Degradable composite material with high moisture barrier property and water resistance

Abstract

The invention relates to a degradable composite material with high moisture barrier property and waterproofness. The degradable composite material comprises a paperboard and biodegradable films covering the two sides of the paperboard. Wherein the inner side of the paperboard is covered with a polylactic acid film, and the outer side is covered with a biodegradable composite film; the inner side film is coated in a spraying mode, and the outer side film coating mode is that a chitosan-based film is sprayed firstly, and after the film is formed, a PVA-based composite film is covered on the chitosan-based film in a curtain coating or soaking mode. The double-layer film is tightly combined with the paperboard, so that the mechanical property of the board is further enhanced, the paperboard is endowed with excellent water vapor and gas barrier property, and the material is endowed with good waterproofness due to the surface hydrophobicity of the outer side film. The composite material can be used in the fields of paper-based beverage containers requiring gas barrier property and the like.

Description

Technical Field

[0001] The present invention relates to a paper-plastic composite material, and in particular to a preparation method of a paper-plastic composite material with high water vapor barrier property and waterproof property. Background Art

[0002] Cardboard has become the most widely used packaging container of various types based on its environmental protection and good mechanical properties, and is used in a variety of different types of packaging products. Typically, paper cups, as disposable containers for various beverages, are also widely used. Since they are easily infiltrated and deformed by water, they are used immediately and discarded immediately, and they are not often considered as containers for storing beverages for a long time. However, with the improvement of people's environmental protection requirements, people hope to further develop the functionality of cardboard. Some companies have begun to develop degradable cardboard materials that can achieve high sealing performance within a certain period of time, that is, have high water vapor and other gas barrier properties such as oxygen and carbon dioxide, in order to achieve the sealing of liquid beverages.

[0003] For this purpose, different methods are adopted. Typically, a film is laminated on the surface of the cardboard. For example, a paraffin film layer is provided inside the cardboard, and a PE film is covered by a spraying process. These methods are all beneficial to improving the barrier property to varying degrees and can ensure that the cardboard is not wetted by water. However, problems still exist. On the one hand, the barrier property of the paper-plastic composite material prepared by this method still cannot meet the requirements for sealing liquid beverages. On the other hand, such polymer film layers are often not degradable, and their lack of environmental protection also greatly limits their use. In order to develop such special materials, more special treatments need to be carried out on the cardboard while maintaining degradability and achieving excellent water vapor barrier properties. In view of this problem, the present invention makes full use of the multi-layer composite mode, uses biodegradable films with different functions, and realizes the above goals based on the good combination and synergistic effect between the multi-layers. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of non-biodegradability and poor barrier property after the composite of cardboard and plastic film, and to provide a paper-plastic composite material with excellent water vapor and gas barrier properties and biodegradability, and its preparation process.

[0005] The purpose of the present invention is achieved by the following technical solutions: A degradable composite material with high water vapor barrier property and waterproof property, comprising cardboard and films covered on both sides thereof; wherein, a polylactic acid film is covered on the inner side of the cardboard, and a biodegradable composite film is covered on the outer side.

[0006] Furthermore, the biodegradable composite film includes a chitosan-based film closely attached to the surface of the cardboard and a PVA-based composite film outside it, and is characterized in that: The main components and ingredients of the chitosan-based film are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 25 - 50 Surface modified montmorillonite 0.6 - 1.2 Small molecule alcohol 3 - 6 Aldehyde group eight - arm polyethylene glycol 3 - 8 The main components and ingredients 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 alcohol 3 - 6 Boric acid 2.2 - 6.4 Aldehyde group eight - arm polyethylene glycol 3 - 8.

[0007] Furthermore, the degree of modification of the quaternary ammonium salt modified chitosan is expressed by the number of substituted hydroxyl groups and amino groups in the unit molecular chain of chitosan, and it is between 0.6 - 1.2.

[0008] Furthermore, the degree of substitution of the cellulose acetate propionate is expressed by the degree of substitution of hydroxyl groups in the unit molecular chain of cellulose, and it is between 1.8 - 2.8.

[0009] Furthermore, the surface modified montmorillonite is obtained by surface - modifying montmorillonite with a silane coupling agent. The mass dosage of the modifier is between 3 - 8% of the montmorillonite, and the particle size of the modified montmorillonite is between 30 - 300 μm; preferably, the modification is carried out using a silane coupling agent through a water - ethanol system, and the dosage of the modifier is between 4 - 8% of the mass of the montmorillonite.

[0010] Furthermore, the molecular weight of the aldehyde group eight - arm polyethylene glycol is between 2000 - 10000, and its molecular formula is as follows:

[0011] Furthermore, the small molecule alcohol is one of ethylene glycol, glycerol, and 1,2 - butanediol.

[0012] Furthermore, the molecular weight of the PVA is between 20000 - 100000, and the degree of alcoholysis is higher than 75%.

[0013] Furthermore, boric acid is added to the outer PVA - based composite film, which can provide the formation of boron - oxygen dynamic cross - links between boron atoms and oxygen atoms of PVA in the film, thereby strengthening the tear resistance and flexibility of the film, and significantly improving the overall hydrophobicity of the film after casting.

[0014] Furthermore, the cardboard is a cardboard formed from pulp without special surface treatment, including but not limited to white cardboard, corrugated cardboard, and honeycomb cardboard.

[0015] Furthermore, the process of covering the inner side with a polylactic acid film is to apply a spraying process to one surface of the cardboard for film covering; the spraying process can adopt the general polylactic acid spraying cardboard film covering process, or can also adopt the new processes described in patents 202010593546.8 and 202210792935.2.

[0016] Furthermore, the process of covering the outer side of the cardboard with a biodegradable composite film is as follows: I: Surface treatment of the cardboard: Prepare a weak acid solution with a mass concentration of 2 - 4%, spray it onto the surface of the cardboard to be film covered, keep the temperature at 50 - 80°C, and process for 10 - 15 minutes until the surface of the cardboard is dried without an obvious water film. II: Primary film covering: 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 group octabranched polyethylene glycol. The mass concentration of the aqueous solution is between 6 - 12%, the casting temperature is between 40 - 60°C, and the casting speed is controlled at 30 - 60 cm / min. III: Secondary film covering: Dissolve PVA in water at 75 - 90°C 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 group octabranched polyethylene glycol to the solution, stir evenly to form a film covering solution A. Carry out secondary film covering of the film covering solution A on the surface that has been film covered in II, and carry out casting on a casting machine at 30 - 50°C. The casting speed is controlled between 20 - 40 cm / min. After casting and drying, the final film covered cardboard is obtained.

[0017] Furthermore, the thickness of the polylactic acid film on the inner side of the cardboard is between 200 - 400 μm; the thickness of the chitosan-based film on the outer side of the cardboard is between 120 - 240 μm, and the thickness of the PVA-based composite film is between 80 - 160 μm.

[0018] Furthermore, the performance testing methods of the materials involved in the present invention are as follows: Since the mechanical properties after paper-plastic composite are mainly affected by the properties of the cardboard, and the main variable in the invention is the influence of the biodegradable composite film on the outer side, the mechanical properties of the film cast on the surface of a polytetrafluoroethylene plate prepared under the same process conditions are measured separately. 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 impact strength of the film is tested according to the standard of GB / T 9639.1 - 2008 "Plastics films and sheets - Test method for impact resistance - Free fall 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 Plastic Films and Sheets". The overall gas barrier property and water vapor barrier property after paper-plastic composite were tested according to GB / T 1038-2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method" and "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Weight Gain and Loss Method". All tests were carried out with the biodegradable composite film side as the outer side. The bonding strength between the outer biodegradable composite film and the cardboard was expressed by the peel strength of the paper film. The hydrophobicity of the outer surface of the outer biodegradable composite film was determined by testing the water contact angle of the film, which was used to characterize the waterproof property of the film.

[0019] Furthermore, the beneficial effects of the present invention are as follows: Coating both sides of the cardboard with films provides double barrier protection. Among them, coating the inner side with a polylactic acid film not only enhances the gas barrier property but also has a hydrophobic effect, so as to adapt to the application as a beverage container. The outer biodegradable composite film includes an inner chitosan-based film. The casting solution of this film has good wettability with paper fibers and can be tightly combined with them. Its special formulation system endows this film with good film-forming property. The surface-modified montmorillonite in it is a layered particle, which can improve the barrier property of the film. The aldehyde-functionalized octa-arm polyethylene glycol in the formulation can react with the amino group in chitosan to crosslink chitosan and enhance the overall strength of the film. A PVA-based film was cast on the surface of the chitosan-based film. The pure PVA film itself has good strength and gas barrier property, but its water vapor barrier property is poor and it is hydrophilic and easy to absorb water. Therefore, boric acid that can be dissolved at high temperature and precipitated at low temperature was added to the formulation system to strengthen the film strength by using boron-oxygen dynamic bonds. Boron atoms provide a certain degree of hydrophobicity. The surface-modified montmorillonite further improves the barrier property of the film. The aldehyde-functionalized octa-arm polyethylene glycol added to the film can further undergo a Schiff base reaction with the amino group in the chitosan film during casting to strengthen the bonding between the two layers of films. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the paper-plastic composite material in Example 1.

[0021] The following will describe in detail the exemplary implementation methods of the present invention. However, these implementation methods are only for illustrative purposes, and the present invention is not limited thereto. Example 1

[0022] As Figure 1 shown, a degradable composite material with high water vapor barrier property and waterproof property includes a cardboard 1 and films covered on both sides thereof; wherein, a polylactic acid film 3 is covered on the inner side of the cardboard, and a biodegradable composite film 2 is covered on the outer side.

[0023] The biodegradable composite film 2 includes a chitosan-based film 2-1 closely attached to the surface of the cardboard and a PVA-based composite film 2-2 outside it, and is characterized in that: The main components and ingredients of the chitosan-based film are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 36 Surface modified montmorillonite 0.8 Small molecule alcohol 4.2 Aldehydo-octaarm poly(ethylene glycol) 6 The main components and ingredients of the PVA-based composite film are as follows: PVA 100 Sodium citrate 4.2 Surface modified montmorillonite 0.8 Small molecule alcohol 4.2 Boric acid 5.4 Aldehydo-octaarm poly(ethylene glycol) 6.

[0024] The degree of modification of the quaternary ammonium salt modified chitosan is 0.8.

[0025] 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 2.1.

[0026] The surface modified montmorillonite is obtained by surface modification of montmorillonite with a silane coupling agent KH550, and the mass dosage of the modifier is 4.5% of the montmorillonite. The particle size of the modified montmorillonite is between 30 - 200 μm.

[0027] The molecular weight of the aldehydo-octaarm poly(ethylene glycol) is 4500.

[0028] The molecular weight of the PVA is 32000 and the degree of alcoholysis is 85%.

[0029] The small molecule alcohol is ethylene glycol.

[0030] The cardboard is white cardboard with a thickness of 0.5 mm.

[0031] The process of covering the inner side with a polylactic acid film is to implement a spraying process for film covering on one side surface of the cardboard, using a general spraying process.

[0032] The process of covering the outer side with the biodegradable composite film is as follows: I: Surface treatment of the cardboard: Prepare an acetic acid solution with a mass concentration of 3%, spray it onto the surface of the cardboard to be film-covered, keep the temperature at 60 °C, and treat for 12 minutes and dry until there is no obvious water film on the surface of the cardboard; II: Primary Coating of the Paperboard: 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 group octabranched polyethylene glycol. The mass concentration of the aqueous solution is 9%, the casting temperature is 55 °C, and the casting speed is 45 cm / min; III: Secondary Coating of the Paperboard: Dissolve PVA in water at 85 °C to prepare an aqueous solution with a mass concentration of 8%. Then add sodium citrate, surface modified montmorillonite, small molecule alcohol, boric acid, and aldehyde group octabranched polyethylene glycol to the solution and stir evenly to prepare Coating Solution A. Apply Coating Solution A for secondary coating on the surface coated in II, and carry out casting at 45 °C on a casting machine with a casting speed of 30 cm / min. After drying, the final coated paperboard is obtained.

[0033] The thickness of the polylactic acid film on the inner side of the paperboard is 320 μm; the thickness of the chitosan-based film on the outer side of the paperboard is 220 μm, and the thickness of the PVA-based composite film is 100 μm.

[0034] The properties of the materials involved in Example 1 are shown in Table 1.

[0035] Example 2 A degradable composite material with high water vapor barrier property and waterproof property, comprising a paperboard and the films covered on both sides thereof; wherein, a polylactic acid film is covered on the inner side of the paperboard, and a biodegradable composite film is covered on the outer side.

[0036] The biodegradable composite film comprises a chitosan-based film closely attached to the surface of the paperboard and a PVA-based composite film outside thereof, and is characterized in that: The main components and compositions of the chitosan-based film are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 42 Surface modified montmorillonite 1.0 Small molecule alcohol 4.5 Aldehyde group octabranched polyethylene glycol 6 The main components and compositions of the PVA-based composite film are as follows: PVA 100 Sodium citrate 5.0 Surface modified montmorillonite 0.8 Small molecule alcohol 3.8 Boric acid 5.8 Aldehyde group octabranched polyethylene glycol 6.5.

[0037] The modification degree of the quaternary ammonium salt modified chitosan is 1.0.

[0038] The substitution degree of the cellulose acetate propionate, expressed by the substitution degree of hydroxyl groups in the unit molecular chain of cellulose, is 2.2.

[0039] The surface-modified montmorillonite is obtained by surface-modifying montmorillonite with silane coupling agent KH560. The mass dosage of the modifier is 5.2% of the montmorillonite, and the particle size of the modified montmorillonite is between 30 - 240 μm.

[0040] The molecular weight of the aldehyde group octa-armed polyethylene glycol is 6200.

[0041] The molecular weight of the PVA is 54000, and the degree of alcoholysis is 90%.

[0042] The small molecule alcohol is glycerol.

[0043] The cardboard is white cardboard with a thickness of 0.6 mm.

[0044] The process of covering the inner side with a polylactic acid film is to implement a spraying process for film coating on one side surface of the cardboard, using a general spraying process.

[0045] The process of covering the outer side with a biodegradable composite film is as follows: I: Surface treatment of the cardboard: Prepare a hydrochloric acid solution with a mass concentration of 3.5%, spray it onto the surface of the cardboard to be film-coated, keep the temperature at 65 °C, treat for 10 minutes, and dry until there is no obvious water film on the cardboard surface; II: Primary film coating of the cardboard: Implement casting on the outer side 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 group octa-armed polyethylene glycol. The mass concentration of the aqueous solution is 10%, the casting temperature is 50 °C, and the casting speed is 40 cm / min; III: Secondary film coating of the cardboard: Dissolve PVA in water at 85 °C to prepare an aqueous solution with a mass concentration of 8%. Then add sodium citrate, surface-modified montmorillonite, small molecule alcohol, boric acid, and aldehyde group octa-armed polyethylene glycol to the solution, stir evenly to prepare the film coating solution A. Perform secondary film coating of the film coating solution A on the film-coated surface in II, implement casting on a casting machine at 40 °C, with a casting speed of 25 cm / min, and obtain the final film-coated cardboard after drying.

[0046] The thickness of the polylactic acid film on the inner side of the cardboard is 360 μm; the thickness of the chitosan-based film on the outer side of the cardboard is 200 μm, and the thickness of the PVA-based composite film is 140 μm.

[0047] The properties of the materials involved in Example 2 are shown in Table 1.

[0048] Example 3 A degradable composite material with high water vapor barrier property and waterproof property, including a cardboard and the films covered on both sides thereof; wherein, a polylactic acid film is covered on the inner side of the cardboard, and a biodegradable composite film is covered on the outer side.

[0049] The biodegradable composite film includes a chitosan-based film closely attached to the surface of the cardboard and a PVA-based composite film outside it, and is characterized in that: The main components and ingredients of the chitosan-based film are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 24 Surface modified montmorillonite 1.2 Small molecule alcohol 5.4 Aldehyde group octa-arm polyethylene glycol 6.4 The main components and ingredients of the PVA-based composite film are as follows: PVA 100 Sodium citrate 4.6 Surface modified montmorillonite 0.6 Small molecule alcohol 3.2 Boric acid 4.6 Aldehyde group octa-arm polyethylene glycol 7.2.

[0050] The modification degree of the quaternary ammonium salt modified chitosan is 0.8.

[0051] The substitution degree of the cellulose acetate propionate is expressed as 2.4 in terms of the hydroxyl substitution degree of the unit molecular chain in cellulose.

[0052] The surface modified montmorillonite is obtained by surface modification of montmorillonite with silane coupling agent KH560. The mass dosage of the modifier is 6.5% of the montmorillonite, and the particle size of the modified montmorillonite is between 40 - 300 μm.

[0053] The molecular weight of the aldehyde group octa-arm polyethylene glycol is 8000.

[0054] The molecular weight of the PVA is 68000, and the alcoholysis degree is 92%.

[0055] The small molecule alcohol is ethylene glycol.

[0056] The cardboard is white cardboard with a thickness of 0.8 mm.

[0057] The process of covering the inner side with a polylactic acid film is to implement a spraying process for film covering on one side surface of the cardboard, using a general spraying process.

[0058] The process of covering the outer side with the biodegradable composite film is as follows: I: Surface treatment of the cardboard: Prepare a hydrochloric acid solution with a mass concentration of 3%, spray it onto the surface of the cardboard to be film-covered, keep the temperature at 70 °C, and treat for 12 minutes and dry until there is no obvious water film on the surface of the cardboard; II: Primary Coating of the Cardboard: 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 group octabranched polyethylene glycol. The mass concentration of the aqueous solution is 8.5%, the casting temperature is 55 °C, and the casting speed is 45 cm / min; III: Secondary Coating of the Cardboard: Dissolve PVA in water at 90 °C 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 group octabranched polyethylene glycol to the solution and stir evenly to prepare coating solution A. Carry out secondary coating of coating solution A on the surface coated in II, and carry out casting on a casting machine at 45 °C with a casting speed of 32 cm / min. After drying, the final coated cardboard is obtained.

[0059] The thickness of the polylactic acid film on the inner side of the cardboard is 310 μm; the thickness of the chitosan-based film on the outer side of the cardboard is 180 μm, and the thickness of the PVA-based composite film is 150 μm.

[0060] The properties of the materials involved in Example 3 are shown in Table 1.

[0061] Example 4 A degradable composite material with high water vapor barrier property and waterproof property, comprising a cardboard and the films covered on both sides thereof; wherein, a polylactic acid film is covered on the inner side of the cardboard, and a biodegradable composite film is covered on the outer side.

[0062] The biodegradable composite film includes a chitosan-based film closely attached to the surface of the cardboard and a PVA-based composite film outside it, and is characterized in that: The main components and ingredients of the chitosan-based film are as follows: Quaternary ammonium salt modified chitosan 100 Cellulose acetate propionate 48 Surface modified montmorillonite 0.9 Small molecule alcohol 3.2 Aldehyde group octabranched polyethylene glycol 5.6 The main components and ingredients of the PVA-based composite film are as follows: PVA 100 Sodium citrate 5.2 Surface modified montmorillonite 1.2 Small molecule alcohol 5.4 Boric acid 3.8 Aldehyde group octabranched polyethylene glycol 6.4.

[0063] The modification degree of the quaternary ammonium salt modified chitosan is 1.2.

[0064] The substitution degree of the cellulose acetate propionate, expressed as the substitution degree of hydroxyl groups in the unit molecular chain of cellulose, is 2.4.

[0065] The surface-modified montmorillonite is obtained by surface-modifying montmorillonite with silane coupling agent KH550. The mass dosage of the modifier is 4.8% of the montmorillonite, and the particle size of the modified montmorillonite is between 30 - 260 μm.

[0066] The molecular weight of the aldehyde group octa-arm polyethylene glycol is 8000.

[0067] The molecular weight of the PVA is 48000, and the degree of alcoholysis is 95%.

[0068] The small molecule alcohol is 1,2-butanediol.

[0069] The cardboard is white cardboard with a thickness of 0.6 mm.

[0070] The process of covering the inner side with a polylactic acid film is to implement a spraying process for film covering on one side surface of the cardboard, using a general spraying process.

[0071] The process of covering the outer side with a biodegradable composite film is as follows: I: Surface treatment of the cardboard: Prepare an acetic acid solution with a mass concentration of 3.5%, spray it onto the surface of the cardboard to be film-covered, keep the temperature at 75 °C, and treat for 10 minutes and dry until there is no obvious water film on the cardboard surface; II: Primary film covering of the cardboard: Casting is implemented on the outer side surface after treatment. The casting solution is an aqueous solution containing quaternary ammonium salt-modified chitosan, cellulose acetate propionate, surface-modified montmorillonite, small molecule alcohol, and aldehyde group octa-arm polyethylene glycol. The mass concentration of the aqueous solution is 11%, the casting temperature is 52 °C, and the casting speed is 42 cm / min; III: Secondary film covering of the cardboard: Dissolve PVA in water at 85 °C 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 group octa-arm polyethylene glycol to the solution, stir evenly to prepare the film covering solution A. Perform secondary film covering of the film covering solution A on the surface covered in II, implement casting on a casting machine at 48 °C, with a casting speed of 35 cm / min, and obtain the final film-covered cardboard after drying.

[0072] The thickness of the polylactic acid film on the inner side of the cardboard is 280 μm; the thickness of the chitosan-based film on the outer side of the cardboard is 210 μm, and the thickness of the PVA-based composite film is 100 μm.

[0073] The properties of the materials involved in Example 4 are shown in Table 1.

[0074] Comparative Example 1 Compared with Example 1, no polylactic acid film covering is carried out on the inner side of the cardboard, and other processes and formulations are the same. The thickness of the chitosan-based film on the outer side of the obtained cardboard is 210 μm, and the thickness of the PVA-based composite film is 110 μm.

[0075] The barrier properties of the materials prepared in Comparative Example 1 are shown in Table 2. As can be seen from the table, its barrier property only decreases slightly, indicating that in this paper-plastic composite material, the main barrier is the biodegradable composite film on the outer side.

[0076] Comparative Example 2 Compared with Example 1, the outer side of the cardboard is not covered with a biodegradable composite film, and other processes and formulations are the same. The thickness of the polylactic acid film on the inner side of the obtained cardboard is 320 μm.

[0077] The barrier properties of the materials prepared in Comparative Example 2 are shown in Table 2. Merely covering the polylactic acid film cannot meet the requirements of barrier properties.

[0078] Comparative Example 3 Compared with Example 1, only a chitosan-based film is covered on the outer side of the cardboard, and the PVA-based composite film is not covered. Other processes and formulations are the same. The thickness of the polylactic acid film on the inner side of the obtained cardboard is 300 μm, and the thickness of the chitosan-based film on the inner side of the obtained cardboard is 220 μm.

[0079] The barrier properties of the materials prepared in Comparative Example 3 are shown in Table 2. Its barrier characteristics are also poor, indicating that good barrier properties cannot be achieved only by the chitosan-based film.

[0080] Comparative Example 4 Compared with Example 1, only a PVA-based composite film is directly covered on the outer side of the cardboard, and the chitosan-based film is not covered. Other processes and formulations are the same. The thickness of the polylactic acid film on the inner side of the obtained cardboard is 320 μm, and the thickness of the PVA-based composite film on the inner side of the obtained cardboard is 120 μm.

[0081] The barrier properties of the materials prepared in Comparative Example 4 are shown in Table 2.

[0082] Among them, the PVA-based composite film on the outer side is prone to separation and generate pores because it cannot be tightly combined with the fibers, resulting in a significant decrease in barrier properties. Data measurement cannot be achieved after multiple tests, and the requirements of barrier properties cannot be met.

[0083] Table 1. Properties of the biodegradable composite film on the outer side of the cardboard, barrier properties of the paper-plastic composite material, and paper-film peeling properties in the examples

[0084] Table 2. Overall barrier properties of the paper-plastic composite biodegradable composite materials in the comparative examples

Claims

1. A degradable composite material with high water vapor barrier and waterproof properties, comprising a paperboard and films covering both sides thereof; wherein: The inner side of the paperboard is covered with a polylactic acid film, and the outer side is covered with a biodegradable composite film; the biodegradable composite film comprises a chitosan-based film close to the surface of the paperboard and a PVA-based composite film thereon, and is characterized in that: The main ingredients and 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 alcohol 3-6 Aldehyde eight-arm polyethylene glycol 3-8 The main ingredients and 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 alcohol 3-6 Boric acid 4.2-8.4 Aldehyde eight-arm polyethylene glycol 3-8.

2. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The modification degree of the quaternary ammonium salt modified chitosan is between 0.6 and 1.2, which is expressed by the number of substituted hydroxyl groups and amine groups in the unit molecular chain of chitosan.

3. The degradable composite material with high water vapor barrier and waterproof properties according to 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, which is between 1.8 and 2.

8.

4. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The surface-modified montmorillonite is obtained by surface-modifying the montmorillonite with a silane coupling agent, the mass dosage of the modifier is between 3% and 8% of the montmorillonite, and the particle size of the modified montmorillonite is between 30 and 300 μm.

5. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The molecular weight of the aldehyde eight-arm polyethylene glycol is between 2000 and 10000.

6. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The small molecule alcohol is one of ethylene glycol, propylene glycol and 1,2-butanediol.

7. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The biodegradable composite film coating process on the outer side of the paperboard is as follows: I: Surface treatment of paperboard: Prepare a weak acid solution with a mass concentration of 2-4%, spray it on the surface of the paperboard to be coated, maintain the temperature at 50-80℃, and dry it for 10-15 minutes until there is no obvious water film on the surface of the paperboard; II: Primary coating: Casting is performed on the treated paperboard surface. The casting liquid is an aqueous solution containing quaternary ammonium salt-modified chitosan, cellulose acetate propionate, surface-modified montmorillonite, small molecule alcohol, and aldehyde-based eight-arm polyethylene glycol. The mass concentration of the aqueous solution is between 6-12%, the casting temperature is between 40-60°C, and the casting speed is controlled at 30-60cm / min. III: Secondary coating: PVA is dissolved in 75-90℃ water to prepare an aqueous solution with a mass concentration between 6-12%, and then all sodium citrate, surface modified montmorillonite, small molecule alcohol, boric acid and aldehyde eight-arm polyethylene glycol are added to the solution, and stirred evenly to form coating liquid A. The coating liquid A is secondarily coated on the coated surface in II, and the casting is carried out at 30-50℃ on a casting machine. The casting speed is controlled between 20-40cm / min, and the final coated paperboard is obtained after the cast film is dried.

8. The degradable composite material with high water vapor barrier and waterproof properties according to claim 1, characterized in that: The paperboard is formed from pulp and has not been specially surface treated.

9. The degradable composite material with high water vapor barrier and waterproof properties according to 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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