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Polyvinyl alcohol (PVA) is one of the few biodegradable synthetic resins from petroleum-based sources that can alleviate white pollution in the environment. PVA film materials have excellent properties, such as high barrier, high transparency, high toughness, biocompatibility, and adjustable water solubility. However, due to the presence of hydrophilic hydroxyl groups in the side chain of PVA resin, when PVA film is placed in a humid or water environment, swelling or even dissolution will occur, which greatly limits its application. Therefore, it is necessary to modify PVA resin to improve water resistance without reducing other properties and can also impart various functionalities to it, thereby widening the application range. This paper reviews the water-resistant modification methods of polyvinyl alcohol and the application of water-resistant films and provides an outlook on the development trend of PVA water-resistant films.

The structure and physicochemical properties of polyvinyl alcohol (PVA) and PVA/glycerol films have been investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA), and advanced scanning probe microscopy (SPM). In the pure PVA films, SPM allowed us to observe ribbon-shaped domains with a different frictional and elastic contrast, which apparently originated from a correlated growth or assembly of PVA crystalline nuclei located within individual PVA clusters. The incorporation of 22% w/w glycerol led to modification in shape of those domains from ribbon-like in pure PVA to rounded in PVA/glycerol 22% w/w films; changes in the relative intensities of the XRD peaks and a decrease in the amorphous halo in the XRD pattern were also detected, while the DTA peak corresponding to the melting point remained at almost the same temperature. For higher glycerol content, FT-IR revealed additional glycerol-characteristic peaks presumably related to the formation of glycerol aggregates, and XRD, FT-IR, and DTA all indicated a reduction in crystallinity. For more than 36% w/w glycerol, the plasticization of the films complicated the acquisition of SPM images without tip-induced surface modification. Our study contributes to the understanding of crystallinity in PVA and how it is altered by a plasticizer such as glycerol.

Fungal growth in table grapes (Vitis vinifera cv. beauty seedless) is triggered by Botrytis cinerea, Penicillium sp., Aspergillus sp., and Rhizopus stolonifera during post-harvest storage. Due to the safety aspects, this research aimed to develop antifungal packaging embedded with essential oils (EOs) to alleviate the fungal decay of table grapes (TG). The various levels of EOs (0.5–5%, v/v) from clove, cinnamon, thyme, peppermint, lemon, bergamot, ginger, spearmint, and lemongrass were tested against Aspergillus sp. The results attained in radial growth, disk diffusion method, minimal inhibitory concentration, and minimal fungicidal concentration revealed that 1% clove essential oil (CEO) showed higher efficacy against Aspergillus sp. compared to the untreated control and other treatments. CEO at the 1% level exhibited a pleasant odor intensity in TG than the other EOs. The active polyvinyl alcohol (7% PVA) film with 1% CEO resulted in lower weight loss, disease severity, and TG berry drop than the control and other treated samples. Additionally, the acceptance score in the TG sample wrapped with a PVA film containing 1% CEO was augmented. Therefore, the PVA film with 1% CEO retarded the fungal growth and prolonged the shelf life of TG during storage of 21 days at 13 °C and 75% relative humidity (RH).

Ag nanoparticles were in-situ grown on the surface of MXene nanosheets to prepare thermally conductive hetero-structured MXene@Ag fillers. With polyvinyl alcohol (PVA) as the polymer matrix, thermally conductive MXene@Ag/PVA composite films were fabricated by the processes of solution blending, pouring, and evaporative self-assembly. With the same mass fraction, MXene@Ag-III (MXene/Ag, 2:1, w/w) presents more significant improvement in thermal conductivity coefficient (λ) than MXene@Ag, single MXene, Ag, and simply blending MXene/Ag. MXene@Ag-III/PVA composite films show dual functions of excellent thermal conductivity and electromagnetic interference (EMI) shielding. When the mass fraction of MXene@Ag-III is 60 wt.%, the in-plane λ (λ ∥ ), through-plane λ (λ ⊥ ), and EMI shielding effectiveness (EMI SE) are 3.72 and 0.41 W/(m·K), and 32 dB, which are increased by 3.1, 1.3, and 105.7 times than those of pure PVA film (0.91 and 0.18 W/(m·K), and 0.3 dB), respectively. The 60 wt.% MXene@Ag-III/PVA composite film also has satisfying mechanical and thermal properties, with Young’s modulus, glass transition temperature, and heat resistance index of 3.8 GPa, 58.5 and 175.3 °C, respectively.

The current work explores the potential use of commercial Chinese bayberry tannin (BT) to develop antioxidant PVA-based films using solvent casting process for packaging applications. The effect of BT concentration on opacity, water resistance and antioxidant capacity of resulting films was investigated. Properties like tensile strength, thermal behavior, and morphological aspects were also characterized. The experimental results showed that PVA/BT films formed with uniformly brown color and generally good transparency, offering good antioxidant ability. The PVA film containing BT presented slightly higher water resistance according to the results of moisture content and water vapor permeability, especially at low BT content (<10 wt%). The PVA can be compounded with up to 10 wt% BT without any obvious deterioration in the tensile strength. The PVA/BT films exhibited better thermal degradation behavior compared with PVA alone because of the chemical bonds of PVA-BT and the formation of char at high temperature. Based on the results, PVA incorporated with Chinese bayberry tannin may provide broader formulation options for packaging materials with antioxidant action. Graphical Abstract Development of Antioxidant Packaging Film Based on Chinese Bayberry Tannin Extract and Polyvinyl Alcohol

With N , N ′-methylenebisacrylamide (MBA) and polyvinyl alcohol (PVA) as raw materials, a polymer (PVA-MBA) containing N -halamine precursor functional groups was obtained via grafting reaction between the active hydroxyl groups on PVA and α , β -unsaturated functional groups of MBA under the catalysis of sodium carbonate in an aqueous solution. An acyclic N -halamine precursor-grafted PVA (MBA-PVA) film was formed by simply spreading PVA-MBA aqueous solution in a glass dish and drying it. An antimicrobial acyclic N -halamine-grafted PVA (PVA-MBA-Cl) film was achieved by spraying the diluted sodium hypochlorite solution onto the surface of PVA-MBA film. The performance test of PVA-MBA-Cl film under the optimal preparation conditions showed that the tensile performance and the hydrophobicity were improved, compared to the PVA film. The storage stability test indicated that the oxidative chlorine content Cl + (atoms/cm 2 ) of the as-prepared PVA-MBA-Cl film only reduced by 14.3% after storage for 9 weeks, showing that the antibacterial N -halamine functional groups in PVA-MBA-Cl film has excellent storage stability under room temperature. Antibacterial test showed that the PVA-MBA-Cl film had very strong antibacterial efficacies and could completely kill 1.28 × 10 6  CFU/mL S. aureus and 1.89 × 10 6  CFU/mL E. coli within 1 min. Therefore, PVA-MBA-Cl film will have more potential applications in food package.

Hemicellulose is the second most abundant natural polysaccharide and a promising feedstock for biomaterial synthesis. In the present study, the hemicellulose of loblolly pine was obtained by the alkali extraction-graded ethanol precipitation technique, and the hemicellulose-polyvinyl alcohol (hemicellulose-PVA) composite film was prepared by film casting from water. Results showed that hemicellulose with a low degree of substitution is prone to self-aggregation during film formation, while hemicellulose with high branching has better compatibility with PVA and is easier to form a homogeneous composite film. In addition, the higher molecular weight of hemicellulose facilitates the preparation of hemicellulose-PVA composite film with better mechanical properties. More residual lignin in hemicellulose results in the better UV shielding ability of the composite film. This study provides essential support for the efficient and rational utilization of hemicellulose.

Quaternary ammonium compounds are active functional groups that can inhibit bacterial growth and reduce drug resistance. In this study, we prepared hybrid nanoparticles (NPs) comprising quaternary ammonium cellulose derivatives (CBHE-QAn) and citric acid (CA). Firstly, cellulose 6-bromohexanoyl ester (CBHE) was synthesized by esterification of cellulose with 6-bromohexanoyl chloride. Then, diverse CBHE-QAn (CBHE-QA8, CBHE-QA10, CBHE-QA12, CBHE-QA14, and CBHE-QA16) were synthesized by the reaction of CBHE with five tertiary amine compounds, namely, N,N-dimethyloctylamine, N,N-dimethyldecylamine, N,N-dimethyldodecylamine, N,N-dimethyltetradecylamine, and N,N-dimethylhexadecylamine. The hybrid NPs were formed through electrostatic interactions between CBHE-QAn and CA and named CBHE-QAn/CAx (where x represents the mass ratio of CA). These spherical NPs with average diameters of 70–145 nm exhibited excellent antibacterial activity against gram-positive bacterium S. aureus and gram-negative bacterium E. coli. Furthermore, adding CBHE-QA16/CA35 NPs to a polyvinyl alcohol (PVA) matrix via a solvent casting method significantly enhanced the antibacterial activity and improved the tensile strength. With 5 wt.% of CBHE-QA16/CA35 NPs, the tensile strength of the PVA composite film increased to 53.4 MPa (47.2% higher than that of the pure PVA film). Moreover, the PVA/CBHE-QA16/CA35 composite films showed excellent antibacterial efficiency.

Lignin, the second most abundant natural polymer, is a by-product of the biorefinery and pulp and paper industries. This study was undertaken to evaluate the properties and estimate the prospects of using lignin as a by-product of the pretreatment of common reed straw (Phragmites australis) with deep eutectic solvents (DESs) of various compositions: choline chloride/oxalic acid (ChCl/OA), choline chloride/lactic acid (ChCl/LA), and choline chloride/monoethanol amine (ChCl/EA). The lignin samples, hereinafter referred to as Lig-OA, Lig-LA, and Lig-EA, were obtained as by-products after optimizing the conditions of reed straw pretreatment with DESs in order to improve the efficiency of subsequent enzymatic hydrolysis. The lignin was studied using gel penetration chromatography, UV-vis, ATR-FTIR, and 1H and 13C NMR spectroscopy; its antioxidant activity was assessed, and the UV-shielding properties of lignin/polyvinyl alcohol composite films were estimated. The DES composition had a significant impact on the structure and properties of the extracted lignin. The lignin’s ability to scavenge ABTS+• and DPPH• radicals, as well as the efficiency of UV radiation shielding, decreased as follows: Lig-OA > Lig-LA > Lig-EA. The PVA/Lig-OA and PVA/Lig-LA films with a lignin content of 4% of the weight of PVA block UV radiation in the UVA range by 96% and 87%, respectively, and completely block UV radiation in the UVB range.

A highly efficient light-induced aggregation of porphyrin molecules in solution was recently reported for 4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid (TPPS). Here, we demonstrate that rhodamine 6G (R6G) and pseudoisocyanine (PIC) also show efficient light-induced aggregation in unsaturated aqueous solution, being detected with a multichannel lock-in amplifier as the absorbance decrease/increase in the monomers/aggregates, induced by a laser at 633 nm, which is non-resonant off their main monomer absorption wavelengths. The light-induced aggregation states are H-aggregates that are hardly formed in the thermal equilibrium. The similar absorbance changes are absent in the monomer molecules fixed in polyvinyl alcohol (PVA) films. The aggregation efficiency defined as ( Δ A / A ) / ( U t r a p / k B T ) , where A is the absorbance of the monomers, Δ A is the absorbance increase in the aggregates, U t r a p is the optical gradient force potential, and k B T is the thermal energy at room temperature, is approximately 100 for R6G and 500 for PIC, which are much smaller than that of TPPS.