1 Introduction

The electrospinning technique has emerged as the most efficient approach for the large-scale manufacture of polymeric nanofibres over the previous decade, according to research and industry trends [1]. Electrospun nanofibrous membranes have fewer than 100 nm in diameter, with a higher ratio of surface area to volume, higher porosity, and various pore size distribution [2]. Electrospun nanofibrous membranes can be easily adjusted by adding additives to the nanofibre, covering the surface of the nanofiber with a specific layer with the help of functional groups or materials [3]. These membranes have been shown to be helpful in various disciplines, including pharmaceuticals, biomedicine, food industries, catalysis, gas separation, and water treatment [4]. In addition, such composite nanofibers are ideal candidates for biotechnology, textiles, membranes/filters, sensors, and other applications due to their outstanding characteristics and multi-functionality [5]. There is increasing interest in antimicrobial nanofibers in academic and industry circles, as they represent a unique region combining nanofiber intrinsic features with biocidal action. However, various procedures, for example, phase separation, drawing, self-assembly, and template synthesis, are utilized for polymeric nanofiber synthesis. Unique fiber generating ability that has ranged from a few micrometres to nanometers and better versatility made the electrospinning technique very popular and cost-effective and able to produce continuous nanofibers [6]. Electrospinning is an essential and straightforward technology that may be used on various polymers. A basic electrospinning setup can be made by filling a syringe with a polymeric solution with a metal needle, power supply, and collector made of metal. A power supply is coupled with a high-voltage electric field and a polymer solution with constant flow [6, 7]. In their research of Bihter Zeytuncu et al. [8]. found the following physical properties from the nanofibrous membrane shown in Table 1.

Table 1 Physical properties of the nanofibrous membrane [8]
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The antibacterial effect of graphene has been attributed to various processes, including oxidative stress, membrane stress, and electron transfer. Graphene has activated the anti-bacterial on nanofibers. Graphene can also show antibacterial action by electron transfer since it may function as an electron acceptor and remove electrons from bacterial nanofibers, which may, in turn, impair the integrity of the membrane [9]. Besides this, highly directed structures and networks are formed inside the polymeric materials when nanofibers are reinforced with nanofillers like graphene nanoparticles, improving nanofibers’ electrical, mechanical, and thermal properties [10].

This study aims to synthesize nanofibrous membranes incorporating graphene with neem and PVA for biomedical applications and food packaging. PVA is a biodegradable, water-soluble and chemical-resistant material. It is highly flexible, has good barrier characteristics, and is non-toxic [11,12,13,14,15,16,17,18,19,20,21]. Besides, attention is paid to evaluating the morphology of the developed membrane by FTIR, SEM, XRD, and EDX analysis. Antibacterial performance is assessed against gram-positive as well as gram-negative bacteria. For further study, a moisture management test is performed. The experimental results have shown that the synthesized nanofibrous membranes can be used in biomedical applications such as tissue engineering, cancer diagnosis and treatment, medical protective equipment, etc. Furthermore, the thermal behaviour of the nanofibrous membranes is investigated to prove its suitability for packaging applications.

In this study, the novelty is that it combines graphene nanoparticles with plant extract to improve strength, barrier effect, and conductivity in connection to biological properties for better packaging materials. This makes it different from other works available in the literature and declares its originality. It can also be suggested in drug-loaded systems, skin wound dressings and other health issues and packaging applications. Besides, it can be used for desalination and water treatment.

2 Materials and methods

2.1 Materials

To ensure the versatile application of the membrane, Graphene nanoparticle is used to incorporate with the Polyvinyl alcohol solution. The Graphene NPS are collected from Shanghai Ruizheng Chemical Technology Co., Ltd of China. The provided nanoparticles have almost 95 wt% purity, 50 X 50 nm diameter, 3.4 to 7 nm thickness, 6 to 10 layers, 105 Sm−1 electrical conductivity, 100 to 300 m2/g SSA, 0.5% sulfur content, and 0.5% oxygen content. PVA was purchased from S. A. scientific store in Dhaka, Bangladesh. PVA with a density of 1.19–1.31 g/cm3 collected from the local market is a binding agent. As a synthetic polymer, PVA possesses water solubility properties, better tensile strength, and flexibility. Besides this, PVA has a high oxygen and aroma barrier characteristics suitable for superior film-forming, emulsifying and adhesive properties. Neem leaves are collected from the university garden for beneficial extraction processes in biomedical applications.

2.2 Methods

2.2.1 PVA solutions preparation

Polyvinyl alcohol (PVA) powder is dissolved in water and vigorously stirred for 2 h at a temperature of 80 °C. 10% w/v concentrated PVA solution was obtained by mixing 10 gm PVA polymer with 100 mL de-ionized water at 80 °C. Due to the lengthy process, the end outcome would be a clear and translucent PVA solution. To keep the solution consistent, a condenser was employed to reduce the temperature and prevent water evaporation in the surrounding.

2.2.2 Neem extract preparation

The neem leaves were first harvested from Azadirachta indica trees on Bangladesh’s Dhaka University of Engineering and Technology (DUET) campus. The leaves were dried for 5 days under the sun at 37 °C after washing them three times with de-ionized water. After that, 20 g of dried leaves were pulverized and combined with 50 millilitres of distilled water in a 200 mL beaker. Later, the mixture was agitated at 60 °C temperature for 1 h with the help of a magnetic stirrer. The Whatman filter paper was used to filter the mix when the solution turned yellow.

2.2.3 Preparation of nanofibre membranes

This study used three different types of electrospinning samples for nanofibrous membranes. For the first sample-R1, 88.5% PVA solution was mixed with 1.5% graphene and 10% neem extract, and the combination was thoroughly mixed because of the higher conductivity of homogeneous electrospinning solutions. The second sample-R2 (94% PVA + 1% graphene + 5% neem extract) and the third Sample-R3 (99% PVA + 1% graphene) were prepared in the same way shown in Table 1. After that, a syringe having a diameter of 0.9 mm was used to inject the electrospun solution. The nanofibres were gathered on a drum collector’s nonwoven fabric. Electrospinning had the following parameters: The distance between the spinneret and the fiber collector was 15 cm, the voltage power supply was 25 kV, the spinning solution feed rate was 0.5 mL/h, and the temperature was 25 °C. Finally, at room temperature, the membranes were dried. Figure 1 shows the nanofiber membrane preparation process. Table 2 shows the constituents ratio of different samples.

Fig. 1
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Preparation of nanofibre membranes

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Table 2 Different samples with solution ratio
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2.3 Characterization

2.3.1 Fourier transformed infrared spectroscopy test

Fourier transforms infrared spectra of the nanofibrous membranes were measured by the FTIR spectrometer made by Perkin Elmer with 500 to 4000 cm−1 range wavelengths. The experiment was performed to find the presence of different organic, inorganic and polymeric compounds on the surface of the prepared materials.

2.3.2 X-Ray diffraction test

German Bruker D8 advance-made X-ray polycrystalline diffractometer was employed to measure the crystalline structure of the nanofibrous membrane at a scanning speed of 3°/min with a scanning angle ranging 5°–50°. Same-sized circle-shaped samples were cut for the test. This analysis identified the crystallinity of the synthesized materials.

2.3.3 Surface morphology test

The surface morphology of the synthesized nanofibrous membranes was analyzed by scanning electron microscopy coupled with an EDX analyzer. The nanofibrous membrane was dispersed in ultra-pure water, and the solution was collected dropwise by a glass slide. The membrane was then dried by air, followed by gold spraying. Maintaining 20 kV accelerating voltage, the membrane was taken for SEM analysis. The nanofibrous membranes were observed by conductive adhesive after cutting and pasting on an electron microscopy platform before SEM analysis. The SEM images were captured at various resolutions. EDX analysis was performed to identify multiple chemical elements in the prepared materials.

2.3.4 Antibacterial test

A popular method called Kirby–Bauer disk diffusion was used to test the bacterial activity of the sample R1, R2, and R3 membranes against S. aureus, a gram-positive bacterium, and Pseudomonas, as a gram-negative bacterium. In this method, the developed nanofibrous membranes were cut with the dimension of 4.5 × 4.5 cm2 and kept with 2 mL bacteria diluting CFU/mL in a 9 mL falcon tube. Capping loosely, all the flasks were kept on a shaking incubator to be surprised at 120 rpm for 2 h at 37 °C temperature. Dilutions were made using buffer solutions, and 0.1 mL of the dilutions of each was kept on nutritional agar. The inoculation plates were incubated for 18–24 h at 37 °C before being counted. Also, a similar procedure was followed in the bacterial reduction test.

The following equation is used to calculate % of reduction,

$$ \% \;{\text{of}}\;{\text{reduction = }}\frac{{B - {\text{A}}}}{{\text{B}}} \times 100 $$

After 2 h of contact time and test samples of the falcon tube and control, the surviving pieces are A and B. The colony forming unit (CFU) is computed using a 0.1 mL plate capacity.

Transfer a loopful of fungal spores to 5 mL of sterile normal saline using a loop. Using a shaker, I homogenized the mixture. Using sterile cotton-tipped swabs, streak the mixture on Sabouraud Dextrose Agar (SDA) plates many times. Transfer 25 µL of each sample’s test concentrations into the holes previously drilled on agar media using a cup borer. Place a tiny block of fabric sample on SDA media that has been once contaminated with fungus in the case of the Fabrics sample. Allow 30 min for the dishes to cool to room temperature before serving. At 30 °C for 24 h, incubate the plates. Measure the diameter of clear zones by placing the scales on a black surface and interpreting the results.

2.3.5 Moisture management test

The moisture management property of the developed nanofibrous membrane was analyzed by UK based SDL Atlas-made M290 moisture management tester based on the method of AATCC 195-2009. This standard was used to evaluate absorption rate, spreading speed, wetting time, and maximum wetting radius of the inner and outer surface so that the mat can be categorized by its interaction with liquid.

2.3.6 Thermal test

Thermogravimetric and differential scanning calorimeter analyses were performed to evaluate the thermal property of the developed nanofibrous membranes. TGA analysis was performed by TGA, Perkin Elmer, USA, under a nitrogen environment, maintaining a 30 mL/min flow rate. The thermal behaviours of the nanofibrous membranes were investigated by TGA at a heating rate of 10 °C from the temperature range of 0 to 800 °C. USA-made DSC 2910 TA instrument was employed to evaluate the DSC analysis from room temperature to 800 °C at a 5 °C/min cooling rate.

3 Result and discussion

3.1 FTIR analysis

The FTIR analysis identified the presence of organic, inorganic and polymeric materials. Figure 2 shows the FT-IR curve of the nanofibrous membrane R1, R2, and R3 composed of mainly complex ingredients such as alcohol, primary amine, alkane, alkene, tertiary amide, inine, aliphatic ether groups [22]. All the samples show similar kinds of characteristic peaks, but the presence of neem increased the intensity of the spectra. Sample R1 shows medium stretching cyclic alkene (C=C) band at 1567 cm−1. The presence of strong stretching alcohol and medium stretching primary amine is attributed at 3295 cm−1 for the sample R1 and R2, which shifted to 3294 cm−1 at the sample R3. Medium stretching alkane C–H is attributed at 2941 cm−1 and 2911 cm−1. Characteristic absorption peak 1603 cm−1 represents strong stretching tertiary amide C=O at sample R1 which is shifted to 1707 cm−1 and 1714 cm−1 for the R2 and R3 [23]. Characteristic strong stretching alkene C=C peak is attributed at 1420 cm−1. The adsorption band at 1330 cm−1 corresponded to the medium trying inine C=N group. The intense and broadband peak at 1142 cm−1 was caused by the C–O intense stretching aliphatic ether group [24]. The diffraction peak at 1377 cm−1 belongs to the medium stretching phenol O–H group at samples R2 and R3 [25, 26]. Phenolic compounds contribute to developing human health. Phenolic compounds help to decrease biological systems’ degradation. The phenol stimulates bone formation, proliferation, mineralization, osteoblast survival, and differentiation. Besides, the differentiation of osteoclast cells is inhibited by phenols. Phenols promote bone formation and reduce bone resorption. Furthermore, phenols promote cross-linking of dentine and increase its mechanical stability [27]. At R3, the characteristic peak 1567 cm−1 is attributed to the medium stretching cyclic alkene C=C. Similar and overlapping distinct peaks were observed from the R1, R2, and R3. New absorption peaks were observed in R2 and R3, indicating that graphene and neem mixture in the membrane both physically and chemically. The results also suggest that the graphene and neem were successfully enwrapped in the nanofibrous membranes [28]. The presence of different compounds in FTIR analysis is shown in Table 3.

Fig. 2
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FTIR spectra of the developed nanofibrous membranes

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Table 3 FTIR analysis data table of the synthesized nanofibers membrane
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3.2 XRD analysis and crystallographic structure

The XRD pattern of nanofibrous membranes samples R1, R2, and R3 is shown in Fig. 3a to c. Analysis nanofibrous membranes covered with aluminium foil were used in this XRD experiment. XRD profile analysis confirmed the presence of α and γ phases in the developed nanofibrous membranes [29, 30]. Strong interaction among PVA, graphene and neem made the membranes smoother, confirming lower crystalline properties [31, 32]. Aluminium foil samples R1, R2, and R3 were fined in this region with 2 = 35 to 90 al peaks. Sample R1 has several Bragg reflections corresponding to the (002), (110), (200), (300), (210). R2 to the (020), (220), (040), (420), (440) sets of lattice planes and R3 to the (200), (220), (040), (420), (440) sets of lattice planes are also detected. An orthorhombic crystal system with three mutually perpendicular axes having unequal lengths was observed for samples R1, R2 and Hexagonal crystal for sample R3. A hexagonal system is a main structure category with four axes and three of equal length set at 120° to one another. Sample R1 lattice parameters a = 7.75, b = 5.90, c = 16.86 and Sample R2lattice parameters a = 11.45, b = 18.45, c = 5.45. In the same way for sample R3, a = b = 32.70, c = 22.70. Crystalline structure plays a critical role in determining the physical properties of the nanofibrous membrane. The crystal structure greatly affects tensile strength, yielding strength, and flexibility [33]. It is found from the experiments that close-packed and more complex structures are inherently harder [34]. The addition of neem decreases the number of peaks, indicating a decrease in the crystallinity of the membrane. The crystallinity decrease reduces the membrane’s strength and makes it less close-packed.

Fig. 3
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XRD crystallographic structure analysis of the developed nanofibrous membrane a R1, b R2, c R3

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3.3 Morphology of nanofibrous membranes without coating

SEM analysis was performed to observe the morphological orientation of nanofibrous membranes without coated aluminium foil at magnifications of 2 K to 20 K to get a good quality image with a voltage of 10 kV (Fig. 4). The average size of the particle was calculated by the Image J software shown in Fig. 5a to c [35]. The surface morphology of samples R1, R2, and R3 was analyzed by SEM image. Figure 4a to c depict all SEM images. Sample R1 and R2 nanofibrous membranes had a uniform cylindrical shape, the random orientation of nanofibers, and a smooth surface consistent with other literature [36]. However, in the nanofibrous membranes sample R3, there were numerous fractures. The SEM images of nanofibrous membranes showed that both beaded structures and the appearances could not confirm the even distribution of neem and graphene in the electrospun fibers. Incorporating neem and graphene with PVA might modify the local molecular interactions and topology [37, 38].

Fig. 4
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SEM images of the without coated samples a R1, b R2, c R3

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Fig. 5
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Average particle size comparison of the developed nanofibrous membranes a R1, b R2, c R3

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To summarize, the paternity of neem extract affects surface morphology outcomes. The fiber had a good surface finish, uniform thickness, and good filament-forming action in this region where nanofibrous membranes of R1 and R2 were used. Sample R3 fibers displayed uneven thickness, apparent fiber breakage, and many bubbles and adhesions among the nanofibrous membranes ‘fibers. Because only PVA and graphene nanoparticles were utilized, and the graphene influences the fiber. Micropores are observed from the SEM images, which suggests that the prepared nanofibrous membranes can be used for desalination. The average particle size is 461.5 nm, 370.7 nm, and 276.9 nm for samples R1, R2, and R3, respectively. The results indicate that the size of particles is increased with the increase of neem extract (Fig. 5).

3.4 Morphology of coated nanofibrous membranes on aluminium foil

To obtain images of acceptable quality, an SEM analysis was used to investigate the morphological orientation of nanofibrous membranes covered with aluminium foil at magnifications of ×100 to ×50,000 with a voltage of 5–15 kV [35]. The surface morphologies of PVA/neem membranes containing graphene nanoparticles are shown in Figs. 6a to h, 7a to h, and 8a to h. The surface of the PVA/neem composite membrane has many graphene nanoparticles grafted on it. The nano-sized graphene particles tended to agglomerate and disseminate onto the PVA/neem membrane surface as the concentration of graphene nanoparticles increased. It was difficult to wash and remove graphene nanoparticles from the membrane surface, which could be attributed to graphene’s self-assembly and the intense contact between graphene, Neem, and PVA polymer. Besides, the characters are smooth and free from foreign particles. Voids and cracks are not observed in the images. This makes the material mechanically more robust.

Fig. 6
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SEM analysis of the sample R1 at different magnification with coating at a 100X, b 5000X, c 5000X, d 10,000X, e 20,000X and f 50,000X

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Fig. 7
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SEM analysis of the sample R2 at different magnification with coating at a 100X, b 5000X, c 5000X, d 10,000X, e 20,000X, f 30,000X, g 30,000X and h 50,000X

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Fig. 8
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SEM analysis of the sample R3 at different magnification with coating at a 100X, b 100X, c 1000X, d 1000X, e 2000X, f 5000X, g 5000X and h 20,000X

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3.5 Elemental analysis of coated nanofibrous membranes

Aside from the essential ingredients, an EDX analysis confirmed the presence of chemical production. The area of distinct samples was concentrated during the EDX analysis, and the peaks are displayed in Fig. 9a to c. The samples’ percentages of oxygen and carbon atoms were validated by the EDX analysis with an accelerating voltage of 15 kV in the K shell. This EDX was performed on an aluminium foil paper, and Al’s weight and atomic percentage were also displayed for all samples. Since all examples are conductive based on the weighted rate of graphene, sample R1, R2, and R3 has 21.21%, 11.9%, and 11.39% of carbon in mass; 1.36%, 11.58%, and 12.77% of oxygen in the group; 77.43%, 77.33% and 75.84% of aluminium in mass. The results show that the absence of neem increases the mass percentages of C, which plays a good role in determining the physical and chemical properties of the nanofibrous membranes. Literature suggests that the increase in carbon percentages increases the mechanical properties of the materials. Carbon plays a significant role in interacting with dislocations and changing microstructure, thus improving mechanical properties [39]. Tables 4, 5 and 6 shows the EDX data table.

Fig. 9
figure 9figure 9

Elemental analysis of coated nanofibrous membranes for sample a R1, b R2, c R3

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Table 4 EDX data for the sample R1
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Table 5 EDX data for the sample R2
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Table 6 EDX data for the sample R3
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3.6 Particle analysis of nanofibrous membranes

The particle distribution on the nanofibrous membrane’s surfaces and a nanofibrous membranes coating layer on aluminum foil was addressed in Figs. 10a to c and 11a to c. For nanofibrous membranes, the mean particle distribution areas through projected surfaces are 2.345, 17.02, and 2.125, respectively, whereas, for coated membranes on aluminium foil, the mean particle distribution areas are 1.574, 1.707, and 0.917, respectively. The findings showed nanofibrous membranes have higher particle distribution areas than coated membranes. When considering nanofibrous membranes without coating, the number of particles is 2481, 358, and 2749 for R1, R2, and R3 test samples, respectively, with percentage coverage of 48.1 per cent, 50.37 per cent, and 48.29 per cent, and densities of 0.2055, 0.02965, and 0.2277 particles/mm2. When nanofibrous membranes are utilized as a coating, the number of particles is indicated as 2749, 4954, and 5629, respectively, with a percentage coverage of 37.55 per cent, 73.4 per cent, and 44.82 per cent for samples R1, R2, and R3. The particle densities for coated nanofibrous membranes samples were 0.2391, 0.4308, and 0.4895 particles/ respectively. In terms of coverage percentage, the distribution area of particles, the thickness of particles, and particle number, there are noticeable differences across the samples, which affected their thermal properties greatly. This is because graphene nanoparticles, PVA, and neem extract, for various examples, have different collision properties. These findings are consistent with those seen in the literature [40, 41].

Fig. 10
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Particle Analysis of Nanomembrane without Aluminum Foil

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Fig. 11
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Particle analysis of nanofibrous membranes with aluminum foil for sample a R1, b R2 and c R3

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3.7 Surface roughness analysis of nanofibrous membranes

Figures 12a to d, 13a to d, 14a to d, 15a to d, 16a to d and 17a to d show the surface roughness of nanofibrous membranes with and without covering materials under various chemical compositions. The average surface roughness of the Graphene/PVA (R3) nanofibrous membrane is 10.73 µm. The values for Graphene/PVA/5 per cent neem extract (R1) and Graphene/PVA/10 per cent neem extract (R2) are 12.91 µm and 14.59 µm, respectively. The addition of neem increases the surface roughness of the materials. However, it is good to have surface roughness as it helps the material to be attached to the human skin. However, the average surface roughness is much reduced when similar hybrid chemical compositions are coated on aluminium foils. The average surface roughness of coated layers R1, R2, and R3 is 2.085 µm, 1.210 µm, and 2.668 µm, respectively. It is interesting to observe that the roughness of nanofibrous membranes is higher than the roughness of the membrane as a coating layer. This is because coating reduces the surface roughness.

Fig. 12
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Surface roughness analysis the sample R1 without aluminum foil

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Fig. 13
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Surface roughness analysis the sample R2 without aluminum foil

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Fig. 14
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Surface roughness analysis the sample R3 without aluminum foil

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Fig. 15
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Surface roughness analysis the sample R1 with aluminum foil

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Fig. 16
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Surface roughness analysis the sample R2 with aluminum foil

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Fig. 17
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Surface roughness analysis the sample R3 with aluminum foil

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There is a relation between these rough values and high-level crystallographic misalignment. Changing the compositional stacking and the concentrations of elements can lead to significant changes in surface roughness and, as a result, adhesion behaviour under coating conditions. Furthermore, the coated layers appeared smooth and homogeneous compared to the nanofibrous membrane, with no visible gaps between valleys and ridges. On the contrary, the nanofibrous surface membrane had apparent peaks and valleys, which increased the roughness of the membrane surface. These findings corroborated the SEM findings that the surface protrusions were covered in Graphene nanoparticles. The tendencies of the conclusions of this investigation are almost identical to those found in prior studies [42,43,44,45].

3.8 Bacterial reduction test

Bacterial reduction test of the developed nanofibrous membrane R1, R2, and R3 against E-coli shown in Fig. 18a to c. Among the samples, R3 offers the maximum bacterial reduction performance because of the higher percentages of neem extract present in the membrane, whereas R2 shows moderate antibacterial performance. The presence of neem in the membrane may damage the cell membrane destroying the cell integrity, which causes the death of bacteria [46, 47]. Neem contains methanolic extract in it, which shows excellent antibacterial activity. Very few concentrations also offer a good inhibition zone in the antibacterial test [48]. Besides, neem oil also effectively kills multidrug-resistant bacteria [49]. PVA provided some antibacterial properties to the R3 [50]. The presence of phenol confirmed by FTIR analysis in neem is mainly responsible for the bacterial reduction by the membrane. The bacterial reduction test results suggest that the prepared nanofibrous membranes can be used for biomedical applications.

Fig. 18
figure 18

Bacterial reduction test of the sample a R1, b R2, c R3

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3.9 Moisture management test (MMT)

It is challenging to synthesize nanofibrous membranes that can be used for wound dressing in clinical applications to maintain a dermal level moist environment. The moisture management features of the nanofibrous membranes generated by mixing PVA, graphene, and neem extract in this research are shown in Fig. 19a to f and Table 7, respectively. The top surface of R1, R2, and R3 has a wetting time of 5–8 s, indicating quick wetting. All samples had the same maximum absorption rate, which could be due to a coincidence.

Fig. 19
figure 19

Moisture management test of the samples R1 a AATCC, b water location versus time; R2 c AATCC, d water location versus time; R3 e AATCC, f water location versus time

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Table 7 MMT data table for samples R1, R2, and R3
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Nanofibrous membranes become more hydrophilic, allowing them to absorb more liquid. The wetted radius for all samples was the same, and due to its moisture-spreading power, the fastest spreading speed was obtained from R3 from the top side and R1 from the bottom. Considering all the criteria, R1 and R2 had the fastest absorbing nature compared to R3. The result indicates that the nanofiber will transfer the absorbent to the external environment after drinking them. R1’s moisture management properties were projected to be significantly improved due to its high extract concentration. However, as the fraction of graphene increased, the absorption rate decreased. In this scenario, sample R3 has the lowest absorption rate compared to samples R1 and R2. If raising the percentage of neem extract absorption rate was high but increasing the share of graphene spreading speed was high, the results of all samples were positive.

3.10 TGA analysis

Figure 20 shows the TGA curve illustrating the thermal response of PVA and PVA/neem nanofibrous membranes implanted with graphene nanoparticles. PVA nanofibrous membranes have a higher amorphous area; hence their melting point is 190 °C or 227 °C [48]. At higher temperatures of 240 °C, 220 °C, and 250 °C, adding neem and graphene to samples R1, R2, and R3 resulted in faster initial deterioration. R1 and R3 nanofibrous membranes are significantly more resistant to heat destruction than R2 nanofibrous membranes, as evidenced by this. Despite significant weight loss due to moisture evaporation and no clear polymer breakdown, the produced nanofibrous membranes are thermally stable up to 220 °C. At 800 °C, sample R1 had 2.84%, R2 2.12%, and R3 1.79% of their initial weight. The graphs show that the addition of neem makes the materials more thermally stable. Literature shows that adding neem increases the materials’ thermal stability [51].

Fig. 20
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TGA analysis of samples

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3.11 DSC analysis

Figure 21a to c shows DSC thermograms of electrospinning from samples R1, R2, and R3. Amorphous behaviour with evident crystallization or fusion peaks in the measured range of 0 to 800 °C at a rate of 10 °C per minute. The exothermic curve for sample R1 was relatively big and crisp, peaking at 296.7 °C. Similarly to sample R2, R3 has a reasonably extensive and steep exothermic curve with peaks at 296.1 and 231.1 °C. However, the exothermic curves of all samples became broad and obtuse, and the peak migrated to a higher temperature. This suggested that the electro-spun nanofibrous membranes’ crystalline microstructure has matured. Also, endothermic behavior with observable crystallization or fusion peaks in the measurement of samples R1, R2, and R3 are found at 242.6 °C, 265.3 °C, and 276.1 °C. Endothermic peaks are recorded for Sample R1 at 103 °C, 242.6 °C, 307.2 °C, 457 °C, 534.9 °C; for R2 at 338.3 °C, 470.6 °C, 530.7 °C; for R3 at 276.1 °C, 520 °C corresponding to the denaturation temperature (Td) as well as melting temperature (Tm) which is in agreement with the literature [52,53,54]. The thermal properties of the nanofibrous membranes were developed by the cross-linking treatment suggested by literature [55]. Besides, the addition of neem makes materials thermally stable [56].

Fig. 21
figure 21

DSC analysis of the samples a R1, b R2, c R3

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4 Conclusion

The preparation and characterization of the Graphene/PVA and PVA/Graphane/neem nanofiber membranes are described in this paper. The results showed that the Graphene/PVA and PVA/Graphane/neem nanofiber membranes considerably enhanced their water resistance. Furthermore, TGA data indicated that chemical cross-linking between Graphene/PVA and PVA/Graphane/neem improved thermal stability. The method used in this study provided a unique way to make graphene/PVA and PVA/Graphane/neem nanofiber membranes. Water dissolving was not a problem for the nanofiber membranes that were created. Furthermore, the PVA/Graphane/neem nanofiber membranes were effective and efficient against gram-negative bacteria E-coli. Graphene/PVA and PVA/Graphane/neem nanofiber membranes have outstanding antibacterial characteristics making them exciting materials for food packaging, biomedical engineering, and air filtration applications.