A degradable composite material having high water vapor barrier properties and water resistance

Abstract

The present application relates to a kind of degradable composite material with high water vapor barrier and waterproof, including paperboard and the biodegradable film covered on both sides thereof. Wherein, polylactic acid film is covered on the inside of paperboard, and biodegradable composite film is covered on the outside thereof;The inside film is covered by spraying, and the outside film is covered by first spraying chitosan-based film, and PVA-based composite film is cast or immersed on the chitosan-based film after film formation. Due to the close combination of double-layer film and paperboard, the mechanical properties of the board are further enhanced, and the paperboard is also endowed with excellent water vapor and gas barrier properties. The hydrophobicity of the surface of the outer film endows the material with good waterproofness. The composite material can be used in the field of paper-based beverage containers requiring gas barrier.

Description

Technical Field

[0001] This invention relates to a paper-plastic composite material, and more particularly to a method for preparing a paper-plastic composite material with high water vapor barrier and waterproof properties. Background Technology

[0002] Cardboard, due to its environmental friendliness and good mechanical properties, has become the most widely used packaging container, found in a variety of packaging products. Typically, paper cups are widely used as disposable containers for various beverages. Because they are easily soaked and deformed by water, they are typically used immediately and discarded, and are not considered for long-term beverage preservation. However, with increasing environmental awareness, there is a desire to further develop the functionality of cardboard. Some companies have begun developing biodegradable cardboard materials that can achieve high sealing performance for a certain period, possessing high barrier properties against water vapor and other gases such as oxygen and carbon dioxide, to seal liquid beverages.

[0003] To this end, various methods have been employed, a typical example being the coating of paperboard surfaces. These include placing a paraffin film layer inside the paperboard or covering it with a PE film using a spraying process. These methods all contribute to improved barrier properties to varying degrees and ensure the paperboard remains unwetted. However, problems persist. On one hand, the barrier properties of paper-plastic composites prepared in this way still do not meet the requirements for sealing liquid beverages. On the other hand, these polymer films are often non-degradable, and their lack of environmental friendliness greatly limits their use. To develop such special materials that maintain degradability while achieving excellent water and vapor barrier properties, more specialized treatments are needed on the paperboard. To address this problem, this invention fully utilizes a multi-layer composite approach, employing biodegradable films with different functionalities. Based on the good bonding and synergistic effect between the multi-layer films, the aforementioned objectives are achieved. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of paperboard-plastic film composites being non-biodegradable and having poor barrier properties, and to provide a paper-plastic composite material with excellent water vapor and gas barrier properties and biodegradability, as well as its preparation process.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A biodegradable composite material with high water vapor barrier and waterproof properties includes a cardboard and films covering both sides thereof; wherein the inner side of the cardboard is covered with a polylactic acid film and the outer side is covered with a biodegradable composite film.

[0007] Furthermore, the biodegradable composite film comprises a chitosan-based film tightly attached to the surface of the paper substrate and an external PVA-based composite film, characterized in that:

[0008] The main components and composition of the chitosan-based membrane are as follows:

[0009] Quaternary ammonium salt modified chitosan 100

[0010] Cellulose acetate propionate 25-50

[0011] Surface-modified montmorillonite 0.6-1.2

[0012] Small molecule alcohols 3-6

[0013] Aldehyde-based octagonal polyethylene glycol 3-8

[0014] The main components and elements of the PVA-based composite film are as follows:

[0015] PVA 100

[0016] Sodium citrate 3-5.5

[0017] Surface-modified montmorillonite 0.6-1.2

[0018] Small molecule alcohols 3-6

[0019] Boric acid 2.2-6.4

[0020] Aldehyde-based octagonal polyethylene glycol 3-8.

[0021] Furthermore, the degree of modification of the quaternary ammonium salt modified chitosan is expressed as the number of substituted hydroxyl and amino groups in the unit molecular chain of chitosan, which is between 0.6 and 1.2.

[0022] Furthermore, the degree of substitution of the cellulose acetate propionate, expressed as the degree of substitution of hydroxyl groups in the unit molecular chain of cellulose, is between 1.8 and 2.8.

[0023] Furthermore, the surface-modified montmorillonite is obtained by surface modification of montmorillonite with a silane coupling agent, the amount of the modifier being between 3-8% of the montmorillonite by mass, and the particle size of the modified montmorillonite being between 30-300 μm; preferably, the modification is carried out using a silane coupling agent through a water-ethanol system, and the amount of the modifier being between 4-8% of the montmorillonite by mass.

[0024] Furthermore, the molecular weight of the aldehyde-based octahedral polyethylene glycol is between 2000 and 10000, and its molecular formula is as follows:

[0025]

[0026] Furthermore, the small molecule alcohol is one of ethylene glycol, glycerol, and 1,2-butanediol.

[0027] Furthermore, the molecular weight of the PVA is between 20,000 and 100,000, and the degree of alcoholysis is higher than 75%.

[0028] Furthermore, boric acid is added to the outer PVA-based composite film, which can provide boron atoms and oxygen atoms of PVA in the film to form boron-oxygen dynamic crosslinks, thereby enhancing the tear resistance and flexibility of the film, and significantly improving the overall hydrophobicity of the film after casting.

[0029] Furthermore, the cardboard is cardboard formed from pulp without undergoing special surface treatment, including but not limited to white cardboard, corrugated cardboard, and honeycomb cardboard.

[0030] Furthermore, the process of covering the inner side with polylactic acid film is to perform a spray coating process on one side surface of the cardboard; the spray process adopts the common polylactic acid spray cardboard coating process, or the new process described in patents 202010593546.8 and 202210792935.2 can be used.

[0031] Furthermore, the biodegradable composite film coating process on the outer side of the cardboard is as follows:

[0032] I: Surface treatment of cardboard: Prepare a weak acid solution with a mass concentration of 2-4%, spray it onto the surface of the cardboard to be coated, maintain the temperature at 50-80℃, treat for 10-15 minutes and dry until there is no obvious water film on the surface of the cardboard;

[0033] II: One-time coating: Casting is carried out on the surface of the treated cardboard. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octagonal polyethylene glycol. The mass concentration of the aqueous solution is between 6-12%, the casting temperature is between 40-60℃, and the casting speed is controlled at 30-60cm / min.

[0034] III: Secondary Coating: Dissolve PVA in water at 75-90℃ to prepare an aqueous solution with a mass concentration between 6-12%. Then add all sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid and aldehyde-based octahedral polyethylene glycol to the solution and stir evenly to form coating solution A. Apply coating solution A to the surface that has already been coated in II for secondary coating. Casting is carried out on a casting machine at 30-50℃ with the casting speed controlled between 20-40cm / min. After the cast film is dried, the final coated paperboard is obtained.

[0035] Furthermore, the thickness of the polylactic acid film on the inner side of the paperboard is between 200-400 μm; the thickness of the chitosan-based film on the outer side of the paperboard is between 120-240 μm; and the thickness of the PVA-based composite film is between 80-160 μm.

[0036] Furthermore, the performance testing methods for the materials involved in this invention are as follows:

[0037] Since the mechanical properties of paper-plastic composites are mainly affected by the properties of the paperboard, the main variable in this invention is the influence of the biodegradable composite film on the outside. Therefore, the mechanical properties of the film cast on the surface of a polytetrafluoroethylene sheet under the same process conditions were measured separately.

[0038] 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";

[0039] 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";

[0040] The puncture resistance of the membrane was tested according to GB / T 37841-2019 "Test Method for Puncture Resistance of Plastic Films and Sheets";

[0041] The overall gas barrier and water vapor barrier properties of the paper-plastic composite were tested according to GB / T 1038-2000 "Gas permeability test method for plastic films and sheets - differential pressure method" and "Water vapor permeability test for plastic films and sheets - cup weight gain and weight loss method". All tests were conducted with the biodegradable composite film side as the outside.

[0042] The bonding strength between the outer biodegradable composite film and the paperboard is expressed by the peel strength of the paper film.

[0043] The hydrophobicity of the outer surface of the biodegradable composite membrane was determined by the membrane's water contact angle test, which was used to characterize the membrane's waterproofness.

[0044] Furthermore, the beneficial effects of the present invention are as follows:

[0045] The double-sided lamination of the cardboard provides double barrier protection. The polylactic acid film on the inner side not only enhances gas barrier properties but also provides hydrophobicity, making it suitable for use as a beverage container.

[0046] The outer biodegradable composite membrane includes an inner chitosan-based membrane. This membrane has good wettability with the casting liquid and paper fibers, and can be tightly bonded to them. Its special formulation system gives this membrane good film-forming properties. The surface-modified montmorillonite in it is a layered particle, which can improve the barrier properties of the membrane. The aldehyde-based octahedral polyethylene glycol in the formulation and the amino groups in chitosan can react to crosslink chitosan to improve the overall strength of the membrane.

[0047] PVA-based films are cast onto the surface of chitosan-based films. Pure PVA films have good strength and gas barrier properties, but poor water vapor barrier properties and are hydrophilic and easily absorb water. Therefore, boric acid, which can be dissolved at high temperatures and precipitated at low temperatures, is added to the formulation system. The boron-oxygen dynamic bond is used to strengthen the film strength, and the boron atoms provide a certain degree of hydrophobicity. Surface-modified montmorillonite further improves the barrier properties of the film. The aldehyde-based octahedral polyethylene glycol added to the film can further undergo a Schiff base reaction with the amino groups in the chitosan film during casting to strengthen the bond between the two layers of film. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the paper-plastic composite material in Example 1.

[0049] 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.

[0050] Example 1

[0051] like Figure 1 As shown, a biodegradable composite material with high water vapor barrier and waterproof properties includes a cardboard 1 and films covering both sides of it; wherein, the inner side of the cardboard is covered with a polylactic acid film 3 and the outer side is covered with a biodegradable composite film 2.

[0052] The biodegradable composite film 2 comprises a chitosan-based film 2-1 tightly attached to the surface of the paper substrate and a PVA-based composite film 2-2 outside thereon, characterized in that:

[0053] The main components and composition of the chitosan-based membrane are as follows:

[0054] Quaternary ammonium salt modified chitosan 100

[0055] Cellulose acetate propionate 36

[0056] Surface-modified montmorillonite 0.8

[0057] Small molecule alcohols 4.2

[0058] Aldehyde-based octagonal polyethylene glycol 6

[0059] The main components and elements of the PVA-based composite film are as follows:

[0060] PVA 100

[0061] Sodium citrate 4.2

[0062] Surface-modified montmorillonite 0.8

[0063] Small molecule alcohols 4.2

[0064] Boric acid 5.4

[0065] Aldehyde-based octagonal polyethylene glycol 6.

[0066] The degree of modification of the quaternary ammonium salt-modified chitosan is 0.8.

[0067] The degree of substitution of the cellulose acetate propionate is expressed as 2.1, which is the degree of substitution of the hydroxyl groups in the unit molecular chain of cellulose.

[0068] The surface-modified montmorillonite was obtained by surface modification of montmorillonite with silane coupling agent KH550, the mass amount of the modifier being 4.5% of the montmorillonite, and the particle size of the modified montmorillonite being between 30-200 μm.

[0069] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 4500.

[0070] The PVA has a molecular weight of 32,000 and a degree of alcoholysis of 85%.

[0071] The small molecule alcohol is ethylene glycol.

[0072] The cardboard is white cardboard with a thickness of 0.5 mm.

[0073] The process of covering the inner side with polylactic acid film involves applying a spray coating process to one side surface of the cardboard, using a general spray process.

[0074] The process of covering the outer side with a biodegradable composite membrane is as follows:

[0075] I: Surface treatment of cardboard: Prepare a 3% acetic acid solution and spray it onto the surface of the cardboard to be coated. Maintain the temperature at 60℃ and treat for 12 minutes. Dry until there is no obvious water film on the surface of the cardboard.

[0076] II: First-time lamination of cardboard: Casting is carried out on the outer surface of the treated film. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octahedral polyethylene glycol. The mass concentration of the aqueous solution is 9%, the casting temperature is 55℃, and the casting speed is 45cm / min.

[0077] III: Secondary lamination of paperboard: Dissolve PVA in water at 85℃ to prepare an 8% (w / w) aqueous solution. Then add sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid and aldehyde-based octahedral polyethylene glycol to the solution and stir evenly to prepare lamination solution A. Apply lamination solution A to the surface of the lamination in II for secondary lamination. Perform casting at 45℃ on a casting machine at a casting speed of 30cm / min. After drying, the final laminated paperboard is obtained.

[0078] The polylactic acid film on the inner side of the cardboard has a thickness of 320 μm; the chitosan-based film on the outer side of the cardboard has a thickness of 220 μm, and the PVA-based composite film has a thickness of 100 μm.

[0079] The properties of the materials involved in Example 1 are shown in Table 1.

[0080] Example 2

[0081] A biodegradable composite material with high water vapor barrier and waterproof properties includes a cardboard and films covering both sides thereof; wherein the inner side of the cardboard is covered with a polylactic acid film and the outer side is covered with a biodegradable composite film.

[0082] The biodegradable composite film comprises a chitosan-based film tightly attached to the surface of the paperboard and an external PVA-based composite film, characterized in that:

[0083] The main components and composition of the chitosan-based membrane are as follows:

[0084] Quaternary ammonium salt modified chitosan 100

[0085] Cellulose acetate propionate 42

[0086] Surface-modified montmorillonite 1.0

[0087] Small molecule alcohol 4.5

[0088] Aldehyde-based octagonal polyethylene glycol 6

[0089] The main components and elements of the PVA-based composite film are as follows:

[0090] PVA 100

[0091] Sodium citrate 5.0

[0092] Surface-modified montmorillonite 0.8

[0093] Small molecule alcohol 3.8

[0094] Boric acid 5.8

[0095] Aldehyde-based octagonal polyethylene glycol 6.5.

[0096] The degree of modification of the quaternary ammonium salt-modified chitosan is 1.0.

[0097] The degree of substitution of the cellulose acetate propionate is expressed as 2.2, which is the degree of substitution of the hydroxyl groups in the unit molecular chain of cellulose.

[0098] The surface-modified montmorillonite was prepared by surface modification of montmorillonite with silane coupling agent KH560, the mass amount of the modifier being 5.2% of the montmorillonite, and the particle size of the modified montmorillonite being between 30-240 μm.

[0099] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 6200.

[0100] The PVA has a molecular weight of 54,000 and a degree of alcoholysis of 90%.

[0101] The small molecule alcohol is glycerol.

[0102] The cardboard is white cardboard with a thickness of 0.6 mm.

[0103] The process of covering the inner side with polylactic acid film involves applying a spray coating process to one side surface of the cardboard, using a general spray process.

[0104] The process of covering the outer side with a biodegradable composite membrane is as follows:

[0105] I: Surface treatment of cardboard: Prepare a 3.5% hydrochloric acid solution and spray it onto the surface of the cardboard to be coated. Maintain the temperature at 65℃ and treat for 10 minutes. Dry until there is no obvious water film on the surface of the cardboard.

[0106] II: First-time lamination of cardboard: Casting is carried out on the outer surface of the treated film. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octagonal polyethylene glycol. The mass concentration of the aqueous solution is 10%, the casting temperature is 50℃, and the casting speed is 40cm / min.

[0107] III: Secondary lamination of paperboard: Dissolve PVA in water at 85℃ to prepare an 8% aqueous solution. Then add sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid and aldehyde-based octa-arm polyethylene glycol to the solution and stir evenly to prepare lamination solution A. Apply lamination solution A to the surface of the lamination in II for secondary lamination. Perform casting at 40℃ on a casting machine at a casting speed of 25cm / min. After drying, the final laminated paperboard is obtained.

[0108] The polylactic acid film on the inner side of the cardboard has a thickness of 360 μm; the chitosan-based film on the outer side of the cardboard has a thickness of 200 μm, and the PVA-based composite film has a thickness of 140 μm.

[0109] The properties of the materials involved in Example 2 are shown in Table 1.

[0110] Example 3

[0111] A biodegradable composite material with high water vapor barrier and waterproof properties includes a cardboard and films covering both sides thereof; wherein the inner side of the cardboard is covered with a polylactic acid film and the outer side is covered with a biodegradable composite film.

[0112] The biodegradable composite film comprises a chitosan-based film tightly attached to the surface of the paperboard and an external PVA-based composite film, characterized in that:

[0113] The main components and composition of the chitosan-based membrane are as follows:

[0114] Quaternary ammonium salt modified chitosan 100

[0115] Cellulose acetate propionate 24

[0116] Surface-modified montmorillonite 1.2

[0117] Small molecule alcohols 5.4

[0118] Aldehyde-based octagonal polyethylene glycol 6.4

[0119] The main components and elements of the PVA-based composite film are as follows:

[0120] PVA 100

[0121] Sodium citrate 4.6

[0122] Surface-modified montmorillonite 0.6

[0123] Small molecule alcohols 3.2

[0124] Boric acid 4.6

[0125] Aldehyde-based octagonal polyethylene glycol 7.2.

[0126] The degree of modification of the quaternary ammonium salt-modified chitosan is 0.8.

[0127] The degree of substitution of the cellulose acetate propionate is expressed as the degree of substitution of hydroxyl groups in the unit molecular chain of cellulose, which is 2.4.

[0128] The surface-modified montmorillonite was prepared by surface modification of montmorillonite with silane coupling agent KH560, the mass amount of the modifier being 6.5% of the montmorillonite, and the particle size of the modified montmorillonite being between 40-300 μm.

[0129] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 8000.

[0130] The PVA has a molecular weight of 68,000 and a degree of alcoholysis of 92%.

[0131] The small molecule alcohol is ethylene glycol.

[0132] The cardboard is white cardboard with a thickness of 0.8 mm.

[0133] The process of covering the inner side with polylactic acid film involves applying a spray coating process to one side surface of the cardboard, using a general spray process.

[0134] The process of covering the outer side with a biodegradable composite membrane is as follows:

[0135] I: Surface treatment of cardboard: Prepare a 3% hydrochloric acid solution and spray it onto the surface of the cardboard to be coated. Maintain the temperature at 70°C and treat for 12 minutes. Dry until there is no obvious water film on the surface of the cardboard.

[0136] II: First-time coating of paperboard: Casting is carried out on the surface of the treated paperboard. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octahedral polyethylene glycol. The mass concentration of the aqueous solution is 8.5%, the casting temperature is 55℃, and the casting speed is 45cm / min.

[0137] III: Secondary lamination of paperboard: Dissolve PVA in water at 90℃ to prepare an aqueous solution with a mass concentration of 7%. Then add sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid and aldehyde-based octa-arm polyethylene glycol to the solution and stir evenly to prepare lamination solution A. Apply lamination solution A to the lamination surface in II for secondary lamination. Perform casting at 45℃ on a casting machine with a casting speed of 32cm / min. After drying, the final laminated paperboard is obtained.

[0138] The polylactic acid film on the inner side of the paperboard has a thickness of 310 μm; the chitosan-based film on the outer side of the paperboard has a thickness of 180 μm, and the PVA-based composite film has a thickness of 150 μm.

[0139] The properties of the materials involved in Example 3 are shown in Table 1.

[0140] Example 4

[0141] A biodegradable composite material with high water vapor barrier and waterproof properties includes a cardboard and films covering both sides thereof; wherein the inner side of the cardboard is covered with a polylactic acid film and the outer side is covered with a biodegradable composite film.

[0142] The biodegradable composite film comprises a chitosan-based film tightly attached to the surface of the paperboard and an external PVA-based composite film, characterized in that:

[0143] The main components and composition of the chitosan-based membrane are as follows:

[0144] Quaternary ammonium salt modified chitosan 100

[0145] Cellulose acetate propionate 48

[0146] Surface-modified montmorillonite 0.9

[0147] Small molecule alcohols 3.2

[0148] Aldehyde-based octagonal polyethylene glycol 5.6

[0149] The main components and elements of the PVA-based composite film are as follows:

[0150] PVA 100

[0151] Sodium citrate 5.2

[0152] Surface-modified montmorillonite 1.2

[0153] Small molecule alcohols 5.4

[0154] Boric acid 3.8

[0155] Aldehyde-based octagonal polyethylene glycol 6.4.

[0156] The degree of modification of the quaternary ammonium salt-modified chitosan is 1.2.

[0157] The degree of substitution of the cellulose acetate propionate is expressed as the degree of substitution of hydroxyl groups in the unit molecular chain of cellulose, which is 2.4.

[0158] The surface-modified montmorillonite was obtained by surface modification of montmorillonite with silane coupling agent KH550, the mass amount of the modifier being 4.8% of the montmorillonite, and the particle size of the modified montmorillonite being between 30-260 μm.

[0159] The molecular weight of the aldehyde-based octagonal polyethylene glycol is 8000.

[0160] The PVA has a molecular weight of 48,000 and a degree of alcoholysis of 95%.

[0161] The small molecule alcohol is 1,2-butanediol.

[0162] The cardboard is white cardboard with a thickness of 0.6 mm.

[0163] The process of covering the inner side with polylactic acid film involves applying a spray coating process to one side surface of the cardboard, using a general spray process.

[0164] The process of covering the outer side with a biodegradable composite membrane is as follows:

[0165] I: Surface treatment of cardboard: Prepare a 3.5% acetic acid solution and spray it onto the surface of the cardboard to be coated. Maintain the temperature at 75°C and treat for 10 minutes. Dry until there is no obvious water film on the surface of the cardboard.

[0166] II: First-time lamination of cardboard: Casting is carried out on the outer surface of the treated film. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octahedral polyethylene glycol. The mass concentration of the aqueous solution is 11%, the casting temperature is 52℃, and the casting speed is 42cm / min.

[0167] III: Secondary lamination of paperboard: Dissolve PVA in water at 85℃ to prepare an aqueous solution with a mass concentration of 9.5%. Then add sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid and aldehyde-based octa-arm polyethylene glycol to the solution and stir evenly to prepare lamination solution A. Apply lamination solution A to the lamination surface in II for secondary lamination. Perform casting at 48℃ on a casting machine with a casting speed of 35cm / min. After drying, the final laminated paperboard is obtained.

[0168] The polylactic acid film on the inner side of the paperboard has a thickness of 280 μm; the chitosan-based film on the outer side of the paperboard has a thickness of 210 μm, and the PVA-based composite film has a thickness of 100 μm.

[0169] The properties of the materials involved in Example 4 are shown in Table 1.

[0170] Comparative Example 1

[0171] Compared to Example 1, no polylactic acid coating was applied to the inside of the cardboard, while other processes and formulations remained the same. The resulting cardboard had a chitosan-based film thickness of 210 μm and a PVA-based composite film thickness of 110 μm on the outside.

[0172] The barrier properties of the material prepared in Comparative Example 1 are shown in Table 2. As can be seen from the table, its barrier properties only decreased slightly, which indicates that the outer biodegradable composite film plays the main role in barrier properties in this paper-plastic composite material.

[0173] Comparative Example 2

[0174] Compared to Example 1, the paperboard was not covered with a biodegradable composite film on the outside, but all other processes and formulations were the same, and the thickness of the polylactic acid film on the inside of the resulting paperboard was 320 μm.

[0175] The barrier properties of the materials prepared in Comparative Example 2 are shown in Table 2. Simply covering them with a polylactic acid film cannot meet the barrier requirements.

[0176] Comparative Example 3

[0177] Compared to Example 1, only a chitosan-based film was covered on the outside of the cardboard, without a PVA-based composite film. All other processes and formulations were the same. The thickness of the polylactic acid film on the inside of the cardboard was 300 μm, and the thickness of the chitosan-based film on the inside of the cardboard was 220 μm.

[0178] The barrier properties of the material prepared in Comparative Example 3 are shown in Table 2. Its barrier properties are also poor, indicating that chitosan-based membranes alone cannot achieve good barrier properties.

[0179] Comparative Example 4

[0180] Compared to Example 1, only a PVA-based composite film is directly covered on the outside of the cardboard, without covering it with a chitosan-based film. All other processes and formulations are the same. The thickness of the polylactic acid film on the inside of the cardboard is 320 μm, and the thickness of the PVA-based composite film on the inside of the cardboard is 120 μm.

[0181] The barrier properties of the material prepared in Comparative Example 4 are shown in Table 2.

[0182] Among them, the outer PVA-based composite film is more likely to separate and produce pores because it cannot be tightly bonded to the fiber, resulting in a significant decrease in barrier properties. Multiple tests failed to measure the data, and the barrier properties did not meet the requirements.

[0183] Table 1. Performance of the biodegradable composite film on the outer side of the cardboard, barrier properties of the paper-plastic composite material, and peel performance of the paper film in the examples.

[0184]

[0185] Table 2. Overall Barrier Properties of Comparative Paper-Plastic Composite Biodegradable Composite Materials

[0186]

Claims

1. A biodegradable composite material with high water vapor barrier and waterproof properties, comprising cardboard and films covering both sides thereof; wherein, The cardboard is covered with a polylactic acid film on the inner side and a biodegradable composite film on the outer side; the biodegradable composite film includes a chitosan-based film tightly attached to the surface of the cardboard and a PVA-based composite film thereon, characterized in that: The main components of the chitosan-based membrane are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 25-50 Surface-modified montmorillonite 0.6-1.2 Small molecule alcohols 3-6 Aldehyde-based octagonal polyethylene glycol 3-8 The main components of the PVA-based composite film are as follows: PVA 100 Sodium citrate 3-5.5 Surface-modified montmorillonite 0.6-1.2 Small molecule alcohols 3-6 Boric acid 4.2-8.4 Aldehyde-based octagonal polyethylene glycol 3-8.

2. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The degree of modification of the quaternary ammonium salt modified chitosan is expressed by the number of substituted hydroxyl and amino groups in the unit molecular chain of chitosan, which is between 0.6 and 1.

2.

3. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The degree of substitution of the cellulose acetate propionate is expressed as the degree of substitution of hydroxyl groups in the unit molecular chain of cellulose, and is between 1.8 and 2.

8.

4. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The surface-modified montmorillonite is obtained by surface modification of montmorillonite with a silane coupling agent. The mass amount of the silane coupling agent is between 3% and 8% of the montmorillonite, and the particle size of the modified montmorillonite is between 30 and 300 μm.

5. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The molecular weight of the aldehyde-based octagonal polyethylene glycol is between 2000 and 10000.

6. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The small molecule alcohol is one of ethylene glycol, glycerol, and 1,2-butanediol.

7. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The biodegradable composite film coating process on the outside of the cardboard is as follows: I: Surface treatment of cardboard: Prepare a weak acid solution with a mass concentration of 2-4%, spray it onto the surface of the cardboard to be coated, maintain the temperature at 50-80℃, treat for 10-15 minutes, and dry until there is no obvious water film on the surface of the cardboard; II: One-time coating: Casting is carried out on the surface of the treated cardboard. The casting solution is an aqueous solution containing quaternary ammonium salt modified chitosan, cellulose acetate propionate, surface modified montmorillonite, small molecule alcohol, and aldehyde-based octagonal polyethylene glycol. The mass concentration of the aqueous solution is between 6-12%, the casting temperature is between 40-60℃, and the casting speed is controlled at 30-60cm / min. III: Secondary Coating: Dissolve PVA in water at 75-90℃ to prepare an aqueous solution with a mass concentration between 6-12%. Then add all sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid, and aldehyde-based octahedral polyethylene glycol to the solution and stir evenly to form coating solution A. Coating solution A is then used to perform a secondary coating on the surface of the chitosan-based film already coated in II. Casting is carried out on a casting machine at 30-50℃ with the casting speed controlled between 20-40cm / min. After the cast film is dried, a coated paperboard with a biodegradable composite film on the outside is obtained.

8. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The cardboard is formed from pulp and has not undergone special surface treatment.

9. The biodegradable composite material with high water vapor barrier and waterproof properties as described in claim 1, characterized in that, The thickness of the polylactic acid film on the inner side of the paperboard is between 200-400 μm; the thickness of the chitosan-based film on the outer side of the paperboard is between 120-240 μm; and the thickness of the PVA-based composite film is between 80-160 μm.

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