CN110358099B

CN110358099B - PVA-based composite material and precursor, remolded product, composite hydrogel, composite film, preparation and application thereof

Info

Publication number: CN110358099B
Application number: CN201910576264.4A
Authority: CN
Inventors: 刘小孔; 牛文文
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2021-07-30
Anticipated expiration: 2039-06-28
Also published as: CN110358099A; WO2020259723A1

Abstract

The invention discloses a PVA-based composite material, a precursor, a remolded product, composite hydrogel, a composite film, preparation and application thereof. The preparation method of the PVA-based composite material precursor comprises the following steps: precipitating a solution obtained by uniformly mixing a polyvinyl alcohol aqueous solution and a tannic acid aqueous solution, and separating and collecting precipitates; wherein the mass ratio of the tannic acid to the polyvinyl alcohol is 0.016: 1 or more. The composite material, the composite hydrogel and the composite film provided by the invention have the advantages of improved strength, greatly improved toughness and the like, and also have the advantages of water processability, ultraviolet light absorption, fresh-keeping performance, degradability and plasticity.

Description

PVA-based composite material and precursor, remolded product, composite hydrogel, composite film, preparation and application thereof

Technical Field

The invention relates to a PVA-based composite material, a precursor, a remolded product, composite hydrogel, a composite film, preparation and application thereof.

Background

At present, a few methods for improving the toughness of PVA (polyvinyl alcohol) by using TA (tannic acid) exist, and because most of PVA is crystalline polymer, PVA composite materials modified by using TA reported in the prior art are basically crystal form products.

For example, Yu Guan et al (Yu Guan, Bio-impregnated natural polymeric cross-linking poly (vinyl alcohol) films with linear integrated string h and hardness, RSC Advances, 2016,6, p69966) disclose a method for improving toughness of PVA by using TA, in which a TA solution is added dropwise to a PVA solution, and water is evaporated at 40 ℃ to obtain a TA-PVA composite film. The mass of TA added into the composite film accounts for 1-10% of the mass of PVA, and the result shows that the crystallization of PVA is not damaged, and the toughening effect of the obtained composite material is not ideal.

In addition, Ya-Nan Chen et al also disclose a method for preparing Shape Memory hydrogel by blending PVA-TA (Ya-Nan Chen, Poly (vinyl alcohol) -Tannic Acid Hydrogels with Excellent Mechanical Properties and Shape Memory devices, ACS Applied Materials & Interfaces, 2016,8, p27199-27206), although the authors indicate that the XRD results in FIG. 2(b) show that PVA-TA hydrogel has no three characteristic diffraction peaks and is amorphous. It is noteworthy, however, that the XRD patterns of both PVA-TA hydrogel products in FIG. 2(b) of this document exhibit characteristic peaks at 20 ℃ after magnification, and that the intensities are not weak.

Further, the specific structure of the PVA-TA hydrogel should be determined by comparing the XRD diffraction peak patterns with those of the PVA hydrogel, and the XRD diffraction peak of the PVA dry substance is detected in FIG. 2(b) of the document and is not the XRD diffraction peak of the PVA hydrogel, but the structure of the hydrogel cannot be accurately defined by comparing the PVA-TA hydrogel with the PVA dry substance.

In order to further verify the structure of the composite hydrogel Obtained in the document, the inventor of the present application repeated the XRD detection process of the PVA hydrogel many times, and also consulted the XRD spectrum of the PVA hydrogel reported in fig. 2 of the prior art (Rosa ricardi, X-ray Diffraction Analysis of Poly (vinyl alcohol) Hydrogels, objective by free Freezing and Thawing technologies, Macromolecules,2004,5,37, p1923), and found that there is a characteristic Diffraction peak at about 20 °, which is completely consistent with the characteristic peak at 20 ° exhibited by the XRD spectrum of two PVA-TA hydrogel products in fig. 2(b) of the document Ya-Nan Chen et al; more importantly, the spectrograms of the two PVA-TA hydrogels in the figure 2(b) reported by Ya-Nan Chen et al are basically completely matched with the aspects of peak intensity, peak shape and peak position no matter compared with the XRD spectrograms of the PVA hydrogels obtained by repeated experiments or the XRD spectrograms of the PVA hydrogels reported by the literature, which shows that the PVA-TA hydrogels reported by Ya-Nan et al can only be regarded as the crystal structure consistent with the PVA hydrogels. That is, the hydrogel obtained from the document published by Ya-Nan Chen et al cannot be reasonably confirmed to have an amorphous structure.

Disclosure of Invention

The invention aims to overcome the defect that the PVA-TA hydrogel in the prior art still keeps the crystal form structure of the PVA hydrogel, so that the mechanical properties such as toughness and the like cannot meet the requirements, and provides a PVA-based composite material, a precursor, a remolded product, a composite hydrogel, a composite film, preparation and application thereof. The composite material precursor, the composite material, the composite hydrogel and the composite film provided by the invention have the advantages of improved strength, greatly improved toughness and the like, and also have the advantages of water processability, ultraviolet light absorption, fresh-keeping performance, easy degradability and plasticity.

The invention provides a preparation method of a PVA-based composite material precursor, which comprises the following steps: precipitating a solution obtained by uniformly mixing a polyvinyl alcohol aqueous solution and a tannic acid aqueous solution, and separating and collecting precipitates; wherein the mass ratio of the tannic acid to the polyvinyl alcohol is 0.016: 1 or more.

In the present invention, the preparation method of the PVA-based composite precursor preferably includes the steps of: mixing the aqueous solution of polyvinyl alcohol and the aqueous solution of tannic acid uniformly, adjusting the pH to be below 6.35, precipitating, separating and collecting the precipitate.

The pH regulator used for adjusting the pH is a conventional raw material in the field, preferably a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is preferably 0.5-3 mol/L, more preferably 1 mol/L.

Among them, as a result of experiments, the lower the pH value, the more advantageous the amorphous state is, so that the pH value has no lower limit, and may be as low as 0.1, 0.5, 1.0, or the like. Based on the consideration of saving the amount of the pH regulator, the pH is preferably adjusted to 2.0 to 5.26, more preferably 2.0.

In the present invention, the polyvinyl alcohol is conventional in the art and abbreviated as PVA, for example, in a preferred embodiment of the present application, polyvinyl alcohol having a Mw molecular weight of 146000 and a degree of hydrolysis of 99% is selected from the group consisting of those commercially available from Sigma-Aldrich.

In the present invention, the tannic acid is conventional in the art, abbreviated as TA and Mw is 1701, for example, in a preferred embodiment of the present application, tannic acid available from Alfa Aesar alpha Elsa is selected.

In the present invention, the method of uniformly mixing preferably comprises the following steps: adding a polyvinyl alcohol aqueous solution into a tannic acid aqueous solution; the addition is preferably carried out dropwise. It should be noted that: precipitation occurs whenever one drop of polyvinyl alcohol solution is added to the aqueous tannic acid solution, i.e. the mass ratio of tannic acid to polyvinyl alcohol is not limited or restricted by a maximum critical value, for example up to 10000:1, 1000: 1. 100:1, 50:1, etc.

In the present invention, the ratio of the mass of the tannic acid to the mass of the polyvinyl alcohol is preferably (0.25: 1) to (1: 0.5), for example, 0.25:1, 0.5:1, 0.75:1, 1:1, 1:0.75 and 1:0.5, more preferably 0.5:1, from the viewpoints of the overall reaction yield, the performance of the precursor of the composite material, and the like. In the present invention, unless otherwise specified, the mass ratio refers to a charge ratio.

In view of the reaction yield, the mass ratio of tannic acid to polyvinyl alcohol is preferably (0.5: 1) to (1: 0.75), and a reaction yield of 81% or more, more preferably (0.75:1) to (1:1), and a reaction yield of 87% or more can be achieved. The reaction yield is the mass percentage of the precipitate obtained after the reaction is centrifuged and dried, which accounts for the sum of the mass of the tannic acid and the polyvinyl alcohol in the raw materials.

The polyvinyl alcohol aqueous solution is obtained by uniformly mixing polyvinyl alcohol powder and deionized water and then heating and dissolving. The heated dissolution is a routine operation in the art, such as 95 deg.C oil bath heating. The maximum concentration of the polyvinyl alcohol in the aqueous solution of polyvinyl alcohol may correspond to the maximum solubility of polyvinyl alcohol in water, and the concentration of polyvinyl alcohol is preferably less than 125mg/mL (or less than 12.5% in terms of mass percentage), for example, 10 to 125mg/mL, and more preferably 10 mg/mL.

The concentration of tannic acid in the aqueous solution of tannic acid is preferably 250mg/mL or less (or 25% or less in terms of mass percentage concentration), for example, 10 to 250mg/mL, and more preferably 10 mg/mL.

In the present invention, the operation of separating and collecting the precipitate is a conventional operation in the art, and is preferably achieved by centrifugation; the centrifugation treatment can be performed under the conventional operation conditions in the art, preferably at 8000-10000 rpm for 8-15 minutes in a centrifuge, and more preferably at 9500rpm for 10 minutes in a centrifuge.

The invention also provides a PVA-based composite material precursor prepared by the preparation method.

In the invention, the PVA-based composite material precursor prepared by the preparation method is in an amorphous state or a mixed state of the amorphous state and a crystal form, and the crystallinity detected by infrared spectroscopy is less than 34%.

In the present invention, according to the preparation method of the present application, in a preferable embodiment corresponding to the mass ratio (0.25: 1) to (1: 0.5) of the tannic acid to the polyvinyl alcohol, the mass ratio of the tannic acid to the polyvinyl alcohol in the obtained PVA-based composite material precursor is (0.74:1) to (1:0.65), and the number ratio of the tannic acid molecules to the polyvinyl alcohol monomers in the PVA-based composite material precursor is (1: 52) to (1: 25). The number ratio of the tannin molecules to the polyvinyl alcohol in the PVA based composite material precursor is the repeating structural unit (namely-C) of the tannin molecules and the polyvinyl alcohol in the PVA based composite material precursor₂H₄O-) and the mass ratio of the tannic acid to the polyvinyl alcohol refers to the mass ratio of tannic acid molecules to polyvinyl alcohol molecules in the PVA-based composite material precursor, wherein the tannic acid molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form supermolecular aggregates.

In the present invention, the precursor of the PVA-based composite material is preferably in an amorphous state, and accordingly, the crystallinity thereof is 0. According to a preferred embodiment of the present application, when the mass ratio of tannic acid to polyvinyl alcohol in the preparation method is in the range of (0.5: 1) to (1: 0.5) (e.g., 0.5:1, 1:1, 1: 0.5), the mass ratio of tannic acid to polyvinyl alcohol in the composite material precursor is in the range of (0.86:1.0) to (1.0:0.65), the number ratio of tannic acid molecules to polyvinyl alcohol monomers in the PVA-based composite material precursor is in the range of (1: 45) to (1:25), and the resulting composite material precursor is in an amorphous state.

In addition, in the preparation scheme of the PVA-based composite material precursor, the minimum critical value of the mass ratio of the tannin to the polyvinyl alcohol is 0.016: 1.0, the crystallinity degree corresponding to the pH value is not adjusted to be 34 percent, which indicates that the precursor of the PVA composite material is in a mixed state of amorphous and crystal forms. According to the reaction mechanism of the precursor, when the mass ratio of the tannic acid to the polyvinyl alcohol is more than 0.016: 1, the morphology of the PVA composite precursor is between amorphous and a mixed state with a crystallinity of less than 34%.

The invention also provides a PVA-based composite material precursor, which is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules through hydrogen bonds; the PVA based composite material precursor is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

In the present invention, the crystallinity is calculated from the references (o.n. trentinikov, Determination of the degree of crystallinity of poly (vinyl) by FTIR Spectroscopy, Journal of Applied Spectroscopy,2012,4,79, p 525).

Specifically, the crystallinity data is based on formula (1) at page 525 of this document:

α(％)＝-13.1+89.5(A₁₁₄₄/A₁₀₉₄) (1)

and (3) combining the actual peak position, adjusting the peak position to be calculated by the formula (2):

α(％)＝-13.1+89.5(A₁₁₄₂/A₁₀₈₅) (2)

in the present invention, preferably, the PVA composite precursor is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the composite material precursor has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm-¹The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

In the present invention, the mass ratio of tannic acid to polyvinyl alcohol in the PVA-based composite material precursor is preferably (0.74:1) to (1:0.65), more preferably (0.86:1.0) to (1.0: 0.65); and/or the number ratio of the tannin molecules to the polyvinyl alcohol monomers in the PVA based composite material precursor is (1: 52) - (1:25), preferably (1: 45) - (1: 25). In the precursor of the composite material, the number ratio of the tannin molecules to the polyvinyl alcohol is the molar ratio of the tannin molecules to the repeating structural units of the polyvinyl alcohol in the precursor of the PVA-based composite material, and the mass ratio of the tannin molecules to the polyvinyl alcohol is the mass ratio of the tannin molecules to the polyvinyl alcohol molecules in the precursor of the PVA-based composite material, wherein the tannin molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form the supermolecule aggregate.

The invention also provides a preparation method of the PVA-based composite material, which comprises the following steps: and forming and drying the PVA-based composite material precursor.

In the present invention, the forming is a conventional operation in the art, and means that a TA-PVA-based composite material precursor can be formed into a material of any shape or structure by a mold, the shape and structure of the material depend on the shape and structure of the mold, and the material can be a shape commonly found in the art, such as a sheet, a wire, a particle, and the like, but is not limited to the specific types.

Wherein, when the PVA-based composite material is a sheet, the preparation method thereof preferably comprises the steps of: pressing the PVA-based composite material precursor into a sheet, and drying.

Wherein the pressing is a conventional operation in the art, for example, the PVA-based composite material precursor is placed in two polyimide films and press-formed at room temperature.

Wherein, the pressing is performed in the conventional equipment in the field, and is generally realized in a fixed press, and the pressure of the fixed press is preferably 1-5 MPa, and more preferably 4 MPa. The pressing time is conventional in the field, and is, for example, 0.017 to 30 minutes.

According to the preparation method of the invention, the thickness of the PVA-based composite material sheet conventionally used in the field can be prepared, for example, the thickness is less than 1.75mm, and preferably 0.075-1.75 mm.

The invention also provides the PVA-based composite material prepared by the preparation method.

In the invention, the PVA-based composite material prepared by the preparation method is in an amorphous state or a mixed state of the amorphous state and a crystal form, and the crystallinity detected by infrared spectroscopy is less than 34%.

In the present invention, the thickness of the resulting composite material may be conventional in the art, for example, 30 μm to 1.75mm, according to the preparation method of the present application.

In the present invention, according to the preparation method of the present application, in a preferable embodiment corresponding to the mass ratio (0.25: 1) to (1: 0.5) of the tannic acid to the polyvinyl alcohol, the mass ratio of the tannic acid to the polyvinyl alcohol in the PVA-based composite material obtained is (0.74:1) to (1: 0.65); the number ratio of the tannin molecules to the polyvinyl alcohol monomers in the PVA-based composite material is (1: 52) - (1: 25). In the PVA-based composite material, the number ratio of the tannin molecules to the polyvinyl alcohol is the molar ratio of the tannin molecules to the repeating structural units of the polyvinyl alcohol in the PVA-based composite material, and the mass ratio of the tannin molecules to the polyvinyl alcohol is the mass ratio of the tannin molecules to the polyvinyl alcohol molecules in the PVA-based composite material, wherein the tannin molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form supermolecule aggregates.

In the present invention, the PVA-based composite material obtained is preferably in an amorphous state, and accordingly, has a crystallinity of 0. According to a preferred embodiment of the present application, when the mass ratio of tannic acid to polyvinyl alcohol in the preparation method is in the range of (0.5: 1) to (1: 0.5) (e.g., 0.5:1, 1:1, 1: 0.5), the mass ratio of tannic acid to polyvinyl alcohol in the composite material is (0.86:1.0) to (1.0:0.65), the amount ratio of tannic acid molecules to polyvinyl alcohol monomers in the PVA-based composite material is (1: 45) to (1:25), and the resulting composite material is in an amorphous state.

In addition, in the preparation scheme of the composite material, the minimum critical value of the mass ratio of the tannin to the polyvinyl alcohol is 0.016: 1.0, the crystallinity degree corresponding to the pH value is not adjusted to be 34 percent, which indicates that the PVA composite material is in a mixed state of amorphous state and crystal form. According to the reaction mechanism of the composite material, when the mass ratio of the tannic acid to the polyvinyl alcohol is more than 0.016: 1, the morphology of the PVA composite is between amorphous and a mixed state with a crystallinity of less than 34%.

The invention also provides a PVA-based composite material, which is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules by hydrogen bonds; the PVA based composite material is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

In the present invention, preferably, the PVA composite material is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the composite material has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

In the present invention, the mass ratio of tannic acid to polyvinyl alcohol in the PVA-based composite material is preferably (0.74:1) to (1:0.65), more preferably (0.86:1.0) to (1.0: 0.65); and/or the number ratio of the tannin molecules to the polyvinyl alcohol monomers in the PVA based composite material is (1: 52) - (1:25), preferably (1: 45) - (1: 25). In the PVA-based composite material, the number ratio of the tannin molecules to the polyvinyl alcohol is the molar ratio of the tannin molecules to the repeating structural units of the polyvinyl alcohol in the PVA-based composite material, and the mass ratio of the tannin molecules to the polyvinyl alcohol is the mass ratio of the tannin molecules to the polyvinyl alcohol molecules in the PVA-based composite material, wherein the tannin molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form supermolecule aggregates.

The invention also provides a remodeling method of the PVA-based composite material, which comprises the following steps: and (3) taking the PVA-based composite material, swelling, molding and drying.

In the present invention, the swelling is a conventional operation in the art, that is, the PVA-based composite material is saturated with water by using a solvent which is conventional in the art, and the solvent is preferably an aqueous solution having a pH of not more than 9.0, more preferably deionized water or an acidic aqueous solution, further more preferably an acidic aqueous solution having a pH of 1.0 to 2.5, and particularly preferably an acidic aqueous solution having a pH of 2.0. The acid may be of a type conventional in the art, such as hydrochloric acid. In a preferred embodiment of the present application, the solvent used for swelling is hydrochloric acid having a pH of 2.0.

In the remodeling method, the molding refers to a material with any shape or structure obtained by molding through a mold, the shape and structure of the material depend on the shape and structure of the mold, and the material can be in a shape common in the art, such as a sheet, a wire, a granule, and the like, but is not limited to the specific types shown in these embodiments.

In selecting specific operation parameters, the forming is the same as the forming operation in the preparation process of the PVA based composite material, for example, in preparing a sheet, the pressing parameters are preferably as described above.

The invention also provides a remolded product obtained by the remolding method.

In the invention, the remolded product prepared by the remolding method is in an amorphous state or a mixed state of the amorphous state and a crystal form, and the crystallinity detected by infrared spectroscopy is less than 34%.

In the present invention, preferably, the remodeled product is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the remolded product has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

The invention also provides a preparation method of the PVA-based composite hydrogel, which comprises the following steps: soaking the PVA-based composite material in an aqueous solution with the pH value not more than 9.0 to reach water absorption saturation.

Wherein, the raw material for preparing the PVA-based composite hydrogel is preferably PVA-based composite material with the thickness of 150-1000 μm.

The aqueous solution having a pH of not more than 9.0 may be an acidic aqueous solution, a neutral aqueous solution or a weakly alkaline aqueous solution having a pH of not more than 9.0, such as deionized water, which is conventional in the art.

The invention also provides the PVA-based composite hydrogel prepared by the preparation method.

In the invention, the PVA-based composite hydrogel prepared by the preparation method is in an amorphous state or a mixed state of the amorphous state and a crystal form, and the crystallinity detected by infrared spectroscopy is less than 34%.

In the present invention, preferably, the PVA-based composite hydrogel is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the composite hydrogel has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

It will be appreciated by those skilled in the art that infrared, DSC measurements of the crystallinity of the composite hydrogel require drying of the hydrogel, so the criteria for evaluation are consistent with the dry state of the composite.

In the present invention, the mass ratio of tannic acid to polyvinyl alcohol in the PVA-based composite hydrogel is preferably (0.74:1) to (1:0.65), more preferably (0.86:1.0) to (1.0: 0.65); and/or the number ratio of the tannin molecules to the polyvinyl alcohol in the PVA-based composite hydrogel is (1: 52) to (1:25), preferably (1: 45) to (1: 25). In the PVA-based composite hydrogel, the number ratio of the tannin molecules to the polyvinyl alcohol is the molar ratio of the tannin molecules to the repeating structural units of the polyvinyl alcohol in the PVA-based composite hydrogel, and the mass ratio of the tannin molecules to the polyvinyl alcohol is the mass ratio of the tannin molecules to the polyvinyl alcohol molecules in the PVA-based composite hydrogel, wherein the tannin molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form supermolecule aggregates.

The invention also provides PVA-based composite hydrogel which is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules through hydrogen bonds; the PVA-based composite hydrogel is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

In the present invention, preferably, the PVA composite hydrogel is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the composite hydrogel has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

The invention also provides a preparation method of the PVA-based composite film, which comprises the following steps: and stretching the PVA-based composite hydrogel, and drying.

Wherein the stretching is a conventional operation in the art, for example, biaxial stretching or uniaxial stretching may be used.

The invention also provides the PVA-based composite film prepared by the preparation method.

In the invention, the PVA-based composite film prepared by the preparation method is in an amorphous state or a mixed state of the amorphous state and a crystal form, and the crystallinity detected by infrared spectroscopy is less than 34%.

In the present invention, it is preferable that the PVA-based composite film is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the PVA-based composite film does not have diffraction peak of PVA near 20 degrees, and the infrared pattern does not have 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

The thickness of the PVA-based composite film may be a conventional film thickness in the art, for example, 5 to 30 μm, preferably 25 to 30 μm.

In the present invention, the weight ratio of tannic acid to polyvinyl alcohol in the PVA-based composite film is preferably (0.74:1) to (1:0.65), more preferably (0.86:1.0) to (1.0: 0.65); and/or the number ratio of the tannin molecules to the polyvinyl alcohol monomers in the PVA based composite film is (1: 52) to (1:25), preferably (1: 45) to (1: 25). In the PVA-based composite film, the number ratio of the tannin molecules to the polyvinyl alcohol is the molar ratio of the tannin molecules to the repeating structural units of the polyvinyl alcohol in the PVA-based composite film, and the mass ratio of the tannin molecules to the polyvinyl alcohol is the mass ratio of the tannin molecules to the polyvinyl alcohol molecules in the PVA-based composite film, wherein the tannin molecules and the polyvinyl alcohol molecules are combined by hydrogen bonds to form supermolecule aggregates.

The invention also provides a PVA-based composite film which is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules by hydrogen bonds; the PVA based composite film is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

In the present invention, preferably, the PVA composite film is in an amorphous state. In a specific embodiment, the amorphous state is determined by XRD, infrared, small angle X-ray scattering, DSC, all four measurements taken together. Specifically, the XRD pattern of the composite film has no diffraction peak of PVA near 20 degrees, and the infrared pattern has no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result.

The invention also provides the application of the PVA-based composite film as a food packaging bag or a freshness protection package. Can absorb ultraviolet rays and has antibacterial effect.

On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.

The reagents and starting materials used in the present invention are commercially available.

The positive progress effects of the invention are as follows: the PVA-based composite material, the composite hydrogel and the composite film provided by the invention have the advantages of improved strength, greatly improved toughness and the like, and also have the advantages of water processability, ultraviolet light absorption, fresh-keeping performance, easy degradability and plasticity.

Drawings

FIG. 1 is a graph of the thickness of the composite material of example 1 as a function of press time;

FIG. 2 is a drawing curve of composite materials of effect example 1 in which PVA and different monomer mass ratios are used;

FIG. 3 is a diagram showing effects of example 1 before and after stretching (i is before stretching, and ii is after stretching);

FIG. 4 is a diagram showing a sample of effect example 1 capable of withstanding the weight of a 25 kg bucket;

FIG. 5 is an X-ray diffraction pattern of PVA and PVA/TA complex in Effect example 1;

FIG. 6 is a Fourier transform infrared spectrum of PVA, TA and PVA/TA complex of effect example 1;

FIG. 7 is a small angle X-ray scattering diagram of PVA and PVA/TA complex in effect example 1;

FIG. 8 shows the difference in the effects of PVA, TA and PVA/TA Complex in example 1DSC curves obtained by scanning calorimetry are shown, wherein a) to h) respectively represent PVA and TA_0.25-PVA_1.0Complex, TA_0.50-PVA_1.0Complex, TA_0.75-PVA_1.0Complexes, TA_1.0-PVA_1.0，TA_1.0-PVA_0.75And TA_1.0-PVA_0.50The test results of the complex;

FIG. 9 is a diagram showing the composite material of example 5 after being molded;

FIG. 10 shows effects in TA of example 2_0.50-PVA_1.0A tensile profile of the hydrogel of the composite;

FIG. 11 is a mechanical property tensile curve of the composite film in Effect example 3;

FIG. 12 shows the results of the test of the degradation performance of the composite film in effect example 3, in which (a) is TA_0.50-PVA_1.0Film sample, (b) is TA_0.50-PVA_1.0The film was just placed in aqueous NaOH (pH 13); (c) is TA_0.50-PVA_1.0Schematic representation of complete dissolution of film after 3 days;

FIG. 13 is a tensile curve of a remodeled sample of Effect example 4;

FIG. 14 is a nuclear magnetic spectrum of PVA, TA and PVA/TA complex in Effect example 5;

FIG. 15 is an IR spectrum of the composite of example 6;

FIG. 16 is an XRD pattern of the composite material of example 6;

FIG. 17 shows the DSC measurement of the composite material of example 6;

fig. 18 is a tensile curve of the composite of comparative example 1.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.

In the following examples, the sources of experimental starting materials are as follows:

polyvinyl alcohol (PVA, Mw ca.146000, 99% hydrolysis, purchased from Sigma-Aldrich Co.);

tannic acid (TA, Mw ca.1701, from Alfa Aesar alpha Aisha Co.)

EXAMPLE 1 preparation of composite Material

The preparation method of the composite material comprises the following steps:

1. adding 15 g of PVA powder into 285 g of deionized water, heating (oil bath at 95 ℃) to dissolve, and obtaining a PVA aqueous solution with the mass fraction of 5%;

2. mixing a 10mg/mL TA aqueous solution and a 10mg/mL PVA solution in a TA to PVA mass ratio of 0.25:1.0,0.50:1.0,0.75-1.0,1.0-1.0,1.0-0.75 and 1.0-0.50, and adjusting the pH value of the mixed solution to 2.0 by using 1mol/L hydrochloric acid under stirring to obtain a precipitate;

3. centrifuging the precipitate with a centrifuge to obtain a precursor, pressing and molding with a press (or glass sheet), and drying.

The specific yield test results are shown in table 1 below:

table 1 test results for different mass ratios

The reaction yield is the mass of dried precipitate obtained by the reaction, which accounts for the percentage of the sum of the mass of the tannic acid and the polyvinyl alcohol in the raw materials.

Further, this example also performed a composite press test:

the volume is 6cm³The precipitate (referred to as formula TA) of_0.50-PVA_1.0) Samples of sheets (hereinafter also referred to as "composites" or "composite films") having different thicknesses were obtained by pressing for different times, the pressure of the stationary press during pressing was 4MPa, and the thicknesses of the resulting composite materials were as shown in table 2 and in fig. 1.

TABLE 2 thickness results obtained at different pressing times

Pressing time (min)	Thickness (mm) of the composite Material
		0.017	1.75
0.05	1.32
		0.133	0.8
2	0.52
		5	0.45
10	0.25
		17	0.2
22	0.15
		30	0.075

In addition, TA is also obtained by controlling the pressing time in the embodiment_0.50-PVA_1.0350 μm, 750 μm and 1000 μm composite sheet under the formula.

EXAMPLE 2 preparation of composite hydrogel

150 μm thick PVA and 150 μm thick TA prepared in example 1 were separately mixed_0.50-PVA_1.0Composite film, TA 150 μm thick_1.0-PVA_0.50The composite film was bubbled in deionized water until the sample was saturated with water (referred to as a hydrogel).

EXAMPLE 3 preparation of composite film

The preparation process of the film comprises the following steps: the three composite hydrogels of example 2 were each biaxially stretched and fixed to give a film thickness of about 30 μm after drying for 20 minutes (thickness can be controlled by the degree of stretching).

EXAMPLE 4 composite remodeling

And (3) remodeling: first, TA having a thickness of 75 μm was introduced_0.50-PVA_1.0Cutting the composite film into 10 pieces with the size of 4 cm by 3 cm, soaking the cut pieces in hydrochloric acid with the pH value of 2.0 for five hours, and fusing the pieces into a thicker block; cutting the fused compound into a heart shape, putting the heart-shaped sample cut by hands into a large heart-shaped mould for pressing, filling the mould with the sample after a period of time, and drying to obtain the heart-shaped sample.

Effect example 1 Performance test of PVA-based composite Material

(1) Ultraviolet-visible light transmission test

For a PVA sheet with a thickness of 75. mu.m, TA with different thicknesses (75 μm, 150 μm, 350 μm, 750 μm, 1000 m) from those obtained in example 1_0.50-PVA_1.0The composite was tested for uv-vis transmission.

The results show that: the 5 samples prepared in this experiment have high transparency in the visible region and can absorb ultraviolet light.

(2) Mechanical Properties 1 (in FIGS. 2-3, PVA with a thickness of 350 μm and the composite materials prepared in example 1 and having different monomer mass ratios and a thickness of 350 μm were stabilized in an environment with a humidity of 33% for five days before the test)

(2a) The tensile curves of the composite materials prepared from PVA and example 1 at different monomer mass ratios are shown in fig. 2, and the results show that: relative to pure PVAThe composite material has higher yield strength, and the elongation at break of the composite material shows a trend of increasing and then decreasing. Wherein, TA_0.50-PVA_1.0The yield strength is increased from 55.6MPa (PVA) to 101MPa, and the elongation at break is increased from 246% to 422%.

(2b) Tests were carried out on the strength and toughness of the PVA and of the composites prepared in example 1 with different monomer mass ratios (0.25:1.0,0.50:1.0,0.75-1.0,1.0-1.0,1.0-0.75 and 1.0-0.50) and the results show that: the composite material has higher yield strength relative to pure PVA, and the fracture toughness of the composite material shows a tendency of increasing and then decreasing, wherein TA_0.50-PVA_1.0The yield strength increased from 55.6MPa (PVA) to 101MPa, and the fracture toughness increased from 82.9 joules per gram to 242 joules per gram.

(2c)TA_0.50-PVA_1.0The actual graphs before and after stretching of the sample (i is before stretching, and ii is after stretching) are shown in FIG. 3, and the results show that: the composite material may be stretched to 4.6 times its original length.

(2d) FIG. 4 shows TA with a mass of 0.85 g_0.50-PVA_1.0The sample (length, width, thickness: 220, 20, 0.15mm) can be lifted individually from a 25 kg bucket.

(3) Mechanical Properties 2

(3a) The tensile curves at different humidity conditions (0%, 22%, 33%, 43%, 53%, 75%) were tested on PVA sheets having a thickness of 350 μm, and the results showed: PVA is very sensitive to humidity, and has high yield strength and low elongation at break in low humidity environment, and the yield strength of PVA is greatly reduced along with the increase of humidity.

(3b) For TA with thickness of 350 μm_0.50-PVA_1.0Composites, tested on the tensile curve under different humidity conditions (0%, 22%, 33%, 43%, 53%, 75%) and the results showed: composite material TA_0.50-PVA_1.0The material is insensitive to humidity, and high yield strength and elongation at break are maintained in daily environment humidity (0-75%).

(3c) For a PVA sheet having a thickness of 350 μm and a TA having a thickness of 350 μm_0.50-PVA_1.0The complex being tested inThe results of toughness values under different humidity conditions show that: in the daily ambient humidity (0% -75%), compared with PVA, the composite material TA_0.50-PVA_1.0The ultra-high fracture toughness is maintained.

(4) The X-ray diffraction patterns of PVA and PVA/TA complex are shown in FIG. 5;

in FIG. 5, four diffraction curves correspond to PVA and TA sequentially from top to bottom_0.50-PVA_1.0、TA_1.0-PVA_1.0And TA_1.0-PVA_0.50And (3) sampling.

(5) The Fourier transform infrared spectrogram of PVA, TA and PVA/TA complex is shown in FIG. 6;

description of the drawings: FIG. 5 is XRD showing that the addition of tannic acid inhibits the crystallization of PVA, and this is also concluded from the IR spectrum of FIG. 6, which is supported by the literature at a wavelength of 1142cm^-1The peak appeared in the reaction solution was linearly related to the crystallinity of PVA, and it was found that the wavelength was 1142cm after tannic acid was added^-1The peak at (a) disappeared.

In FIG. 6, only the IR spectrum of PVA shows the peak of the crystallization band (1142 cm)^-1At positions) of (a) and no peak of the crystalline band appears in the complex.

(6) The small angle X-ray scattering pattern of PVA and PVA/TA complex is shown in FIG. 7, and the results show that: compared with PVA, no scattering peak appears in the PVA/TA composite, which indicates that the material is uniform and has no structure.

(7) DSC curves of the PVA, TA, and PVA/TA complexes by differential scanning calorimetry are shown in FIG. 8, in which a) to h) represent PVA and TA, respectively_0.25-PVA_1.0Complex, TA_0.50-PVA_1.0Complex, TA_0.75-PVA_1.0Complexes, TA_1.0-PVA_1.0，TA_1.0-PVA_0.75And TA_1.0-PVA_0.50Test results for the complexes. The results show that: in the process of cooling down the PVA, a crystallization peak appears, and the cooling down curve of the compound does not have the crystallization peak.

With reference to FIGS. 5, 6, 7 and 8, the XRD pattern of the composite material shows no diffraction peak of PVA at about 20 degrees, and the infrared pattern shows no 1142cm^-1The peak of the crystalline band at the wavelength position is free from a scattering peak in a small-angle X-ray scattering spectrum, and no crystalline peak appears in a temperature-lowering curve in a DSC result. The combination of these effects indicates that the composite material is in an amorphous state.

(8) The PVA-based composite material is subjected to a folding test, and a display sample is TA_0.50-PVA_1.0(original sample, length, width, thickness 120 x 80 x 0.1 mm).

The specific operation steps are as follows: the sample was folded into an airplane, then the folded sample was unfolded, and the creased sample was repaired at 90% humidity for 10 h.

The folded repair method specifically operates as follows: the natural reduction is carried out in an environment with the humidity of 90%, and the conclusion is that the material can be recovered, no crease is left, which indicates that the sample has good toughness, and the crease can disappear under the high humidity.

(9) Degradation Properties

And (3) degradation process: 3X 0.075 cm of PVA and compound were buried in soil 8cm deep, removed at fixed times, washed, dried and weighed.

Specific data of the PVA and composite soil degradation curves are shown in Table 3. The conclusion shows that: the tannin is added into the compound, so that the degradation speed of PVA is greatly accelerated.

TABLE 3 degradation rate results obtained for different degradation times

Rate of degradation	10 days	25 days	35 days	45 days
					PVA	8.4％	16.2％	22.9％	29.1％
TA_0.50-PVA_1.0	26.9％	32.8％	41.4％	57.5％
					TA_1.0-PVA_0.50	53.6％	62.5％	68.2％	86.2％

EXAMPLE 5 preparation of composite materials of other shapes

The precipitate obtained in step 3 of example 1 was collected and placed in a lantern-shaped mold, and dried to form a lantern-shaped bulk material, as shown in fig. 9. The composite material of the present application can be shaped by a mold to give any shape or structure.

Effect example 2 Performance testing of PVA-based composite hydrogel

TA in example 2_0.50-PVA_1.0The tensile profile of the hydrogel of the composite is shown in figure 10. The results show that: the composite hydrogel has larger elongation at break, can be stretched by nearly 1200 percent, and also provides a foundation for the subsequent preparation of composite films.

In addition, for TA_0.50-PVA_1.0Complexes and TA_1.0-PVA_0.50The hydrogel obtained from the compound is subjected to XRD, infrared and smallThe angle X-ray scattering and DSC are detected, the same experimental conclusion as that in the figure 5-8 is obtained, and the prepared composite hydrogel product is in an amorphous state.

Effect example 3 performance test of PVA-based composite film

(1) TA prepared in example 3_0.50-PVA_1.0The tensile curve of the mechanical properties of the composite film (thickness 30 μm) is shown in FIG. 11. The results show that: the composite film has high yield strength and can meet the use requirement.

(2) Fresh-keeping property

Will TA_0.50-PVA_1.0The film prepared by the compound is wetted by deionized water at the edge and pressed together to prepare an open bag, then oranges are put into the bag, finally the mouth of the bag is wetted by deionized water and pressed together, the mouth is sealed, and the bag is placed indoors (the temperature is 19 ℃ and the humidity is 20%) to observe the condition of the oranges, and the result shows that the oranges deteriorate quickly under the natural state; and the deterioration speed of the oranges is obviously slowed down when the oranges are coated by the composite film. The result shows that the composite film has good fresh-keeping function.

(3) Degradation Properties

The results of the degradation performance test are shown in FIG. 12, in which (a) TA_0.50-PVA_1.0A film having dimensions of length, width, and thickness of 30, 25, 0.03 mm; (b) will TA_0.50-PVA_1.0Putting the film into NaOH aqueous solution (pH is 13); (c) TA (TA)_0.50-PVA_1.0The film was completely dissolved after 3 days.

(4) Form of the composition

In addition, for TA_0.50-PVA_1.0Complexes and TA_1.0-PVA_0.50The composite film obtained by the composite is subjected to four detections of XRD, infrared, small-angle X-ray scattering and DSC, and the experimental conclusion same as that in figures 5-8 is obtained, which indicates that the prepared composite film product is in an amorphous state.

EXAMPLE 4 Performance test of remolded product obtained after remolding of PVA-based composite Material

(1) Mechanical properties

The remolded samples from example 4 were tested for tensile curve and the results are shown in figure 13.

The 4 samples in the figure are respectively obtained by remolding the same composite material for 1 time, 2 times, 3 times and 4 times according to the method of example 4, and the results show that the mechanical properties of the remolded samples are not reduced by four times of remolding.

(2) Form of the composition

In addition, four detections of XRD, infrared ray, small-angle X-ray scattering and DSC are carried out on samples obtained by remodeling for 1 time, 2 times, 3 times and 4 times, and the same experimental conclusion as that of the images in the figures 5-8 is obtained, which indicates that the prepared remodeling product is still in an amorphous state.

Effect example 5 Nuclear magnetic Spectroscopy of composite Material

The NMR spectra of PVA, TA and PVA/TA complex are shown in FIG. 14, and the monomer amounts obtained from NMR spectra are shown in Table 4.

TABLE 4 test results for different monomer mass ratios

In Table 4, the monomer amount ratio (detection value, TA: PVA) means the repeating structural unit of TA molecule and PVA in the composite material (i.e., -C)₂H₄O-) which is obtained by measuring nuclear magnetism of the composite material dissolved in deuterated dimethyl sulfoxide.

The mass ratio (detection value, TA: PVA) is the mass ratio of TA to PVA in the composite material, and is obtained by conversion based on the combination of the molecular weight and the monomer amount ratio.

Effect example 6 form of PVA composite precursor

For TA in example 1_0.50-PVA_1.0And TA_1.0-PVA_0.50The precursor of the PVA composite material obtained under the formula is subjected to four detections of XRD, infrared, small-angle X-ray scattering and DSC, and the experimental conclusion same as that in figures 5-8 is obtained, which indicates that the prepared precursor is in an amorphous state.

Example 6 the mass ratio of tannic acid to polyvinyl alcohol was 0.016: 1 preparation of the composite Material

This example was obtained on the basis of example 1, replacing only the mass ratio of TA to PVA by 0.016: 1, in addition, in the present example, pH was adjusted without using a pH adjuster, and the pH value in the mixed system of TA and PVA was found to be 5.26, and the remaining process conditions were not changed. The infrared spectrum of the obtained composite material is shown in fig. 15.

In this example, the crystallinity is calculated from the reference (o.n. trentinikov, Determination of the degree of crystallinity of poly (vinyl alcohol) by FTIR Spectroscopy, Journal of Applied Spectroscopy,2012,4,79, p 525).

α(％)＝-13.1+89.5(A₁₁₄₄/A₁₀₉₄) (1)

the actual peak position in fig. 15 is adjusted to be calculated by formula (2):

α(％)＝-13.1+89.5(A₁₁₄₂/A₁₀₈₅) (2)

that is, the crystallinity α (%) - (13.1 +89.5 (a)₁₁₄₂/A₁₀₈₅)＝-13.1+89.5(1.411/2.699)＝34％

Fig. 16 and 17 show XRD patterns and DSC detection results of the composite material obtained in this example. The XRD spectrum shows that the composite material of the embodiment also has a crystallization peak of PVA near 20 degrees, and in addition, the DSC detection result shows that the crystallization peak appears in the cooling curve, but the overall peak shape is not sharp and is far inferior to the obvious cooling crystallization peak appearing in the cooling curve of PVA.

By combining the crystallinity, XRD pattern and DSC detection results, the composite material prepared in this example is in a mixed state of crystalline state and amorphous state.

Example 7

This example was obtained based on example 1, and was modified only to "add one drop of 10mg/mL PVA solution to 10mg/mL TA aqueous solution (in this case, the input ratio of tannic acid to polyvinyl alcohol was regarded as 10000: 1)", and the rest of the process conditions were not changed. The results show that precipitation also occurs, and further composite materials are prepared. The obtained composite material is subjected to four detections of XRD, infrared, small-angle X-ray scattering and DSC, and the experimental conclusion same as that in figures 5-8 is obtained, which shows that the prepared composite material is still in an amorphous state.

Comparative example 1 comparative experiment for substituting tannic acid with other substances capable of forming hydrogen bonds

This comparative example is TA in example 1_0.50-PVA_1.0Only equivalent amount of tannic acid is replaced by polyacrylic acid (PAA) on the basis of the test, and other raw materials and process conditions are not changed.

The mechanical properties of the obtained composite material are shown in fig. 18. The tensile curve results show that, although the yield strength is improved compared with that of PVA, the elongation at break is not obviously improved and cannot meet the requirement compared with FIG. 2.

Claims

1. A preparation method of a PVA-based composite material is characterized in that the PVA-based composite material is a sheet material, and the preparation method comprises the following steps: pressing the PVA-based composite material precursor into a sheet, and drying;

A. the PVA-based composite material precursor is as follows: the preparation method of the PVA-based composite material precursor comprises the following steps of uniformly mixing a polyvinyl alcohol aqueous solution and a tannic acid aqueous solution to obtain a solution precipitate, and separating and collecting the precipitate; wherein the mass ratio of the tannic acid to the polyvinyl alcohol is 0.016: 1 or more; alternatively, the first and second electrodes may be,

B. the precursor of the PVA-based composite material is as follows: a supermolecule aggregate formed by combining tannin molecules and polyvinyl alcohol molecules through hydrogen bonds; the PVA based composite material precursor is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

2. The method of preparing a PVA-based composite material according to claim 1, wherein the method of preparing a precursor of a PVA-based composite material according to the embodiment a comprises the steps of: mixing the aqueous solution of polyvinyl alcohol and the aqueous solution of tannic acid uniformly, adjusting the pH to be below 6.35, precipitating, separating and collecting the precipitate.

3. The method for producing a PVA-based composite material according to claim 2, wherein the pH adjusting agent for adjusting the pH is a hydrochloric acid solution.

4. The method for preparing a PVA-based composite material according to claim 3, wherein the concentration of the hydrochloric acid solution is 0.5 to 3 mol/L.

5. The method for producing a PVA-based composite material according to claim 2, wherein the pH is adjusted to 2.0 to 5.26.

6. The method of preparing a PVA-based composite material according to claim 1, wherein the manner of uniformly mixing as described in the embodiment a comprises the steps of: adding the polyvinyl alcohol aqueous solution into the tannic acid aqueous solution.

7. The method of preparing a PVA-based composite material according to claim 6, wherein the addition is performed by dropping.

8. The method for producing a PVA based composite material according to claim 1, wherein the mass ratio of the tannic acid to the polyvinyl alcohol in the embodiment A is (0.25: 1) - (1: 0.5).

9. The method for producing a PVA based composite material according to claim 1, wherein the mass ratio of the tannic acid to the polyvinyl alcohol is (0.5: 1) - (1: 0.75).

10. The method for producing a PVA-based composite material according to claim 8 or 9, wherein the mass ratio of tannic acid to polyvinyl alcohol is 0.5: 1.

11. The method for producing a PVA-based composite material according to claim 8 or 9, wherein the mass ratio of the tannic acid to the polyvinyl alcohol is (0.75:1) - (1: 1).

12. The method for preparing a PVA-based composite material according to claim 1, wherein the aqueous solution of polyvinyl alcohol according to the scheme A is prepared by uniformly mixing polyvinyl alcohol powder with deionized water and then heating and dissolving the mixture.

13. The method of preparing a PVA-based composite material according to claim 1, wherein the concentration of the polyvinyl alcohol in the aqueous polyvinyl alcohol solution described in the embodiment A is 125mg/mL or less.

14. The method for preparing a PVA-based composite material according to claim 13, wherein the concentration of the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 10 to 125 mg/mL.

15. The method of preparing a PVA-based composite material according to claim 1, wherein the concentration of tannic acid in the aqueous solution of tannic acid described in the embodiment A is 250mg/mL or less.

16. The method for preparing a PVA-based composite material according to claim 14, wherein the concentration of tannic acid in the aqueous solution of tannic acid is 10 to 250 mg/mL.

17. The method of preparing a PVA based composite material according to claim 1, wherein the operation of separating and collecting the precipitate in the embodiment A is a centrifugation treatment.

18. The method for preparing a PVA-based composite material according to claim 17, wherein the centrifugation is carried out in a centrifuge at 8000 to 10000rpm for 8 to 15 minutes.

19. The method for preparing a PVA-based composite material according to claim 18, wherein the centrifugation treatment is centrifugation in a centrifuge at 9500rpm for 10 minutes.

20. The method for preparing the PVA-based composite material according to any one of claims 1 to 19, wherein the PVA-based composite material precursor according to the scheme B has a mass ratio of tannic acid to polyvinyl alcohol of (0.74:1) - (1: 0.65).

21. The method for preparing the PVA-based composite material according to claim 20, wherein the mass ratio of the tannic acid to the polyvinyl alcohol in the precursor of the PVA-based composite material is (0.86:1.0) - (1.0: 0.65).

22. The method for preparing the PVA-based composite material according to any one of claims 1 to 19, wherein the number ratio of the tannin molecules to the monomers of the polyvinyl alcohol in the precursor of the PVA-based composite material according to the scheme B is (1: 52) - (1: 25).

23. The method for preparing the PVA-based composite material according to claim 22, wherein the amount ratio of the tannin molecules to the monomers of the polyvinyl alcohol in the precursor of the PVA-based composite material is (1: 45) - (1: 25).

24. The method for preparing the PVA-based composite material according to any one of claims 1 to 19, wherein the pressing is performed by putting the PVA-based composite material precursor in two polyimide films and performing press forming at room temperature.

25. The method of making a PVA-based composite as claimed in any one of claims 1 to 19, wherein said pressing is effected in a fixed press.

26. The method for preparing a PVA-based composite material according to claim 25, wherein the pressure of the fixed press is 1 to 5 MPa.

27. The method of making a PVA-based composite as recited in claim 26, wherein said fixed press has a pressure of 4 MPa.

28. The method of preparing a PVA-based composite material according to claim 25, wherein the pressing time is 0.017 to 30 minutes.

29. A PVA-based composite material produced by the production method according to any one of claims 1 to 28.

30. The PVA-based composite material according to claim 29, wherein said PVA-based composite material is in an amorphous state or a mixture of an amorphous and a crystalline state, and has a crystallinity of 34% or less as measured by infrared spectroscopy.

31. The PVA-based composite material according to claim 29, wherein the PVA-based composite material has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.74:1) - (1: 0.65).

32. The PVA-based composite material according to claim 31, wherein the PVA-based composite material has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.86:1.0) - (1.0: 0.65).

33. The PVA-based composite material according to claim 29, wherein the PVA-based composite material comprises the tannin molecule and the polyvinyl alcohol in a monomer amount ratio of (1: 52) - (1: 25).

34. The PVA-based composite material according to claim 33, wherein the PVA-based composite material comprises the tannin molecule and the polyvinyl alcohol in a monomer amount ratio of (1: 45) - (1: 25).

35. The PVA-based composite material according to claim 29, wherein said PVA-based composite material has a thickness of 30 μm to 1.75 mm.

36. A method of reshaping a PVA-based composite as in any one of claims 29 to 35, comprising the steps of: and (3) taking the PVA-based composite material, swelling, molding and drying.

37. A method of remodeling a PVA-based composite material as described in claim 36, wherein said solvent used for swelling is an aqueous solution having a pH of not more than 9.0.

38. A method of remodeling a PVA-based composite material as described in claim 37, wherein said solvent used for swelling is deionized water or an aqueous acidic solution.

39. A method of reshaping a PVA based composite as in claim 37, wherein the swelling is with an aqueous acidic solution having a pH of =1.0 to 2.5.

40. A method of reshaping a PVA-based composite as in claim 37, wherein the swelling is with an aqueous acidic solution having a pH = 2.0.

41. A remodeled product produced by a remodeling method as claimed in any one of claims 36 to 40.

42. A remodelled product according to claim 41, wherein the remodelled product is amorphous or a mixture of amorphous and crystalline forms and has a crystallinity as measured by infra-red spectroscopy of less than 34%.

43. A preparation method of PVA-based composite hydrogel is characterized by comprising the following steps: soaking the PVA-based composite material according to any one of claims 29 to 35 in an aqueous solution with a pH of not more than 9.0 to reach water absorption saturation.

44. The method for preparing the PVA-based composite hydrogel according to claim 43, wherein the PVA-based composite hydrogel is prepared from a PVA-based composite material having a thickness of 150 μm to 1000 μm.

45. The method for producing a PVA-based composite hydrogel according to claim 43, wherein the aqueous solution having a pH of not more than 9.0 is an acidic aqueous solution, a neutral aqueous solution or a weakly alkaline aqueous solution having a pH of not more than 9.0.

46. The method of preparing a PVA-based composite hydrogel according to claim 43, wherein the aqueous solution having a pH of not more than 9.0 is deionized water.

47. A PVA-based composite hydrogel prepared by the preparation method according to any one of claims 43 to 46.

48. The PVA-based composite hydrogel according to claim 47, wherein the PVA-based composite hydrogel is in an amorphous state or a mixture of an amorphous state and a crystalline state, and has a crystallinity of 34% or less as measured by infrared spectroscopy.

49. The PVA-based composite hydrogel according to claim 47, wherein the PVA-based composite hydrogel has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.74:1) - (1: 0.65).

50. The PVA-based composite hydrogel according to claim 49, wherein the PVA-based composite hydrogel has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.86:1.0) - (1.0: 0.65).

51. The PVA-based composite hydrogel according to claim 47, wherein the amount ratio of the tannin molecules to the polyvinyl alcohol in the PVA-based composite hydrogel is (1: 52) - (1: 25).

52. The PVA-based composite hydrogel according to claim 51, wherein the ratio of the number of the tannin molecules to the number of the polyvinyl alcohol monomers in the PVA-based composite hydrogel is (1: 45) - (1: 25).

53. A PVA-based composite hydrogel is characterized in that the PVA-based composite hydrogel is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules through hydrogen bonds; the PVA-based composite hydrogel is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

54. The PVA-based composite hydrogel according to claim 53, wherein the PVA-based composite hydrogel has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.74:1) - (1: 0.65).

55. The PVA-based composite hydrogel according to claim 54, wherein the PVA-based composite hydrogel has a mass ratio of the tannic acid to the polyvinyl alcohol of (0.86:1.0) - (1.0: 0.65).

56. The PVA-based composite hydrogel according to claim 53, wherein the PVA-based composite hydrogel comprises tannic acid molecules and polyvinyl alcohol in a monomer amount ratio of (1: 52) - (1: 25).

57. The PVA-based composite hydrogel according to claim 56, wherein the ratio of the number of the tannin molecules to the number of the polyvinyl alcohol monomers in the PVA-based composite hydrogel is (1: 45) - (1: 25).

58. A preparation method of a PVA-based composite film is characterized by comprising the following steps: stretching and drying the PVA-based composite hydrogel according to any one of claims 47 to 57.

59. The method of producing a PVA based composite film according to claim 58, wherein the stretching is biaxial stretching or uniaxial stretching.

60. A PVA-based composite film produced by the production method according to claim 58 or 59.

61. The PVA-based composite film of claim 60, wherein the PVA-based composite film is in an amorphous state or a mixture of an amorphous and a crystalline form, and has a crystallinity as measured by IR spectroscopy of 34% or less.

62. The PVA-based composite film according to claim 60, wherein the PVA-based composite film has a mass ratio of tannic acid to polyvinyl alcohol of (0.74:1) - (1: 0.65).

63. The PVA-based composite film according to claim 62, wherein the PVA-based composite film has a mass ratio of tannic acid to polyvinyl alcohol of (0.86:1.0) - (1.0: 0.65).

64. The PVA-based composite film according to claim 60, wherein the PVA-based composite film has a monomer amount ratio of tannic acid molecules to polyvinyl alcohol of (1: 52) - (1: 25).

65. The PVA-based composite film according to claim 64, wherein the PVA-based composite film has a monomer amount ratio of tannic acid molecules to polyvinyl alcohol of (1: 45) - (1: 25).

66. The PVA-based composite film of claim 60, wherein the PVA-based composite film has a thickness of 5 to 30 μm.

67. The PVA-based composite film of claim 66, wherein the PVA-based composite film has a thickness of from 25 to 30 μm.

68. A PVA-based composite film is characterized in that the PVA-based composite film is a supermolecular aggregate formed by combining tannin molecules and polyvinyl alcohol molecules through hydrogen bonds; the PVA based composite film is in an amorphous state; or a mixed state of amorphous and crystal forms, and the crystallinity detected by infrared spectroscopy is less than 34 percent.

69. The PVA-based composite film according to claim 68, wherein the PVA-based composite film has a mass ratio of tannic acid to polyvinyl alcohol of (0.74:1) - (1: 0.65).

70. The PVA-based composite film according to claim 69, wherein the PVA-based composite film has a mass ratio of tannic acid to polyvinyl alcohol of (0.86:1.0) - (1.0: 0.65).

71. The PVA-based composite film of claim 68, wherein the PVA-based composite film comprises the tannin molecule and the polyvinyl alcohol in a monomer amount ratio of (1: 52) - (1: 25).

72. The PVA-based composite film according to claim 71, wherein the PVA-based composite film has a monomer amount ratio of tannic acid molecules to polyvinyl alcohol of (1: 45) - (1: 25).

73. The PVA-based composite film of claim 68, wherein the PVA-based composite film has a thickness of from 5 to 30 μm.

74. The PVA-based composite film of claim 73, wherein the PVA-based composite film has a thickness of from 25 to 30 μm.

75. Use of the PVA-based composite film according to any one of claims 60 to 74 as a food packaging bag or a freshness protection package.