Development of Antimicrobial and Antistatic Textile for Industrial Air Management Systems

Plain woven fabric was manufactured using polyester multifilament 33 tex × 2 yarns and polyester multifilament 33 tex yarns in the warp and weft. The warp and weft densities of the fabric used were 28.5 cm^-1 and 15.2 cm^-1. The surface density of the fabric was 245 ± 8 g/m² and the thickness 0.35 ± 0.01 mm.

The woven samples were subjected to treatment with Si Bac-Pure, which is a technology developed by a Portuguese company called Smart Innovation, Lda. One of the advantages of this technology is the ease of application as well as its non-toxicity [24]. There are neither heavy metals nor silver used in the manufacture of this product, and it is an eco-friendly product as well. Benzalkonium chloride (BKC) is the active antimicrobial agent in this product. By using the wet impregnation method, BKC was applied to the textile materials in order to cover them with the compound. The antimicrobial treatment included: mixing 41 ml/l Si Bac-Pure with 7 ml/l auxiliary Smart Fix into an aqueous solution at 30 °C, with a bath pH of 6-6.5 and absorption rate of 70 %, for 15 min. There was then a 15 minute drying period at 120 °C, followed by the application of the product.

The samples were washed and dried 20 times after the antimicrobial treatment, and then their antimicrobial activity was determined. The specimens had to be washed for 15 ± 0.5 min at 40 ± 2 °C using 3 g/l washing powder, following ISO 6330:2012 [25]. Afterwards, the specimens were rinsed three times with water at 20 ± 2 °C. The rinsing procedure took 1 ± 0.1 min each. Upon rinsing, the specimens were spin-dried for 1 ± 0.1 min and dried for 24 hours in a standard atmosphere.

Reference cultures of micro-organisms such as Staphylococcus epidermidis (ATCC 12228), Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (ATCC 13883), Pseudomonas aeruginosa (ATCC 27853), and Proteus mirabilis (ATCC 12459) were used to determine the antimicrobial activity effect of the textile fabric and Candida albicans (ATCC 10231) to determine its antifungal activity effect. Reference bacterial cultures were grown for 20-24 hours at 37.0 °C. Reference Candida albicans fungus cultures were grown for 3 days at 25.0 °C. Suspensions of the micro-organisms grown were prepared. The turbidity of the micro-organism suspension was determined by the McFarland standard, which measures the number of micro-organisms in 1 ml of suspension. In 1 ml of the microorganism suspension prepared for the experiment, it should be about 1.5×10⁸ CFU/ml [CFU=colony-forming unit].

Antibacterial and antifungal activity of the samples was revealed using the agar diffusion plate test method. The standard method ISO 20645:2004 [26] was used in the present study. The antibacterial activity of the textile fabric was evaluated against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Proteus mirabilis before and after 1, and after 20 washing cycles. The antifungal activity of sterile textile tissue was determined against Candida albicans. Textiles such as woven, knitted and flat are subject to ISO 20645:2004, which specifies a procedure for determining the effectiveness of antibacterial treatments. In addition to testing fibres incorporated with antibacterial agents, ISO 20645:2004 also applies to hydrophilic, air-permeable materials. This procedure requires a minimum amount of diffusion of an antibacterial solution into test agar. Strips of sterile textile fabric were cut into 12 × 12 mm pieces for the ISO 20645:2004 test. Then, 10 ml of liquid 45 °C TSA (tryptic soy agar) and 1 ml of bacterial suspension were added to each sterile Petri dish. The contents of the Petri dish were mixed. After the agar hardened, samples of textile materials were positioned on the agar surface in a Petri dish using sterile tweezers. Test samples were incubated on tryptic soy agar (TSA) for 24 h at 37 °C. After incubation, the Petri dishes with samples were maintained at room temperature for 24 h. Finally, the inhibition zone was calculated using equation 1 [3].

1H=D−d2$$H = {{D - d} \over 2}$$

Where, H represents the inhibition zone, D the total diameter of the sample, and d is the diameter of the sample. The unit of measurement is in mm.

The criteria for the evaluation of the antimicrobial and antifungal effect by the agar diffusion test [3] are stated in Table 1.

b) A partial consideration shall be given to the extent of the inhibition. If an inhibition zone is large, it may indicate that there are significant reserves of active substances or that the product has not been adequately bonded to the substrate.

c) Absence of growth even in the absence of inhibition zones may be a good effect, as such a zone may not have formed due to low diffusibility of the active substance.

d) ”As good as no growth” indicates the limits of efficacy.

e) A reduction in bacterial expansion indicates a reduction in the number of colonies or in the diameter of the colonies.

After establishing that, in the case of certain bacteria, there is no non-growth zone around small samples, it was decided to expand the study with larger samples. Therefore, the analysis of the antibacterial activity of textile fabrics in liquid nutrient medium-triptic soy broth (TSB) was extended. The assay in the liquid nutrient medium allows to increase the size of the test sample by increasing the amount of antibacterial agent in the nutrient medium (TSB). The standard method SN 195920-1992 [27] was used for this test. The strips of sterile textile fabric were cut into 12×60 mm pieces. For each sample, 5 sterile tubes with 10 ml of triptic soy broth (TSB) were used. 1 sample 12×60 mm strip was added to 1 tube, 2 sample 12×60 mm strips to 2 tubes, 3 sample 12×60 mm strips to 3 tubes, and 4 sample 12×60 mm strips to 4 tubes. Then, 0.1 ml of the test bacterial suspension was added to each tube. Test samples were incubated in tryptic soy broth (TSB) for 24 h at 37 °C. After incubation, Petri dishes with samples were kept at room temperature for 24 h. After culturing the sample, the TSB was assessed for signs of bacterial growth: TSB was cloudy - bacteria growing; TSB was clear – bacteria did not grow. The samples were evaluated as follows: the sample of a textile fabric that was antibacterially active – bacteria do not grow, TSB is clear, and the sample of textile fabric that was antibacterially inactive – bacteria growing, TSB is cloudy. The controls are presented as follows: –

KS + - TSB cloudy, S. epidermidis grows (0.1 ml of S. epidermidis suspension was added to the tube with TSB);

The EN ISO 1149-1 :2006 standard [28] specifies a test method for materials to be used in the production of protective clothing with electrostatic dissipation for prevention of incendiary discharge. A surface resistance of ≤2.5×10⁹ Ω was the minimum compliance value according to this standard. Electrostatic properties of a material are determined in order to understand its electrical behaviour, especially the build-up and discharge of static electricity. By attracting and retaining particles through electrostatic forces, electrostatic properties contribute to the effectiveness of air filtration systems.

The samples were identified as sample 0 – antibacterial textile fabric before washing, sample 1 – antibacterial textile fabric after 1 washing cycle, and sample 2 – antibacterial textile fabric after 20 washing cycles. These identifications were applicable for antifungal activity as well.

During the experiments, the standard atmospheric conditions were 20±2 °C and 65±4 °C, respectively, as stipulated by ISO 139:2005 [29].

The antibacterial activity level of the polyester woven textile fabric against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Proteus mirabilis before and after 1 and 20 washing cycles is presented in Table 2 and Figure 1. The level of antifungal activity of the textile fabric against Candida albicans before and after 1 and 20 washing cycles is presented in Table 2 and Figure 2. The antibacterial and antifungal effect is assessed as good, but with limited efficacy or an insufficient effect according to the growth of the tested bacteria Staphylococcus epidermidis, Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis and the fungus Candida albicans under the sample and around the sample.

Fig. 1.

Fig. 2.

The findings of the antifungus activity of the textile fabric against Candida albicans are presented in Figure 2. The control was performed with an antimicrobial uncoated textile fabric.

All treated specimens displayed very good antimicrobial activity, as is presented in Table 2 and Figures 1. There were some variations in antimicrobial activity depending on the washing cycles; nevertheless, once treated, all fabric samples exhibited a good effect. The unwashed fabric shows a 8.14 mm inhibition zone for Staphylococcus epidermidis bacteria, a 2.1 mm inhibition zone for Escherichia coli, a 7.0 mm inhibition zone for Staphylococcus aureus, a 3.0 mm inhibition zone for Klebsiella pneumoniae, a 3.8 mm inhibition zone for Pseudomonas aeruginosa, a 1.3 mm inhibition zone for Proteus mirabilis and a 1.8 mm inhibition zone for Candida albicans fungus. Based on these results, it can be inferred that the antibacterial agent BKC and the material investigated were able to form strong bonds. Thus, this antimicrobial finish can be recommended for polyester woven fabrics. Simultaneously, all treated woven fabrics displayed good antifungal activity, as is presented in Table 2 and Figure 2. A non-growth zone around the sample of unwashed fabric was found against the bacteria Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Proteus mirabilis and against the fungus Candida albicans. A non-growth zone around the sample after the first washing cycle was found only against Staphylococcus epidermidis and Staphylococcus aureus bacteria. After 20 washing cycles, there was no non-growth zone around the samples. It is noteworthy that bacteria and fungus do not grow under all samples. It is important for antimicrobial finishing, however, to achieve antimicrobial activity that is resistant to washing. Results from the present clearly demonstrate that good antimicrobial activity against Staphylococcus epidermidis bacteria and Staphylococcus aureus bacteria remains after the first washing cycle. After 20 washing cycles, the developed sample showed good antimicrobial activity with no inhibition zone. The absence of an inhibition zone after 20 washing cycles indicates that the antibacterial activity of the material had decreased or disappeared. Repeated washing cycles may lead to leaching of the antibacterial agent, reducing its concentration on the textile surface and thus reducing its efficacy [30]. This antimicrobial finishing shows excellent results, especially since it a) is extremely easy to apply, b) works well with other wet finishing methods, and c) is very durable against microbes.

The sample of a textile fabric is antibacterial active when bacteria do not grow and TSB is clear. On the other hand, if bacteria grow and TSB is cloudy, then the sample of textile fabric is antibacterial inactive.

Sample 0 and Sample 1 inhibited the growth (bacteria did not grow and TSB was clear) of Staphylococcus epidermidis in all tubes regardless of the sample size. Sample 2 did not inhibit the growth (bacteria grew and TSB was cloudy) of Staphylococcus epidermidis in all tubes regardless of the sample size. Escherichia coli growth was inhibited (bacteria did not grow and TSB was clear) only by sample 0. Samples 1 and 2 did not inhibit the growth (bacteria grew and TSB was cloudy) of Escherichia coli in all tubes regardless of the sample size.

The result of the electrostatic effect of the antimicrobial treated woven fabric, as a side effect, is presented in Table 3. The effect of washing on the electrostatic property is also evaluated and stated in Table 3. The surface resistance must be ≤2.5×10⁹ Ω (this is a minimum compliance value according to the standard).

The resistance of the woven fabric was found as 1.75×10¹² Ω before antimicrobial treatment. This resistance value is not enough to be applicable for protective textiles with electrostatic dissipation for preventing incendiary discharge. The value of the resistance of the fabric decreased after antimicrobial treatment, reaching 1.17×10⁹ Ω. This is two times lower than the minimum compliance value, which is sufficient for protective applications. The resistance of the polyester woven fabric increased after washing, reaching 2.38×10⁹ Ω. This is within the limits of error with the minimum possible value, and due to that this is not recommended for protective applications. After 2^nd washing, the resistance reaches much higher values than required and cannot be used for protective applications. The antimicrobial treated woven fabric could be used for non-washable antistatic air management systems only.