A biodegradable high-strength high-toughness high-barrier composite film

Abstract

The present application relates to a kind of biodegradable high toughness high barrier composite film, including inner layer PVA-based composite film and outer layer chitosan-based composite film, double layer is obtained by flow casting composite, combination is realized between double layer by dynamic bond, after double layer is compounded, film treatment is carried out using double pull process, the film has excellent strength, toughness and water, gas barrier property, water vapor barrier property is significantly stronger than ordinary pure PVA film, also has surface antibacterial property, can be applied to food, pharmaceutical packaging field.

Description

Technical Field

[0001] This invention relates to a method for preparing a biomass-based composite material, and more particularly to a method for preparing a biodegradable membrane material with high strength, high toughness and excellent water and air barrier properties. Background Technology

[0002] Although plastic materials have excellent performance and wide applicability, they are derived from petroleum products and cannot be degraded. Therefore, finding high-performance and renewable alternative materials has become the top priority of current materials research.

[0003] Film materials constitute a huge portion of packaging materials and are widely used in various packaging systems. However, due to their inherent thinness and lightness, higher demands are placed on their mechanical and functional properties in packaging. Besides basic mechanical properties such as strength and tear resistance to ensure the integrity and physical protection of the packaging film, certain types of packaging, such as food and pharmaceutical packaging, also require films with good gas barrier properties, water vapor barrier properties, and antibacterial properties. This places higher demands on film development. Biomass materials can replace plastics and are easy to process into films; however, due to the intrinsic structural characteristics of major biomass materials such as polyester, starch, chitosan, and chitin, it is difficult to achieve the desired ideal properties when used independently.

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

[0005] To achieve superior mechanical properties and barrier properties in biomass membrane materials and replace plastic materials, various modification methods have been used. Physicochemical methods are employed to modify different biomasses. Blending is the most common method; by adding tougher PBAT and rigid PLA / PHA, a significant improvement in toughness is achieved, and this method is widely used in packaging bags and films, but it only meets general application requirements. Other toughening methods, such as using starch, polycaprolactone, and other biomasses, as well as synthetic polymers like polyether polyester, polybutylene succinate, styrene-butyl acrylate-acrylic acid copolymer, polyurethane, and polyamide, have also been used to improve the toughness of biopolyesters, all of which have improved the overall performance of the material to some extent, but functionalities such as high barrier properties and water resistance are still difficult to achieve. While adding common nanomaterials such as nano-silica, titanium dioxide, and montmorillonite can enhance the strength and barrier properties of the membrane to some extent, nanoparticles themselves are prone to aggregation, making it difficult to achieve ideal performance. Some chemical synthesis methods targeting raw materials, such as grafting and copolymerization, can significantly improve the performance of the processed film, but these processes are often complex and difficult to promote. Furthermore, since biopolyesters themselves belong to the biomass category, they often have a certain degree of water absorption, which also seriously affects their application. Meanwhile, multilayer composites are also a method to improve the performance of membrane materials. The most typical examples are multilayer composites in plastic films, such as composites of plastic and aluminum film layers, and composites of PE and PVOH film layers, resulting in membrane materials with excellent barrier properties. In the field of biomass membranes, because the barrier properties of a single layer are inherently poor, although multilayer composites can effectively improve the mechanical properties of the membrane, simple composites do not significantly improve barrier properties.

[0006] To address the above issues, this patent develops a novel biomass-based bilayer composite membrane. By combining the reactive bonding of multilayer membranes with a bi-stretching process, the membrane achieves tight bonding and synergistic barrier properties, thus demonstrating significant application potential. Summary of the Invention

[0007] The purpose of this 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 and high water and air barrier properties, as well as its preparation process.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A biodegradable, high-strength, high-barrier composite membrane comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein...

[0010] The main components and elements of the inner PVA-based composite film are as follows:

[0011] PVA 100

[0012] Sodium citrate 3-5.5

[0013] Surface-modified montmorillonite 0.5-1.2

[0014] Ethylene glycol 1.0-3.0

[0015] Amino-polyethylene glycol folic acid 6.5-12.5

[0016] The main components and elements of the outer chitosan-based composite membrane are as follows:

[0017] Quaternary ammonium salt modified chitosan 100

[0018] Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecule 15-30

[0019] Aldehyde-based octagonal polyethylene glycol 10-22.5.

[0020] Furthermore, the molecular weight of the amino-polyethylene glycol folic acid is between 12,000 and 30,000, and its molecular formula is as follows:

[0021] .

[0022] Furthermore, the molecular weight of the PVA is between 20,000 and 40,000, and the degree of alcoholysis is greater than 75%.

[0023] Furthermore, the particle size of the surface-modified montmorillonite is between 20-200 μm; the purpose of surface modification of montmorillonite is to improve the hydrophilicity of montmorillonite, thereby improving its dispersibility in PVA film; preferably, the modification is carried out using a silane coupling agent through a water-ethanol system, and the amount of modifier is between 4-8% of the mass of montmorillonite.

[0024] Furthermore, the addition of ethylene glycol is beneficial to improving the flexibility of the membrane.

[0025] Furthermore, the molecular weight of the aldehyde-based octahedral polyethylene glycol is between 4000 and 10000, and its molecular formula is as follows:

[0026] .

[0027] Furthermore, the quaternary ammonium salt modified chitosan often uses 2,3-epoxypropyltrimethylammonium chloride as a modifier, which achieves the incorporation of quaternary ammonium salt groups through reaction with hydroxyl and amino groups in the chitosan macromolecule. The degree of modification is expressed as the degree of hydroxyl substitution in the unit molecular chain of chitosan, which is between 0.6 and 1.2.

[0028] Furthermore, the molecular formula of the poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide is as follows:

[0029] .

[0030] Furthermore, the preparation process of the membrane is as follows:

[0031] I: Casting of the inner PVA-based composite film: Dissolve PVA in water at 75-90℃ to prepare an aqueous solution with a mass concentration of 8-12%. Then add sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid to the solution. After stirring evenly, cast the film on a casting machine at 35-45℃ with a casting speed controlled at 30-60cm / min.

[0032] II: Surface spraying treatment of inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution with a mass concentration of 3-6% of α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer.

[0033] III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the spray layer is completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based octa-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℃.

[0034] IV: Biaxial stretching of composite membrane: After drying the bilayer membrane at room temperature, a biaxial stretching process is performed, wherein the longitudinal and transverse stretching ratio is between 1.5:2.4; the stretching temperature is between 45-60℃, and the final membrane is obtained.

[0035] Furthermore, the molecular formula of the α-aminoglutaric acid is as follows:

[0036] .

[0037] Furthermore, the purpose of spraying the surface layer with the α-aminoglutaric acid aqueous solution is to enable the amino and carboxyl groups to bind with the upper and lower layers through dipole moments, and to enhance the bonding between the two layers through the Schiff base reaction of the amino, hydroxyl and outer aldehyde groups under acid catalysis.

[0038] Furthermore, the exposed hydroxyl and amino groups in the inner PVA-based composite film will undergo a Schiff base reaction with the aldehyde groups in the outer chitosan-based composite film.

[0039] Furthermore, 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.

[0040] Furthermore, the performance testing method for the membrane material is as follows:

[0041] The tensile strength and elongation at break of the film were tested according to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets";

[0042] The tear strength of the film was tested according to GB / T 16578.1-2008 "Determination of tear resistance of plastic films and sheets";

[0043] The impact strength of the membrane was tested according to GB / T 9639.1-2008 "Test methods for impact resistance of plastic films and sheets - free-falling dart method - Part 1: step method";

[0044] The puncture resistance of the membrane was tested according to GB / T 37841-2019 "Test Method for Puncture Resistance of Plastic Films and Sheets";

[0045] The carbon dioxide and oxygen barrier properties of the membrane were tested according to GB / T 1038-2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method";

[0046] The moisture permeability of the membrane was tested according to GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Weight Gain and Weight Loss Method".

[0047] Furthermore, the performance range of the membrane material is as follows:

[0048] Thickness: 0.2-0.4mm; Tensile strength (MPa): 26-38; Elongation at break (%): 144-231;

[0049] Transverse tear strength (kN / m): 224-285; Longitudinal tear strength (kN / m): 182-224;

[0050] Water vapor transmission rate (cm) 3 / (m 3 ·24hr·MPa)): 4.2-16.4;

[0051] CO2 transmission rate (cm) 3 / (m 3 (24hr MPa) ): 14.6-42.8

[0052] O2 transmittance (cm) 3 / (m 3 ·24hr·MPa)): 22.1-53.4.

[0053] Furthermore, the beneficial effects of this invention are as follows: It employs a bilayer composite and bi-stretching process to achieve high strength, toughness, and high barrier properties in the biomass-based membrane. The main raw material formulations in both layers are biodegradable, ensuring the membrane's environmental friendliness. Within the bilayer, the inner PVA-modified membrane inherently possesses excellent gas barrier properties, while the outer chitosan-based membrane acts as a synergist, providing synergistic and auxiliary gas barrier performance. A special spray bonding process strengthens the bond between the two layers using non-covalent bonds, further enhancing the synergy of strength and barrier properties. Bi-stretching after membrane composite formation promotes the composite orientation of molecular chains, further improving the mechanical properties and barrier properties of the composite membrane material.

[0054] Exemplary embodiments of the present invention will be described in detail below. However, these embodiments are for illustrative purposes only, and the present invention is not limited thereto.

[0055] Example 1

[0056] A biodegradable, high-strength, high-barrier composite membrane comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein...

[0057] The main components and elements of the inner PVA-based composite film are as follows:

[0058] PVA 100

[0059] Sodium citrate 4.2

[0060] Surface-modified montmorillonite 0.8

[0061] Ethylene glycol 2.5

[0062] Amino-polyethylene glycol folic acid 8.2

[0063] The main components and elements of the outer chitosan-based composite membrane are as follows:

[0064] Quaternary ammonium salt modified chitosan 100

[0065] Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecule 22.6

[0066] Aldehyde-based octagonal polyethylene glycol 15.4.

[0067] The molecular weight of the amino-polyethylene glycol folic acid is 18,000.

[0068] The PVA has a molecular weight of 32,000 and a degree of alcoholysis of 85%.

[0069] 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 amount of modifier is 6.5% of the montmorillonite.

[0070] The degree of modification of the quaternary ammonium salt-modified chitosan is expressed as 0.8, which is the degree of hydroxyl substitution in the unit molecular chain of chitosan.

[0071] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 6000.

[0072] The membrane is prepared using the following process:

[0073] I: Casting of the inner PVA-based composite film: PVA is dissolved in water at 86℃ to prepare an aqueous solution with a mass concentration of 9.5%. Then, sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid are added to the solution. After stirring evenly, the film is cast at 40℃ on a casting machine with a casting speed controlled at 45cm / min.

[0074] II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution with a mass concentration of 4.5% of α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer.

[0075] III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the spray layer is completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt-modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based 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℃.

[0076] IV: Biaxial stretching of the composite membrane: After drying the bilayer membrane at room temperature, a biaxial stretching process is performed, with a longitudinal and transverse stretching ratio of 2.1; the stretching temperature is 55℃, to obtain the final membrane.

[0077] The performance of the membrane in Example 1 is shown in Table 1.

[0078] Example 2

[0079] A biodegradable, high-strength, high-barrier composite membrane comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein...

[0080] The main components and elements of the inner PVA-based composite film are as follows:

[0081] PVA 100

[0082] Sodium citrate 4.6

[0083] Surface-modified montmorillonite 0.6

[0084] Ethylene glycol 2.2

[0085] Amino-polyethylene glycol folic acid 10.6

[0086] The main components and elements of the outer chitosan-based composite membrane are as follows:

[0087] Quaternary ammonium salt modified chitosan 100

[0088] Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonopropyl)ammonium hydroxide macromolecule 26.8

[0089] Aldehyde-based octagonal polyethylene glycol 13.2.

[0090] The molecular weight of the amino-polyethylene glycol folic acid is 22,000.

[0091] The PVA has a molecular weight of 26,000 and a degree of alcoholysis of 90%.

[0092] 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 amount of modifier is 5.2% of the montmorillonite.

[0093] The degree of modification of the quaternary ammonium salt-modified chitosan is expressed as the degree of hydroxyl substitution in the unit molecular chain of chitosan, which is 1.0.

[0094] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 8000.

[0095] The membrane is prepared using the following process:

[0096] I: Casting of the inner PVA-based composite film: PVA is dissolved in water at 80℃ to prepare an aqueous solution with a mass concentration of 10.5%. Then, sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid are added to the solution. After stirring evenly, the film is cast at 42℃ on a casting machine with a casting speed controlled at 50cm / min.

[0097] II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution with a mass concentration of 5.2% of α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer.

[0098] III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the spray layer is completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based 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℃.

[0099] IV: Biaxial stretching of the composite membrane: After drying the bilayer membrane at room temperature, a biaxial stretching process is performed, with a longitudinal and transverse stretching ratio of 2.4; the stretching temperature is 55℃, to obtain the final membrane.

[0100] The performance of the membrane in Example 2 is shown in Table 1.

[0101] Example 3

[0102] A biodegradable, high-strength, high-barrier composite membrane comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein...

[0103] The main components and elements of the inner PVA-based composite film are as follows:

[0104] PVA 100

[0105] Sodium citrate 3.2

[0106] Surface-modified montmorillonite 1.0

[0107] Ethylene glycol 2.8

[0108] Amino-polyethylene glycol folic acid 8.4

[0109] The main components and elements of the outer chitosan-based composite membrane are as follows:

[0110] Quaternary ammonium salt modified chitosan 100

[0111] Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecule 21.4

[0112] Aldehyde-based octagonal polyethylene glycol 18.6.

[0113] The molecular weight of the amino-polyethylene glycol folic acid is 28,000.

[0114] The PVA has a molecular weight of 26,000 and a degree of alcoholysis of 90%.

[0115] 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 amount of modifier is 6.5% of the montmorillonite.

[0116] The degree of modification of the quaternary ammonium salt-modified chitosan is expressed as 0.9, which is the degree of hydroxyl substitution in the unit molecular chain of chitosan.

[0117] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 6500.

[0118] The membrane is prepared using the following process:

[0119] I: Casting of the inner PVA-based composite film: PVA is dissolved in water at 85°C to prepare an aqueous solution with a mass concentration of 11.2%. Then, sodium citrate, surface-modified montmorillonite, ethylene glycol, and amino polyethylene glycol folic acid are added to the solution. After stirring evenly, the film is cast at 45°C on a casting machine with a casting speed controlled at 55 cm / min.

[0120] II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution with a mass concentration of 3.8% of α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer.

[0121] III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the spray layer is completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based 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℃.

[0122] IV: Biaxial stretching of the composite membrane: After drying the bilayer membrane at room temperature, a biaxial stretching process is performed, with a longitudinal and transverse stretching ratio of 1.8; the stretching temperature is 55℃, to obtain the final membrane.

[0123] The performance of the membrane in Example 3 is shown in Table 1.

[0124] Example 4

[0125] A biodegradable, high-strength, high-barrier composite membrane comprises an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein...

[0126] The main components and elements of the inner PVA-based composite film are as follows:

[0127] PVA 100

[0128] Sodium citrate 4.5

[0129] Surface-modified montmorillonite 1.2

[0130] Ethylene glycol 2.1

[0131] Amino-polyethylene glycol folic acid 7.2

[0132] The main components and elements of the outer chitosan-based composite membrane are as follows:

[0133] Quaternary ammonium salt modified chitosan 100

[0134] Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecule 27.8

[0135] Aldehyde-based octagonal polyethylene glycol 20.8.

[0136] The molecular weight of the amino-polyethylene glycol folic acid is 16,000.

[0137] The PVA has a molecular weight of 34,000 and a degree of alcoholysis of 92%.

[0138] 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 amount of modifier is 5.6% of the montmorillonite.

[0139] The degree of modification of the quaternary ammonium salt-modified chitosan is expressed as 0.8, which is the degree of hydroxyl substitution in the unit molecular chain of chitosan.

[0140] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 7200.

[0141] The membrane is prepared using the following process:

[0142] I: Casting of the inner PVA-based composite film: PVA is dissolved in water at 88℃ to prepare an aqueous solution with a mass concentration of 10.6%. Then, sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid are added to the solution. After stirring evenly, the film is cast at 38℃ on a casting machine with a casting speed controlled at 36cm / min.

[0143] II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution with a mass concentration of 3.8% of α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer.

[0144] III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the spray layer is completely dry. The casting solution is a weakly acidic solution containing quaternary ammonium salt modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based 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℃.

[0145] IV: Biaxial stretching of the composite membrane: After drying the bilayer membrane at room temperature, a biaxial stretching process was performed, with a longitudinal and transverse stretching ratio of 1.6; the stretching temperature was 48℃, to obtain the final membrane.

[0146] The performance of the membrane in Example 4 is shown in Table 1.

[0147] Comparative Example 1

[0148] Compared to Example 1, the spraying of α-aminoglutaric acid aqueous solution was omitted in the preparation process, while all other processes and formulation ratios remained the same. The properties of the prepared membrane are shown in Table 1. As shown in the table, the overall mechanical properties of the membrane, such as elongation at break and tensile strength, were reduced, and the gas barrier properties were also significantly decreased. This is because the lack of interaction between the intermediate connecting layers resulted in insufficient bonding between the two layers, which may lead to defects during processes such as bistretching, thus affecting performance. In particular, the presence of even small defects will significantly affect the gas barrier properties.

[0149] Comparative Example 2

[0150] Compared to Example 1, the membrane prepared using only an inner PVA-based composite membrane without subsequent spraying and outer chitosan-based composite membrane application processes yielded the properties shown in Table 1. As the table shows, the tensile strength and gas barrier properties of the membrane decreased significantly. Although the PVA-based membrane itself has good performance, without the synergistic effect of the double-layer composite, its performance still cannot reach a high level.

[0151] Comparative Example 3

[0152] Compared to Example 1, ethylene glycol and amino-polyethylene glycol folic acid were not added in the preparation of the inner PVA-based composite membrane, while other formulations and processes remained completely identical. The properties of the prepared membrane are shown in Table 1. As shown in the table, the mechanical properties and barrier properties of the membrane still decreased significantly. This may be due to the reduced flexibility of the inner membrane and the weakened interaction with the outer membrane, resulting in poor molecular chain orientation during the biaxial stretching process, thus affecting the performance.

[0153] Comparative Example 4

[0154] Compared to Example 1, without performing the bistretching process after membrane formation, the properties of the prepared membrane are shown in Table 1. As shown in the table, the mechanical properties of the membrane decreased, and the water vapor and gas barrier properties decreased significantly. Without the bistretching process, the molecular chains did not undergo orientation, resulting in a decrease in its interception of small gas molecules.

[0155] Table 1. Performance of membrane materials prepared in examples and comparative examples

[0156] 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, high-barrier composite membrane, comprising an inner PVA-based composite membrane and an outer chitosan-based composite membrane, wherein, The main components of the inner 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 Amino-polyethylene glycol folic acid 6.5-12.5 The main components of the outer chitosan-based composite membrane are as follows: Quaternary ammonium salt modified chitosan 100 Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecule 15-30 Aldehyde-based octagonal polyethylene glycol 10-22.5 The invention is characterized in that: in the preparation of the biodegradable, high-strength, high-barrier composite membrane, after the inner PVA-based composite membrane is cast, an aqueous solution of α-aminoglutaric acid is sprayed onto its surface, and then the outer chitosan-based composite membrane is further cast onto the sprayed surface; after the membrane is formed and dried, a biaxial stretching process is further performed to obtain the final membrane material; the aldehyde groups in the outer chitosan-based composite membrane will undergo a Schiff base reaction with the amino and hydroxyl groups in the inner PVA-based composite membrane and the α-aminoglutaric acid sprayed onto its surface during the casting process, thereby strengthening the bonding of the bilayer membrane.

2. The biodegradable, high-strength, high-barrier composite membrane as described in claim 1, characterized in that, The preparation process of the biodegradable, high-strength, high-barrier composite membrane is as follows: I: Casting of the inner PVA-based composite film: Dissolve PVA in water at 75-90℃ to prepare an aqueous solution with a mass concentration of 8-12%. Then add sodium citrate, surface-modified montmorillonite, ethylene glycol and amino polyethylene glycol folic acid to the solution. After stirring evenly, cast the film on a casting machine at 35-45℃ with a casting speed controlled at 30-60cm / min. II: Surface spraying treatment of the inner PVA-based composite film: After the PVA-based composite film is cast, an aqueous solution containing α-aminoglutaric acid is uniformly sprayed onto the film to form a spray liquid film layer. The mass concentration of the aqueous solution is 3-6%. III: Casting of the outer chitosan-based composite film: A secondary casting process is performed on the film before the sprayed liquid film layer is completely dry. The casting liquid is a weakly acidic solution containing quaternary ammonium salt modified chitosan, poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide macromolecules, and aldehyde-based octa-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℃. IV: Biaxial stretching of composite membrane: After drying the bilayer membrane at room temperature, it is subjected to biaxial stretching treatment, wherein the longitudinal and transverse stretching ratio is 2.1; the stretching temperature is between 45-60℃, and the final membrane is obtained.

3. The biodegradable, high-strength, high-barrier composite membrane as described in claim 1, characterized in that, The molecular weight of the amino-polyethylene glycol folic acid is between 12,000 and 30,000.

4. The biodegradable, high-strength, high-barrier composite membrane as described in claim 1, characterized in that, The degree of modification of the quaternary ammonium salt modified chitosan is expressed as the degree of hydroxyl substitution in the unit molecular chain of chitosan, which is between 0.6 and 1.

2.

5. The biodegradable, high-strength, high-barrier composite membrane as described in claim 1, characterized in that, The PVA has a molecular weight between 20,000 and 40,000 and a degree of alcoholysis greater than 75%.

6. The biodegradable, high-strength, high-barrier composite membrane as described in claim 1, characterized in that, The molecular weight of the aldehyde-based octagonal polyethylene glycol is between 4,000 and 10,000.

7. The biodegradable, high-strength, high-barrier composite membrane as described in 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.