Fabrication of multifunctional ZnO@tannic acid nanoparticles embedded in chitosan and polyvinyl alcohol blend packaging film

The multifunctional ZnO@TA@PVA/CH films with antibacterial, antioxidant, and UV blocking properties are as-prepared as illustrated in Fig. 1. The possible mechanism of surface modification on ZnO NPs with TA acid involves two proposed mechanisms through formation of hydrogen bonding between –OH of tannic acid with ZnO NPs surface and formation of a π-complex between the surface of ZnO NPs and tannic acid containing phenyl groups through sharing of π-electrons of phenolic rings present in the tannic acid with 4S orbital on Zn+2 via a coordination bonding32.Figure 1A schematic diagram of suggested mechanism of ZnO@TA formation and construction of ZnO@TA@CH/PVA films.FTIRFigure 2 illustrates the FTIR spectrum to determine the specific functional groups or chemical bonds for ZnO NPs, TA, ZnO@TA, CH/PVA, and ZnO@TA@CH/PVA film.Figure 2ZnO NPs, TA, ZnO/TA, CH/PVA, and ZnO/TA@PVA/CH.For ZnO NPs, the absorption peak at 414, 572, and 820 cm-1 corresponds to metal–oxygen (ZnO stretching vibrations) vibration mode33,34,35,36.For FTIR spectra of tannic acid show a significant absorption of about 3480–3000 cm−1 with a wide and strong band centered at 3225 cm−1. This band is corresponded to the broad and strong H-bonded hydroxyl groups (O–H) as well as the C–H bond (aromatic medium). Tannic acid consists of aromatic esters due to the signal properties of carbonyl groups C=O stretching (1699 cm−1) and C–O (1313–1187 cm−1). The in-plane bending of C–O–H group occurs at 1607–1535 cm−1, and the out-of-plane bending was assigned to 872 cm−137. Bands at 1607–1445 cm−1 associated with C–C of aromatic compounds. Various peaks in the 1085–755 cm−1 associated with substituted benzene ring38.For FTIR spectrum of ZnO@TA, the characteristic bands of the ZnO@TA nanoparticles and pristine TA were remarkably comparable, resembling the conventional peaks of TA. It could be claimed that the interaction is pronounced as a π-complex between tannic acid containing phenyl groups and the surface of ZnO NPs. Moreover, the characteristic peaks of aromatic C=C of tannic acid at 1445 cm−1 and 1607 cm−1 were disappeared, indicating the participation of the C=C group in the creation of the coordination complex. This could be due to the interaction of π-electrons of phenolic rings in tannic acid with the 4S orbital on Zn+2 via a coordination link, generating a sandwich-like structure32. A significant shift in the band assigned to the hydroxyl groups (O–H) H-bonded and C–H (aromatic medium) at 3225 cm−1 to 3377 cm−1 with somewhat sharpness due to the proposed coordination and hydrogen bonding between ZnO NPs and TA. The out-of-plane bending was assigned to 867 cm−1 shift to 820 cm−1. These findings indicate that the hydroxyl group of TA could form hydrogen bonding with ZnO39. The absorption peak at 414 cm−1 which corresponds to metal–oxygen (ZnO stretching vibrations) vibration mode is strongly observed in ZnO@TA.For the virgin CH/PVA IR curve has a substantial peak at 3291 due to the overlapping of the -OH and NH2 groups of PVA and CH, besides a peak at 2861 related to –CH group28. These peaks are signatures of polysaccharides and can be witnessed in other polysaccharide spectra40. Other peaks at 1649 are due to the C=N amine bond of CH, and at 1561 to NH3+, which is formed by NH2 deformation in acidic conditions. CH2 bending and CH3 symmetrical deformations have been verified with bands at 1423 and 1375 cm−1, respectively. The absorption peak at 1143 cm−1 indicates asymmetric stretching of the C–O–C bridge. The peaks at 1032 and 923 cm−1 indicate C-O stretching.41 which is characteristic of saccharide structure of chitosan.FTIR spectrum of ZnO@TA@CH/PVA film showed the same spectrum of CH/PVA film with minor shift. The addition of ZnO@TA into CH/PVA causes a minor shift from 3280 to 3292 cm−1 due to hydrogen bonding between CH/PVA and ZnO@TA. The absorption peaks which correspond to metal–oxygen (ZnO stretching vibrations at 414 cm−1) of ZnO@TA is powerfully detected in FTIR spectrum of ZnO@TA@CH/PVA indicating the inclusion of ZnO@TA.X-ray diffraction analysisFigure 3 verified XRD patterns of ZnO NPs, TA, ZnO@TA, CH/PVA, and ZnO@TA@CH/PVA. The ZnO NPs exhibited 2Theta at 32.0°, 34.6°, 36.4°, 47.7°, 56.8°, 62.0°, 66.7°, 68.1°, 69.2°, 71.9°, and 77.1°, respectively that were corresponding to diffraction planes (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202), respectively. XRD spectrum profile of ZnO verified hexagonal wurtzite phase42.Figure 3XRD patterns of ZnO NPs, tannic acid (TA), ZnO@TA, CH/PVA, and ZnO@TA@CH/PVA films.The average grain crystallite size Scherer equation of ZnO NPs were estimated utilizing Scherer equation and have an estimated value equaled 1.727 nm. No noticeable peaks of crystalline phase were observed in the XRD patterns of TA, but characteristic two signals (2θ = 11.2° and 24.9°), representing the amorphous nature of TA.The XRD pattern of the ZnO@TA showed crystalline diffraction peaks with minor shift at 2θ = 32.0°, 34.6°, 38.2°, 44.0°, and 56.8° were observed clearly which are indexed by diffraction planes (100), (002), (101), (102), and (110) of ZnO NPs (Li, et al. 2016).The X-ray diffraction profiles of CH/PVA and ZnO@TA@CH/PVA films are shown in Fig. 3. The XRD profile of CH/PVA and ZnO@TA@CH/PVA films are very similar. The CH/PVA film diffractogram exhibits peaks in 2 Theta = 16.9°, 23.2°, and 34.6° where amorphous diffraction peaks at 2 Theta = 23.2° is indicative of the blending of CH/PVA43. The 2θ value at 19.43° revealed the crystal structure of PVA, which was found across all diffraction patterns of the generated composite films was shifted to 22.4° may be attributable to blending with chitosan. The specific signals of ZnO@TA are not observed in diffractogram of ZnO@TA@CH/PVA indicating that trace amount of ZnO@TA was altered when added to CH/PVA matrix. In order to determine the crystallinity alteration of CH/PVA film when ZnO@TA was added, the crystallinity index of ZnO@TA@CH/PVA was calculated by the following equation (Eq. 16):$${\text{X}}_{\text{i}} \%=\frac{{\text{A}}_{\text{C}}}{{\text{A}}_{\text{C}}+{\text{A}}_{\text{a}}} \, \times \text{100 }$$
(16)
where, Ac and Aa are crystalline area and amorphous, respectively44.The crystallinity index % of CH/PVA was 67.07% while ZnO@TA@PVA/CH showed a slight increase with inclusion of ZnO@TA given 71.44%.Transmission electron microscopy analysisTEM reveals the microscopic structural characteristics of ZnO NPs. Figure 4 shows TEM images of ZnO NPs, where ZnO NPs appear to have a uniform and spherical shape with particle size within the range of 4.95–25.72 nm. These results were consistent with that reported by Razieh Galal et al. (2010)45. Figure 4 depicts the selected electron diffraction area of ZnO NPs revealing the nano-crystalline structure of ZnO NPs which accords with XRD analysis.Figure 4TEM and selected electron diffraction area of ZnO.Particle size and zeta potential measurementsFigure 5 shows the Zeta Potential and particle size distribution of ZnO@TA. ZnO@TA NPs have a mean hydrodynamic diameter of 663.8 ± 0.57 nm. Tannic acid aggregation on ZnO NPs arose due to the impact of acidic medium caused by TA molecule46, results in the formation of ZnO@TA complex could be the cause of the increased mean hydrodynamic diameter (MHD) of ZnO@TA. Abebe Belay et al. (2015) recently noticed a similar effect. When caffeic acid was added to the ZnO NPs, it was observed that the MHD of the ZnO@caffeic acid NPs increased. When the concentration of ZnO NPs was 7.55 × 10–6 M, the MHD of ZnO/caffeic acid was 295 nm. When ZnO NPs concentration was 7.55 × 10–6 and 1.30 × 10–5 M, respectively, the MHD of ZnO@caffeic acid increased to 396 and 955 nm47.Figure 5Particle size distribution of ZnO@TA NPs.The Zeta Potential, which represents the NPs’ surface charge, is one significant factor which influences particle stability. If the electric charge on the particle surface is larger, the NPs are not likely to assemble. The Zeta Potential numerical value of ZnO@TA is − 27.83 mV. This indicates ZnO@TA NPs complex are well stabilized due to repulsive forces that prevent aggregations upon aging. The recognized range of the Zeta Potential to provide adequate stability in solution is − 30 to − 20 mV or + 20 to + 30 mV, according to Mojtaba Taghizadeh et al.39,48. Almost the same results were reported by Xiaojia He et al. (2016), the Zeta potential larger than—25 of TA@TiO2 NPs49.Surface morphologyFigure 6 displays SEM image of ZnO@TA as well as mapping and EDAS data. ZnO@TA showed spherical shape in clusters. The existence of ZnO NPs with homogenous distribution in ZnO@TA is further supported by mapping images. In EDAX spectrum, the proportional elemental composition of ZnO nanoparticles in ZnO@TA was confirmed using the energy dispersive X-rays Analysis (EDAX) tool, as illustrated in Figure 6, by measuring the intensity of the characteristic emitted X- rays. In synthesized ZnO@TA nanoparticles, EDAX revealed only the presence of three elements: carbon, zinc and oxygen. The atomic percent compositions of elements are 59.25%, 38.52%, and 2.23% for C, O, and Zn respectively50.Figure 6SEM images, EDAX spectrum of ZnO@TA NPs and mapping image.Figure 7 shows SEM, EDAX, mapping images of CH/PVA and ZnO@TA@CH/PVA films. PVA/CH film shows uniform smooth surface, without any fracture and air bubbles. The surface image of ZnO@TA@CH/PVA film exhibits surface roughness due to inclusion of ZnO@TA NPs. The proportional elemental composition of CH/PVA film shows three elements namely, C, O, and N with atomic percent 49.89%, 44.41%, and 5.7%, respectively. However, the proportional elemental composition of ZnO@TA@CH/PVA film was 55.27%, 36.97%, 5.7%, 2.06% for C, O, N, and Zn, respectively. The mapping images of the film reveal that ZnO@TA nanoparticles are uniformly distributed in ZnO@TA@CH/PVA film matrix as demonstrated in Fig. 7.Figure 7SEM, EDAX, mapping of CH/PVA and ZnO@TA@CH/PVA films.Barrier propertiesTable 2 demonstrates the impact of changing ZnO@TA concentrations on barrier properties. WVP measures the rate of moisture that crosses the film, being an important property to be accounted for in packaging applications51.
Table 2 Influence of ZnO@TA concentrations (mg) WVP and OP of ZnO@TA@CH/PVA film.As expected, WVP of ZnO@TA@CH/PVA films tend to diminish with the incorporation of ZnO@TA NPs compared with CH/PVA control film which is generally explained by the physical crosslinking of ZnO@TA NPs nanocomposite, which will diminish the diffusion of water vapor and gases33.The WVP of ZnO@TA@CH/PVA films shows a significant decrease with increasing ZnO@TA concentrations (p˂0.05) in comparison with CH/PVA control. There is no significance difference between PVA/CH films containing ZnO@TA concentrations of 10 and 30 mg however, WVP of ZnO@TA@CH/PVA film containing 50 mg significantly differ than the other films. May be at that concentration (50 mg) is sufficient to cause more crosslinking to CH/PVA films thus restrict mobility of the polymer chains and consequently decreasing the transport of gases. The lowest WVP is 31.98 ± 1.68 g.mm/m2.kPa.day which related to ZnO@TA(50)@CH/PVA compared with PVA/CH control film 43.52 ± 1.01 g.mm/m2.kPa.day as typed in Table 1.The O2 gas barrier property is another significant factor influencing shelf life of fresh packed food. The oxygen permeability of ZnO@TA@CH/PVA film exhibits a significant decrease in OP (p < 0.05). The decreasing sequence of OP is 0.641 ± 1.50 × 10–2, 0.358 ± 1.00 × 10–1, 0.246 ± 1.29 × 10–1, and 0.144 ± 5.03 × 10–2 c.c/m2 day corresponding to CH/PVA, ZnO@TA(10)@CH/PVA, ZnO@TA(30)@CH/PVA, and ZnO@TA(50)@CH/PVA, respectively as shown in Table 2. This drastic decreasing behavior could be due to crosslinking reasons as mentioned before. Furthermore, ZnO@TA nanoparticles have the potential to develop tortuous pathways that significantly reduce the size of matrix pore channels52.Other researchers have previously documented the same trend, a study reported by Song et al. (2023) indicated that ZnO/plant polyphenols/cellulose/polyvinyl alcohol films showed better water vapor barrier properties than PVA, with a WVP of 12.7 g m−2 h−1 and 10.8 to 7.5 g m−2 h−153. In another study worth mentioning in which chitosan and tannic acid were crosslinked in neutral and mildly basic circumstances to create chitosan-tannic acid composite films. The pristine chitosan film had strong transmission rates, as evidenced by its WVTR and OTR of 956 g/m2⋅day and 0.39 cc/m2⋅day, respectively. The chitosan-tannic acid composite films, on the other hand, exhibited noticeably lower transmission rates than the native chitosan film because of the formation of a denser structure as a result of physical crosslinks between the two substances19.Solubility of ZnO@TA@CH/PVA filmThe influence of ZnO@TA changing concentrations on ZnO@TA@CH/PVA film solubility is shown in Fig. 8. The changing concentration of ZnO@TA has significant impact on solubility of the films (P < 0.05). The solubility of ZnO@TA@CH/PVA films drastically tend to decrease with increasing loadings of ZnO@TA. The solubility percentages are 64.35 ± 2.4 %, 47.65 ± 2.2 %, 36.68 ± 1.1%, and 30.36 ± 1.4% that are belonged to CH/PVA, ZnO@TA(10)@CH/PVA, ZnO@TA(30)@CH/PVA, and ZnO@TA(50)@CH/PVA films. These results may be ascribed to crosslinking reasons and development of more hydrogen bonding between ZnO@TA and functional groups of base film components as mentioned before.Figure 8Effect of ZnO@TA changing concentrations on ZnO@TA@ CH/PVA film solubility. a–d: different superscript letters represent significant difference at 5% level of probability (P < 0.05).Water contact angles measurements (WCA)Figure 9, shows the WCA of CH/PVA and ZnO@TA@CH/PVA films containing different concentrations of ZnO@TA. According to a general theory, a contact angle that is smaller (below 90°) indicates a material’s hydrophilic character, whereas a greater value (above 90°) shows a material’s hydrophobic nature. The contact angle of CH/PVA film is 76.6°. For ZnO@TA concentrations of 10, 30, and 50 mg, respectively, the contact angles of ZnO@TA@CH/PVA films are increased by 7.18%, 19.19%, and 33.42%, respectively. These findings may due to ZnO@TA addition-induced roughness to the surface of ZnO@TA@CH/PVA films occurred.Figure 9Water contact angles images of ZnO@TA@PVA/CH films.Mechanical propertiesTable 3 depicts tensile strength and elongation % at break of ZnO/TA@ PVA/CH as a function of increasing ZnO@TA concentrations. The tensile strength of neat PVA/CH film was 30.47 ± 0.96 MPa. As the loading of ZnO@TA increase, tensile strength of ZnO@TA @PVA/CH composite films significantly increases (p < 0.05). Tensile strength of ZnO@TA @PVA/CH composite films are 37.47 ± 1.09, 43.33 ± 1.21, and 48.72 ± 0.23 MPa up to 10, 30, and 50 mg of ZnO@TA loadings, respectively. That enhancement in tensile strength may be attributable to stronger intermolecular forces that can occur between the polymer chains (PVA/CH) and ZnO@TA. When hydroxyl groups of PVA/CH and ZnO@TA nanoparticles interact, covalent and hydrogen bonds developed due to presence of extensive tannic acid hydroxyl moiety, thereby increasing the molecular force. The development of cross links between polymer chains was facilitated by the ZnO@TA. Therefore, films containing ZnO@TA nanoparticles had a more compact film matrix structure, which resulted in the development of stronger films16,19. This tensile enhancement is agreed with results reported by Aswathy Jayakumar et al. (2023), active and intelligent composite films based on polyvinyl alcohol, chitosan, zinc oxide nanoparticles, and sweet purple potato extract. The tensile strength of the chitosan/polyvinyl film was 13.0 MPa and increased to 30.8 MPa for chitosan/polyvinyl film composite film containing zinc oxide nanoparticles, and sweet purple potato extract54.
Table 3 Influence of ZnO@TA concentrations (mg) tensile strength and elongation % at break of ZnO@TA@PVA/CH film.Youngs modulus of ZnO@TA @PVA/CH composite films significantly increases (p < 0.05). Young`s modulus of ZnO@TA @PVA/CH composite films are 1436.66 ± 47.5, 1905.52 ± 29.3, and 2163.46 ± 61.4 MPa up to 10, 30, and 50 mg of ZnO@TA loadings, respectively compared with control 1034.32 ± 52.8 MPa.Additionally, table 3 shows the effects of ZnO@TA changing loadings on the elongation at break of PVA/CH composite films. As can be seen, the percentage of elongation at break significantly decreased with increasing of ZnO@TA concentration (p < 0.05). Despite the increased increments, there is no significant difference between control film and PVA/CH containing 10 mg ZnO@TA. PVA/CH film showed an elongation at break of 35.10 ± 2.3%, whereas the nanocomposites with 10, 30 and 50 mg ZnO@TA showed an elongation at break of 32.54 ± 1.07, 27.02 ± 2.19, and 19.62 ± 2.3%, respectively. This is because the rigidity of matrix increased by adding ZnO@TA. Moreover, strong interaction between ZnO@TA and PVA/CH chains could restrict chain movements and consequently blocks its ability to flow and reduce its ductility55. Further, the significant improvement in tensile strength accompanied with decreasing in elongation at break which can be translated as ZnO@TA NPs addition can behave as an efficient reinforcing agent. Notably, the distribution of nanofillers and their interaction with the polymer matrix are strongly correlated with the reinforcing effect in nanocomposite films56. Considering the EDAX image in Fig. 7, the significant tensile improvement can be attributed to the homogeneity dispersion of ZnO@TA NPs within CH/PVA film forming strong interfacial adhesion which minimizes phase separation and allows efficient stress transfer at the interface57. Indeed, the addition of ZnO@TA NPs in the CH/PVA film matrix enhances mechanical performance. In 2023, Su Jin Lee and colleagues created a multifunctional chitosan (CH) film that contains 0.5–1.0 weight %of tannic acid (TA). Tris buffer (pH 8.5) and phosphate-buffered saline (CH-TA/P) were used to neutralize the chitosan films. The virgin CH’s tensile strength and elongation % at break were 58.1 ± 5.1 MPa and 8.1 ± 1.8%, respectively. On the other hand, CH-TA0.5/P, CH-TA0.5/T, CH-TA1.0/P, and CH-TA1.0/T films had significantly greater tensile strengths at 109.8 ± 4.9, 134.0 ± 5.1, 63.0 ± 8.1, and 112.8 ± 8.2 MPa, respectively19.Antioxidant activityDPPH free radicals scavenging activity, in which DPPH functions as a reducing agent or electron donor, is one of the frequently used techniques for determining antioxidant activity. In the presence of antioxidants, DPPH radicals change from a dark violet color to a transparent color and the absorbance at 517 nm is measured to determine the proportion of DPPH antioxidant activity. Figure 10 depicts the percentage of free radical-scavenging activity of ZnO@TA@PVA/CH films as a function of ZnO@TA concentrations. ZnO@TA@PVA/CH films show a significant increasing in DPPH antioxidant activity in the developed ZnO@TA@PVA/CH films with increasing ZnO@TA when compared control film (p < 0.05). The DPPH radical-scavenging activity % of ZnO@TA@PVA/CH films increased gradually to 50.0 ± 2.7%, 60.21 ± 4.0%, and 69.35 ± 1.6%, respectively with the increasing concentration of ZnO@TA from 10 to 50 mg, respectively compared with PVA/CH film (11.29 ± 3.2%). The PVA/CH control film reveals a moderate scavenging activity. However, the increasing in antioxidant activity could be due the galloyl groups in tannic acid may contribute to its potent hydrogen and electron-donating properties58. Similarly, Fig. 10 the ABTS radical scavenging ability. The antioxidant activities of CH/PVA, ZnO@TA(10)@CH/PVA, ZnO@TA(30)@CH/PVA, ZnO@TA(50)@CH/PVA films were 32.29 ± 1.1%, 70.0 ± 1.23%, 83.21 ± 1.61%, and 90.95 ± 2.12%, respectively. ZnO@TA@CH/PVA film has superior antioxidant activity towards ABTS more than DPPH radicals. Previous study reports have documented the same phenomenon, a novel antioxidant-containing zinc oxide (ZnO) nanoparticle was created by immobilizing the antioxidant 3-(3,4-dihydroxyphenyl)-2-propenoic acid, also known as caffeic acid, CA), on the surfaces of ZnO nanoparticles treated with micro-dielectric barrier discharge (DBD) plasma. ZnO@CA nanoparticles efficiently scavenged ABTS radicals at concentrations ranging from 20 to 100 µM, with activity ranging from 44.99 to 73.68%, respectively17. Also, research has been done on the polyvinyl alcohol-based film’s antioxidant capacity when lignin nanoparticles loaded with potassium sorbate (LNP@PS). Pure PVA is not capable of scavenging DPPH. However, the color of the mixture of DPPH and film extracts steadily lightened and eventually turned orange when the ratio of LNP@PS and/or TA added to the composite film increased. This suggested that there was strong antioxidant activity in the composite films. The intensity of the DPPH absorption peak was significantly reduced and the free radical scavenging activity (RSA) increased to 50.9% after only 1% of LNP@PS (LNP@PS-1-TA-0) was added to PVA. With LNP@PS-3-TA-5, the ideal RSA value of 92.6% was attained59.Figure 10DPPH scavenging ability % of ZnO@TA@PVA/CH films as a function of ZnO@TA concentrations. (a–h) Non-identical letters denote statistical difference (p < 0.05).UV-shielding propertiesFood packaging transparency is an essential concern in packaging materials, and it has a clear impact on consumer choices5,60. Food shelf life can be reduced by microbial development and/or biochemical processes like oxidation. Exposure to UV light can accelerate lipid oxidation in packaged food, which can cause food to deteriorate. Thus, foods, especially those with high fat content, require antimicrobial packaging materials with potent UV light blocking capabilities property61. Although PVA is the most often used packaging material, it has poor UV-shielding qualities. However, PVA UV-shielding performance has been improved by mixing it with biomaterials and nanoparticles62 that improve UV absorbance. Furthermore, adding a third phase to the PVA/biomaterials mixture, such as nanomaterials filler, could improve the UV-blocking properties9,63. The optical characteristics of the PVA/CH and ZnO@TA @PVA/CH films have been assessed using digital images Fig. 11A. As the ZnO@TA content increased, all of the ZnO@TA @PVA/CH films turned pale brown. Figure 11B depicts the UV transmittance of neat PVA/CH and ZnO@TA @PVA/CH films using various ZnO@TA NP ratios which illustrate the effect of ZnO@TA NP ratios on the UV-shielding properties of the PVA/ CH films. Corresponding to the equations the transmittance of UV-A (320–400) and UV-B (280–320) were implemented to explore UV Shielding properties. The virgin PVA/CH film exhibits an excellent UV shielding capacity where UV transmittance of UVA (91.414%) and UVB (99.198%) and that can be attributed to hydrogen bonding as a HOMO–LUMO interaction between PVA and CH.Figure 11(A) UV-shielding properties of CH/PVA and ZnO/TA@CH/PVA films. (B) Transparency images of CH/PVA and ZnO/TA@CH/PVA films with different loadings of ZnO@TA.On the other side, the incorporation of ZnO@TA NP on PVA/CH film shows an increase in the UV shielding capacity with the ratio increasing where UVA (98.58518%) and UVB (99.21196%) of 10% ZnO@TA @PVA/CH, UVA (98.56131%) and UVB (99.56156%) of 30% ZnO@TA@PVA/CH, and UVA (99.959%) and UVB (99.994%) of 50% ZnO@TA@PVA/CH. This is due to π → π* transition and locally excited πi → πj* transition in benzene rings of TA, σ → σ* between O–Zn–O and hydrogen bonding as a HOMO–LUMO interaction between PVA-TA-CH.Multiple investigators have already documented similar behaviors, for example, the biocomposite ZnO/plant polyphenols/cellulose/polyvinyl alcohol film was created. According to the light shielding study, the cellulose/PVA film contained 1wt% of ZnO/polyphenol mixture can virtually completely filter UV and visible light53. In a nother investigation, lignin nanoparticles loaded with potassium sorbate (LNP@PS) as additives to polyvinyl alcohol-based active packaging films have been explored. Pure PVA films show terrible UV-shielding performance but outstanding optical transparency, with transmittance ratios of 80%, particularly in the UVA and UVB regions, and 90% in the visible light range. The UV shielding performance increased from 96.78 to 989.99% when comparing film containing 3% LNP@PS/3% TA and 3% LNP@PS/5%TA, and from 94.79 to 989.99% when comparing with film containing 1% LNP@PS/5%TA and 3% LNP@PS/5%TA, respectively. Both showed a notable decrease in UV transmittance59.Thermal decomposition analysis studiesThe thermodynamic properties of CH/PVA and ZnO@TA@CH/PVA composite films were investigated using thermogravimetric analysis, as illustrated in Fig. 12. The initial weight loss for all the produced films took place between 25 and 130 °C, which might be attributable to the loss of absorbed water molecules, notably the weight loss increased after adding ZnO@TA attributed to the degradation of tannins small molecules such as CO, CO2, and phenol from high molecular weight macromolecules into smaller chain fragments64. The initial decomposition temperature of ZnO@TA @CH/PVA composite film was slightly elevated to 242 °C when contrasted with CH/PVA film (235 °C) with weight loss percentage. The rise in early degradation temperature could be related to the inclusion of ZnO@TA nanoparticles as shown in Table 5.Figure 12TGA profile of (a) PVA/CH and (b) ZnO@TA @PVA/CH films.CH/PVA film exhibits three-stage decomposition however, ZnO@TA @CH/PVA film has four degradation steps. The major second thermal decomposition step for CH/PVA is in the temperatures range 136.45–278.14 °C was attributed to the thermal decomposition of chitosan by deacetylation4. ZnO@TA @CH/PVA film sifts to higher temperature range (142.54–304.0 °C) and that may be attributed to the thermal stability of ZnO@TA@CH/PVA film films being better than CH/PVA film after addition of ZnO@TA NPs (Table 4). This temperature range is linked to the dehydration of the saccharide rings, depolymerisation, and decomposition of the polymer units65.
Table 4 Thermal degradation kinetic parameters of CH/PVA and ZnO@TA @CH/PVA films.And the maximum weight loss rate temperature was slightly increased with the addition of ZnO@TA content from 42.77 wt % to 67.0 wt.% owing to the strong interfacial interactions between the functional groups of ZnO@TA and the macromolecular chains of CH/PVA.The thermal decomposition of PVA as per previous report66,67 occurred between 391.72 and 489.43 °C and 404.03–459.97 °C for CH/PVA and ZnO@TA @CH/PVA respectively. The third decomposition range of ZnO@TA @CH/PVA is between 303.65 and 373.79 °C which could be attributed to two reasons the first is the depolymerisation/hydrolysis of tannic acid64 and the second is the thermal degradation of cross-linked bond (hydrogen bond) forming via tannins polyols occurred with PVA and chitosan beside to the degradation of zinc oxide nanoparticles of ZnO@TA @CH/PVA film (Table 4). Previous research has shown that zinc oxide nanoparticles can operate as thermal insulators by limiting the mobility of polymer chains. This demonstrated the thermal stability of the generated composite films and was consistent with prior results68. The knowledge of Ea allows detecting reaction mechanism over a wide temperature range. The total activation energy (Ʃ Ea) of ZnO@TA @CH/PVA is higher than CH/PVA. The Ʃ Ea are −0.02803 K J mol−1 and −0.03620 K J mol−1 for CH/PVA and ZnO@TA@CH/PVA, respectively (Table 4). This result indicates that ZnO@TA @CH/PVA film is more thermally stable than CH/PVA film.Antimicrobial studiesFigure 13 shows the antimicrobial activity against Gram-Positive Bacteria: Staphylococcus aureus, pathogenic yeast Candida albicans and crops pathogen: Aspergillus flavus. All films show antimicrobial influence against all tested microorganisms. As shown in Table 5, the inhibition zones (mm) significantly increase with increasing loadings of ZnO@TA, the effective concentration of ZnO@TA is 50 mg at which ZnO@TA@CH/PVA film exhibits the largest inhibition zone (11 ± 1.0 mm) against Staphylococcus aureus compared with amoxicillin/clavulanic positive control (26 ± 1.0 mm) and 12.3 ± 0.57 mm and 13.6 ± 0.57 mm for Aspergillus flavus and Candida albicans, respectively compared with clotrimazole fungal positive control 15.0 ± 1.0 mm and 14.6 ± 0.57 mm, respectively. Several studies have demonstrated the efficacy of zinc oxide nanoparticles for bacterial membrane disruption, enzymatic inhibition, interaction with genes and proteins, and protein inactivation69.Figure 13Inhibition zones generated by C: CH/PVA control film, D: ZnO@TA (10 mg)@PVA/CH, B: ZnO@TA (30 mg)@PVA/CH, and A: ZnO@TA(50 mg)@PVA/CH.Table 5 Inhibition zones readings caused by CH/PVA and ZnO@TA@PVA/CH films with different loadings of ZnO@TA.Previous studies have shown comparable behavior, Kyong-Hoon Choi et al. (2017) have reported preparation of a new zinc oxide (ZnO) nanoparticle with antioxidant capabilities. The ZnO nanoparticles were treated with micro-dielectric barrier discharge (DBD) plasma to immobilize the antioxidant 3-(3,4-dihydroxyphenyl)-2-propenoic acid (caffeic acid, CA). ZnO@CA nanoparticles shown strong antibacterial action against Escherichia coli and Staphylococcus aureus, including resistant strains like methicillin-resistant S. aureus17. Also, cellulose/PVA film containing (1.0 wt% zinc oxide/plant polyphenols was created by Da Song and Li-Wei Ma et al. (2023) through straightforward hydrothermal and casting techniques. The study evaluated the antibacterial activities of against Escherichia coli and staphylococcus aureus, achieving 4.4 and 6.3 mm inhibition zones, respectively53. A study has been reported by Denice S. Vicentini et al. (2010) has prepared ZnO nanoparticles have been produced from polyester using the Pechini method, which involves reacting citric acid and ethylene glycol. The resulting ZnO nanoparticles were then mixed with varying concentrations of polyoxyethylene sorbitan monooleate, or Tween 80 (T80), to create blend films of chitosan (CH) and poly (vinyl alcohol) (PVA). When the films’ antibacterial activity was evaluated, the ZnO nanoparticle-containing films demonstrated antibacterial activity against the bacterium species Staphylococcus aureus. Without ZnO nanoparticles added, the S. aureus species microorganisms in the films continued to be viable; but, when exposed to ZnO nanoparticles, they ceased to be viable. Consequently, these findings imply that the ZnO nanoparticles’ presence is what causes the antibacterial activity11,70. Another study examined the efficiency of chitosan-coated film with varied quantities of Moringa oleifera seed powder (MOSP) as reinforcement agent and tannic acid (TA) as a crosslinker reported by Raja Venkatesan et al. (2024). The biocomposite films, with 10.0 wt.% MOSP content, showed increased antimicrobial and antifungal activity against bacteria like Staphylococcus aureus, E. coli, A. niger, and Candida albicans, making them ideal food packaging materials71.