Composite material for forming paper-plastic composite bags and preparation method thereof

Abstract

The present invention provides a composite material for forming paper-plastic composite bags and a preparation method thereof. The preparation method comprises: S100, preparing modified polypropylene carbonate; S200, using an aqueous polyurethane containing the modified polypropylene carbonate as a sizing agent to prepare a paper base layer; S300, using raw materials including the modified polypropylene carbonate and polybutylene terephthalate adipate to prepare a polymer layer; S400, hot-pressing the paper base layer and the polymer layer to obtain the composite material. In the composite material of the present invention, the paper base layer and the polymer layer are tightly bonded, resulting in higher mechanical strength, easy degradation, and environmental friendliness.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging materials, and in particular to a composite material for forming a paper-plastic composite bag and a preparation method thereof. Background Art

[0002] Paper-plastic composites are widely used in the packaging of food, cosmetics, and pharmaceuticals due to their excellent moisture-proof, oil-proof, and drop-resistant properties. For example, paper-plastic-aluminum composite packaging materials are widely used in the packaging of liquid dairy products, plant-based protein beverages, and other products. In the production of printed materials such as posters, leaflets, and labels, paper-plastic composites are highly favored due to their smooth surface and high gloss. In addition, paper-plastic composite notebook covers, folders, and file boxes are not only beautiful but also highly durable. In summary, paper-plastic composites are gradually being applied to various fields due to their unique performance and cost advantages, and are gaining popularity in the market.

[0003] In existing technologies, various lamination methods, including dry coating, wet coating, and hot melt lamination, can achieve the lamination of plastic and paper. However, paper-plastic composites still have the following shortcomings: How to improve the bonding strength between the paper-based material and the polymer material has always been a technical problem that those skilled in the art have been committed to solving. Summary of the Invention

[0004] One of the problems solved by the present invention is how to provide a composite material for forming a paper-plastic composite bag with a high degree of bonding between a paper-based material and a polymer material and a higher mechanical strength.

[0005] To solve at least one of the above problems, the present invention provides a method for preparing a composite material for forming a paper-plastic composite bag, the preparation method comprising:

[0006] S100, preparing modified polypropylene carbonate;

[0007] S200, using water-based polyurethane containing modified polypropylene carbonate as a sizing agent to prepare a paper base layer;

[0008] S300, preparing a polymer layer using raw materials including modified polypropylene carbonate and polybutylene terephthalate adipate;

[0009] S400, hot-pressing the paper base layer and the polymer layer to obtain a composite material.

[0010] In the above technical solution, S100 specifically includes:

[0011] S110, uniformly mixing an antioxidant, a first chain extender, maleic anhydride, a methacrylic acid monomer, and polypropylene carbonate to obtain a first mixture;

[0012] S120, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 h to 2.5 h, and then extruding and granulating the mixture to obtain modified polypropylene carbonate.

[0013] In any of the above technical solutions, in S110, the mass ratio of antioxidant: first chain extender: maleic anhydride: methacrylic acid monomer: polypropylene carbonate is (1-2): (2-4): (3-5): (15-20): 100.

[0014] In any of the above technical solutions, the antioxidant includes at least one of the following or a combination thereof: antioxidant 1010, antioxidant 1076, antioxidant 1098; and / or the first chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, BASF ADR-4380.

[0015] In any of the above technical solutions, S200 specifically includes:

[0016] S210, mixing dibutyltin dilaurate, polyester diol, and isophorone diisocyanate, reacting at a temperature of 80° C. to 85° C. for 3 to 4 hours, and then cooling to obtain a second mixture;

[0017] S220, mixing Tween 60, ethylenediamine, the second mixture, modified polypropylene carbonate, ethyl acetate and water and performing ultrasonic emulsification to obtain a sizing agent;

[0018] S230, 8g / m 2 Up to 12g / m 2 The sizing agent is applied to the base paper to obtain a paper base layer.

[0019] In any of the above technical solutions, in S210, the mass ratio of dibutyltin dilaurate: polyester diol: isophorone diisocyanate = (0.2-0.4): (80-120): 100; and / or in S220, the mass ratio of Tween 60: ethylenediamine: second mixture: modified polypropylene carbonate: ethyl acetate: water = (4-6): (4-6): (15-20): (10-15): (40-50): 100.

[0020] In any of the above technical solutions, S300 specifically includes:

[0021] S310, uniformly mixing the compatibilizer, the second chain extender, the modified polypropylene carbonate and the polybutylene terephthalate adipate to obtain a third mixture;

[0022] S320 , melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain a polymer layer.

[0023] In any of the above technical solutions, in S310, the mass ratio of compatibilizer:second chain extender:modified polypropylene carbonate:polybutylene terephthalate adipate is (1-2):(1-2):(50-60):100.

[0024] In any of the above technical solutions, the compatibilizer includes at least one of the following or a combination thereof: succinic anhydride, maleic anhydride, ethylene-methyl acrylate-glycidyl methacrylate; and / or the second chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, BASF ADR-4380.

[0025] The present invention also provides a composite material for forming a paper-plastic composite bag. The composite material is obtained by using the preparation method of any of the above technical solutions.

[0026] Beneficial effects

[0027] The present invention provides a method for preparing a composite material for forming paper-plastic composite bags. The method first prepares modified polypropylene carbonate, then uses an aqueous polyurethane containing the modified polypropylene carbonate as a sizing agent to prepare a paper base. Subsequently, a polymer layer is prepared using raw materials including the modified polypropylene carbonate and polybutylene terephthalate adipate. Finally, the paper base and polymer layer are hot-pressed to obtain the composite material. One improvement of the present invention over the prior art is that the paper-plastic composite material is prepared using polypropylene carbonate as the raw material. Polypropylene carbonate is a material produced by copolymerizing carbon dioxide and propylene oxide and has excellent biodegradability, making it more environmentally friendly. The paper used in the paper-plastic composite material requires sizing to improve its water resistance. Sizing agents typically used are rosin sizing or polyurethane, which have significant surface property differences from polypropylene carbonate, making effective sizing difficult. Even after heat and pressure sizing, the sizing agents tend to separate and flake. To address this issue, the present invention improves the sizing agent used in the paper-plastic composite material, considering the tightness of the composite between the polypropylene carbonate polymer and the paper base material. The invention uses waterborne polyurethane as a sizing agent and modifies the waterborne polyurethane sizing agent with polypropylene carbonate, so as to improve the composite tightness between the polypropylene carbonate polymer material and the paper base material, thereby making the mechanical strength of the product higher. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description of the specific embodiments of the present invention.

[0029] Unless otherwise specified, the reagents and raw materials used in the present invention can be purchased from commercial sources. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0030] An embodiment of the present invention provides a method for preparing a composite material for forming a paper-plastic composite bag, the method comprising:

[0031] S100, preparing modified polypropylene carbonate;

[0032] S200, using water-based polyurethane containing modified polypropylene carbonate as a sizing agent to prepare a paper base layer;

[0033] S300, preparing a polymer layer using raw materials including modified polypropylene carbonate and polybutylene terephthalate adipate;

[0034] S400, hot-pressing the paper base layer and the polymer layer to obtain a composite material.

[0035] Polypropylene carbonate (PPC), also known as poly(methyl ethylene carbonate), is a new aliphatic polyester made from carbon dioxide, propylene oxide, and / or 1,4-butanediol (BDO). It is a fully biodegradable, environmentally friendly plastic. The molecular structure of PPC contains numerous ester and carbonate bonds, which imparts its chemical stability and excellent biocompatibility. Its molecular structure can be linear, branched, or cyclic, with a molecular weight typically ranging from several thousand to several hundred thousand. Plastics made from PPC are transparent and non-toxic, making them suitable for applications such as food packaging and medical materials. They also exhibit excellent barrier properties, particularly in oxygen.

[0036] In order to obtain a composite material for forming a paper-plastic composite bag, the present invention first modifies polypropylene carbonate. The polypropylene carbonate of the present invention is obtained through commercial procurement, and the modification method is to graft the polypropylene carbonate with methacrylic acid monomer.

[0037] In order to modify polypropylene carbonate, S100 specifically includes:

[0038] S110, uniformly mixing an antioxidant, a first chain extender, maleic anhydride, a methacrylic acid monomer, and polypropylene carbonate to obtain a first mixture;

[0039] S120, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 h to 2.5 h, and then extruding and granulating the mixture to obtain modified polypropylene carbonate.

[0040] Specifically, in S110 , the mass ratio of antioxidant: first chain extender: maleic anhydride: methacrylic acid monomer: polypropylene carbonate is (1-2): (2-4): (3-5): (15-20): 100.

[0041] Preferably, in S110 , the mass ratio of the antioxidant: the first chain extender: maleic anhydride: methacrylic acid monomer: polypropylene carbonate is 1:3:5:15:100.

[0042] In some embodiments of the present invention, the antioxidant includes at least one of the following or a combination thereof: antioxidant 1010, antioxidant 1076, and antioxidant 1098.

[0043] In some embodiments of the present invention, the first chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, and BASF ADR-4380.

[0044] The reason for adopting the above steps is that, despite its excellent biocompatibility, polypropylene carbonate has poor thermal stability. During the extrusion molding process, polypropylene carbonate is prone to chain scission and degradation at high temperatures. This results in demanding processing conditions for polypropylene carbonate, and the low-temperature brittleness and weather resistance of the finished product are not ideal.

[0045] To address these issues, the present invention combines methacrylic acid monomers with poly(propylene carbonate) materials, using maleic anhydride as a compatibilizer. The abundant carboxyl groups in the methacrylic acid monomers react chemically with the terminal hydroxyl groups of the poly(propylene carbonate), thereby producing a poly(propylene carbonate) material containing ester bonds. The formation of these ester bonds suppresses chain scission degradation of the poly(propylene carbonate) material at high temperatures, thereby improving the thermal stability, processing properties, and weather resistance of the poly(propylene carbonate) material.

[0046] After the modified polypropylene carbonate is prepared, the present invention uses the waterborne polyurethane containing the modified polypropylene carbonate as a sizing agent to prepare a paper base layer.

[0047] In order to prepare the paper base layer, S200 specifically includes:

[0048] S210, mixing dibutyltin dilaurate, polyester diol, and isophorone diisocyanate, reacting at a temperature of 80° C. to 85° C. for 3 to 4 hours, and then cooling to obtain a second mixture;

[0049] S220, mixing Tween 60, ethylenediamine, the second mixture, modified polypropylene carbonate, ethyl acetate and water and performing ultrasonic emulsification to obtain a sizing agent;

[0050] S230, 8g / m 2 Up to 12g / m 2 The sizing agent is applied to the base paper to obtain a paper base layer.

[0051] Specifically, in S210 , the mass ratio of dibutyltin dilaurate:polyester diol:isophorone diisocyanate=(0.2-0.4):(80-120):100.

[0052] Preferably, in S210 , the mass ratio of dibutyltin dilaurate:polyester diol:isophorone diisocyanate is 0.2:80:100.

[0053] Specifically, in S220, the mass ratio of Tween 60:ethylenediamine:second mixture:modified polypropylene carbonate:ethyl acetate:water=(4-6):(4-6):(15-20):(10-15):(40-50):100.

[0054] Preferably, in S220 , the mass ratio of Tween 60:ethylenediamine:second mixture:modified polypropylene carbonate:ethyl acetate:water is 6:4:15:15:50:100.

[0055] It should be noted that, in the present invention, those skilled in the art may select the base paper to be sized, or adjust the corresponding preparation process to obtain the base paper according to actual needs.

[0056] Illustratively, the base paper of the present invention is prepared by the following process: mixing raw materials including a wet strength agent, aluminum sulfate, a filler, and wood pulp to obtain a pulp; applying the pulp to a web to form a wet paper sheet; and pressing and drying the wet paper sheet to obtain the base paper. The filler may be silica, kaolin, titanium dioxide, montmorillonite, or the like. The wood pulp may be bleached softwood or hardwood pulp.

[0057] Those skilled in the art can select and adjust the equipment, raw materials and process parameters used in pulping, papermaking and pressing according to actual needs. The base paper manufacturing is an existing technology and will not be described in detail in the present invention.

[0058] The purpose of sizing is to enhance the impermeability of paper-based finishing materials so that they can better resist the penetration of liquids such as water and grease, thereby keeping them dry and neat. In addition, the sizing agent can form a protective film on the surface of the paper-based finishing material, which helps prevent it from tearing and wrinkling, thereby improving the strength and stability of the paper. The present invention selects a surface sizing method for sizing, that is, a thin layer of sizing agent is sprayed on the surface of the paper-based finishing material to form a protective film on the surface of the base paper. The surface sizing process of the present invention is carried out on a papermaking machine. After the base paper is sizing with the sizing agent, the paper base layer can also be dried and calendered.

[0059] One of the improvements made by the present invention over the prior art is the use of modified polypropylene carbonate to formulate a sizing agent. The sizing agent of the present invention is a water-based polyurethane obtained by reacting a polyester diol with isophorone diisocyanate. Dibutyltin dilaurate serves as a catalyst to accelerate the reaction rate during polyurethane synthesis, shorten synthesis time, and improve production efficiency. After dibutyltin dilaurate, polyester diol, and isophorone diisocyanate are mixed and reacted at a temperature of 80°C to 85°C for a certain period of time, a second mixture, serving as a prepolymer, is obtained. Subsequently, this second mixture is mixed with ethylenediamine, which forms a nucleophilic addition product with the isocyanate and further participates in the polymerization reaction, thereby improving reaction efficiency. Tween 60 is used as an emulsifier, and modified polypropylene carbonate, ethyl acetate and water are mixed with the second mixture to obtain an aqueous polyurethane emulsion containing modified polypropylene carbonate. The aqueous polyurethane emulsion containing modified polypropylene carbonate is used as a sizing agent and applied to base paper, which not only improves the water resistance of the paper but also evenly applies the modified polypropylene carbonate on the surface of the base paper.

[0060] Preferably, S210 is performed under nitrogen protection. During the S210 reaction, stirring is performed at a rate of 200 to 400 rpm. In the later stage of the reaction, the mass fraction of -NCO groups can be measured using the di-n-butylamine method. When the mass fraction reaches 5% to 6% of the theoretical value, the prepolymerization is completed to obtain the second mixture serving as the prepolymer.

[0061] Preferably, S220 is performed at a temperature of 35° C. to 40° C., and stirring is performed at a rate of 200 rpm to 400 rpm during the reaction in S220. In S220, Tween 60, modified polypropylene carbonate, and ethyl acetate are first mixed, and then ethylenediamine, the second mixture, and water are added, and further mixing is performed, and ultrasonic emulsification is performed to achieve uniformity.

[0062] In order to prepare the polymer layer, S300 specifically includes:

[0063] S310, uniformly mixing the compatibilizer, the second chain extender, the modified polypropylene carbonate and the polybutylene terephthalate adipate to obtain a third mixture;

[0064] S320 , melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain a polymer layer.

[0065] In S310 , the mass ratio of compatibilizer:second chain extender:modified polypropylene carbonate:polybutylene terephthalate adipate is (1-2):(1-2):(50-60):100.

[0066] Preferably, in S310 , the mass ratio of the compatibilizer: the second chain extender: the modified polypropylene carbonate: the polybutylene terephthalate adipate is 1:2:50:100.

[0067] Preferably, the compatibilizer includes at least one of the following or a combination thereof: succinic anhydride, maleic anhydride, and ethylene-methyl acrylate-glycidyl methacrylate.

[0068] Preferably, the second chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, BASF ADR-4380.

[0069] In S320, melt extrusion can be performed using a twin-screw extruder. The length-to-diameter ratio of the twin-screw extruder is 36:1, and the speed of the twin-screw extruder is 200 rpm to 300 rpm. Preferably, the process temperature of each section of the twin-screw extruder is: zone 1 is 150°C to 155°C, zone 2 is 155°C to 160°C, zone 3 is 160°C to 165°C, and zone 4 is 165°C to 170°C.

[0070] In S400, a hot press is used to hot-press the paper base layer and the polymer layer at a temperature of 120° C. to 130° C. to obtain a composite material.

[0071] Example 1

[0072] This embodiment provides a composite material for forming a paper-plastic composite bag, and the preparation method thereof is as follows:

[0073] S1. Mixing antioxidant 1010, BASF ADR-4370, maleic anhydride, methacrylic acid monomer, and polypropylene carbonate in a mass ratio of antioxidant 1010: BASF ADR-4370: maleic anhydride: methacrylic acid monomer: polypropylene carbonate = 1:3:5:15:100 to obtain a first mixture;

[0074] S2, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 hours, and then extruding and granulating the mixture to obtain modified polypropylene carbonate;

[0075] S3. Dibutyltin dilaurate, polyester diol, and isophorone diisocyanate are mixed in a mass ratio of dibutyltin dilaurate: polyester diol: isophorone diisocyanate = 0.2:80:100, and reacted at 80° C. for 3 h and then cooled to obtain a second mixture;

[0076] S4. According to the mass ratio of Tween 60: ethylenediamine: second mixture: modified polypropylene carbonate: ethyl acetate: water = 6:4:15:15:50:100, Tween 60, ethylenediamine, second mixture, modified polypropylene carbonate, ethyl acetate and water are mixed and ultrasonically emulsified to obtain a sizing agent;

[0077] S5, 8g / m 2 The sizing agent is applied to the base paper to obtain a paper base layer;

[0078] S6. Succinic anhydride, BASF ADR-4370, modified polypropylene carbonate, and polybutylene terephthalate adipate are uniformly mixed in a mass ratio of succinic anhydride: BASF ADR-4370: modified polypropylene carbonate: polybutylene terephthalate adipate = 1:2:50:100 to obtain a third mixture;

[0079] S7, melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain a polymer layer;

[0080] S8. Using a hot press, hot press the paper base layer and the polymer layer at a temperature of 125±2° C. to obtain a composite material.

[0081] Example 2

[0082] This embodiment provides a composite material for forming a paper-plastic composite bag, and the preparation method thereof is as follows:

[0083] S1. Mixing antioxidant 1010, BASF ADR-4370, maleic anhydride, methacrylic acid monomer, and polypropylene carbonate in a mass ratio of 2:2:3:20:100 to obtain a first mixture.

[0084] S2, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 hours, and then extruding and granulating the mixture to obtain modified polypropylene carbonate;

[0085] S3. Dibutyltin dilaurate, polyester diol, and isophorone diisocyanate are mixed in a mass ratio of dibutyltin dilaurate: polyester diol: isophorone diisocyanate = 0.4:100:100, and reacted at 80° C. for 3 h and then cooled to obtain a second mixture;

[0086] S4. According to the mass ratio of Tween 60: ethylenediamine: second mixture: modified polypropylene carbonate: ethyl acetate: water = 4:6:20:10:40:100, Tween 60, ethylenediamine, second mixture, modified polypropylene carbonate, ethyl acetate and water are mixed and ultrasonically emulsified to obtain a sizing agent;

[0087] S5, 10g / m 2 The sizing agent is applied to the base paper to obtain a paper base layer;

[0088] S6. Succinic anhydride, BASF ADR-4370, modified polypropylene carbonate, and polybutylene terephthalate adipate are uniformly mixed in a mass ratio of succinic anhydride: BASF ADR-4370: modified polypropylene carbonate: polybutylene terephthalate adipate = 1:1:60:100 to obtain a third mixture;

[0089] S7, melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain a polymer layer;

[0090] S8. Using a hot press, hot press the paper base layer and the polymer layer at a temperature of 125±2° C. to obtain a composite material.

[0091] Comparative Example 1

[0092] This comparative example provides a composite material for forming a paper-plastic composite bag, and its preparation method is as follows:

[0093] S1. Mixing antioxidant 1010, BASF ADR-4370, maleic anhydride, methacrylic acid monomer, and polypropylene carbonate in a mass ratio of antioxidant 1010: BASF ADR-4370: maleic anhydride: methacrylic acid monomer: polypropylene carbonate = 1:3:5:15:100 to obtain a first mixture;

[0094] S2, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 hours, and then extruding and granulating the mixture to obtain modified polypropylene carbonate;

[0095] S3. Succinic anhydride, BASF ADR-4370, modified polypropylene carbonate, and polybutylene terephthalate adipate are uniformly mixed in a mass ratio of succinic anhydride: BASF ADR-4370: modified polypropylene carbonate: polybutylene terephthalate adipate = 1:2:50:100 to obtain a third mixture;

[0096] S4, melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain a polymer layer;

[0097] S5. Using a hot press, hot-press the paper base layer and the polymer layer at a temperature of 125±2° C. to obtain a composite material, wherein the paper base layer is purchased through commercial channels.

[0098] Performance Testing

[0099] First, the samples obtained in Example 1, Example 2 and Comparative Example 1 were subjected to artificial accelerated aging at 365 nm and 20 W / m 2 The samples obtained in Example 1, Example 2, and Comparative Example 1 were irradiated with an ultraviolet light source at a temperature of 60° C. and a humidity of 80 RH for 10 days. After artificial accelerated aging, the physical and chemical properties of the samples were tested. The specific data are shown in Table 1.

[0100] Table 1

[0101] Serial number Example 1 Example 2 Comparative Example 1 Elongation at break 178.2％ 172.5％ 153.6％ tensile strength 11.4MPa 10.8MPa 8.6MPa

[0102] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for preparing a composite material for forming a paper-plastic composite bag, characterized in that: The preparation method comprises: S100, preparing modified polypropylene carbonate; S200, using the aqueous polyurethane containing the modified polypropylene carbonate as a sizing agent to prepare a paper base layer; S300, preparing a polymer layer using raw materials including the modified polypropylene carbonate and polybutylene terephthalate adipate; S400, hot-pressing the paper base layer and the polymer layer to obtain the composite material; S100 specifically includes: S110, uniformly mixing an antioxidant, a first chain extender, maleic anhydride, a methacrylic acid monomer, and polypropylene carbonate to obtain a first mixture; S120, kneading the first mixture at a temperature of 170° C. to 175° C. for 2 h to 2.5 h, and then extruding and granulating the mixture to obtain the modified polypropylene carbonate.

2. The preparation method according to claim 1, characterized in that In S110, the mass ratio of antioxidant: first chain extender: maleic anhydride: methacrylic acid monomer: polypropylene carbonate is (1-2): (2-4): (3-5): (15-20):

100.

3. The preparation method according to claim 1, characterized in that The antioxidant comprises at least one of the following or a combination thereof: antioxidant 1010, antioxidant 1076, antioxidant 1098; and / or The first chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, and BASF ADR-4380.

4. The preparation method according to any one of claims 1 to 3, characterized in that S200 specifically includes: S210, mixing dibutyltin dilaurate, polyester diol, and isophorone diisocyanate, reacting at a temperature of 80° C. to 85° C. for 3 to 4 hours, and then cooling to obtain a second mixture; S220, mixing Tween 60, ethylenediamine, the second mixture, the modified polypropylene carbonate, ethyl acetate and water and performing ultrasonic emulsification to obtain the sizing agent; S230, 8g / m 2 Up to 12g / m 2 The sizing agent is applied to the base paper to obtain the paper base layer.

5. The preparation method according to claim 4, characterized in that In S210, the mass ratio of dibutyltin dilaurate: polyester diol: isophorone diisocyanate = (0.2-0.4): (80-120): 100; and / or In S220, the mass ratio of Tween 60:ethylenediamine:second mixture:modified polypropylene carbonate:ethyl acetate:water is (4-6):(4-6):(15-20):(10-15):(40-50):

100.

6. The preparation method according to claim 4, characterized in that S300 specifically includes: S310, uniformly mixing the compatibilizer, the second chain extender, the modified polypropylene carbonate and the polybutylene terephthalate adipate to obtain a third mixture; S320 , melt-extrude the third mixture at a temperature of 150° C. to 170° C. to obtain the polymer layer.

7. The preparation method according to claim 6, characterized in that In S310 , the mass ratio of compatibilizer:second chain extender:modified polypropylene carbonate:polybutylene terephthalate adipate is (1-2):(1-2):(50-60):

100.

8. The preparation method according to claim 6, characterized in that The compatibilizer includes at least one of the following or a combination thereof: succinic anhydride, maleic anhydride, ethylene-methyl acrylate-glycidyl methacrylate; and / or The second chain extender includes at least one of the following or a combination thereof: BASF ADR-4370, BASF ADR-4368, and BASF ADR-4380.

9. A composite material for forming a paper-plastic composite bag, characterized in that: The composite material is obtained by the preparation method according to any one of claims 1 to 8.