Enhancement the Structural and Electrical Properties of PVA by the Additive of Y2O3 and SrCO3 Nanoparticles and Apply as the Antibacterial

INTRODUCTION 

Nanocomposites, created by combining different materials, structures, and compositions, display a broad spectrum of properties that are highly suitable for a variety of applications. As a result, there has been considerable focus on multifunctional materials in the nanocomposite sector [1, 2].

Polyvinyl alcohol (PVA) is a polymer that has garnered considerable attention from researchers because of its distinctive physical and chemical properties [3]. PVA is a multifunctional polymer that is utilized in various industries. The main factors that contribute to this phenomenon are their extraordinary optical properties, lightweight nature, and great mechanical qualities. Polyvinyl alcohol (PVA) is extensively utilized in various applications such as adhesives, drug delivery systems, coatings, and fuel cells. Because of the strong hydrogen bonds produced by hydroxyl groups, both internally and externally, PVA exhibits a high melting point that roughly matches its breakdown temperature. Due to this particular attribute, the melting procedure of PVA presents difficulties, which is why it is more beneficial to handle it by utilizing water-based solutions [4]. Because of its compatibility with the human body, it can also be used as a therapeutic substance [5]. Furthermore, PVA possesses the capacity to selectively adsorb metallic ions, including copper, palladium, and mercury. Polyvinyl alcohol (PVA) is a polymer represented by the chemical formula (C₂H₄O)_x. The substance exhibits a density within the range of 1.19 to 1.31 g/cm³ and a melting point of 230℃. This thermoplastic polymer experiences rapid breakdown when exposed to temperatures exceeding 200℃. The substance’s structure is flexible and is defined by the existence of C–O–C connections. Furthermore, it possesses the capability to undergo dissolution in organic solvents, a propensity to interact with water, a structure characterized by crystals, and the potential to provide self-lubrication [6]. 

Yttrium oxide (Y₂O₃) is a highly significant substance in the field of advanced ceramics. Furthermore, (Y₂O₃) is favoured as a host material because of its exceptional chemical durability, elevated thermal stability, strong refractory property, resistance to corrosion, low phonon energy, and high refractive index [7]. Y₂O₃ (III) oxide, also referred to as yttria, diyttrium trioxide, yttrium sesquioxide, is an oxide that is stable in air and insoluble in water. It has diverse applications in the fields of material science and inorganic chemistry [8]. 

Strontium carbonate (SrCO₃) has a high dielectric constant, dispersion frequency constant, and low temperature coefficient, making it a promising chemical [9]. Strontium carbonate is essential to the electrical and glass industries [10]. As a bio-crystallization model, strontium carbonate’s unusual crystal structure has been extensively studied [11]. Self-assembly monolayers [12], thermos evaporated stearic membrane [13], and polyanionic additives [14] have been used to improve the production of crystalline SrCO₃from water [15]. 

This work focuses on the synthesis of a nanocomposite consisting of PVA/Y₂O₃/SrCO₃ and the subsequent investigation of its structural and electrical properties and apply as the antibacterial.

MATERIALS AND METHODS

1g of PVA was dissolved in 50 mL of distilled water firstly for 30 minutes at RT, then continue for another 20 minutes under 75-80^oC using magnetic stirrer until to PVA solvent. The resulting solution was cast onto clean glasses Petri dish and kept it under air at RT for 240h for drying process till the solvent gets completely evaporated.  PVA with different concentration for Y₂O₃ and SrCO₃ NPs (0, 1, 2, 3 and 4) wt.% were fellow the same procedure to prepare nanocomposite films. The thickness of the produced films was about 0.12 mm.

To show the chemical make-up of the samples that were prepared, FTIR (Bruker business, type vertex -70 spectrometer, German origin) was used at room temperature, covering the range of 4000-500 cm^{− 1}. To determine the surface morphology of the films, researchers used a (FESEM, INSPECT S50, firm, Japan origin, type FEI Customer ownership) and optical microscope (OM) provided by Olympus (Top View, type Nikon-73346). The dielectric characteristic were studied at (f=100 Hz to 5 ×10⁶ Hz) by LCR meter (HIOKI 3532-50 LCR HI TESTER).  

The dielectric constant, έ is given by [16] 

wherever, Cp is capacitance of matter, thickness (d in cm), A= (in cm²). Dielectric loss, ε˝ is calculated by [17]: 

Wherever, D: dispersion factor. The A.C electrical conductivity is determined by [18]: 

RESULT AND DISCUSSION 

The optical microscope reveals changes in the surface morphology of (PVA/ Y₂O₃/SrCO₃) nanocomposites. Fig. 1 depicts the nanocomposites (PVA/Y₂O₃/ SrCO₃) captured using an optical microscope (OM) at a 10x magnification. The image depicts the organization of Y₂O₃ and SrCO₃ nanoparticles in the (PVA/Y₂O₃/ SrCO₃) nanocomposite. At lower concentrations, the Y₂O₃ and SrCO₃ nanoparticles aggregate to form clusters. Increasing the concentrations of Y₂O₃ and SrCO₃ nanoparticles in the (PVA) polymer results in the formation of a network of pathways within the polymer. These pathways allow charge carriers to flow, hence causing a modification in the material characteristics. This behavior agrees with [19,20].

FESEM is used for the purpose of examining the distribution of nanoparticles within the polymer, and then verifying the effect of those particles of Y₂O₃/SrCO₃ on those nanocomposites. Fig. 2 shows FESEM images of films made from (PVA/Y₂O₃/SrCO₃) nanocomposites with varying amounts of Y₂O₃ and SrCO₃ NPs with a scale 1 μm. FESEM images of pure PVA polymer show that the surface is smooth and homogenous, which mean the successful this method to fabricated this film. Many Y₂O₃ and SrCO₃ particles, at lesser concentrations, are broadly disseminated throughout the surface of the nanocomposite and are finely dispersed without aggregating. On the surface, nanoparticles are dispersed at random and take on the shape of spheres, much like grains. When Y₂O₃ and SrCO₃ NPs are present in high concentrations, the nanoparticles aggregate and cluster, suggesting that there may be interaction between the two substances. This result is agreed with researches [21].

The freshly synthesized pure PVA and PVA/Y₂O₃/SrCO₃ nanocomposite were characterized using FTIR. Fig. 3 shows the FTIR spectra of pure PVA and PVA with Y₂O₃ and SrCO₃ nanoparticle concentrations from 500 to 4000 cm^-1. Pure PVA has a large absorption band at 3272.40 cm^-1 due to the stretching vibration of the alcohol group (OH) in the polymer matrix chain [22]. The C-H group has symmetric stretching vibrations at 2926.16 cm⁻¹. The stretching vibration of the C=C bond was observed at 1731.34 cm⁻¹, while the bending vibration of the O–H bond was observed at 1661.22 cm⁻¹. At 1541.18 cm^-1, chitosan absorbs due to its amino group stretching vibration. A bending vibration was observed at 1441.23 cm⁻¹ for the C-H group. Infrared Spectroscopy was used to measure crystallinity by analyzing the peak at 1128.38 cm⁻¹ [23, 24]. Crystalline polymeric chains impact this peak’s magnitude. According to the literature [25, 26], this peak represents the symmetric C-C bond stretching mode or C-O bond stretching in a specific chain region. Two neighboring OH groups on the same side of the carbon chain plane form an intramolecular hydrogen bond [23]. The C-O stretching vibrations occurred at 1082.86 cm⁻¹. Peaks at 845.02 and 625.13 cm⁻¹ correlate with powerful C-O-C and modest C=C bending vibrations [27].

The additive concentration (1, 2, 3, and 4) wt. % of Y₂O₃ and SrCO₃ NPs to PVA polymer in images b, c, d, and e changed some band intensities and shifted others. This graphic shows that Y₂O₃ and SrCO₃ NPs interact with polymer matrix. The FTIR showed no interactions between PVA polymer matrix and Y₂O₃ and SrCO₃ NPs. This outcome matches researchers [28]. 

The dielectric constant was determined using equation 1. The frequency-dependent fluctuation of the dielectric constant for all specimens of the (PVA/Y₂O₃/SrCO₃) nanocomposite is illustrated in Fig. 4. The results indicate a reduction in the dielectric constant with increasing applied frequency, attributed to the varying polarization states. However, at lower frequencies, the polarization of the space charge significantly contributes to increasing the dielectric constant. As the frequency of the electrical field increases, the influence of polarization on the frequency increase becomes less significant and more noticeable. As a result of this activity, the dielectric constant values decrease for all samples, which in turn causes various forms of polarizations to occur at higher frequencies. This phenomenon arises from the difference in mass between an ion and an electron. Electronic polarization is the only type of polarization that can occur at higher frequencies because of the difference in mass. This difference allows electrons to respond to fluctuations in the field, even at very high frequencies [29].

Fig. 5 demonstrates the impact of Y₂O₃ and SrCO₃ nanoparticles on the dielectric constant at a frequency of 100 Hz. The relationship between the dielectric constant and the concentration of Y₂O₃ and SrCO₃ NPs is clearly evident, as the dielectric constant increases proportionally with an increase in concentration. This could be attributed to the formation of a cohesive network by Y₂O₃ and SrCO₃ nanoparticles within the nanocomposite. The microscopic photographs of these nanocomposites clearly demonstrated this. This discovery exhibits same behavior as that demonstrated in [30, 31].

The dielectric loss of nanocomposites was determined using equation 2. The Fig. 6 displays the frequency-dependent dielectric loss of the nanocomposite (PVA/Y₂O₃/SrCO₃). This graph illustrates that the dielectric loss of nanocomposites (PVA/Y₂O₃/SrCO₃) diminishes as the applied electric field increases. An elevated concentration of Y₂O₃ and SrCO₃ nanoparticles leads to a corresponding rise in the dielectric loss. As the frequency rises, there is a relatively small alteration in the level of dielectric loss. At high frequencies, many forms of polarization can occur [32]. The Fig. 7 illustrates that an growth in the content of Y₂O₃ and SrCO₃ results in an rise in the amount of ionic charge carriers. This, in turn, leads to an increase in the value of dielectric loss. This behavior becomes evident as the weight percentage of nanoparticles is raised. This is agreed with the results of researchers [33]

In order to find the A.C. electrical conductivity, its variation with regard to relation (3) was computed. For the (PVA/Y₂O₃/SrCO₃) composite, the frequency-to- σ_A.C relationship is shown in Fig. 8. The graph shows that when the frequency goes up, the electrical conductivity goes up as well. Reasons for this include localized charge carrier mobility and higher-level conduction band stimulation. Two factors that impact the electrical conductivity of alternating current (A.C.) are the movement of the main chain and the movement of ions. Specifically, the increase in σ_A.C at low frequencies can be attributed to interfacial polarization, while the increase in conductivity at intermediate and high frequencies is caused by the flow of electrons. The data presented in Fig. 9 indicate that higher concentrations of Y₂O₃ and SrCO₃ NPs in nanocomposites lead to an elevated conductivity of the nanocomposites. This phenomenon arises due to an augmentation in the quantity of ionic charge carriers, along with the establishment of an uninterrupted network of Y₂O₃ and SrCO₃ nanoparticles within the composites. These results agree with other [33].

We assessed the antibacterial efficacy of PVA/Y₂O₃/SrCO₃ nanocomposites against both gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus). The results of these tests at the various concentrations are shown in Fig. 10. The figure illustrates that the nanocomposite films exhibited a larger inhibition zone against gram-positive (S. aureus) compounds in comparison to gram-negative (E. coli) compounds. Table 1 illustrates how the inhibitory zone’s diameter increases as graphene nanoparticle concentration rises, peaking at 18 mm for gram-negative bacteria (E. coli). The antibacterial properties of nanostructures are assumed to be caused by reactive oxygen species (ROS) generated by nanoparticles. Positive charges are present in nanocomposite nanoparticles, while negative charges are present in bacteria. Because of this, the bugs will be instantly killed by oxidation brought on by electromagnetic contact. Bacterial proteins and DNA most likely break down due to singlet oxygen (₁O²). Reactive oxygen species (ROS) are primarily responsible for the antibacterial properties of nanocomposites containing nanoparticles. These radicals include superoxide (O^-2), hydroxyl (OH), and hydrogen peroxide (H₂O₂) [34].

CONCLUSION

This study provides a concise overview of a very efficient casting technique employed in the manufacturing of PVA/Y₂O₃/SrCO₃ nanocomposites. The OM images displayed the formation of interconnected channels inside the polymeric matrix due to the presence of electrically charged particles, which became more pronounced with higher concentrations of nanoparticles. The examination using Field Emission Scanning Electron Microscopy (FESEM) showed that the Y₂O₃ and SrCO₃ nanoparticles were evenly spread and uniformly distributed within the polymer PVA matrix.  FTIR analysis conclusively verified the existence of a discernible interaction between Y₂O₃/SrCO₃ and the PVA polymer matrix. The PVA/Y₂O₃/SrCO₃ nanocomposites’ dielectric constant and dielectric loss reduction as the frequency of the applied electric field increases. In contrast, the electrical conductivity of alternating current increases with frequency. The dielectric constant, dielectric loss and the conductivity of PVA/Y₂O₃/SrCO₃ nanocomposites at all concentrations growth with increasing concentrations of Y₂O₃ and SrCO₃ nanoparticles. Finally, the PVA/Y₂O₃/SrCO₃ nanocomposites were examined as antibacterial against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and exhibited that the inhibition zone diameter increments with the rise in Y₂O₃ and SrCO₃ content. The nanocomposite exhibited activity against antibacterial. 

CONFLICT OF INTEREST

The authors declare that there is no conflict of interests regarding the publication of this manuscript.