BaTiO3 Nanoparticles Embedded Antibacterial Cotton Fabric with UV Protection Characteristics

ABSTRACT Barium Titanate (BaTiO3) nanoparticles were mixed with a stock paste containing an acrylate-based binder to prepare pigment paste. The formulated paste was applied to the cotton fabric by utilizing screen printing followed by drying and curing. The coated fabric was characterized for surface and elemental composition and uniform deposition of BaTiO3 nanoparticles was observed with minimal agglomeration. The resultant fabric showed an effective bacterial reduction greater than 99% against Escherichia coli and Staphylococcus aureus, and after 15 laundering cycles, the modified fabric showed a bacterial reduction of over 98%. The loaded fabric is capable of blocking harmful ultraviolet (UV) radiations. The modification of the cotton surface did not significantly change its intrinsic properties like water vapor permeability, air permeability, fabric stiffness, and other mechanical properties. The developed product has considerable possibilities and provides a good substitute for antibiotic materials for use in medical products and everyday apparel.


Introduction
Cotton fabrics are a popular choice in our society. In addition to apparel and home textile, cotton is widely used in the manufacturing of sportswear, health care, and medical textile including surgical, sanitary, and hygiene products (Elhalawany et al. 2020;Liu et al. 2019;Montaser et al. 2020;Nhlapo et al. 2019;Sela et al. 2020;Wong, Li, and Yeung 2005). At present, many researchers have reported their studies to enhance the functionality of cotton including wrinkle-free, fire resistance, photoyellowing, dye fixation, antibacterial, ultraviolet (UV) protection, and self-cleaning activity (Fu et al. 2021;Jabar, Adedayo, and Odusote 2021;Li et al. 2020;Qi et al. 2016).

Preparation of the stock paste
Before screen printing, the stock paste preparation was done by together mixing liquid ammonia (1.2%), urea (2.8%), cross-linkable acrylate copolymer (22%), antifoaming agent TC (0.5%), siliconecontaining emulsifier (0.5%), silicone-based softener (0.5%), and fixing agent (1.4%) and continuously stirring in water (67.5%) at room temperature for 10 min. The paste desired viscosity level was obtained by adding thickener (3.5%) to the resultant mixture. Then, the mixture was stirred continuously for 10 min to get a uniform stock paste. The fixing agent improved wet fastness while the defoamer reduced foam production during stock paste preparation and deaerated print pastes throughout the printing process, thus, reducing the formation of foam streaks. The thickener provided the print pastes with outstanding flowing qualities and gave the prints strong edges and luster.

Pigment paste preparation
For pigment paste preparation, BT NPs were added to the stock paste mixture in two varying concentrations of 10% and 20% and stirred to prepare a homogenous paste. The 10% BT pigment concentration entails mixing 9 g of stock paste with 1 g of BT, and the 20% signifies mixing 8 g of stock paste with 2 g of BT. Pigment paste concentrations of less than 10% were disregarded because it was impossible to achieve a uniform distribution on the cotton surface, and concentrations of more than 20% BT were neglected because the investigation goal was to obtain the best results at the lowest possible cost of BT.

Fabric coating process
The pristine cotton was initially washed with deionized water at room temperature to remove any impurity and then dried for 24 h. Pigment paste was applied uniformly onto the fabric surface through a screen having 165 mess size, followed by drying and curing at 120°C for 05 and 07 min, respectively. Additionally, the preparation of samples coated solely with stock paste was done, so that the impact of the binding agents on the antibacterial and UV protection qualities could be assessed. The softener imparted softness to a coated fabric. The use of softener in print paste strengthened the prints' durability to dry rubbing and produced a pleasantly dry, soft, non-sticky handle with better luster.

Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy
ATR-FTIR spectra of pure cotton, BT, and coated cotton were recorded to identify the various chemical groups introduced in the samples before and after coating. The sample measurements (50 scans/sample) were done on Spectrometer-2 (Perkin Elmer).

X-ray diffraction (XRD)
XRD analysis for pure cotton, BT, and coated cotton (before and after washing) were done on a powder X-ray diffractometer (Rigaku Corporation Smart Lab 9 kW) with 2θ scanned from 10° to 70°.

Field emission-scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectrometer (EDS)
To observe the distribution of BT on the cotton surface, the samples before and after coating were analyzed using FE-SEM (JFEI SEM-450) with an energy-dispersive X-ray spectrometer (EDS). Before scanning, the samples were provided with gold spray.

X-ray photoelectron spectroscopy (XPS)
XPS analyses were carried out on an X-ray photoelectron spectrometer (Nexsa base, Thermofisher Scientific) to measure elemental composition as well as the chemical and electronic state of the atoms within the uncoated and coated cotton.

Antibacterial assessment
The gram-positive bacteria, Staphylococcus aureus (S. aureus), and gram-negative bacteria, Escherichia coli (E. coli) were used for the antibacterial activity test as per AATCC 100-2004 test method. By using the following equation, the bacterial reduction (R) percentage was determined: where D and C, respectively, represent the control and BT NPs loaded samples bacteria colony forming units (CFU) (Kumar, Sharma, and Vaish 2022b). Further, the antibacterial test was carried out for fabric obtained after 15 washing cycles.

Water vapor and air permeability, mechanical properties, and coating durability measurement
The fabric water vapor permeability, air permeability, tensile, and abrasion resistance measurements were performed as per ASTM E-96, ASTM D-737, ASTM D-5034, and ASTM D-4685 standards, respectively. The fabric stiffness was evaluated in terms of bending length and flexural rigidity. The coating's endurance was measured using ISO 105-C10:2006.

Ultraviolet-visible (UV-VIS) spectroscopy
The UV spectrophotometer (Shimadzu UV-2600) was utilized to analyze the UV absorption spectra of the samples. The UV protection factor (UPF) was measured using a Perkin Elmer UV-vis Spectrophotometer as per Australian/New Zealand Test Standard AS/NZS 4399:1996. Figure 1 depicts the ATR-FTIR of pure cotton, BT NPs, and BT-coated fabric. In pure cotton (Figure 1(a)), the broad band observed from 3272 to 3336 cm −1 refers to the hydroxyl (OH) group present in cotton and water. The C-H stretching vibration bands were observed at 2902 and 2851 cm −1 . The band at 1634 cm −1 is attributed to the water molecule OH bending vibration present in cotton. The CH 2 symmetric bending of cellulose was observed at 1425 cm −1 . The C-H and C-O bending vibrations of the cellulose are related to the bands at 1364 and 1312 cm −1 . A band at 1159 cm −1 is attributed to the C-O-C stretching, and 1028 cm −1 is assigned to the C-O stretching of C-6 in cellulose (Portella et al. 2016). In BT FTIR analysis (Figure 1(b)), a sharp prominent absorption band observed at 494 cm −1 and a weak band seen at 858 cm −1 can be attributed to Ti-O bond vibration (Kumar and Luthra 2021). In BT-NP-coated cotton fabric, the band appearing at 1737 cm −1 can be contributed to C=O stretching, while the C=C bond band was seen at 1657 cm −1 which relates to the acrylate-based binder. After coating, a band observed at 493 cm −1 on the cotton surface relates to Ti-O bond vibration. Thus, the presence of spectrum bands of acrylate-based binder and BT on the coated cotton confirms the successful embedding of BT NPs on the fabric surface.

XRD analysis
XRD patterns of the pristine cotton, pure BT, and BT coated sample (before and after laundering) are shown in Figure 2. In pure cotton, the diffraction peaks observed at 2θ = 14.7°,16.72°, 22.79°, and 34.46° are attributed to the (110), (110), (200) and (004) Figure 3 shows the FE-SEM analysis carried out to examine the surface morphologies. The pure cotton fibers had a twisted ribbon-type appearance, while on applying the stock paste, the fibers were seen sticking together by some gummy-like substance. When pigment paste was applied, the uniform deposition of BT NPs was observed on the fabric surface for both 20% and 10% concentrations with   minimal agglomeration. The coated particles were so firmly attached to the fabric surface by the acrylate binder that after 15 laundry cycles they continued to be retained inside the binder matrix. EDX analysis was performed to find out the surface elemental composition of coated cotton. In pristine cotton, only carbon and oxygen atoms were found (Supplementary Material Fig. S1); however, in coated fabric (Figure 3g), barium (Ba) and titanium (Ti) atoms were also observed with decreased carbon and oxygen content. This demonstrates that BT NPs were present in good concentration on cotton. Further, EDX mapping of coated fabric (Supplementary Material Fig. S2) showed a slight decrease in Ba and Ti content after 15 washing cycles with increased O and C atoms due to the formation of more hydrogen bonds on the cotton surface during washing. Therefore, both SEM and EDX results confirm that BT NPs were incorporated on the fabric surface. Figure 4 shows the chemical state of C, O, Ba, and Ti evaluated in pure cotton and coated fabric by XPS. Both spectra showed two intense signals of C 1s and O 1s at 285 and 532 eV, which correspond to the binding energy of the C-C and C-H bonds and cellulose, respectively (Belgacem et al. 1995;Bhat et al. 2011;Kang et al. 2017). In coated fabric, Ba 4d peaks were observed at 88.9 and 90.7 eV, corresponding to 5/2 and 3/2 spin-orbit components, respectively, while Ti 2p peak was observed at 458 eV (Khan et al. 2021;Wegmann, Watson, and Hendry 2004). Table 1 presents a study of the bacterial reduction activity of BT NPs embedded fabric against E. coli and S. aureus. After 24 h bacterial treatment, only 5% bacteria reduction was observed for stock paste applied fabric, while the 20% and 10% BT NPs coated fabric showed a bacterial reduction of 99.8% and 99.4%, respectively. The treated fabric retained its antibacterial activity of more than 98% for both BT NPs concentrations even after 15 laundering cycles, indicating that BT NPs remained firmly attached to the cotton surface. Figure 5 shows the antibacterial activity of coated cotton fabric for E. coli. After 24-h contact period, many damaged areas were noticed by the SEM analysis throughout the sample (Figure 5f). Cotton has higher moisture regain and porosity due to which it is easily attacked by microorganisms. After incubation, the bacterial cells adhered to the pristine cotton swatches, and bacterial colony formation took place, thus damaging the fabric surface. However, BT being ferroelectric killed bacteria colonies on the exposed 10% BT coated surface (washed fabric) and thus prevented the fibers from bacterial damage (Figure 5g). So, even after washing, fabric treated with a 10% pigment concentration can effectively reduce microorganisms. BT bacterial reduction property is assigned to its ferroelectric nature resulting in spontaneous polarization, which kills bacteria when they come into contact with coated cotton's surface. It is assumed that the negatively charged cell wall of both gram-positive and gram-negative bacteria interacts with NPs or ions and is significantly impacted by the size, shape, charge properties, etc., of the nanoparticles. The antibacterial mechanism of BaTiO 3 is not examined comprehensively. However, Sasikumar et al. (2018) have reported that BT NPs can attach and interact with the membrane components, which disrupts cells and kills bacteria. Marin et al. (2021) have elaborated in their study that in an acidic environment, Ba 2+ releases from BaTiO 3 spontaneously apart from TiO 2 which can react with water and produces hydroxyl and free radicals. It was believed that the presence of such radicals damages nucleic acid, bacterial cell walls, and other structures of the bacteria. In this study, we anticipate screen-printed BT NPs generating an analogous impact. It is also expected that this antibacterial effect can be further increased in the presence of some external stimuli such as UV light, mechanical strain, or temperature variation. This is due to the fact that BT is known for photocatalysis, piezocatalysis, and pyrocatalysis.  The results of this study were also compared to those in the literature, as shown in Table 2. The results were compared with work previously reported on chitosan, Ag, Zn, Cu, Ti NPs, and their derivatives because there is no study available that evaluates the antibacterial activity of BT NPs on textile. In contrast to results published in other studies in the literature, the prepared samples demonstrated effective antibacterial performance. Since BT has been claimed to be nontoxic, environmentally acceptable, and inexpensive, this study has opened a new window to investigate the potential application of ferroelectric materials in textiles.

Assessment of UV property
Due to the depletion of the ozone layer, long-term exposure to these UV radiations can cause serious health hazards like skin reddening, acne, photoaging, and skin cancer. Figure 6 shows that BaTiO 3 is UV active in the region of UVA and UVB with absorption peaks in the range of 300-330 nm. The coated fabric is capable of blocking harmful UV rays and thus can prevent humans from different skin

Effect of coating on cotton properties
After coating, it becomes essential to evaluate the water vapor permeability, air permeability, stiffness, and other mechanical properties of the modified fabric. Table 3 illustrates the effect of BT coating on cotton intrinsic properties. The water vapor permeability for pure cotton, 20% BT, and 10% BT were observed as 44.7, 41.9 ± 2, and 42.6 ± 2 g/m 2 /h, respectively. As compared to coating work reported in the literature, herein prepared modified cotton shows better permeability (Xu et al. 2017;Zhou et al. 2021). The air permeability of pristine cotton was measured as 174 cm 3 /s/cm 2 , while for 20% and 10% BT coated cotton fabric, the air permeability values were found as 161 cm 3 /s/cm 2 , and 166 cm 3 /s/cm 2 , respectively. The fabric stiffness of pristine cotton and coated cotton was measured in terms of bending length and flexural rigidity. For pure cotton, Figure 6. UV absorption spectra of treated samples. the bending length was observed as 43 mm with a flexural rigidity of 14.009 μN.m. After 10% BT coating, the bending length and flexural rigidity were measured as 47 mm and 18.966 μN.m, respectively. The 20% BT coated cotton showed bending length and flexural rigidity of 49 mm and 21.933 μN.m, respectively. The tensile strength for pristine cotton and BT coated (20% and 10%) was measured as 124 N, 122 N, and 123 N, while abrasion resistance was observed as 38,000, 35000, and 37,000 rubs, respectively. These findings suggest that the intrinsic qualities of pure cotton were not significantly affected by surface modification.

Conclusions
A durable cotton fabric with antibacterial and UV protection properties was prepared by successfully coating pristine cotton with BaTiO 3 nanoparticles in two different concentrations of 10% and 20%. A simple and versatile screen printing technique was employed for embedding these BT NPs on cotton fabric. The results of FTIR, XRD, FE-SEM, and XPS demonstrated that the BT NPs were effectively loaded on the cotton surface. The coated BT NPs remained strongly adhered to the fabric surface even after 15 laundering cycles. The modified fabric showed excellent reduction greater than 99% for both E. coli and S. aureus. After laundering (15 cycles), the 20% and 10% BT coated cotton depicted UPF values of 73.48 and 68.77, respectively, showing excellent UV protection. Additionally, the BaTiO 3 coating had no discernible impact on the inherent qualities of cotton, including air and water permeability, fabric stiffness, tensile strength, and abrasion resistance. For use in technical textiles and everyday clothing, the BaTiO 3 -coated cotton has great potential.