Sage Journals: Discover world-class research

Abstract

In this study, a polybutylene terephthalate (PBT) antimicrobial masterbatch containing silver, zinc, and copper antimicrobial agents was added to polyethylene terephthalate (PET) and spun into an antimicrobial partially oriented yarn which was then texturized into a draw-textured yarn (DTY). Filtration pressure rise and spinning tests indicated that the silver antimicrobial masterbatch had the best long-term spinnability. In addition, the strength and elongation of the antimicrobial DTY were reported to match practical standards, indicating that PET containing a silver antimicrobial agent can contribute to a smooth spinning process. In an antibacterial test of gram-negative and gram-positive bacteria before and after finishing, only the silver fabric maintained over 99.99% antibacterial effectiveness. Thereafter, the silver textile was tested for strains of influenza A virus H1N1 and H3N2 to evaluate its antiviral activity before and after dyeing; the textile containing 2% silver antimicrobial agent exhibited optimal antiviral effectiveness. In conclusion, the silver-containing fabrics exhibited long-lasting antibacterial and antiviral effects.

Keywords

Polyethylene terephthalate filament inorganic antimicrobial agent antibacterial antivirus silver

Introduction

The nonbiodegradable polyesters polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are the most well-studied and widely utilized polymers worldwide. They are employed as raw materials in a variety of goods, such as textiles, beverage bottles, and packaging.^1–3 Semicrystalline thermoplastic polymers, including PET and PBT, are best known for their outstanding chemical resistance, moisture resistance, electrical insulation, and flexibility.^4,5 Since the solubility and chemical structures of these two polyesters are very similar, they have good mixing compatibilities in specific quantities. PBT is structurally identical to PET, but has a longer alkyl chain between the two parabens, allowing it to be more flexible.⁶

Antimicrobial fabric treatment prevents microbial contamination, lowers the risk of cross-contamination in public spaces, and improves safety and comfort. The antimicrobial processing agents for textiles can be divided into organic and inorganic agents. The advantages of using inorganic antimicrobial agents over organic agents in textiles are their high resistance, safety, and thermal stability. However, the compatibility of inorganic antimicrobial agents and organic materials (such as polyester and polyamide) is poor, and is one of the spinning technologies investigated in this study.

Precious metals, such as silver, zinc, and copper, are employed to achieve the antimicrobial properties of inorganic antibacterial agents that are often used in textile products. Several studies^7–9 have suggested the substantial antimicrobial action of metal ions on both gram-negative and gram-positive bacteria. However, the antimicrobial finishing used in the past was post-processing (such as the resin-finishing process); therefore, its antimicrobial durability was inferior, and resulted in a product with a rough feel. To overcome the shortcomings of post-processing, an antimicrobial masterbatch was added to the fiber for an additional amount of antimicrobial agent, which led to a better antimicrobial effect that lasts longer than that of post-processing techniques. Furthermore, the fabric is not affected by the contamination of the processing agent (such as resin), and is comfortable to touch.

In response to the COVID-19 pandemic, the development of functional fabrics, with antibacterial and antiviral effects, has become an urgent demand. It is challenging to evenly mix the inorganic antimicrobial agents with organic substances (such as polyesters and polyamines). Uneven mixing leads to a decrease in fiber strength and elongation.¹⁰ Further, there are problems of yellowing and failure of antimicrobial effectiveness during manufacturing and processing.^11,12 The literature reports that certain commercial antimicrobial products have been launched; however, only a few practical studies have been published. In fact, it is considerably difficult to manufacture antimicrobial products because they are either too expensive or not washable.^13,14 Therefore, in this study, we aimed to explore the feasibility of using inorganic antimicrobial agents in polyester fiber spinning and the effects of the types and contents of antimicrobial agents on spinnability, fiber properties, dyeing hue, and antibacterial and antiviral durabilities before and after the finishing process.

Experimental

Materials

The PBT chip, with a melting point of 226°C and density of 1.26–1.36 g/cm³, was purchased from SHINKONG Synthetic Fibers Corporation Ltd., Taiwan. The PET chip (TiO₂: 0.3 wt%, intrinsic viscosity: 0.62 dl/g), with a melting point of 253°C, was purchased from Far Eastern New Century Corporation Ltd., Taiwan. The silver-magnesium-aluminum-phosphate-borate complex (with a silver content of 1.8%) was purchased from ISHIZUKA Glass Corporation Ltd., Japan, with ZAF-HS specified as the silver antimicrobial agent (AgA). Zinc oxide (with a zinc content of 5 wt%) was purchased from Jia Fu Technology Corporation Ltd., Taiwan, with JF-002-P as the zinc antimicrobial agent (ZnA). Copper iodide (CuI) (with a copper content of 5 wt%) was purchased from Jia Fu Technology Corporation Ltd., Taiwan, with JF-003-P as the copper antimicrobial agent (CuA).

Experimental equipment

Spinning machine

(1) Barmag pilot machine, Germany, Type: PILOT.

(2) Feature: Ready for production with a few kilograms of materials and the parameters can be changed rapidly.

Draw-Texturing machine

(1) Taiwan exc-fiber company, Type: TTRI-001.

(2) Feature: Take-up speed: 2000–5000 m/min.

Experimental procedure

In this experiment, PBT and 20 wt% of the three inorganic antimicrobial agents (silver, zinc, and copper) were mixed in a twin-screw mixer to produce three types of PBT antimicrobial batches: silver antimicrobial masterbatch (AgM), zinc antimicrobial masterbatch (ZnM), and copper antimicrobial masterbatch (CuM). First, 95 wt% PET was mixed with a 5 wt% antimicrobial masterbatch in a spinning machine to produce antimicrobial partially oriented yarn (POY). Next, an antimicrobial draw-textured yarn (DTY) was manufactured using a draw texturizing machine and knitted into a fabric for evaluation. Three different proportions of AgM (2.5, 5.0, and 10.0 wt%) were added to the PET polymer for spin tests. The experimental process is explained using the flowchart in Figure 1.

Figure 1.

Flowchart detailing the various steps of the experiment.

Detection of antimicrobial fabrics

Scanning electron microscopy

The surface morphologies of the antimicrobial agents and their dispersion in PBT were observed using a 15 kV electron beam with a resolution of 0.7 nm. Scanning electron microscopy (SEM) was performed using a JEOL FESEM-7900F field-emission SEM.

Thermogravimetric analysis

Thermogravimetric analyses (TGAs) of the three masterbatches were performed (TA Instruments, type: Q-5000) in an air environment at a heating rate of 10°C/min and a temperature range of 25–800°C to observe the variations in weight loss of the antimicrobial agents, antimicrobial masterbatches, and antimicrobial fibers.

Color difference

The CIE L*a*b* system is perceived as a combination of red and yellow, red and blue, green and yellow, and green and blue. In this color space, the color coordinates in the rectangular coordinate system are as follows: L* represents the lightness coordinate, a* represents the red/green coordinate (with +a* and −a* representing red and green, respectively), and b* represents the yellow/blue coordinate (with +b* and −b* representing yellow and blue, respectively). The CIELAB color difference is typically expressed as ΔE*, defined as an equally weighted combination of the coordinate differences (L*, a*, b*), and calculated as the distance between two points in a three-dimensional space, that is, the total color difference ∆E* = (∆L*² + ∆a*² + ∆b*²)^1/2, where ΔL*, Δa*, and Δb* represent the differences in lightness, red/green difference, and yellow/blue difference, respectively.¹⁵ The values of L*, a*, and b* were measured using a Nippon Denshoku color meter NE 4000.

Antibacterial test method

The JIS L1902:2015 is a standard for the determination of the antibacterial activity and efficacy of textiles.¹⁶ The bacterial liquid absorption method was applied using bacterial species, such as gram-negative bacteria (Pneumococcus pneumoniae) and gram-positive bacteria (Escherichia coli and Staphylococcus aureus). First, to prepare the test pieces, six test and six control samples were collected and cut into appropriate sizes (18 mm²) to obtain a mass of approximately 40 ± 0.05 g. Three test and three control samples were measured immediately after inoculation, and the remaining three samples of each type were measured immediately after inoculation.

Next, the test was performed using a 0.2 mL sterile pipette to accurately inoculate the test piece with the prepared test inoculation solution at multiple locations. Immediately after inoculation, 20 mL saline was added to each vial of the three test and three control samples, the caps of the vials were then closed and they were rinsed. Thereafter, 0.2 mL of the inoculated bacterial solution was added to a 30 mL sample bottle together with an 18 mm² standard cloth for measurement after 24 h of incubation. Thus, the test sample adsorbed approximately 40,000 bacteria and nutrients. After culturing at 37°C for 24 h, the sample was removed and the bacteria were washed out using 20 mL of physiological saline. Thereafter, 1 mL of bacteria and 9 mL of physiological saline were added to the test tubes and mixed homogeneously. Measurements were performed after incubating the mixture at 37°C for 24 h.

Finally, the bacterial cells on the test piece were measured using the mixed dilution plate method and the antibacterial value R was calculated. The bacteriostatic value R = log ((number of bacteria in the control group after 24 h−number of bacteria in the control group at 0 h)−(number of bacteria in the sample group after 24 h−number of bacteria in the sample group at 0 h)).

Antiviral test method

ISO 18184:2019 is a standard for evaluating the antiviral properties of textiles.¹⁷ The strains of the Influenza A virus H1N1 (ATCC VR-1469) and Influenza A virus H3N2 (ATCC VR-1679) were used for the antiviral test. First, to prepare the test specimens, several 20 × 20 mm² pieces were cut to obtain a mass of 0.40 ± 0.05 g. The yarns were prepared in bundles and cut to approximately 20 mm to obtain the same mass of 0.40 ± 0.05 g. Nine and 12 specimens were obtained for the reference cloth and antiviral test samples, respectively. Thereafter, the specimens were placed in an autoclave for 15 min at 121°C and 103 kPa for sterilization.

Following sterilization, all vials containing the specimens were removed, placed in a safety cabinet, and left to cool down for 60 min. The vial containers were checked for the absence of dew condensation, then capped and closed. Thereafter, three reference specimens and three antiviral test specimens were sterilized and placed in vials, and 20 mL of wash-out solution (SCDLP medium) was added to all vials. The vials were capped and agitated in a vortex mixer five times for 5 s each time. Thereafter, the 5 mL samples of the wash-out solution were placed in fresh tubes. Next, the specimen was inoculated at multiple locations with exactly 0.2 mL of the prepared virus suspension in vials using a pipette, and the vials were capped and closed.

Subsequently, the vials were placed in an incubator for a standard duration of 2 h at 25°C. Immediately after inoculation, the virus was washed out from three of the reference specimens, 20 mL of SCDLP medium was added to the vials, and the vials were capped, closed, and agitated in a vortex mixer five times for 5 s each time to wash out the virus from the specimens. Finally, to wash out the virus after 2 h of contact, 20 mL of the SCDLP medium was added to vials containing three reference and three antiviral test specimens. The containers were capped, closed, and agitated in a vortex mixer five times for 5 s each time to remove the virus from the specimens.

The infectivity titer was determined using a plaque assay. The plaque method was used to measure the infection value based on the extent to which infected virus cells were stained. Measurements of the unstained plaques were used to determine the number of viruses. Antiviral activity (M_v) was calculated as follows:

M_{v} = \log (V_{a} / V_{c}) = \log (V_{a}) - (V_{c})

where M_v is the antiviral activity value, log (V_a) is the common logarithm average of the three infectivity titer values immediately after inoculation with the control specimen, and log (V_c) is the common logarithm average of the three infectivity titer values after 2 h of contact with the antiviral fabric specimen.

Results and discussion

Filtration pressure rise test of antimicrobial masterbatch

Figure 2 shows the SEM images of the silver, zinc, and copper antimicrobial powders. Parts (a) and (b) indicate that the AgA powder particles have particle sizes of approximately 0.5–3 μm; parts (c) and (d) indicate that the ZnA powder particles are flower-like bundles of between 1–5 μm; and parts (e) and (f) indicate that the CuA powders have particle sizes of approximately 0.8–3 μm.

Figure 2.

SEM images exhibiting the surfaces of the antimicrobial agents. (a), (d) AgA; (b), (e) ZnA; and (c), (f) CuA.

Thereafter, an antimicrobial masterbatch containing 20% of the antimicrobial agents was examined. The surface images are depicted in Figure 3, where AgA was uniformly dispersed in AgM with no agglomeration, whereas an agglomeration of approximately 4 μm was observed for ZnA in ZnM and CuA in CuM.

Figure 3.

SEM images exhibiting the surfaces of the antimicrobial masterbatches. (a) AgM, (b) ZnM, and (c) CuM.

To determine whether the added inorganic antimicrobial masterbatch had too many particles agglomerated during the spinning process and whether the inorganic antibacterial agents were separated out by the filter, a filtration pressure rise test was designed to test the dispersion of powder in the masterbatch. The antimicrobial masterbatch and PET particles were mixed in an extruder, and thereafter, the mixed particles were melted and pressed into the filter screen group (pore size 10 μm; five layers of filter screen). Finally, the pressure generated by the filter screen was tested with respect to time.

The dispersion state of the antimicrobial powder in the masterbatch was evaluated based on the extrusion pressure value for 20 min. The lower the filtration test value, the better the dispersion of the antimicrobial powder in the masterbatch. In the filtration pressure rise test, a filtration pressure value below 15 bar indicated good long-term spinnability; if it exceeded 30 bar, the test was stopped. The filtration test values for AgM, ZnM, and CuM were 10.6, 18.8, and >30 bar, respectively, indicating that AgM possessed the best long-term spinnability, followed by ZnM. Although the filtration test value for CuM exceeded 30 bar, the pore size of the filter screen used in the PET fiber spinning factory was 16–20 μm with a five-layer structure and a base pressure of 100 bar. Therefore, CuM can still spin with short-term spinnability.

Antimicrobial partially oriented yarn spinning

The test conditions for 130D/72F POY for the various antimicrobial masterbatches are listed in Tables 1 and 2. Initially, the antimicrobial POY spinning process proceeded normally, and there were no broken filaments. However, higher tension occurs during the take-up processing, mainly because of the short cooling distance of the tow. In the spinning condition setting, there were slight differences between the rotational speeds of godet rollers 1 and 2, and those without smoke generation around the take-up system, indicating that no low-molecular-weight compounds (e.g., TiO₂) escaped during the spinning process. In addition, the take-up tension of 5 wt% ZnM was 41 cN, which was higher than that of the other two masterbatches (25 cN for AgM and CuM). The ZnA powder is a flower-like bundle that causes lower friction; therefore, a higher tension is required. Furthermore, the melt flow indexes (MI) for ZnM and CuM were 1369 and 1014, respectively, which were significantly higher than the 97.9 value for AgM. Therefore, the temperature of the extruder should be lowered and adjusted during spinning tests for ZnM and CuM, as indicated in Table 1.

Table 1.

Test conditions for 130D/72F POY for the various antibacterial masterbatches.

Item	AgM 5% (AgA 1.0%)	ZnM 5% (ZnA 1.0%)	CuM 5.0% (CuA 1.0%)
PET chip drying temperature, °C	120	120	120
Heating temperature of extruder in each zone, °C	264/298/290	257/281/281	257/283/283
Extruder die, °C	290	284	283
Spinning box temperature, °C	290	284	284
Gear pump pressure, bar	118	107	117
Spinneret specification	0.25 mm/72 holes	0.25 mm/72 holes	0.25 mm/72 holes
Gear pump specification, cc/rpm	1.2/13.3	1.2/13.3	1.2/13.3
Oil pump, rpm	27.4	27.4	27.4
Oil pick-up (OPU), %	0.6	0.6	0.6
Godet roller 1, m/min	2406	2407	2407
Godet roller 2, m/min	2510	2510	2510
Take-up tension, cN	25	41	25
Winder speed, m/min	2397	2397	2397
Smoke generation around the pack	No smoke generation	No smoke generation	No smoke generation
MI (270°C)	97.9	1369	1014

Note: ZnA powder is a flower-like bundle that causes lower friction; thus, a high tension is required.

Table 2.

Test conditions for 130D/72F POY for various ratios of AgM.

Item	AgM 2.5% (AgA 0.5%)	AgM 5.0% (AgA 1%)	AgM 10.0% (AgA 2%)
PET chip drying temperature, °C	120	120	120
Heating temperature of extruder in each zone, °C	263/290/290	264/298/290	257/281/281
Extruder die, °C	294	290	281
Spinning box temperature, °C	291	290	282
Gear pump pressure, bar	124	118	113
Spinneret specification	0.25 mm/72 holes	0.25 mm/72 holes	0.25 mm/72 holes
Gear pump specification, cc/rpm	1.2/13.3	1.2/13.3	1.2/13.3
Oil pump, rpm	27.4	27.4	27.4
Oil pick-up (OPU), %	0.6	0.6	0.6
Godet roller 1, m/min	2407	2406	2406
Godet roller 2, m/min	2511	2510	2510
Take-up tension, cN	25	25	27
Winder speed, m/min	2397	2397	2397
Smoke generation around the pack	No smoke generation	No smoke generation	No smoke generation

In the early stage of spinning with 10 wt% AgM, no broken filament was observed. However, feeding was unstable, and the cake had the appearance of a spider web, and the concentration of AgA (2.0%) was higher. This phenomenon also appeared during the finishing process of DTY. Based on the above inferences, the spinnability of 10 wt% AgM is barely acceptable.

Evaluation of yarn properties

Yarn strength (g/den) and elongation (%)

The measured POY denier (den) was between 125–127 den. With an increase in the antimicrobial agent ratio, the yarn strength (g/den) and elongation (%) decreased because the fiber strength can be attributed mainly to the PET polymer, as summarized in Tables 3–6.

Table 3.

Properties of 130D/72F POY for the various antibacterial masterbatches.

Antibacterial POY	Denier (den)	Strength (g/den)	Elongation (%)
AgM 5.0%	127	1.82	152
ZnM 5.0%	127	2.13	156
CuM 5.0%	127	2.13	156

Table 4.

Properties of 130D/72F POY for the various ratios of AgM.

Antibacterial POY	Denier (den)	Strength (g/den)	Elongation (%)
AgM 2.5%	127	1.93	154
AgM 5.0%	127	1.82	152
AgM 10.0%	125	1.61	141

Table 5.

Properties of 75D/72F DTY with various antimicrobial masterbatches.

Antibacterial DTY	Denier (den)	Strength (g/den)	Elongation (%)
AgM 5.0%	74	2.92	26
ZnM 5.0%	75	3.28	28
CuM 5.0%	74	3.29	26

Table 6.

Properties of 75D/72F DTY with various ratios of AgM.

Antibacterial DTY	Denier (den)	Strength (g/den)	Elongation (%)
AgM 2.5%	76	3.17	29
AgM 5.0%	74	2.92	26
AgM 10.0%	75	2.64	27

The elongation of the yarn affects the dyeing behavior and should be controlled under normal conditions. If the elongation of POY is greater than 150%, the amorphous area is too large to allow the dye to move out easily, resulting in a tendency of the cloth to fade after dyeing. In the case of DTY, the elongation was less than 10%, which indicated a smaller amorphous area; thus, the dispersed dye could easily get stuck in the pores of the fiber surface, resulting in poor dyeing speed. Based on the spinning convention, the appropriate values of the elongation for POY and DTY are 140–150% and 20–30%, respectively, which are the optimum conditions for dyeing.^18–20 An analysis of physical properties, as presented in Tables 3–6, indicates that the antimicrobial yarns have achieved the required practical standard.

The stress-strain curves of the antimicrobial yarns are shown in Figure 4. Due to the excellent molecular chain alignment in the DTY fibers, the strain increases with increasing stress, and the initial modulus in the stress-strain curve is not clear, as shown in Figure 4(a). As shown in Figure 4(b), the POY fibers reached the yield point immediately upon stressing; the stress remained unchanged and the strain increased rapidly up to a certain point. Subsequently, the molecular chain orthotropy and stress in the POY fibers increased gradually, causing the fibers to break. In comparison, antibacterial POY has a lower stress and a higher strain.

Figure 4.

The stress and strain curves for DTY (a) and POY (b), using AgA 0.5%, AgA 1.0%, AgA 2.0%, ZnA 1.0%, and CuA 1.0%.

Morphology of antimicrobial fibers

The SEM images of the fiber surface and cross-sectional area illustrate the microscopic morphology when using AgA 1.0%, as shown in Figure 5.

Figure 5.

SEM images of the (a) fiber surface and (b) cross-sectional area.

Since the antimicrobial agents were dispersed during the experiment, a small amount of antimicrobial agent was observed on the surface and cross-sectional area of the antimicrobial fibers.

Thermogravimetric analyzer

Based on the TGA curve presented in Figure 6(a), the weight loss of the silver antimicrobial agent before 300°C was approximately 3.47 wt%, which represents the weight loss of the impurity in the sample. This indicated that there was no visible weight loss from 300–800°C, suggesting that the silver antimicrobial agent was thermally stable and that no thermal degradation reaction occurred. Figure 6(b) indicates that the weight loss was divided into two stages. The first stage of PBT polymer cracking occurred because of the heat cracking interaction between the PBT and PET polymers in the antibacterial agent sample, the second stage occurred because of PET polymer cracking, and the last residual weight represented the inorganic content. The ZnA and CuA had final residual inorganic contents of 8.85% and 5.14%, respectively. The TGA curve demonstrated that the silver, zinc, and copper antimicrobial masterbatches had no weight loss before 300°C, whereas the silver masterbatch had a one-stage weight loss at 400°C, with a final residual inorganic content of 19.38%. Weight loss was reported in two stages in the zinc and copper masterbatches manufactured using a composite antimicrobial powder. The pyrolysis temperatures of PBT and PET polymers were 400°C and 450°C, respectively. The final residual weight was attributed to the inorganic content resulting from the thermal cracking reaction of the PBT and PET polymers in the masterbatch. The final residual inorganic content of the zinc and copper antimicrobial agents was 2.82% and 1.00%, respectively. The TGA results for the antibacterial fabric are presented in Figure 6(c) and (d). The temperature ranged from 25–800°C, and weight loss of the antimicrobial fabric was detected. Before 350°C, the TGA curve demonstrated that antimicrobial fabrics manufactured using a 5% antimicrobial masterbatch underwent no weight loss. A two-stage thermal cracking process occurs when PET is burned in the air. In the first step, residual carbon products are generated, whereas the second stage is concerned with the thermal degradation of the carbon residue. Weight loss in the first stage accelerated as the temperature increased. During combustion, PET generates carbon residues that react with oxygen at 500–600°C, causing a significant weight loss.

Figure 6.

TGA spectra of (a) antimicrobial agents, (b) antimicrobial masterbatches, (c) antimicrobial fabrics, and (d) AgA antimicrobial fabrics with various ratios.

Dyeing hue

Following the refining process, the antimicrobial fabrics were dyed using blue, green, and red disperse dyes before undergoing the soaping process. Thereafter, the dyeing hue values L*, a*, and b* of the antimicrobial fabrics were measured using a Nippon Denshoku color meter (NE 4000). The effect of dyeing the fabrics after the addition of the antimicrobial agents was determined from the color difference value ΔE*. Table 7 presents the color comparisons of the antimicrobial fabrics before and after dyeing them blue, yellow, and red. This indicated that the ΔE* values of the samples were almost below 2, particularly for various wt% values of AgA (0.5, 1.0, and 2.0), indicating that dyeing did not cause any significant chromatic aberration in the silver-containing fabrics. Blue dyeing caused very low chromatic aberration on the ZnA and CuA fabrics, whereas dyeing with the other two colors caused significant chromatic aberration. These results indicate that the silver-containing fabric was less affected than the other two antimicrobial fabrics in terms of chromatic aberration.

Table 7.

Values of L*, a*, b*, and △E* for PET antimicrobial fabrics when dyed with various colors.

Sample	Blue dye				Yellow dye				Red dye
Sample	L*	a*	b*	△E*	L*	a*	b*	△E*	L*	a*	b*	△E*
Normal	21.77	2.22	−21.28		85.18	−9.24	55.45		43.27	55.64	21.30	—
AgA 0.5%	22.56	1.49	−20.82	1.17	84.37	−9.91	54.67	1.31	43.31	54.35	20.91	1.35
AgA 1.0%	22.61	1.41	−20.61	1.35	84.47	−9.30	54.76	0.99	43.63	55.07	21.22	0.68
AgA 2.0%	23.32	1.41	−20.96	1.78	84.37	−8.28	54.40	1.64	44.32	55.32	21.23	1.10
CuA 1.0%	21.63	2.39	−21.50	0.31	83.02	−8.08	43.83	2.94	42.06	54.44	21.07	1.72
ZnA 1.0%	21.49	2.07	−21.29	0.32	83.33	−7.28	54.57	2.51	42.17	52.83	20.82	3.06

Antibacterial test results

Antibacterial activity tests were performed according to JIS L1902:2015. The antibacterial effect of the tested fabric was examined by determining the antibacterial activity of the finished fabric. Test strains of gram-negative (P. pneumoniae) and gram-positive bacteria (E. coli and S. aureus) were used to evaluate the antibacterial effect of the fabric before and after dyeing and finishing. Antibacterial durability is a significant evaluation index for antibacterial fabrics. It is important to note that antibacterial agents on the fabric surface may be lost during washing.

Referring to the washing process of the color fastness test, the antibacterial fabrics were tested after 10 cycles of washing to determine the antibacterial effect. Table 8 indicates that the antibacterial effect on all samples of silver, zinc, and copper fabrics before dyeing was greater than 99.99%. After 10 cycles of washing, the bacterial count after 24 h was less than 20 for silver, 1.6 × 10⁸ for zinc, and 1.4 × 10⁸ for copper, indicating that the antibacterial value of only the silver-containing fabrics was higher than 99.99%, whereas the zinc- and copper-containing fabrics completely lost their antibacterial abilities, as indicated in Table 8. This was because the zinc and copper antimicrobial agents agglomerated in ZnM and CuM during the spinning process, and the antimicrobial agents were partially exposed on the fiber surface. Therefore, some of the zinc and copper particles were washed away during the dyeing and post-finishing processes, which reduced the content of the antimicrobial agents in the fiber. Therefore, the antibacterial abilities of the zinc- and copper-containing fabrics are reduced.

Table 8.

Antibacterial activity tests for silver, zinc, and copper fabrics.

Conditions	Before dyeing		After washing
Sample	Bacterial count after 24 h	Antibacterial value, %	Bacterial count after 24 h	Antibacterial value
Blank	6.3 × 10⁷	0.00	4.3 × 10⁷	0.00%
AgA 1.0%	<20	>99.99	<20	>99.99%
ZnA 1.0%	<20	>99.99	1.6 × 10⁸	-- (#)
CuA 1.0%	<20	>99.99	1.4 × 10⁸	-- (#)

Note. JIS L1902, gram-negative bacteria (Pneumococcus pneumoniae); # = No reduction.

Thereafter, the antibacterial fabrics containing 0.5–2.0% silver were washed 50 times before being tested with gram-positive bacteria (E. coli and S. aureus), leading to a bacterial count of less than 20 after 24 h for all three silver fabrics, indicating that the antibacterial value of all the silver-containing fabrics was higher than 99.99%, as presented in Table 9. In conclusion, as long as the antibacterial fabric contains more than 0.5% silver antimicrobial agent, it has a permanent antibacterial ability.

Table 9.

Antibacterial activity tests including 50 washes of the silver fabrics with various AgA ratios.

Conditions	Before dyeing		After washing
Sample	Bacterial count after 24 h	Antibacterial value	Bacterial count after 24 h<	Antibacterial value
Blank	6.3 × 10⁷	0.00%	4.3 × 10⁷	0.00%
AgA 0.5%	<20	>99.99%	<20	>99.99%
AgA 1.0%	<20	>99.99%	<20	>99.99%
AgA 2.0%	<20	>99.99%	<20	>99.99%

Note. JIS L1902, gram-positive bacteria (Escherichia coli and Staphylococcus aureus).

Antiviral test results

In the antiviral efficacy test based on ISO 18184 (2019), various types of textiles were tested using strains of influenza A virus H1N1 (ATCC VR-1469) and influenza A virus H3N2 (ATCC VR-1679) to evaluate their antiviral activity values, preceded with or without dying. As presented in Table 10, the antiviral activity values (M_v) of the textiles were calculated. The values of M_v for the filament, nonwoven fabric, and knitted swatch (I) were 3.4, 4.2, and 2.2, respectively, which indicated that the efficacy of antiviral activity values for the knitted swatch (I) was good, and those for the filament and nonwoven fabric were excellent. All three textiles (containing 2% AgA) passed the antiviral tests, but knitted swatch (II) (containing 1% AgA) failed because it possessed an M_v value of 0.8. This indicated that an antiviral effect can be achieved in textiles containing 2% silver antimicrobial agents. To compare the finishing conditions, the filament and knitted swatch (I) were subjected to dye finishing, whereas the nonwoven fabric was not processed; all three textiles passed the tests. In addition, the filament and nonwoven fabric were tested with the H3N2 virus, whereas the knitted swatch (I) was tested with the H1N1 virus. All fabrics passed the test regardless of the test virus used (H1N1 or H3N2). In conclusion, regardless of whether the textile had been dyed and the type of virus used for testing, as long as a textile contains 2% silver antimicrobial agent, it has good or excellent antiviral activity. However, the knitted swatch (II), which contained only 1% silver antibacterial agents, did not pass the antiviral test.

Table 10.

Antiviral efficacy tests for the various textiles.

Item name		Filament	Nonwoven fabric	Knitted swatch (I)	Knitted swatch (II)
Test virus		H3N2	H3N2	H1N1	H3N2
AgA %		2	2	2	1
Dye-finishing		Yes	No	Yes	No
Standard cloth	Immediately after inoculation, log [V_a]	6.70	6.48	6.85	6.60
Standard cloth	After 2 h, log [V_b]	6.00	5.84	6.05	6.08
Common logarithm average of infectivity titer value, log [V_c]		3.30	2.30	4.65	5.82
Antiviral activity value M_v = log [V_a]–log [V_c]		3.4	4.2	2.2	0.8
Passed or failed		Pass	Pass	Pass	Fail
Efficacy		Excellent effect	Excellent effect	Good effect	No effect

Remarks: Efficacy of antiviral activity value (informative); Good effect: Antiviral activity value ≧2.0; Excellent effect: Antiviral activity value ≧3.0.

Conclusion

In this study, three types of antimicrobial agents, AgA, ZnA, and CuA, were added and spun into an antimicrobial DTY. The SEM images showed that AgA was uniformly dispersed, whereas an agglomeration of 4 μm was observed for ZnA and CuA. The results of the filtration pressure rise test indicated that AgM had the best long-term spinnability, followed by ZnM, while CuM showed the worst results. Thus, PET containing AgA was able to efficiently complete the spinning process. ZnA and CuA agglomerated in ZnM and CuM during the spinning process, and the antimicrobial agents were partially exposed on the fiber surface. Therefore, some of the ZnA and CuA particles were washed away during the dyeing and post-finishing processes, which reduced the content of antimicrobial agents in the fiber, resulting in reduced antibacterial activity. AgA does not have the disadvantage of particle loss, and permanently retains its antibacterial ability. Therefore, the silver fabric displays long-lasting antibacterial and antiviral effects.

Footnotes

Acknowledgements

The authors are grateful to Far East New Century Corporation, AUSPRING CO., LTD. and Taiwan Textile Research Institute for providing manufacturing equipment to accomplish this work.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Chang-Mou Wu

References

Bergeret

Ferry

Ienny

. Influence of the fibre/matrix interface on ageing mechanisms of glass fibre reinforced thermoplastic composites (PA-6,6, PET, PBT) in a hygrothermal environment. Polym Degrad Stab 2009; 94: 1315–1324.

Jacques

Devaux

Legras

, et al. Reactions induced by triphenyl phosphite addition during melt mixing of PET/PBT blends: chromatographic evidence of a molecular weight increase due to the creation of bonds of two different natures. Polymer 1997; 38: 5367–5377.

Vu-Khanh

Denault

Habib

, et al. The effects of injection molding on the mechanical behavior of long-fiber reinforced PBT/PET blends. Compos Sci Technol 1991; 40: 423–435.

Gao

Jin

Pan

. Depolymerization of poly (trimethylene terephthalate) in hot compressed water at 240–320°C. Polym Degrad Stab 2012; 97: 1838–1843.

Hajiraissi

Parvinzadeh

. Preparation of polybutylene terephthalate/silica nanocomposites by melt compounding: Evaluation of surface properties. Appl Surf Sci 2011; 257: 8443–8450.

Chang

J H

. Comparison of thermomechanical properties and morphologies of polyester nanocomposite fibers: PBT, PET, and PTT polymer. Polym Plast Technol Eng 2008; 47: 791–801.

Azarakhsh

Bahiraei

Haidari

. Electrospun synthesis of silver/poly (vinyl alcohol) nano-fibers: Investigation of microstructure and antibacterial activity. Mater Lett 2022; 309: 131–152.

Mallakpour

Hatami

. Green and eco-friendly route for the synthesis of Ag@Vitamin B9-LDH hybrid and its chitosan nanocomposites: characterization and antibacterial activity. Polymer 2018; 154: 188–199.

Rujitanaroj

Pimpha

Supaphol

. Wound-dressing materials with antibacterial activity from electrospun gelatin fiber mats containing silver nanoparticles. Polymer 2008; 49(21): 4723–4732.

10.

Folarin

Sadiku

Maity

. Polymer-Noble metal nanocomposites. review. International Journal of the Physical Sciences 2011; 6(21): 4869–4882.

11.

Son

. Method for producing antimicrobial cellulose fiber, fiber produced by the method and fabric using the fiber. Patent US20140142281A1, USA, 2014.

12.

Burton

Holm

. Silver-containing antimicrobial articles and methods of manufacture. Patent US20070166399A1,, USA 2016.

13.

Juikar

Waghmare

Murudkar

. Antibacterial regenerated cellulosic fibers and process of preparation thereof. Patent US20190203409A1, USA, 2019.

14.

Edgar

Zhang

. Antibacterial modification of Lyocell fiber: a review. Carbohydr Polym 2020; 250: 116–124.

15.

Leon

Mery

Pedreschi

, et al. Color measurement in L^* a^* b^* units from RGB digital images. Food Res Int 2006; 39: 1084–1091.

16.

JIS L1902 . Textiles, Determination of antibacterial activity and efficacy of textile products, 2015.

17.

ISO 18184 . Textiles—Determination of antiviral activity of textile products, 2019.

18.

Ketema

Worku

. Review on intermolecular forces between dyes used for polyester dyeing and polyester fiber. J Chem 2020; 2020: 1–7.

19.

Patterson

Sheldon

. The dyeing of polyester fibres with disperse dyes. Mechanism and kinetics of the process for purified dyes. Trans. Faraday Soc 1959; 55: 1254–1264.

20.

Lindström

. Chemical and Physical Changes in PET Fibres Due to Exhaust Dyeing: Issues in Thermo-Mechanical Recycling of Dyed PET Textiles. Report. Sweden: University of Borås, 2018.

The effect of inorganic antimicrobial agents on PET filament properties