1 Introduction

Research on advanced materials for air filtration has received significant attention in the last few years due to increased concern about environmental pollution and air quality worldwide [1]. Air filtration with nanofibrous membranes is one of the advanced techniques that increase the efficiency of airborne particle filtration by using nanoscale materials. Due to their tiny holes, these membranes excel at absorbing allergens, pollutants, and particulate matter, surpassing the performance of traditional filters [2]. The primary goal of this advancement in air filtration is to enhance air quality, offering a finer level of filtration for cleaner indoor and outdoor environments. Research on innovative materials, advanced functionalities, and structure is propagating [3, 4]. Silk, a natural protein fiber produced by silkworms, possesses distinctive qualities that make it highly desirable in electrospinning applications. Silk is renowned for its exceptional tensile strength [5]. Silk fibers are robust and exhibit remarkable durability, making them ideal for crafting nanofibers with superior mechanical properties. Additionally, silk's biocompatibility enhances its applicability for various biomedical purposes [6]. The high heat radiant properties of silk fabrics will impart additional functionality of developed hybrid technical cloth for multifunctional applications.

Polyethylene terephthalate (PET) polymer plays a significant role in electrospinning for the creation of nanomembranes designed for air filtration, owing to its distinct characteristics. PET is renowned for its outstanding mechanical strength, making it suitable for producing nanofibers with robust durability-an essential factor in air filtration applications [7]. The unique structure produced by the PET nanocoating on the silk woven will feature exceptional strength, filtration performance, and permeability. Gao et al. [8] reported that MXene incorporated an air filter that exhibits high filtration efficiency(99.7%). However, the pressure drop becomes high, leading to a negative impact on the comfort and breathability properties. Lou along with his team [9] prepared a core filter layer using electrospun polyvinyl butyral and Apocynum venetum extract nanofibrous membranes where filtration performance appeared at 98.3% at a very high-pressure drop of 142 Pa. Moreover, Yuanqiang Xu et al. [10], multi-layer structured nonwoven material created through melt blowing and electrospinning, shows enhanced filtration, but the pressure drop is high. Bonfim and his colleagues' air filter provides decent filtering but lacks functional properties [11]. Moreover, electrospun nanomembrane shows low mechanical performance [12].

There are locks of balance of high filtration and low-pressure drop, along with strong mechanical strength and functional characteristics in existing air filters. Thus, this research aims to develop innovative structured silk woven cloths with rPET nanocoated air-filtering fabric with promising potential for interior use, focusing on achieving a balance between comfort, improved filtration efficiency, durability, and resistance to radiative heat.

2 Experimental

2.1 Materials and chemicals

Silk woven fabric was collected from the Bangladesh Sericulture Development Board, Rajshahi, Bangladesh. rPET bottles were collected from the Gazipur area of Dhaka, Bangladesh. Silver nitrate, dichloromethane, and trifluoroacetic acid were collected from Sigma-Aldrich, Germany. Sodium alginate is sourced from Loba Chemicals, India. The experimental design is given in Table 1.

Table 1 Experimental design for this research
Full size table

2.2 Methods

The manufacturing and synthesis procedure for the creation of a technical cloth entails several crucial processes. To begin, the rPET bottle collection is chopped into small pieces, followed by washed fresh water and dried and woven for 30 min. The 20 gm of rPET is dissolved in a combination of dichloromethane and trifluoroacetic acid in a ratio of 70:30 to produce a solution of rPET. Three hours are then spent stirring this solution to ensure that it is completely dissolved and viscosity maintains 180 cPs. Following this, the neem leaf extract was employed to greenly synthesize AgNPs, whereby silver ions were converted into nanoparticles [13]. Initially, 60 g of finely cut neem leaves were placed in 150 ml of distilled water and boiled for 1 h. Subsequently, 10 ml of the leaf extract was introduced into an 80 ml solution of silver nitrate, and the resulting mixture was continuously stirred using a magnetic stirrer at 80 °C for 1.5 h. The formation of AgNPs was monitored by observing the color change of the reaction mixture, transitioning from transparent yellow to brown, and eventually to a deep brown color. The ultimate procedure entails the production of silk technical cloth by electrospinning, in which a laboratory-based electrospinning machine is utilized to deposit the rPET solution and AgNPs onto silk-woven fabrics. The spinning conditions were established to ensure optimal production of nanofibers. The experimental setup included setting the flow rate at 2.5 ml/hour and applying a positive voltage of 24.0 kV and a negative voltage of 12.0 kV. The collector distance was maintained at 14.5 cm throughout the experiment. These parameters were carefully selected based on preliminary tests and existing literature to achieve the desired nanofiber morphology and quality. The electrospinning process was conducted in an ambient environment with a relative humidity of 66% and a temperature of 28 ºC to minimize any external influences on the spinning process. A sodium alginate solution of 10% is used as a cross-linker between fabric and nanocoating. Producing technical fabric with a nanofibrous coating requires an approximate total of 1.5 h. A possible route of manufacturing the technical cloth from silk woven fabric, rPET, and AgNPs by electrospinning is shown in Fig. 1. Moreover, statistical significance testing was employed to analyze the experimental results obtained from three different sample varieties (S, S-1, S-2), each comprising five samples. The mean values of the samples were calculated, and bar charts were illustrated to depict the standard errors associated with the data.

Fig. 1
figure 1

Methodology of manufacturing the technical cloth from silk woven fabric, rPET, and AgNPs by electrospinning

Full size image

3 Characterizations

Morphological observations of the nano-technical cloth were conducted using a scanning electron microscope (SEM; Hitachi, Japan, SU 1510). The diameter and orientation were analyzed, and porosity was determined by weighing samples and computing volume based on thickness and area data. The porosity % of the developed samples was calculated using the formula by image J software as discussed in reference [14].

$$\text{Porosity \% }= \frac{\text{Area of pores }}{\text{Total area}}\times 100$$
(1)

where, the area of pores is an area occupied by the pores in the SEM image and the total area is the total area occupied by the image.

PFE was determined based on the ASTM method F2299, using a particle counter device (Kanomax, Japan, Model-3910) with 0.3 nm sized particles using the formula –

$$\upeta = \frac{\text{C}1 -\text{ C}2 }{\text{C}1}\times 100\text{\%}$$
(2)

Where, C1 is upstream and C2 is downstream, and η is the PFE.

Meanwhile, tensile properties were evaluated using a universal tensile testing machine equipped with a 300N precise load cell (Testometric, M250-3CT, India) following ASTM D5034 with a 0.11 mm thick cloth at a speed of 300 mm/min. Moisture management properties was evaluated by a moisture management tester (M290, SDL Atlas, HK) following AATCC 195–2009. In addition, using a bench scale instrument, the radiative heat resistance test was conducted in accordance with the protocol outlined by Shaid et al. [15]. After subjecting the materials to a 50 W incandescent bulb at a distance of 20 cm, the test specimens' resistance to radiant heat was ascertained. Heat sensors recorded the rise in temperature of the material exposed to radiative heat and the opposite surface exposed to the environment (250C and 65% RH) every 30 s for 60 min. During the experiment, the temperature sensors were sufficiently insulated with masking tape. Moreover, to assess the antibacterial properties by measuring the zone of inhibition (ZOI) of the developed nanocoated technical cloth for air purification against the bacteria S. aureus and E. coli, the Kirby-Bauer disc diffusion method was employed, using ATCC 6538 standard for S. aureus and ATCC 11775 for E. coli. Moreover, Fourier Transforms Infrared Spectroscopy (FTIR) was conducted (IRPrestige21, Shimadzu Corporation, Japan) to analyze the chemical structure of rPET where the spectra captured in the range of 400–4000 cm−1 at a resolution of 4 cm−1

4 Result and discussion

4.1 Morphological observation

Morphological observation provides valuable insights into the morphology, structure, and properties of developed nanofibrous materials, enabling their development and customization for a wide range of applications [16]. Figure 2 presents images of developed samples, each representing different stages or variations of silk fabric with recycled polyethylene terephthalate (rPET) coating. The raw silk fabric in its untreated state, before any coating or treatment, is seen in Fig. 2a. The texture and shine of raw silk fabric are generally unaltered; however, the color and weave may differ due to the particular silk variety and processing techniques employed. Subsequently, a single layer of rPET coating is applied to the raw silk fabric, as seen in Fig. 2b, to enhance its filtration efficiency for air purification purposes. Furthermore, Fig. 2c illustrates the raw silk fabric that has been treated with a dual-layer rPET coating. Figure 2d presents a lateral perspective of one of the samples that were developed.

Fig. 2
figure 2

Actual image of a raw silk fabric, b silk technical cloth with a single layer of rPET coating, c silk technical cloth with a double layer of rPET coating, and d side view that focus the thickness

Full size image

SEM provides high-resolution images depicting the surface morphology of the nanofibrous membrane, offering insights into the placement, orientation, and dispersion of nanofibers [17, 18]. In Fig. 3a clear and homogeneous fiber formation is evident in the double-layered coating samples. Thick back fibers observed in the images indicate the finer silk yarn from the utilized technical cloth. In addition, Fig. 3b represents an SEM view of sample S, which has only silk fabric without coating. The porosity of raw silk fabrics is 41 ± 3.1%, whereas the nanocoated sample shows a porosity of 14 ± 2.5%. This indicates the area of pores is reduced; thus, the filtration efficiency is drastically increased. Figure 3c indicates the diameter distribution by histograms and the average diameter found at 280.5 ± 4.5 nm by taking 100 samples from various parts of the SEM image by image J. These results indicate that finer fiber formation contributes to high filtration efficiency and improved mechanical strength, enabling the membrane to withstand external pulling forces during use.

Fig. 3
figure 3

SEM image of a silk technical cloth (S-2) with a double layer of rPET coating at two different magnifications, b raw silk woven fabric (S) without any coating, and c the fiber diameter distribution of sample S-2

Full size image

4.2 Particle filtration efficiency and differential pressure analysis

PFE, which measures a filter's ability to draw in and retain airborne particles, is an important metric in air filter research that contributes to the overall efficacy of the system by quantifying the capacity of a filter to eliminate particles of different sizes, which is crucial for air filter research. In the study of filtering materials, differential pressure, which denotes the pressure drop across the filter, is an additional crucial property [11b. Sample S-1, and S-2 obtained 5 ± 1 and 9 ± 1 mm respectively. The antibacterial assay's ZOI indicates how well the produced sample can stop S. aureus and E.coli from growing. More inhibition zones indicate more potent antibacterial qualities [29]. Negatively charged cell membranes and positively charged AgNPs can easily interact with each other, enhancing the antibacterial action [30]. AgNPs penetrated the cell layer and entered the tiny organisms (bacteria). Another way that AgNP interacts with the cell membrane is through the generation of reactive oxygen species (ROS), which leads to oxidative stress and, ultimately, cell death [31]. Once within, AgNPs can damage proteins and enzymes and impair the activity of substances containing phosphorus and sulfur-containing proteins. AgNPs also reside in the electron transport chain, disrupt the mitochondria, and destabilize the ribosome. AgNPs deactivate the bacterium in this way [32]. The vigorous antibacterial activity of the developed sample ensures that the air filter not only collects particulate matter but also stops hazardous germs from growing. When this sample is used as an air filtration system, it will add to the total efficacy of the produced nanofibrous membrane in fostering a safer and healthier atmosphere.

4.7 FTIR analysis

FTIR analysis is a flexible technique that aids in develo** and refining efficient air filtration materials by assisting researchers and manufacturers in comprehending the chemical composition, polymer identification, and functional properties of rPET nano-coated silk technical cloth [33]. It offers details regarding the material's chemical makeup. It assists in determining which particular functional groups are present in the developed technical cloth. In Fig. 12, the FTIR spectra of silk fabric, single coating, and double coating were presented. The carbonyl stretching vibration in the ester group, indicative of the C = O stretching, is observed around 1720–1700 cm−1[34], as demonstrated in Fig. 12 for the developed sample at 1704 cm−1.

Fig. 12
figure 12

FTIR spectra of the developed samples

Full size image

Additionally, the FTIR spectra exhibit C–O–C stretching at 1249 cm−1, aligning with the characteristic groups of rPET [35]. This alignment is supported by the data table, indicating that bands related to C–O–C stretching in the ester group typically occur between 1300–1200 cm−1 [36]. Furthermore, this illustrates N–H stretching at 3270 cm−1, a peak typically associated with N–H stretching vibrations, and C-H bending at 1253 cm−1, affirming the presence of silk fabric. The consistency of these observations strengthens the identification of specific molecular groups within the developed sample [37]. The 1642 cm−1 spectra indicate the presence of the amine group, which has been used in the process AgNO3, and the 1218 cm −1 spectra demonstrate C-O stretching leads to the presence of the leads to the existence of the AgNPs. In addition, cyanate esters (NCO) groups were found in three samples in the 2337 to 2355 cm−1 range. N–H bending is found in peak number 1508 cm−1, indicating the silk fiber. Overall, the alignment of the graph in the S, S-1, and S-2 samples in the characteristic peaks in the graphs indicates the presence of the silk PET and AgNPs. In addition, 2911 cm−1 spectra demonstrate the C-H stretching vibrations in the aliphatic groups of the polysaccharide. C–O–C Stretching (ether linkage) obtained in 1245 cm−1 spectra. This indicates that the sodium alginate is thicker, which makes cross-linking of the nanofibrous coating and silk woven cloth possible.

5 Conclusion

The fabricated technical cloth exhibits enhanced filtration efficiency with a low-pressure drop, improved tensile strength, and antibacterial properties. Additionally, the material demonstrates promising potential as an advanced air filter, as evidenced by its performance in moisture management testing and radiative heat barrier testing. The average PFE for fabric S was 35.41%, resulting in a low DP of 21.9 Pa/cm2. In contrast, fabric S-1, which has an extra rPET nanofibrous coating on the silk substrate, attained a significantly higher PFE of 96.5% and a slightly higher DP of 28.7 Pa/cm2. These results show great filtering efficiency with a low-pressure drop, which is necessary for air purification applications. Moreover, developed samples show good radiative heat barrier performance, like sample S, which shows a moderate radiative heat barrier of 14.50 °C. Furthermore, sample S-1 displays an outstanding barrier of 23.75 °C, while sample S-2 displays a barrier of 25.50 °C. In addition, ZOI was obtained against S. aureus and E.coli, which reveals strong protection against the common bacteria for S-1and S-2 that may develop on the surface of the air filter during use. The tensile strength is found to be 58.42 MPa for S, 58.41 MPa for S-1, and 57.26 MPa for S-2, respectively, comparatively higher than the available filter. Therefore, developed silk-PET nanotechnical cloth would be used as air purifying curtains in windows in homes, offices, and industries to ensure high filtering performance, high strength, and good radiative heat barrier performance to ensure comfort. Future scope available to work with twill, satin weave structured fabric with nano coating to assess the filtration efficiency.