32 TEKSTİL ve KONFEKSİYON 23(1), 2013

(REFEREED RESEARCH)

USE OF SILVER-LOADED ZEOLITES IN THE

ANTIBACTERIAL FINISHING OF COTTON FABRICS

GÜMÜŞ YÜKLÜ ZEOLİTLERİN PAMUKLU KUMAŞLARIN ANTİBAKTERİYEL BİTİM İŞLEMİNDE KULLANIMI

Candan CAN1, Ayşegül KÖRLÜ1*, Mustafa ATEŞ2*

1Ege University, Department of Textile Engineering, İzmir, Turkey 2Ege University, Department of Main and Industrial Microbiology, İzmir, Turkey

Received: 11.01.2012 Accepted: 08.01.2013

ABSTRACT Zeolite is a valuable natural mineral whose usage area has been increasing each passing day having unique features. Having

antibacterial,antifungal and antiviral properties, silver has been safely used for many years in many areas . An antibacterial zeolite can be obtained binding silver ions to zeolite by the ion exchange method. Natural zeolites are pretty good carriers for silver ions, and offer several advantages. In this study, the characteristics of cotton fabrics appliqued by silver-exchanged antibacterial zeolites were investigated.

Key Words: Zeolite, Silver, Antibacterial, Textile, ICP-MS

ÖZET Zeolit sahip olduğu benzersiz özellikleri ile her geçen gün kullanım alanı artan değerli bir doğal mineraldir. Gümüş ise

antibakteriyel, antifungal ve antiviral özellikleri nedeniyle çok uzun yıllardır pek çok alanda güvenle kullanılmaktadır. Gümüş iyonları iyon değişimi metodu ile zeolite bağlanarak antibakteriyel zeolit elde edilebilmektedir. Doğal zeolit, gümüş iyonları için oldukça iyi bir taşıyıcıdır ve pek çok avantaj sağlamaktadır. Bu çalışmada gümüş modifiyeli antibakteriyel zeolit aplike edilmiş pamuklu kumaşların özellikleri incelenmiştir.

Anahtar Kelimeler: Zeolit, Gümüş, Antibakteriyel, Tekstil, ICP-MS

* Corresponding Author: Ayşegül Körlü, aysegul.ekmekci@ege.edu.tr, Tel: +90 232 311 27 55 Fax: +90 232 339 92 22 1. INTRODUCTION

Zeolites have been used in many applications, such as agriculture, water treatment, and the detergent industry. In addition, they are very popular materials for researchers to study. Zeolites were discovered by Fredrick Cronstedt in 1756 (1, 2, 3). Two hundred years after the discovery, the formal study of zeolites began (1).

Barrer presented the microporous structure and the ion exchange properties of zeolites (2).

By improving zeolite chemistry, zeolites could be used in the detergent industry instead of toxic phosphates (2, 4). After the use of zeolites in the

detergent industry began, zeolites were used at Chernobyl and Three Mile Island (nuclear stations) for purification of the radioactive churns (2).

Turkey is one of the richest countries of the world in terms of zeolit reserves. However, Turkey is not taking advantage of the potential that zeolites offer (2, 3). Zeolites are microporous, crystalline aluminosilicates. They are composed of TO4 tetrahedra (T=Si, Al) with O atoms connecting neighboring tetrahedra (3, 5).

The general chemical formula of zeolites is as follows :

(Na,K)x (Mg, Ca, Sr, Ba)y (Alx + 2y Sin-(x

+2y) O2n). m.H2O

The structural formula of zeolites is as follows:

[ Si1-xAlxO2]x- (2)

For a completely siliceous structure, the combination of TO4 (T=Si) units in this fashion leads to silica (SiO2), which is an uncharged solid. Upon incorporation of Al into the silica framework, the +3 charge on the Al makes the framework negatively charged, which requires the presence of extra framework cations (inorganic and organic cations can satisfy this requirement) within the structure to keep the overall framework neutral. The extra framework cations are ion exchangeable and give a rise to the

TEKSTİL ve KONFEKSİYON 23(1), 2013 33

rich ion-exchange chemistry of these materials (5).

Zeolites are microporous minerals; the pore sizes are 2-12 Å. Cations (alkali metals and alkaline earth metals) and water are present in the porous area. Generally, these cations are sodium, potassium, magnesium and calcium. The interaction between cations and the zeolite are so weak that the zeolite can be used as a cation exchanger (2, 6).

Figure 1 illustrates the cation exchange mechanism of a zeolite. The zeolite exchanges Na+ ions with Ag+ ions (7).

There are some studies that describe the usage of cation-exchanged functional zeolites in the textile and

leather industries. The studies have explored the antibacterial qualities, flame retardancy, uv protection, odor and moisture absorption ability and heat-insulating properties of zeolites in the textile and leather industries (2, 8). Japanese researchers produced antibacterial artificial leather by using antibacterial zeolite (9). Yoshikazu et al produced antibacterial recycled polypropylene using cation-exchanged antibacterial zeolite (10). Taisheng et al produced antibacterial shoe lining material by using silver-loaded antibacterial zeolite (11). Ruiwen et al produced antibacterial viscose fiber by using silver-loaded zeolite (12). Ruiling et al, produced antibacterial polyester chips and fibers by using antibacterial zeolite (13). Bozoğlu produced

antibacterial diapers using cation-exchanged silver and zinc zeolite (1). He reported that the diaper had a good antibacterial efficiency toward E.coli but that are there was a color-changing problem (1).

In this study, different concentrations of silver-doped zeolite were applied to cotton fabrics to determine the antibacterial efficiency, washing durability, color –changing characteristics and handling values of fabrics. In addition, the use of these fabrics as medical textiles was examined. This study contributes comprehensive knowledge to the literature about the possibilities of using silver-loaded zeolites applied to cotton fabrics as medical textiles.

Figure 1. Cation exchange mechanism of a zeolite (7)

2. MATERIALS AND METHODS

The fabric used in the experiments was 100 % cotton. The woven fabric was desized, scoured and bleached. Natural zeolite was supplied from Enli Mining A.Ş. (from Manisa-Gördes region). The size of the particles was 30 µm.

First, natural zeolite was loaded with NaCl. Na-zeolite was prepared by stirring a zeolite sample with 1 N NaCl solution at 500 rpm in a 2000 ml closed beaker at 60°C for one week. The NaCl solution was replaced every day. The sample was washed with deionized water several times and dried in an oven at 110°C. The goal of this process was to purify the natural zeolite from other elements, and to increase the cation exchange capacity. Then, the Na-zeolite was loaded by two different concentrations of AgNO3

solution (0,1 M and 0,01 M) in the magnetic stirrer (500 rpm) for two days. After the stirring step, the loaded zeolite was washed with deionized water five times and then dried in an oven at 110°C (14). Modified zeolites were applied to cotton fabrics by the aid of an acrylic-based binder (0,1 M 40 g/l as maximum, 0,01 M 5 g/l as minimum). The application recipe was a modified pigment dyeing recipe. The pick-up values were approximately 80 %.

The amount of silver ions on the cotton fabrics was determined by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) (Agilent ICPMS 7500ce). Treated cotton fabrics were carbonized by an acid solution (HNO3 and HCl) in a microwave oven (MARS Microwave Accelerated Reaction System MARS 5 Version 194AO2). In

addition, an elemental analysis was performed. The surface of the fabric was performed by an SEM (Scanning electron microscope) (FEI Quanta 250 FEG). Antibacterial efficiency tests were carried out according to AATCC 100. Washing durability tests of antibacterial efficiency were determined after 5 and 10 washing cycles. ECE (SDL Atlas reference detergent B) was used in the washing step, and the washing temperature was 60 °C. The washings were performed in a laboratory-type dyeing machine (Termal). Each washing cycle was 30 minutes. A laboratory-type washing machine or Wascator was not used for the washings because of the contamination risk. In addition, samples were dried at room conditions. The whiteness, yellowness and L*, a* and b* values of the fabrics were measured by a

34 TEKSTİL ve KONFEKSİYON 23(1), 2013

spectrophotometer (Hunterlab Ultrascan Pro) according to CIELAB. The fabrics’ handle values were measured by a Shirley Hardness Instrument according to TS 1409.

3. RESULTS AND DISCUSSION

3.1. The Results of ICP-MS and SEM

Treated cotton fabrics were carbonized by an acid solution (HNO3 and HCl) in a microwave oven. In addition, an elemental analysis was performed to

determine the silver ion content of the treated cotton fabrics.

According to Table 1, the silver ion content of the treated fabrics could be higher by increasing the concentration of the silver nitrate used for zeolite modification. The silver ion content of 40 g/l of 0,1 M AgNO3 modified zeolite applied to cotton fabric was 4379,5 ppb, and the silver ion content of 5 g/l of 0,1 M AgNO3 modified zeolite applied to cotton fabric was 53 ppb. The maximum amount of antibacterial

zeolite applied to the fabric was 40 g/l of 0,1 M AgNO3 modified zeolite applied to a cotton fabric sample, and the minimum amount of antibacterial zeolite applied to the fabric was 5 g/l of 0,1 M AgNO3 modified zeolite applied to a cotton fabric sample. There was a significant difference between these samples in terms of the silver ion content. The SEM images supported the data from ICP-MS.

Table 1. Silver Ion Content of the Cotton Fabrics (ICP-MS)

Treated Cotton Fabrics Ag Ion Content (ppb)/ Fabric Quantity (g)

Treated Cotton Fabric with 40 g/l of Zeolite Modified by 0,1 M AgNO3 4379,5

Treated Cotton Fabric with 5 g/l of Zeolite Modified by 0,01 M AgNO3 53

Figure 2. Greige cotton fabric (×120) Figure 3. 40 g/l of 0,1 M AgNO3 zeolite applied to cotton fabric (×120)

Figure 4. 5 g/l of 0,01 M AgNO3 zeolite applied to cotton fabric (×120)

TEKSTİL ve KONFEKSİYON 23(1), 2013 35

Silver ions can be observed clearly on the SEM images. In Figure 3, there are a number of silver ions on the surface of 40 g/l of 0,1 M AgNO3 modified zeolite applied to cotton fabric. In addition, in Figure 4, there are a small number of silver ions on the surface of 5 g/l of 0,1 M AgNO3 modified zeolite applied to cotton fabric. There is not a homogeneous distribution of Ag ions on the fabrics. The SEM images agree with the ICP-MS analysis results.

3.2. Antibacterial Efficiency and Washing Durability

Antibacterial efficiency tests were performed according to the AATCC 100. Gram-positive S. aureus and gram-negative K. pneumoniae were used in the tests. The incubation time was 24 hours. Washing durability tests were performed after 5 and 10 washings.

According to Table 2, the antibacterial efficiency of all the samples was 100 % toward gram-positive S. aureus and gram-negative K. pneumoniae. It was determined that there were no live bacteria on the fabric. This result means that the concentration of the antibacterial agent was high.

Table 2. Washing Durability and Antibacterial Properties of the Treated Fabrics

Treated Cotton Fabric with 40 g/l of Zeolite Modified by 0,1 M AgNO3 Washing Cycles 0. Hour 24. Hour

S. aureus K. pneumoniae S. aureus K. pneumoniae Amount of

Alive Bacteria

Reduction (%) Amount of Alive Bacteria

Reduction (%)

0 100 0 100 0 100 Unwashed 0 0 0 100 0 100

1,12*107 3,9*107 0 100 0 100 5 1,2*107 3,5*107 0 100 0 100

2,92*107 2,6*107 0 100 0 100 10 2,8*107 2,5*107 0 100 0 100

(*) Antibacterial efficiency tests were performed twice. The test results are the total amount of bacteria on a 4,8 cm diameter piece of cotton fabric. In the initial test, 108 cfu/ml bacteria were placed on a 4,8 cm diameter piece of cotton fabric.

Table 3. Washing durability and antibacteraial properties of the treated fabrics

Treated Cotton Fabric with 5 g/l of Zeolite Modified by 0,01 M AgNO3 Washing Cycles 0. Hour 24. Hour

S. aureus K. pneumoniae S. aureus K. pneumoniae Amount of

Alive Bacteria

Reduction (%) Amount of Alive Bacteria

Reduction (%)

8,5*106 6*105 0 100 0 100 Unwashed 7,2*106 3*105 0 100 0 100 1,6*107 4,6*105 0 100 3,5*104 92,39 5

1,25*107 5,7*105 0 100 5,2*104 92,23 2,73*107 2*106 0 100 5,8*105 71 10 3,28*107 1,25*106 0 100 6*105 66,64

(*) Antibacterial efficiency tests were performed twice. The test results are the total amount of bacteria on a 4,8 cm diameter piece of cotton fabric. In the initial test, 108 cfu/ml bacteria were placed on a 4.8 cm diameter piece of cotton fabric.

According to Table 3, the antibacterial efficiency against gram-positive S. aureus and gram-negative K. pneumoniae of the unwashed samples was 100 %. It was determined that there were no live bacteria on the fabric. The antibacterial efficiencies against gram-positive S. aureus were the same after 5 and 10 washing cycles. However, the antibacterial efficiency against gram-negative K. pneumoniae decreased by 92,31 %

after 5 washing cycles and by 68,82 % after 10 washing cycles.

At the beginning of the study, 5 g/l of 0,01 M AgNO3 modified zeolite was thought to be the minimum necessary amount of zeolite and 40 g/l of 0,1 M AgNO3 modified zeolite was thought to be the maximum necessary amount of zeolit in the application recipe. However, after the antibacterial tests, it was determined that 5 g/l of silver nitrate was enough to produce

antibacterial efficiency. In the medical literature, it has been suggested that the concentration of silver nitrate solution for medical treatment should be lower than 0,5 % for human health (15). In this study, the silver nitrate concentrations were limited according to the medical literature and toxic concentrations were not studied. Higher concentrations may cause silver ion accumulation in the human body, which is called argyrosis (15, 16).

36 TEKSTİL ve KONFEKSİYON 23(1), 2013

The toxic effect of silver on bacteria has not yet been completely explained. By investigating the morphological and structural changes of bacterial cells, attempts have been made to determine the mechanism. As a result of these studies, it is known that silver binds to the bacterial membrane and then the bacterial wall affects the –SH groups and inhibits respiration enzymes, causing bacterial death (17).

3.3. Whiteness Index of the Fabrics

The whiteness and yellowness degrees, L*, a* and b* values of the fabrics were measured by a spectrophotometer (Hunterlab Ultrascan Pro) according to the CIELAB formula.

It is observed in Table 4 that there was not a significant difference between the whiteness degrees of greige fabric and treated fabric with (5 g/l 0,01 M AgNO3). However, there was a significant difference between the whiteness degrees of these fabrics and treated fabric with (40 g/l 0,1 M AgNO3). By increasing the silver ions in the cotton fabric, the whiteness degree of the fabric was decreased. There was not a significant difference between greige fabric and treated fabric with 5 g/l of 0,01 M AgNO3 in terms of yellowness, L*, a* and b* values. However, there was a large difference between these fabrics and fabric treated with 40 g/l 0,1 M AgNO3

in terms of yellowness, L*, a* and b* values.

3.4. Handle Values of the Fabrics

The fabrics’ handle values were measured by a Shirley Hardness Instrument according to TS 1409.

As observed in Table 5, there was a significant difference between the hardness values of greige fabric and blank fabric (blank fabric is the fabric that was exposed to the same application solution without zeolite). The reason for the difference was the binder. In addition, the fabric treated with 40 g/l zeolite was the hardest fabric.

4. CONCLUSIONS

As a result of this study, the modification of zeolite by AgNO3 was achieved. An ICP-MS analysis supported this result. By using silver-loaded zeolite in the antibacterial finishing of cotton fabrics, good antibacterial efficiency against gram-positive S.Aureus and gram-negative K. pneumoniae and washing durability were achieved. Increasing the Ag ion content of the cotton fabric increased the antibacterial efficiency and improved the washing durability. The AgNO3 concentration in the modified solution and the amount of silver-loaded zeolite in the application solution played a critical role in the Ag

ion content of the cotton fabrics. However, there was not a homogeneous distribution of Ag ions on the fabrics. The SEM images affirmed this result. It is thought that this problem can be solved by using other application methods.

Increasing the Ag ion concentration on the fabric decreased the whiteness degree of the fabric. It is clear that 40 g/l of 0,1 M AgNO3 is an extremely high concentration. 5 g/l of 0,01 M AgNO3 is an ideal concentration in terms of antibacterial efficiency and whiteness degree.

Silver is a widely used antibacterial agent. However, there are some limitations on its use. Because of these limitations, carriers are used, including certain polymers and inorganic materials. Zeolites are good carriers for silver because silver-loaded zeolites release silver ions slowly and in small amounts. Thus, the antibacterial efficiency lasts for a long time, and the risk of toxic silver exposure decreases (18). Based on the results of the study, it is thought that silver-loaded zeolites can be used in medical textiles.

5. ACKNOWLEDGMENTS

This study is a part of the PhD thesis of Candan CAN.

Table 4. Whiteness degree and yellowness index values of cotton fabrics

Whiteness

CIE Yellowness Index E

313 L* a* b*

Greige Fabric 68,82 8,13 95,51 -0,23 4,43

5 g/l of 0,01 M AgNO3 68,16 7,88 94,85 -0,09 4,21

40 g/l of 0,1 M AgNO3 -70,62 44,52 65,36 4,03 17,29

Table 5. Handle values of the fabrics

Hardness Values

Greige Fabric 7,194

Blank Fabric 12,245

5 g/l of 0,01 M AgNO3 14,678

40 g/l of 0,1 M AgNO3 16,257

TEKSTİL ve KONFEKSİYON 23(1), 2013 37

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