Full-bio-based degradable water-resistant composite film and preparation method thereof

Abstract

The invention relates to a full-bio-based degradable water-resistant composite film and a preparation method thereof. The composite film comprises a composite base material and a modified layer coated on the surface of the composite base material, the composite base material comprises a water-soluble polymer, polysaccharide and polyphenol; the modified layer comprises a metal ion-polyphenol complex. The composite film has the advantages of safety, no toxicity, low cost, good mechanical property, biodegradability, good water resistance, simple preparation method and the like, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of composite films, and in particular to a fully bio-based degradable water-resistant composite film and a preparation method thereof. Background Art

[0002] Polysaccharides, proteins and lipids are the main natural biomass film-forming matrices (or matrices), but a single matrix may have inherent characteristics such as high water solubility, low thermal stability and poor mechanical properties, which hinder its practical application. Therefore, two or more types of matrix materials are usually mixed with each other to improve the comprehensive performance of the composite material. For example, combining proteins with polysaccharides to form a gas barrier film with a network structure can enhance its durability, while the introduction of lipids can improve the water resistance of the film.

[0003] Gelatin is a water-soluble polymer protein with a helical molecular structure. Pure gelatin film has low mechanical strength and strong water absorption. Cellulose is the most abundant natural polysaccharide in nature, and its polyhydroxy structure easily forms hydrogen bonds with gelatin. Mechanical or chemical treatment of cellulose pulp can obtain microfibrillated cellulose with high crystallinity, which has a network structure. This network structure plays a positive role in maintaining the morphology of the gelatin base film and improving durability. However, in order to improve the water resistance of water-soluble matrices such as gelatin, glutaraldehyde and genipin are usually used as cross-linking agents, but glutaraldehyde has certain biological toxicity, and genipin is expensive and less economical. How to obtain a safe, non-toxic, low-cost composite film with both biodegradability and water resistance has always been a problem for relevant technicians. Summary of the invention

[0004] Based on this, the present invention provides a composite film which is safe, non-toxic, low-cost, has good mechanical properties, and has both biodegradability and water resistance, and also provides a method for preparing the composite film.

[0005] The technical solution is as follows:

[0006] A fully bio-based degradable water-resistant composite film, comprising a composite substrate and a modified layer coated on the surface of the composite substrate;

[0007] The composite substrate includes a water-soluble polymer, a polysaccharide and a polyphenol;

[0008] The modified layer includes a metal ion-polyphenol complex.

[0009] In one embodiment, the molecular weight of the water-soluble polymer is 30,000 Da to 300,000 Da.

[0010] In one embodiment, the water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate.

[0011] In one embodiment, the molecular weight of the polysaccharide is 100,000 Da to 1,000,000 Da.

[0012] In one embodiment, the polysaccharide includes one or more of cellulose and chitosan.

[0013] In one of the embodiments, the mass ratio of the polysaccharide to the water-soluble polymer is (1-10):20.

[0014] In one embodiment, the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols.

[0015] In one of the embodiments, the mass ratio of the polysaccharide to the polyphenol is 1:(2-10).

[0016] In one embodiment, the metal ion in the metal ion-polyphenol complex includes Cr 6+ , Cu 2+ , Fe 3 + 、Al 3+ 、Ti 4+ and Ag + One or more of .

[0017] The present invention also provides a method for preparing the above-mentioned fully bio-based degradable water-resistant composite film, comprising the following steps:

[0018] Mixing and dissolving a polysaccharide raw material and a polyphenol in water to prepare a first substrate;

[0019] The aqueous solution of the water-soluble polymer is mixed with the first substrate to react, and dried to form a film to prepare a second substrate;

[0020] A metal ion solution is applied on the surface of the second substrate to prepare a metal ion-polyphenol complex on the surface of the second substrate through a coordination reaction.

[0021] In one embodiment, the polysaccharide raw material and the polyphenol are mixed and dissolved in water to prepare the first substrate, which includes the following steps:

[0022] The polysaccharide raw material is pulverized, mixed and ground with polyphenol to prepare slurry, washed with water to remove free polyphenol, and the substrate is collected as the first substrate.

[0023] In one embodiment, the grinding method is one or more of planetary ball milling, drum ball milling, vibration milling and disc milling.

[0024] In one embodiment, the grinding time is 1 h to 10 h.

[0025] In one embodiment, the polysaccharide raw material includes one or more of cellulose and chitosan.

[0026] In one embodiment, the polysaccharide raw material is cellulose. Further, the polysaccharide raw material includes one or more of wood pulp, bamboo pulp, recycled waste paper pulp, straw pulp, cotton fiber and agricultural and forestry waste fiber raw materials.

[0027] In one embodiment, the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols.

[0028] In one of the embodiments, the mass ratio of the polysaccharide raw material to the polyphenol and water is 1:(2-10):(40-50).

[0029] In one embodiment, the water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate.

[0030] In one embodiment, the preparation method of the aqueous solution of the water-soluble polymer is as follows:

[0031] The water-soluble polymer is dissolved in water at 50° C. to 70° C. to prepare an aqueous solution of the water-soluble polymer.

[0032] In one embodiment, in the step of mixing the aqueous solution of the water-soluble polymer with the first substrate for reaction, the reaction temperature is 50° C. to 70° C.

[0033] In one embodiment, in the step of mixing the aqueous solution of the water-soluble polymer with the first substrate for reaction, the mass fraction of the solute in the mixed solution is 5 wt % to 20 wt %.

[0034] In one embodiment, the method of applying the metal ion solution on the surface of the second substrate is atomization spraying or immersion.

[0035] In one embodiment, the metal ions in the metal ion solution include Cr 6+ , Cu 2+ , Fe 3+ 、Al 3+ 、Ti 4+ and Ag + One or more of .

[0036] In one embodiment, the mass concentration of the metal ion solution is 0.5% to 5%.

[0037] In one embodiment, the temperature of the coordination reaction is room temperature.

[0038] The present invention has at least the following beneficial effects:

[0039] The fully bio-based degradable water-resistant composite film provided by the present invention includes a composite substrate and a modified layer on its surface. Wherein, the composite substrate includes a water-soluble polymer, a polysaccharide and a polyphenol, and the three are mainly connected by hydrogen bonds, so that the composite substrate has both high strength and high toughness, while improving water resistance; the modified layer includes a metal ion-polyphenol complex formed by coordination between polyphenols and metal ions, which not only increases the adhesion fastness, but also avoids the metal ions and moisture from continuing to penetrate into the interior of the composite film to destroy the original cross-linked structure, further improving water resistance, and maintaining the mechanical properties of the composite film. When the interface of the composite film encounters water, due to the shielding of hydrophilic groups such as hydroxyl and carboxyl groups on the surface of the film, there are metal ions and polyphenol complexes precipitated and covered, forming a hydrophobic (or water-repellent) interface with low water adhesion, which can effectively resist the infiltration of water and show excellent water resistance. In addition, the composite film does not contain glutaraldehyde or genipin, is safe and non-toxic, has low production cost, is simple in preparation method, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The contact angle test result between the gelatin substrate and water in Example 2 of the present invention;

[0041] Figure 2 This is the contact angle test result between the fully bio-based degradable water-resistant composite film of Example 2 of the present invention and water. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0044] Where “including,” “having,” and “comprising” are used herein, it is intended to cover a non-exclusive inclusion, and another component may also be added unless explicit limiting terms such as “only,” “consisting of,” etc. are used.

[0045] The words "preferably", "more preferably", "preferably", "better", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the statement of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention. That is, in the present invention, "preferably", "more preferably", "preferably", "better", etc. are only used to describe implementation methods or examples with better effects, but do not constitute a limitation on the scope of protection of the present invention.

[0046] In the present invention, “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0047] In the present invention, "at least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multilayer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of the present invention, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0048] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0049] If not otherwise specified, all steps of the present invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] Unless mentioned to the contrary, terms in the singular may include plural forms and should not be construed as being one in number.

[0051] In the present invention, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0052] In the present invention, room temperature refers to 0°C to 40°C, including but not limited to 10°C to 40°C, or further 20°C to 30°C.

[0053] A single matrix may have inherent properties such as high water solubility, low thermal stability, and poor mechanical properties, which hinder its practical application. Therefore, two or more types of matrix materials are usually mixed to improve the comprehensive performance of the composite material. Compounding gelatin and cellulose can improve the durability, morphology, and water resistance of gelatin, but improving water resistance requires the use of specific cross-linking agents, which increases toxicity or cost.

[0054] Based on the above problems, the present invention provides a composite film which is safe, non-toxic, low-cost, has good mechanical properties, and has both biodegradability and water resistance, and also provides a method for preparing the composite film.

[0055] The technical solution is as follows:

[0056] A fully bio-based degradable water-resistant composite film, comprising a composite substrate and a modified layer coated on the surface of the composite substrate;

[0057] The composite substrate includes a water-soluble polymer, a polysaccharide and a polyphenol;

[0058] The modified layer includes a metal ion-polyphenol complex.

[0059] Polyphenols are important secondary metabolites in plants, mainly found in a large number of fruits and vegetables that people eat daily. Polyphenols have significant antioxidant, antibacterial, anti-allergic and anti-aging functions, and as an important component of natural pigments and a major source of antioxidants, they are widely used in the food and pharmaceutical industries.

[0060] Polysaccharides (such as cellulose or chitin) have a network structure. On the one hand, they contain a large number of hydroxyl groups, which are also easy to form hydrogen bonds between molecules. Polyphenols also have a large number of hydroxyl groups, which is the basis for the interaction between the two. On the other hand, according to the principle of hydrophobic interaction, water-insoluble molecules will gather together to produce lower surface potential energy, thereby minimizing contact with water. Since polysaccharides and most polyphenols (containing hydrophobic aromatic rings) are insoluble in water, the aggregation of polysaccharides and polyphenols will lead to hydrophobic interactions, improving the water resistance of composite substrates and all-biobased degradable water-resistant composite films.

[0061] Water-soluble polymers contain hydrophilic groups, usually carboxyl groups, hydroxyl groups or amino groups, which can easily form hydrogen bonds between molecules. They can combine with polyphenols and polysaccharides through hydrogen bonds to form crosslinks.

[0062] In the present invention, water-soluble polymer, polysaccharide and polyphenol three are mainly connected by hydrogen bonds, so that the composite substrate has both high strength and high toughness, and improves water resistance. And the modified layer includes a metal ion-polyphenol complex formed by coordination of polyphenol and metal ion, which not only increases the adhesion fastness, but also avoids the metal ion and moisture from continuing to penetrate the inside of the composite film to destroy the original cross-linked structure, further improves water resistance, and maintains the mechanical properties of the composite film. After the interface of the composite film encounters water, due to the shielding of hydrophilic groups such as hydroxyl and carboxyl groups on the surface of the film, there are metal ions and polyphenol complexes precipitated and covered, forming a hydrophobic (or water-repellent) interface with low water adhesion, which can effectively resist the infiltration of water, so that the composite film shows excellent water resistance. In addition, the composite film does not contain glutaraldehyde or genipin, is safe and non-toxic, and has low production cost.

[0063] In one embodiment, the water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate. These water-soluble polymers are non-toxic and harmless and have good biocompatibility. At the same time, their molecular chains contain abundant active reactive groups and are easy to form diverse cross-linked structures.

[0064] In one embodiment, the molecular weight of the water-soluble polymer is 30000Da to 300000Da, which is conducive to the synergistic biodegradability, water resistance and mechanical properties of the all-bio-based degradable and water-resistant composite film. Further, the molecular weight of gelatin is 50000Da to 100000Da, the molecular weight of polyvinyl alcohol is 120000Da to 150000Da, and the molecular weight of sodium alginate is 32000Da to 250000Da.

[0065] In one embodiment, the polysaccharide includes one or more of cellulose and chitin. The essence of the interaction between cellulose and polyphenols is the non-covalent interaction mediated by hydrophobic interaction and hydrogen bond. The coexistence of hydroxyl groups on the surfaces of cellulose and polyphenols is conducive to the formation of hydrogen bonds. Hydrogen bonds are generally formed between the oxygen atoms of the glycosidic bonds of cellulose and the hydroxyl groups of polyphenols, which shortens the distance between molecules and is conducive to the generation of van der Waals forces. Hydrophobic interaction refers to the interaction between water and water-insoluble molecules (non-polar molecules). Water-insoluble molecules will gather together to produce lower surface potential energy, thereby minimizing contact with water. Both cellulose and the polyphenols in the present invention are insoluble in water, and aggregation will lead to hydrophobic interactions, and the hydrophobic aromatic rings of polyphenols will promote the occurrence of hydrophobic interactions, thereby improving the hydrophobicity of the all-biobased degradable and water-resistant composite film.

[0066] In one embodiment, the molecular weight of the polysaccharide is 100000Da to 1000000Da, which is conducive to the synergistic biodegradability, water resistance and mechanical properties of the all-bio-based degradable and water-resistant composite film. Further, the molecular weight of cellulose is 100000Da to 200000Da, and the molecular weight of chitin is 500000Da to 1000000Da.

[0067] In one embodiment, the mass ratio of the polysaccharide to the water-soluble polymer is (1-10):20, including but not limited to 1:20, 1:10, 3:20, 1:5, 1:4, 3:10, 7:20, 2:5, 9:20 or 1:2. The polysaccharide and the water-soluble polymer form a cross-linked network structure through non-covalent action, which helps to enhance the mechanical strength and ductility of the polymer matrix. The above mass ratio range can ensure the strength improvement and structural uniformity of the all-biobased degradable and water-resistant composite film after formation.

[0068] In one embodiment, the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols. These plant polyphenols shield the hydrophilic groups in the polymer matrix through hydrophobic interactions and can improve the mechanical strength of the polymer matrix.

[0069] In one embodiment, the mass ratio of the polysaccharide to the polyphenol is 1:(2-10), including but not limited to 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. The above mass ratio can ensure that the polyphenol is uniformly bound to the surface of the polysaccharide in large quantities when the polysaccharide and the polyphenol are mixed and ground.

[0070] In one embodiment, the metal ion in the metal ion-polyphenol complex includes Cr 6+ , Cu 2+ , Fe 3 + 、Al 3+ 、Ti 4+ and Ag + One or more of the above metal ions are easy to produce coordination and complexing effects with polyphenols to achieve the formation of a surface modification layer.

[0071] The present invention also provides a method for preparing the above-mentioned fully bio-based degradable water-resistant composite film, comprising the following steps:

[0072] Mixing and dissolving a polysaccharide raw material and a polyphenol in water to prepare a first substrate;

[0073] The aqueous solution of the water-soluble polymer is mixed with the first substrate to react, and dried to form a film to prepare a second substrate;

[0074] A metal ion solution is applied on the surface of the second substrate to prepare a metal ion-polyphenol complex on the surface of the second substrate through a coordination reaction.

[0075] In one embodiment, the polysaccharide raw material and the polyphenol are mixed and dissolved in water to prepare the first substrate, which includes the following steps:

[0076] The polysaccharide raw material is pulverized, mixed and ground with polyphenol to prepare slurry, washed with water to remove free polyphenol, and the substrate is collected as the first substrate.

[0077] In one embodiment, the grinding method is one or more of planetary ball milling, drum ball milling, vibration milling and disc milling.

[0078] In one embodiment, the grinding method is planetary ball milling with a rotation speed of 500 rpm to 1000 rpm.

[0079] In one embodiment, the grinding time is 1 h to 10 h, including but not limited to 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0080] In one embodiment, the polysaccharide raw material includes one or more of cellulose and chitosan.

[0081] In one embodiment, the polysaccharide raw material is cellulose. Further, the polysaccharide raw material includes one or more of wood pulp, bamboo pulp, recycled waste paper pulp, straw pulp, cotton fiber and agricultural and forestry waste fiber raw materials.

[0082] In one embodiment, the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols.

[0083] In one embodiment, the mass ratio of the polysaccharide raw material to the polyphenol and water is 1:(2-10):(40-50), including but not limited to 1:2:40, 1:3:40, 1:4:40, 1:5:40, 1:6:40, 1:7:40, 1:8:40, 1:9:40, 1:10:40, 1:2:44, 1:3:44, 1:4:44, 1:5: 44, 1:6:44, 1:7:44, 1:8:44, 1:9:44, 1:10:44, 1:2:50, 1:3:50, 1:4:50, 1:5:50, 1:6:50, 1:7:50, 1:8:50, 1:9:50 or 1:10:40, the above mass ratios can ensure that the polysaccharide and polyphenol are mixed and ground in a wet state, so that the polyphenols are uniformly combined on the surface of the polysaccharide in large quantities.

[0084] In one embodiment, the water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate.

[0085] In one embodiment, the preparation method of the aqueous solution of the water-soluble polymer is as follows:

[0086] The water-soluble polymer is dissolved in water at 50° C. to 70° C. to prepare an aqueous solution of the water-soluble polymer.

[0087] In one embodiment, in the step of mixing the aqueous solution of the water-soluble polymer with the first substrate for reaction, the reaction temperature is 50° C. to 70° C. This temperature range is conducive to the full dissolution of the water-soluble polymer in water.

[0088] In one embodiment, in the step of mixing the aqueous solution of the water-soluble polymer with the first substrate, the mass fraction of the solute (including the water-soluble polymer, polyphenols and polysaccharides) in the mixed solution is 5wt% to 20wt%. This concentration range ensures that the solution has an appropriate viscosity, which is conducive to smooth flow and spreading into a film during film forming.

[0089] In one embodiment, the method of applying the metal ion solution on the surface of the second substrate is atomization spraying or immersion. The present invention preferably applies the metal ion solution on the surface of the substrate by atomization spraying. Compared with the treatment process of directly immersing and then drying to load the metal ion-polyphenol complex on the surface of the substrate, the atomization spraying method is simpler to operate, and can make the metal ion-polyphenol complex adhere stably for a long time, and avoid the problem that the solution easily enters the interior of the substrate after multiple immersion of the biomass membrane, causing damage to its own structure and resulting in a rapid decrease in structural strength.

[0090] In one embodiment, the metal ions in the metal ion solution include Cr 6+ , Cu 2+ , Fe 3+ 、Al 3+ 、Ti 4+ and Ag + One or more of .

[0091] In one embodiment, the mass concentration of the metal ion solution is 0.5% to 5%.

[0092] In one embodiment, the temperature of the coordination reaction is room temperature.

[0093] Specific embodiments are listed below to illustrate the present invention.

[0094] The testing method of the present invention is as follows:

[0095] (1) Hydrophobicity test: A contact angle meter equipped with a CDD (Cyclic Delay Diversity) camera was used to measure the static contact angle (accuracy ±1°) of a 5 μL droplet balanced on the film surface.

[0096] (2) Mechanical properties test: According to the test method GB / T 13022-1991, the sample was cut into a dumbbell shape with a width of 10 mm and a gauge length of 50 mm. The loading speed of the testing machine was set to 5 mm min -1 . Three measurements were performed on each sample and the average value was taken.

[0097] Example 1

[0098] (1) Mix the crushed wood pulp (molecular weight of about 120,000 Da) and tea polyphenols in a vibration grinder at a material ratio of 1:5, add an appropriate amount of water to dissolve the tea polyphenols, grind at room temperature for 2 hours, collect the slurry, soak and wash with excess water to remove free polyphenols, and collect and store the precipitated substrate for later use.

[0099] (2) Mix 9 g of gelatin (molecular weight about 70,000 Da) with 90 g of deionized water, heat at 55°C until completely dissolved, take 1 g of ground cellulose substrate and stir to mix with the gelatin solution. After the mixed solution reacts at 60°C for 1 hour, slowly pour the mixed solution into a mold and dry it naturally at room temperature to form a film.

[0100] (3) A 1% by mass copper sulfate solution was prepared and sprayed evenly on the surface of the composite film prepared in step (2) by atomizing spray. After staying for a few seconds, the excess liquid on the surface was immediately wiped off. After natural drying, a fully bio-based degradable and water-resistant composite film was obtained. The hydrophobicity of the gelatin substrate was tested. The hydrophobicity and mechanical properties of the fully bio-based degradable and water-resistant composite film were tested. The results are shown in Table 1.

[0101] Example 2

[0102] (1) The crushed cotton fiber (molecular weight of about 200,000 Da) and tannic acid were mixed in a ball mill filled with deionized water at a material ratio of 1:5, and ball milled at 800 rpm in a planetary ball mill for 2 hours. The slurry was centrifuged and washed with deionized water to remove free tannic acid, and the substrate was collected and stored for later use.

[0103] (2) 8 g of gelatin (molecular weight about 70,000 Da) was mixed with 90 g of deionized water and heated at 50°C until completely dissolved. 2 g of cellulose substrate was taken and stirred with the gelatin solution. After the mixed solution was reacted at 60°C for 1.5 hours, the mixed solution was slowly poured into a mold and naturally dried at room temperature to form a film.

[0104] (3) Prepare a 2% by mass ferric chloride solution, and spray the solution evenly on the surface of the composite film prepared in step (2) by atomizing spraying. After staying for a few seconds, wipe off the excess liquid on the surface immediately. After drying naturally, a fully bio-based degradable and water-resistant composite film is obtained. The hydrophobic properties of the gelatin substrate and the fully bio-based degradable and water-resistant composite film are tested. The results are shown in FIG. Figure 1 and Figure 2 In addition, the mechanical properties of the all-biobased degradable and water-resistant composite film were tested, and the results are shown in Table 1.

[0105] Example 3

[0106] (1) The crushed bamboo pulp fiber (molecular weight of about 150,000 Da) and gallic acid were mixed in a ball mill filled with deionized water at a material ratio of 1:5, and ball milled at 600 rpm in a planetary ball mill for 3 hours. The slurry was centrifuged and washed with deionized water to remove free gallic acid, and the substrate was collected and stored for later use.

[0107] (2) Mix 7 g of polyvinyl alcohol (molecular weight about 120,000 Da) with 90 g of deionized water and heat at 95°C until completely dissolved. Mix 3 g of ground cellulose substrate with the polyvinyl alcohol solution under high-speed stirring. After the mixed solution is reacted at 100°C for 1 h, the mixed solution is slowly poured into a mold and naturally dried at room temperature to form a film.

[0108] (3) A 3% by mass ferric chloride solution was prepared and sprayed evenly on the surface of the composite film prepared in step (2) by atomizing spray. After staying for a few seconds, the excess liquid on the surface was immediately wiped off. After natural drying, a fully bio-based degradable and water-resistant composite film was obtained. The hydrophobicity of the gelatin substrate was tested. The hydrophobicity and mechanical properties of the fully bio-based degradable and water-resistant composite film were tested. The results are shown in Table 1.

[0109] Example 4

[0110] (1) The crushed chitosan (molecular weight of about 800,000 Da) and tannic acid were mixed and ground in a disc mill at a material ratio of 1:10 for 2 hours. The slurry was centrifuged and washed with deionized water to remove soluble matter, and the substrate was collected and stored for later use.

[0111] (2) 5 g of gelatin (molecular weight about 70,000 Da) was mixed with 92.5 g of deionized water and heated at 55°C until completely dissolved. 2.5 g of ground chitin substrate was mixed with the gelatin solution under high-speed stirring. After the mixed solution was reacted at 60°C for 1 h, the mixed solution was slowly poured into a mold and dried naturally at room temperature to form a film.

[0112] (3) A 3% by mass ferric chloride solution was prepared and sprayed evenly on the surface of the composite film prepared in step (2) by atomizing spray. After staying for a few seconds, the excess liquid on the surface was immediately wiped off. After natural drying, a fully bio-based degradable and water-resistant composite film was obtained. The hydrophobicity of the gelatin substrate was tested. The hydrophobicity and mechanical properties of the fully bio-based degradable and water-resistant composite film were tested. The results are shown in Table 1.

[0113] The performance data of the above embodiments are shown in Table 1 below.

[0114] Table 1 Performance results of the products in each embodiment

[0115]

[0116] In summary, the all-biobased degradable and water-resistant composite film provided by the present invention has the advantages of safety and non-toxicity, low cost, good mechanical properties, biodegradability, good water resistance and simple preparation method, and has broad application prospects.

[0117] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A fully bio-based degradable water-resistant composite film, characterized in that: It comprises a composite substrate and a modified layer coated on the surface of the composite substrate; The composite substrate includes a water-soluble polymer, a polysaccharide and a polyphenol; The modified layer includes a metal ion-polyphenol complex.

2. The all-biobased degradable water-resistant composite film according to claim 1, characterized in that: Satisfy one or more of the following (1) to (6): (1) The water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate; (2) The polysaccharide comprises one or more of cellulose and chitin; (3) the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols; (4) The metal ion in the metal ion-polyphenol complex includes Cr 6+ , Cu 2+ , Fe 3+ 、Al 3+ 、Ti 4+ and Ag + One or more of; (5) The mass ratio of the polysaccharide to the water-soluble polymer is (1-10):20; (6) The mass ratio of the polysaccharide to the polyphenol is 1:(2-10).

3. The all-biobased degradable water-resistant composite film according to claim 1 or 2, characterized in that: Satisfy one or more of the following (1) to (2): (1) The molecular weight of the water-soluble polymer is 30000Da to 300000Da; (2) The molecular weight of the polysaccharide is 100,000 Da to 1,000,000 Da.

4. A method for preparing a fully bio-based degradable water-resistant composite film, characterized in that: The steps include: Mixing and dissolving a polysaccharide raw material and a polyphenol in water to prepare a first substrate; The aqueous solution of the water-soluble polymer is mixed with the first substrate to react, and dried to form a film to prepare a second substrate; A metal ion solution is applied on the surface of the second substrate to prepare a metal ion-polyphenol complex on the surface of the second substrate through a coordination reaction.

5. The preparation method according to claim 4, characterized in that: Satisfy one or more of the following (1) to (4): (1) The water-soluble polymer includes one or more of gelatin, polyvinyl alcohol and sodium alginate; (2) The polysaccharide raw material includes one or more of cellulose and chitin; (3) the polyphenols include one or more of tea polyphenols, tannic acid, gallic acid, tannic acid, apple polyphenols and cocoa polyphenols; (4) The metal ions in the metal ion solution include Cr 6+ , Cu 2+ , Fe 3+ 、Al 3+ 、Ti 4+ and Ag + One or more of .

6. The preparation method according to claim 4, characterized in that: Satisfy one or more of the following (1) to (2): (1) The polysaccharide raw material includes one or more of wood pulp, bamboo pulp, recycled waste paper pulp, straw pulp, cotton fiber, chitin and agricultural and forestry waste fiber raw materials; (2) In the step of mixing and dissolving the polysaccharide raw material and the polyphenol in water, the mass ratio of the polysaccharide raw material to the polyphenol and water is 1:(2-10):(40-50).

7. The preparation method according to any one of claims 4 to 6, characterized in that: The polysaccharide raw material and the polyphenol are mixed and dissolved in water to prepare the first substrate, which includes the following steps: The polysaccharide raw material is pulverized, mixed and ground with polyphenol to prepare slurry, washed with water to remove free polyphenol, and the substrate is collected as the first substrate.

8. The preparation method according to claim 7, characterized in that: Satisfy one or more of the following (1) to (2): (1) The grinding method is one or more of planetary ball milling, drum ball milling, vibration milling and disc milling; (2) The grinding time is 1h to 10h.

9. The preparation method according to any one of claims 4 to 6, characterized in that: In the step of mixing the aqueous solution of the water-soluble polymer with the first substrate for reaction, one or more of the following (1) to (2) are satisfied: (1) The reaction temperature is 50°C to 70°C; (2) The mass fraction of the solute in the mixed solution is 5wt% to 20wt%.

10. The preparation method according to any one of claims 4 to 6, characterized in that: Satisfy one or more of the following (1) to (3): (1) applying the metal ion solution on the surface of the second substrate by atomization spraying or immersion; (2) The mass concentration of the metal ion solution is 0.5% to 5%; (3) The temperature of the coordination reaction is room temperature.

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