Biodegradable high-toughness high-barrier composite film

Abstract

The invention relates to a biodegradable high-toughness and high-barrier composite membrane, which comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, the two layers are compounded through tape casting and are combined through dynamic bonds, and after the two layers are compounded, the two layers are subjected to membrane treatment by adopting a double-drawing process to obtain the biodegradable high-toughness and high-barrier composite membrane, and the biodegradable high-toughness and high-barrier composite membrane has excellent strength, toughness and water and gas barrier property. The water vapor barrier property is greatly higher than that of a common pure PVA film, and the film also has surface antibacterial property and can be applied to the field of food and medicine packaging.

Description

Technical Field

[0001] The present invention relates to a method for preparing a biomass-based composite material, and particularly to a method for preparing a biodegradable film material with high strength, high toughness and excellent water and gas barrier properties. Background Art

[0002] Although plastic materials have excellent properties and wide applicability, they are derived from petroleum products and cannot be degraded. Therefore, finding alternative materials with excellent properties and renewable resources has become the top priority in the research of the materials field.

[0003] In packaging materials, film materials are used in large quantities and are widely applied in various different packaging systems. However, due to the very thin nature of the film itself, higher requirements are put forward for its mechanical properties and functionality in packaging. In addition to basic mechanical properties such as high strength and tear resistance to achieve the integrity and physical protection of the packaging film, some packaging, such as food and drug packaging, also requires the film to have good gas barrier properties, water vapor barrier properties, antibacterial properties, etc., which poses higher requirements for the development of the film. Biomass materials can replace plastics and are easily processed into films. However, due to the intrinsic structural characteristics of the main biomasses such as polyester, starch, chitosan, and chitin, it is very difficult to achieve the above-mentioned desired ideal properties when used independently.

[0004] Taking polylactic acid (PLA), which has the largest current usage, as an example, after being processed into a film, it has good flexural modulus and tensile strength, but poor thermal stability and impact resistance, insufficient barrier properties, and has the defect of low melt viscosity during thermoforming processing, which limits its application. Polyhydroxyalkanoates (PHA) are a new generation of biodegradable polyesters, including several types such as poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), etc. They have good strength and certain barrier properties, but their toughness and barrier properties are still not ideal.

[0005] In order to achieve excellent mechanical properties and barrier properties of biomass membrane materials to replace plastic materials, various different methods have been used for modification. For example, physical and chemical methods are used to modify different biomasses. Blending is the most common method. By adding PBAT with better toughness and rigid PLA / PHA for blending, a significant improvement in toughness has been achieved, and it is also widely used in packaging bags and packaging films, but it can only meet the applications with general requirements. Many other toughening methods, such as using starches, polycaprolactone and other biomasses, and using synthetic polymers such as polyether polyester, polybutylene succinate, styrene-butyl acrylate-acrylic acid copolymer, polyurethane, polyamide, etc. have also been applied to improve the toughness of bio-polyesters, and the comprehensive properties of the materials have been improved to a certain extent, but it is still very difficult to achieve its functional properties such as high barrier and water resistance. Adding ordinary nanoparticles such as nano-silica, titanium dioxide, montmorillonite, etc. can strengthen the strength and barrier properties of the membrane to a certain extent, but the nanoparticles themselves are prone to agglomeration, and it is also difficult to achieve ideal properties. Some chemical syntheses for raw materials such as grafting and copolymerization also have a significant improvement in the properties after processing into films, but the processes are often complex and difficult to promote. In addition, since bio-polyesters themselves belong to the category of biomasses, they often have a certain water absorption, which also has a serious impact on applications. At the same time, multi-layer composite is also a method to increase the properties of membrane materials. The most typical example is the use of multi-layer composite in plastic films, the composite of plastic and aluminum film layer, and the composite of PE and PVOH films to obtain membrane materials with very excellent barrier properties. In the field of biomass membranes, due to the poor barrier properties of its single layer itself, although multi-layer composite can effectively improve the mechanical properties of the membrane, simple composite has little improvement in barrier properties.

[0006] To solve the above problems, this patent has developed a new type of biomass-based double-layer composite membrane, which combines the reactive bonding of multi-layer membranes and the double stretching process to achieve the tight bonding and synergistic barrier of the double-layer membrane, and thus shows significant application potential. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of poor mechanical properties and poor barrier properties of biomass-based membrane materials, and to provide a double-layer biodegradable composite membrane with high strength and toughness, high water and gas barrier properties and its preparation process.

[0008] The purpose of the present invention is achieved through the following technical solutions: A biodegradable high-strength, tough and high-barrier composite membrane, comprising an inner layer PVA-based composite membrane and an outer layer chitosan-based composite membrane, wherein, The main components and ingredients of the inner layer PVA-based composite membrane are as follows: PVA 100 Sodium citrate 3 - 5.5 Surface-modified montmorillonite 0.5 - 1.2 Ethylene glycol 1.0 - 3.0 Amino-polyethylene glycol folic acid 6.5 - 12.5 The main components of the outer chitosan-based composite film are as follows: Quaternary ammonium salt modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule 15 - 30 Aldehyde group octa-arm polyethylene glycol 10 - 22.5.

[0009] Furthermore, the molecular weight of the amino-polyethylene glycol folic acid ranges between 12,000 - 30,000, and its molecular formula is as follows: .

[0010] Furthermore, the molecular weight of the PVA ranges between 20,000 - 40,000, and its alcoholysis degree is greater than 75%.

[0011] Furthermore, the particle size of the surface-modified montmorillonite ranges between 20 - 200 μm; the purpose of surface-modifying the montmorillonite is to improve the hydrophilicity of the montmorillonite, thereby improving its dispersibility in the PVA film; preferably, the modification is carried out using a silane coupling agent through a water-ethanol system, and the dosage of the modifier ranges between 4 - 8% of the mass of the montmorillonite.

[0012] Furthermore, the addition of ethylene glycol is beneficial to improving the flexibility of the film.

[0013] Furthermore, the molecular weight of the aldehyde group octa-arm polyethylene glycol ranges between 4,000 - 10,000, and its molecular formula is as follows: .

[0014] Furthermore, the quaternary ammonium salt modified chitosan often uses 2,3-epoxypropyltrimethylammonium chloride as the modifier, and the quaternary ammonium salt group is introduced by reacting with the hydroxyl and amino groups in the chitosan macromolecule. Its modification degree, expressed as the substitution degree of the hydroxyl group in the unit molecular chain of chitosan, ranges between 0.6 - 1.2.

[0015] Furthermore, the molecular formula of the poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide is as follows: .

[0016] Furthermore, the preparation process of the film is as follows: I: Casting of the inner PVA-based composite film: Dissolve PVA in water at 75 - 90 °C to prepare an aqueous solution with a mass concentration ranging from 8 - 12%. Then, add sodium citrate, surface-modified montmorillonite, ethylene glycol, and amino polyethylene glycol folic acid to the solution. After stirring evenly, perform casting on a casting machine at 35 - 45 °C, and control the casting speed at 30 - 60 cm / min; II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast into a film, uniformly spray an aqueous solution with a mass concentration of 3 - 6% of α-aminoglutaric acid dissolved in it onto the film to form a sprayed liquid film layer; III: Casting of the outer chitosan-based composite film: Perform secondary casting on the film when the spraying layer is not completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule, and aldehyde group octa-arm polyethylene glycol. The mass concentration of the solution ranges from 6 - 12%, and the pH value ranges from 5.5 - 6.5; the casting temperature ranges from 40 - 60 °C; IV: Biaxial stretching of the composite film: After drying the double-layer film at room temperature, perform double stretching treatment, where the longitudinal and transverse stretching ratios range from 1.5:2.4; the stretching temperature ranges from 45 - 60 °C to obtain the final film.

[0017] Furthermore, the molecular formula of the α-aminoglutaric acid is as follows: .

[0018] Furthermore, the purpose of spraying the α-aminoglutaric acid aqueous solution on the surface layer is to strengthen the bonding between the two layers by the combination of amino and carboxyl groups with the upper and lower layers through dipole moments, and simultaneously through the Schiff base reaction of amino, hydroxyl, and aldehyde groups on the outer layer under acid catalysis.

[0019] Furthermore, the exposed hydroxyl and amino groups in the inner PVA-based composite film layer will undergo a Schiff base reaction with the aldehyde groups in the outer chitosan-based composite film.

[0020] Furthermore, the thickness of the inner PVA-based composite film ranges from 120 - 240 μm, and the thickness of the outer chitosan-based composite film ranges from 80 - 160 μm.

[0021] Furthermore, the testing method for the film material properties is as follows: The tensile strength and elongation at break of the film are tested according to the standard of GB / T 1040.3 - 2006 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets"; The tear strength of the film is tested according to the standard of GB / T 16578.1 - 2008 "Plastics - Films and sheets - Determination of tear resistance"; The impact strength of the film was tested according to the standard of GB / T 9639.1-2008 "Plastics films and sheets - Determination of impact resistance - Free - falling dart method - Part 1: Staircase method". The puncture resistance of the film was tested according to the standard of GB / T 37841-2019 "Test method for puncture resistance of plastics films and sheets". The carbon dioxide and oxygen barrier properties of the film were tested according to GB / T 1038-2000 "Plastics films and sheets - Determination of gas permeability - Manometric method". The moisture permeability of the film was tested according to GB / T 1037-2021 "Determination of water vapor transmission rate of plastics films and sheets - Cup method for weight gain and weight loss".

[0022] Furthermore, the performance ranges of the film material are as follows: Thickness: 0.2 - 0.4 mm; Tensile strength (MPa): 26 - 38; Elongation at break (%): 144 - 231; Transverse tear strength (kN / m): 224 - 285; Longitudinal tear strength (kN / m): 182 - 224; Water vapor transmission rate (cm 3 / (m 3 ·24hr·MPa)): 4.2 - 16.4; CO2 transmission rate (cm 3 / (m 3 ·24hr·MPa)): 14.6 - 42.8 O2 transmission rate (cm 3 / (m 3 ·24hr·MPa)): 22.1 - 53.4.

[0023] Furthermore, the beneficial effects of the present invention are as follows: The high strength, toughness and high barrier of the biomass - based film are realized by adopting the double - layer composite and double - stretching process. Among them, the main raw material formulations in the double - layer are all biodegradable, ensuring the environmental protection of the film. In the double - layer, the inner PVA - modified film itself has a good gas - barrier basis, and the outer chitosan - based film acts as a synergist, providing gas - barrier synergy and assistance; between the double - layers, based on a special spraying combination process, the combination between the double - layers is strengthened by non - covalent bonds, and further improves the synergy of strength and barrier. Through the biaxial stretching after film compounding, the composite orientation of molecular chains is promoted, further improving the mechanical properties and barrier properties of the composite film material.

[0024] The exemplary implementation methods of the present invention will be described in detail below. However, these implementation methods are only for illustrative purposes, and the present invention is not limited thereto. Example 1

[0025] A biodegradable, high-strength, tough and high-barrier composite film, comprising an inner layer PVA-based composite film and an outer layer chitosan-based composite film, wherein, The main components and ingredients of the inner layer PVA-based composite film are as follows: PVA 100 Sodium citrate 4.2 Surface-modified montmorillonite 0.8 Ethylene glycol 2.5 Amino polyethylene glycol folic acid 8.2 The main components and ingredients of the outer layer chitosan-based composite film are as follows: Quaternary ammonium salt-modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide macromolecule 22.6 Aldehyde group octa-arm polyethylene glycol 15.4.

[0026] The molecular weight of the amino polyethylene glycol folic acid is 18,000.

[0027] The molecular weight of the PVA is 32,000 and the alcoholysis degree is 85%.

[0028] The particle size of the surface-modified montmorillonite is between 20 - 200 μm; the surface of the montmorillonite is modified with KH550 silane modifier, and the dosage of the modifier is 6.5% of the montmorillonite.

[0029] The modification degree of the quaternary ammonium salt-modified chitosan is expressed as 0.8 in terms of the hydroxyl substitution degree of the unit molecular chain in chitosan.

[0030] The molecular weight of the aldehyde group octa-arm polyethylene glycol is 6,000.

[0031] The preparation process of the film is as follows: I: Casting of the inner layer PVA-based composite film: Dissolve PVA in water at 86 °C to prepare an aqueous solution with a mass concentration of 9.5%, then add sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid to the solution, stir evenly, and perform casting on a casting machine at 40 °C, and control the casting speed at 45 cm / min; II: Surface spraying treatment of the inner layer PVA-based composite film: After the PVA-based composite film is cast into a film, uniformly spray an aqueous solution with a mass concentration of 4.5% of α-aminoglutaric acid on the film to form a sprayed liquid film layer; III: Casting of the outer chitosan-based composite film: Secondary casting is carried out on the film when the spraying layer is not completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule, and aldehyde group octa-arm polyethylene glycol. The mass concentration of the solution is 8.5%, and the pH value is 6.0; the casting temperature is 50 °C; IV: Biaxial stretching of the composite film: After drying the double-layer film at room temperature, biaxial stretching treatment is carried out, where the longitudinal and transverse stretching ratios are 2.1; the stretching temperature is 55 °C to obtain the final film.

[0032] The performance of the film in Example 1 is shown in Table 1.

[0033] Example 2 A biodegradable high-strength, high-toughness, and high-barrier composite film includes an inner layer PVA-based composite film and an outer layer chitosan-based composite film, where, The main components and components of the inner layer PVA-based composite film are as follows: PVA 100 Sodium citrate 4.6 Surface-modified montmorillonite 0.6 Ethylene glycol 2.2 Amino polyethylene glycol folic acid 10.6 The main components and components of the outer layer chitosan-based composite film are as follows: Quaternary ammonium salt-modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule 26.8 Aldehyde group octa-arm polyethylene glycol 13.2.

[0034] The molecular weight of the amino polyethylene glycol folic acid is 22000.

[0035] The molecular weight of the PVA is 26000, and the degree of alcoholysis is 90%.

[0036] The particle size of the surface-modified montmorillonite is between 10 - 100 μm; the surface of the montmorillonite is modified with KH560 silane modifier, and the dosage of the modifier is 5.2% of the montmorillonite.

[0037] The degree of modification of the quaternary ammonium salt-modified chitosan is expressed as 1.0 in terms of the hydroxyl substitution degree of the unit molecular chain in chitosan.

[0038] The molecular weight of the aldehyde group octa-arm polyethylene glycol is 8000.

[0039] The preparation process of the film is as follows: I: Casting of the inner PVA-based composite film: Dissolve PVA in water at 80 °C to prepare an aqueous solution with a mass concentration of 10.5%. Then, add sodium citrate, surface-modified montmorillonite, ethylene glycol, and amino-polyethylene glycol folic acid to the solution. After stirring evenly, perform casting on a casting machine at 42 °C, and control the casting speed at 50 cm / min; II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast into a film, uniformly spray an aqueous solution with a mass concentration of 5.2% of α-aminoglutaric acid on the film to form a sprayed liquid film layer; III: Casting of the outer chitosan-based composite film: Perform secondary casting on the film when the spraying layer is not completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule, and aldehyde group octa-arm polyethylene glycol. The mass concentration of the solution is 10.2%, and the pH value is 6.0; the casting temperature is 55 °C; IV: Biaxial stretching of the composite film: After drying the double-layer film at room temperature, perform double stretching treatment, where the longitudinal and transverse stretching ratios are 2.4; the stretching temperature is 55 °C to obtain the final film.

[0040] The performance of the film in Example 2 is shown in Table 1.

[0041] Example 3 A biodegradable high-strength, high-toughness, and high-barrier composite film includes an inner PVA-based composite film and an outer chitosan-based composite film, where The main components and ingredients of the inner PVA-based composite film are as follows: PVA 100 Sodium citrate 3.2 Surface-modified montmorillonite 1.0 Ethylene glycol 2.8 Amino-polyethylene glycol folic acid 8.4 The main components and ingredients of the outer chitosan-based composite film are as follows: Quaternary ammonium salt-modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule 21.4 Aldehyde group octa-arm polyethylene glycol 18.6.

[0042] The molecular weight of the amino-polyethylene glycol folic acid is 28,000.

[0043] The molecular weight of the PVA is 26,000, and the degree of alcoholysis is 90%.

[0044] The particle size of the surface-modified montmorillonite is between 20 - 300 μm; the surface of the montmorillonite is modified with KH550 silane modifier, and the dosage of the modifier is 6.5% of the montmorillonite.

[0045] The degree of modification of the quaternary ammonium salt-modified chitosan is 0.9 expressed by the substitution degree of hydroxyl groups in the unit molecular chain of chitosan.

[0046] The molecular weight of the aldehyde group octa-arm polyethylene glycol is 6500.

[0047] The preparation process of the membrane is as follows: I: Casting of the inner layer PVA-based composite membrane: Dissolve PVA in water at 85°C to prepare an aqueous solution with a mass concentration of 11.2%. Then add sodium citrate, surface-modified montmorillonite, ethylene glycol, and amino polyethylene glycol folic acid to the solution. After stirring evenly, perform casting on a casting machine at 45°C, and control the casting speed at 55 cm / min; II: Surface spraying treatment of the inner layer PVA-based composite membrane: After the PVA-based composite membrane is cast into a film, spray an aqueous solution with a mass concentration of 3.8% of α-aminoglutaric acid dissolved in it evenly on the film to form a sprayed liquid film layer; III: Casting of the outer layer chitosan-based composite membrane: Perform secondary casting on the film when the spraying layer is not completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide macromolecule, and aldehyde group octa-arm polyethylene glycol. The mass concentration of the solution is 10.6%, and the pH value is 6.2; the casting temperature is 52°C; IV: Biaxial stretching of the composite membrane: After drying the double-layer membrane at room temperature, perform biaxial stretching treatment, where the longitudinal and transverse stretching ratios are 1.8; the stretching temperature is 55°C to obtain the final membrane.

[0048] The performance of the membrane in Example 3 is shown in Table 1.

[0049] Example 4 A biodegradable high-strength, high-toughness and high-barrier composite membrane, including an inner layer PVA-based composite membrane and an outer layer chitosan-based composite membrane, where, The main components and ingredients of the inner layer PVA-based composite membrane are as follows: PVA 100 Sodium citrate 4.5 Surface-modified montmorillonite 1.2 Ethylene glycol 2.1 Amino polyethylene glycol folic acid 7.2 The main components and ingredients of the outer layer chitosan-based composite membrane are as follows: Quaternary ammonium salt-modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide macromolecule 27.8 Aldehyde group eight-arm polyethylene glycol 20.8.

[0050] The molecular weight of the amino polyethylene glycol folic acid is 16,000.

[0051] The molecular weight of the PVA is 34,000 and the degree of alcoholysis is 92%.

[0052] The particle size of the surface-modified montmorillonite is between 20 - 400 μm; the surface of the montmorillonite is modified with KH560 silane modifier, and the dosage of the modifier is 5.6% of the montmorillonite.

[0053] The modification degree of the quaternary ammonium salt-modified chitosan is expressed as 0.8 in terms of the hydroxyl substitution degree of the unit molecular chain in chitosan.

[0054] The molecular weight of the aldehyde group eight-arm polyethylene glycol is 7,200.

[0055] The preparation process of the membrane is as follows: I: Casting of the inner layer PVA-based composite membrane: Dissolve PVA in water at 88°C to prepare an aqueous solution with a mass concentration of 10.6%. Then add sodium citrate, surface-modified montmorillonite, ethylene glycol, and amino polyethylene glycol folic acid to the solution, stir evenly, and perform casting on a casting machine at 38°C. The casting speed is controlled at 36 cm / min; II: Surface spraying treatment of the inner layer PVA-based composite membrane: After the PVA-based composite membrane is cast into a film, spray an aqueous solution with a mass concentration of 3.8% of α-aminoglutaric acid evenly on the film to form a sprayed liquid film layer; III: Casting of the outer layer chitosan-based composite membrane: Perform secondary casting on the film when the spraying layer is not completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide macromolecule, and aldehyde group eight-arm polyethylene glycol. The mass concentration of the solution is 10.6% and the pH value is 6.2; the casting temperature is 52°C; IV: Biaxial stretching of the composite membrane: After drying the double-layer membrane at room temperature, perform double stretching treatment, where the longitudinal and transverse stretching ratios are 1.6; the stretching temperature is 48°C to obtain the final membrane.

[0056] The performance of the membrane in Example 4 is shown in Table 1.

[0057] Comparative Example 1 Compared with Example 1, in the preparation process, spraying of the α-aminoglutaric acid aqueous solution is not carried out, and all other processes and formulation ratios are the same. The properties of the prepared film are shown in Table 1. As shown in the table, the overall mechanical properties of the film, such as elongation at break and tensile strength, both decrease, and the gas barrier property also decreases significantly. This is because the lack of interaction of the intermediate connection layer results in insufficient tightness between the double layers, and defects may occur during processes such as double stretching, thereby affecting the performance. Especially once tiny defects appear, the gas barrier property will be significantly affected.

[0058] Comparative Example 2 Compared with Example 1, only the inner layer PVA-based composite film is used, and there is no subsequent spraying and the film attaching process of the outer layer chitosan-based composite film. The properties of the prepared film are shown in Table 1. As shown in the table, the tensile strength and gas barrier property of the film decrease significantly. Although the PVA-based film itself has good properties, without the synergy of double-layer composite, its performance still cannot reach a high level.

[0059] Comparative Example 3 Compared with Example 1, ethylene glycol and amino polyethylene glycol folic acid are not added during the preparation of the inner layer PVA-based composite film, and other formulations and processes are exactly the same. The properties of the prepared film are shown in Table 1. As shown in the table, the mechanical properties and barrier property of the film still decrease significantly. This may be because the flexibility of the inner layer film decreases, and the interaction with the outer layer film weakens, resulting in poor orientation effect of the molecular chains during the double stretching process, thereby affecting the performance.

[0060] Comparative Example 4 Compared with Example 1, the double stretching process after film forming is not carried out. The properties of the prepared film are shown in Table 1. As shown in the table, the mechanical properties of the film decrease, and the water vapor and gas barrier properties decrease significantly. Without double stretching treatment, the molecular chains do not orient, and its interception of gas small molecules decreases.

[0061] Table 1. Properties of the film materials prepared in Examples and Comparative Examples Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Thickness mm 0.26 0.31 0.34 0.28 0.29 0.16 0.27 0.30 Tensile strength MPa 32.8 35.6 29.9 37.2 24.8 19.3 28.3 24.1 Elongation at break % 148.2 127.5 168.5 109.4 82.9 109.7 48.8 133.5 Tear strength (longitudinal / transverse) MPa 192.7 / 158.3 268.4 / 188.1 156.4 / 129.5 238.6 / 195.2 162.6 / 143.7 118.2 / 87.6 109.3 / 87.6 124.3 / 116.5 Puncture resistance N 12.9 13.4 12.1 16.4 12.2 6.4 4.4 10.7 <![CDATA[O2 transmission rate cm 3 (m 3 ·24 h·MPa)]]> 32.6 26.2 42.5 28.1 265.4 591.4 416.6 218.9 <![CDATA[CO2 permeance cm 3 / (m 3 ·24hr·MPa)]]> 18.5 23.6 31.5 15.3 358.5 837.3 599.1 325.8 <![CDATA[Water vapor transmission rate cm 3 / (m 3 ·24hr·MPa)]]> 8.3 10.6 15.4 6.7 1025.7 1854.5 953.7 674.5

Claims

1. A biodegradable high-strength and high-barrier composite film, comprising an inner layer of a PVA-based composite film and an outer layer of a chitosan-based composite film, wherein: The main components and ingredients of the inner layer PVA-based composite film are as follows: PVA 100 Sodium citrate 3-5.5 Surface modified montmorillonite 0.5-1.2 Ethylene glycol 1.0-3.0 Aminopolyethylene glycol folic acid 6.5-12.5 The main components and ingredients of the outer chitosan-based composite membrane are as follows: Chitosan 100 modified by quaternary ammonium salt Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide macromolecule 15-30 Aldehyde eight-arm polyethylene glycol 10-22.5 The invention is also characterized in that, in the preparation of the membrane, after the inner layer PVA-based composite membrane is cast into a film, an α-aminoglutaric acid aqueous solution is sprayed on its surface, and then an outer layer chitosan-based composite membrane is further cast into a film on the sprayed surface; after the film is formed and dried, a double-drawing process is further performed to obtain the final membrane material.

2. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: During the casting process, the aldehyde groups in the outer chitosan-based composite film will undergo a Schiff base reaction with the amino groups and hydroxyls in the inner PVA-based composite film and the α-aminoglutaric acid sprayed on the surface thereof, thereby strengthening the bonding of the double-layer membranes.

3. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The membrane preparation process is as follows: I: Casting of the inner layer PVA-based composite film: PVA is dissolved in 75-90°C water to prepare an aqueous solution with a mass concentration of 8-12%, and then sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid are added to the solution. After stirring evenly, casting is carried out on a casting machine at 35-45°C, and the casting speed is controlled at 30-60cm / min; II: Surface spray treatment of the inner layer PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution containing 3-6% α-aminoglutaric acid is evenly sprayed on the film to form a spray liquid film layer; III: Casting of the outer chitosan-based composite membrane: When the spray layer is not completely dried, a secondary casting is performed on the membrane. The casting liquid is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfonic acid propyl) ammonium hydroxide macromolecules, and aldehyde-based eight-arm polyethylene glycol. The mass concentration of the solution is between 6-12%, and the pH value is between 5.5-6.5; the casting temperature is between 40-60°C; IV: Biaxial stretching of the composite film: After the double-layer film is dried at room temperature, it is subjected to a biaxial stretching treatment, wherein the longitudinal and transverse stretching ratios are between 1.5:2.4; the stretching temperature is between 45-60°C, to obtain the final film.

4. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The molecular weight of the aminopolyethylene glycol folic acid is between 12000 and 30000.

5. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The modification degree of the quaternary ammonium salt modified chitosan is between 0.6 and 1.2, expressed as the substitution degree of hydroxyl groups of the unit molecular chains in the chitosan.

6. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The molecular weight of the PVA is between 20,000 and 40,000, and the alcoholysis degree is greater than 75%.

7. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The molecular weight of the aldehyde eight-arm polyethylene glycol is between 4000 and 10000.

8. The biodegradable high-strength and high-barrier composite film according to claim 1, characterized in that: The thickness of the inner PVA-based composite film is between 120-240 μm, and the thickness of the outer chitosan-based composite film is between 80-160 μm.