 2.

0 ppm

100 ppm

300 ppm

14 6.6 5 20 11.5 9.5 11.1 6.3 3.8

78.3 68.1 65.2 82.5 74.9 71.8 70 63.9 60.1

85.6 76.3 73.9 88.8 82.4 78.9 78.3 72.3 68.8

The effect of different anti-crease agent on the S. aureus bacterial reduction Silver nanoparticles 0 ppm concentration Before rinsing 17 Bacterial reduction 40 g/l Fixapret ECO After rinsing 7.6 percentage After abrasion 7 Before rinsing 24.4 Bacterial reduction 60 g/l Fixapret ECO After rinsing 15.2 percentage After abrasion 13.7 Before rinsing 15.2 Bacterial reduction 50 g/l Cellofix MF After rinsing 9.2 percentage After abrasion 6.2

Table 3.

The effect of different anti-crease agent on the P. aeruginosa bacterial reduction Silver nanoparticles 0 ppm concentration 12.8 Before rinsing Bacterial reduction After rinsing 4.2 40 g/l Fixapret ECO percentage After abrasion 3.1 17 Before rinsing Bacterial reduction After rinsing 9.4 60 g/l Fixapret ECO percentage After abrasion 7.3 9.8 Before rinsing Bacterial reduction After rinsing 3.8 50 g/l Cellofix MF percentage After abrasion 2.3

100 ppm

300 ppm

85 79 72.8 87.6 80.3 73 75.6 68.4 65

93.2 86.5 79.5 95.6 89.9 81 83 76.7 70

100 ppm

300 ppm

75.5 65.3 62.1 79.6 70.4 67.8 65.3 59.9 54.3

82.7 73.6 70.2 85.5 76.1 72.5 70.1 65.7 63.5

Table 4.

Accordingly, the drawback of anti-crease finishing, formaldehyde release, could improve the antibacterial effect and change it to an advantage with up to 20 % bacteria reduction. This formaldehyde release, not to be confused with free formaldehyde, is the amount of formaldehyde that escapes from a fabric into the atmosphere [19]. One of the sources of releasing formaldehyde is uncured resin. At the same time it is difficult to cure 100 % of the applied resin. Therefore, all fabrics will have some formaldehyde, and the amount will

depend on how well the fabric was cured. Another source of formaldehyde release is the crosslink itself. The finish will decompose under certain conditions and will release CH2O. The applied finishing agents were modified to release lower amounts of formaldehyde [19]. However, the finished fabric is prone to release formaldehyde which increases antibacterial effect of the silver nanoparticles for all tested bacteria (Tables 2, 3, and 4). Also, it can be seen that, the amount of formaldehyde released is directly related to the concentration of

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applied finishing agent so that for all tested bacteria, the higher the amount of the crease resist finish applied, the higher formaldehyde release will be with better antibacterial effect. In addition, co-application of the nanoparticles and the finishing agents showed lower resistance against bacteria growth as compared with the pad-dry treated samples. This effect could be due to the reduction in contact of the silver nanoparticles and the bacteria. In other words, the finishing agents created a layer on the fiber surface which acted as a barrier by which the contact between the silver nanoparticle & bacteria is reduced besides there are not enough nanoparticles on the samples surface to kill the bacteria. For example, while the growth of the was completely inhibited with 100 % reduction by the pad dry method, co-application of the nanoparticles with Cellofix ME reduced its resistance to 70 %. Consequently, owing to the necessity of direct contact of the antibacterial agent with bacteria, it is crucial to choose the right finishing agent that does not limit silver nanoparticles accessibility to the surface of textiles goods that is in contact with the surrounding environment. However, the results presented in the Tables 2 to 4 indicate that binding the nanoparticles by the chemicals improved wash and abrasion fastness as compared with the pad dried samples. Moreover, similar to pad dried samples, the wash fastness is much better than abrasion fastness for all samples. This phenomenon is possibly due to the effects of finishing chemicals on the fiber and fabric structures in which they crosslink the cellulose chains and lock the structure together [19]. By comparing Fixapret ECO and Cellofix ME, Tables 2, 3, and 4, the typical differences of crosslinking agents and resin former polymers is revealed. Fixapret ECO is a reactant chemical which improves the wrinkle recovery by crosslinking between adjacent polymer chains while Cellofix ME polymerizes and forms a network between the fibers which keep the nanoparticles far from the reach of the tested bacteria. Subsequently, before washing and abrasion tests, the antibacterial effect of the crosslinking agent is better than the resin former polymers, which is capable of selfcrosslinking to form resinous, three-dimensional polymers as well as crosslinking the cellulose chains. As a result, the formed resin imparts better durability to the applied finish. Due to the above mentioned, they have found non-textile applications as plastics and adhesives, which are also used to modify other polymeric systems. Because of the tendency of self-condensation, they are often called aminoplasts [19]. The adhesive properties of these chemicals improve the durability of the nanoparticles against repeated laundering. On the other hand, the tendency to self-crosslink, adds stiffness to fabrics which is undesirable on abrasion resistance. Abrasion fastness is affected by fabric stiffness. However, losses in the physical properties of the finished samples due to the increase in rigidity of the fiber are unavoidable. P.

aeruginosa

Consequently, lower abrasion fastness is inevitable and it was predictable.

Conclusion This research focuses on the antimicrobial finishing of cotton fabric using colloidal solution of silver nanoparticles. The results indicated that the optimum concentration of nanoparticles depends on the kind of bacteria cell wall structure with 100 to 150 ppm for gram-positive bacterium ( ) and 300 ppm for gram negative bacteria ( and ). Antibacterial finishing of the cotton fabric using pad dry method shows direct relation between drying temperature and antibacterial reduction in which the 140 ºC imparted 100 % bacteria reduction. Due to the low durability to washing and abrasion, this process presents a facile method to temporary antibacterial finishing for specific purposes where washing the textiles is not necessary. Co-application of silver nanoparticles and anti-crease finishing agents including Fixapret ECO and Cellofix ME did not have any adverse effect on wrinkle recovery angle and improved the fastness properties with higher effect for the resin former polymer, Cellofix ME. In addition, formaldehyde release improved the antimicrobial effect. Overall, the results showed that by co-application of silver nanoparticles and the finishing agents, acceptable antimicrobial effect with proper fastness properties could be achieved; accordingly there is no necessity to add another step to general finishing layout for cotton fabric which makes this process so attractive with high feasibility for textile industries. S. aureus

E. coli

P. aeruginosa

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