A polypropylene carbonate-based composite film and a method for preparing the same

Abstract

The application discloses a polypropylene carbonate-based composite film and a preparation method thereof, and belongs to the field of packaging film material preparation. The polypropylene carbonate-based composite film prepared by the application comprises a PBAT heat-sealing layer, a modified PPC layer and a PLA layer, the PBAT heat-sealing layer and the modified PPC layer are bonded through a first bonding layer, and the modified PPC layer and the PLA layer are bonded through a second bonding layer. The preparation raw materials and the preparation raw material ratio of the PBAT heat-sealing layer, the first bonding layer, the modified PPC layer, the second bonding layer and the PLA layer are optimized, so that the compatibility between the raw materials is increased, the whole exhibits excellent high barrier property, thermal stability and mechanical property, the composite film can be biodegraded, is better applied in the field of environment-friendly functional packaging materials, and meets the market use demand.

Description

Technical Field

[0001] This invention relates to the field of packaging film material preparation, and more specifically, to a composite film based on polypropylene carbonate and its preparation method. Background Technology

[0002] With the continuous improvement of living standards and the acceleration of the pace of life, the market demand for barrier membrane materials is increasing. However, most membrane materials are currently non-degradable, and their use and disposal can easily cause environmental pollution. In order to reduce the damage of non-degradable membrane materials to the environment, it is particularly important to develop degradable membrane materials.

[0003] Polylactic acid (PLA) and polycarbonate lactone (PPC) are commonly used as biodegradable materials. PLA possesses excellent optical transparency and mechanical strength, but its poor toughness and barrier properties limit its applications. PPC is an alternating copolymer of carbon dioxide and propylene oxide. However, the presence of ether bonds in the PPC backbone makes the chain segments prone to internal rotation around these bonds, increasing chain flexibility. The highly polar carbonyl groups increase intermolecular forces. Furthermore, the end groups of PPC affect the material's thermal stability. Since the end groups are hydroxyl groups, their presence at high temperatures can cause ester alcoholysis, resulting in a "zipper-like" degradation, thus leading to poor thermal stability in single-layer PPC film products.

[0004] Existing technologies also employ polymer blending methods, blending two or more homopolymers or copolymers to obtain polymer blends. After mixing and dispersing different polymer materials, the mechanical properties and thermal stability of PPC materials are altered. For example, existing technologies use PPC-P, PBAT, and PLA materials to create composite films, which are then cast to produce films with some biodegradability, but with poor overall barrier properties. For instance, Chinese patent application CN202310756023.4 discloses a PPC-P biodegradable flexible film material, mainly composed of the following raw materials: PPCP, PBAT, and PLA, primary antioxidant, secondary antioxidant, opening agent, anti-hydrolysis agent, UV stabilizer, chain extender, plasticizer, and compatibilizer. The film is modified by PBAT and PLA and additives to make PPC-P have good ductility and elongation at break, as well as good heat resistance and impact resistance, and excellent air and moisture permeability. However, the effect of PBAT and PLA blend modification is limited and cannot simultaneously guarantee the thermal stability, barrier properties and mechanical strength of the prepared film, thus limiting its application. Summary of the Invention

[0005] Therefore, in order to solve the problems of poor thermal stability, barrier properties, and mechanical strength of composite films prepared by existing technologies, this invention provides a composite film based on polypropylene carbonate and its preparation method, the specific technical solution of which is as follows:

[0006] A composite film based on polypropylene carbonate, the composite film based on polypropylene carbonate includes a PBAT heat-sealing layer, a modified PPC layer and a PLA layer, wherein the PBAT heat-sealing layer and the modified PPC layer are bonded together by a first adhesive layer, and the modified PPC layer and the PLA layer are bonded together by a second adhesive layer.

[0007] The PBAT heat-sealing layer comprises the following raw materials in parts by weight: 100-110 parts PBAT, 7-12 parts heat stabilizer, 1-5 parts lubricant, and 5-15 parts antioxidant.

[0008] The modified PPC layer comprises the following raw materials in parts by weight: 100-120 parts PPC, 15-25 parts chain extender, 1-10 parts modified composite filler, and 1-7 parts plasticizer A.

[0009] The PLA layer comprises the following raw materials in parts by weight: 80-100 parts PLA, 10-15 parts ethylene-acrylic acid copolymer, 1-5 parts antioxidant, and 1-5 parts plasticizer B;

[0010] Both the first adhesive layer and the second adhesive layer comprise the following raw materials in parts by weight: 30 to 45 parts of polyvinyl alcohol, 25 to 35 parts of maleic anhydride-grafted ethylene polymer, and 1 to 5 parts of compatibilizer.

[0011] Furthermore, the heat stabilizer is prepared by mixing dioctyltin dilaurate and zinc stearate in a mass ratio of 1:(1-3).

[0012] Furthermore, the lubricant is at least one selected from stearic acid, aluminum stearate, calcium stearate, and zinc stearate.

[0013] Furthermore, the compatibilizer is at least one of PP-g-MAH and ethylene-methyl acrylate copolymer.

[0014] Furthermore, the chain extender is at least one selected from isocyanate-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and hexamethylene diisocyanate.

[0015] Furthermore, the modified composite filler is obtained by mixing calcium carbonate and lignin cellulose in a mass ratio of (1-5):1, and then modifying it with a silane coupling agent.

[0016] Furthermore, the plasticizer A is at least one of poly(1,2-propanediol succinate), glycerol, and pentaerythritol.

[0017] Furthermore, the antioxidant is one or a mixture of two of antioxidant 1076 and antioxidant 168.

[0018] Furthermore, the plasticizer B is at least one of tributyl citrate, acetylated triethyl citrate, and acetylated tributyl citrate.

[0019] In addition, the present invention also provides a method for preparing a composite film based on polypropylene carbonate, the preparation method comprising the following steps:

[0020] PBAT, heat stabilizer, lubricant and antioxidant are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 5 min to 10 min at 100℃ to 125℃ to obtain mixed raw material A for preparing PBAT heat seal layer;

[0021] Chain extender was added to PPC, heated to 120℃~130℃, and reacted for 20min~30min. Then chloroform was added and ethanol was used for precipitation to remove small molecules. Modified composite filler and plasticizer A were added in sequence, and the mixture was treated at 100℃~120℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material B for preparing modified PPC layer.

[0022] PLA, ethylene-acrylic acid copolymer, antioxidant and plasticizer B are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 15 min to 20 min at 100℃ to 125℃ to obtain mixed raw material C for preparing PLA layer;

[0023] Polyvinyl alcohol, maleic anhydride-grafted ethylene polymer and compatibilizer are added to a mixer and treated at 100℃~115℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer.

[0024] The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 85℃~180℃. After stepwise biaxial stretching and heat treatment, a composite film based on polypropylene carbonate is obtained.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention optimizes the raw materials and their proportions for preparing the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer, and the PLA layer, thereby increasing the compatibility between the raw materials. The composite film exhibits excellent high barrier properties, thermal stability, and mechanical properties, and is biodegradable, making it well-suited for use in the field of environmentally friendly functional packaging and meeting market demands.

[0027] 2. The present invention obtains a heat stabilizer by mixing dioctyltin dilaurate and zinc stearate in a mass ratio of 1:(1-3) and adding it to the PBAT heat-sealing layer. This not only helps to improve the overall performance of the composite film, but also improves the crystallization rate and ductility of the PBAT heat-sealing layer, which helps to improve the elongation at break of the composite film.

[0028] 3. This invention adds a chain extender to the modified PPC layer. After the chain extender reacts with PPC, the end-capping efficiency is high, the chemical action inhibits the unzipping degradation of PPC, and the thermal decomposition temperature is significantly increased. Furthermore, the addition of a highly compatible modified composite filler increases interfacial and hydrogen bonding interactions, improving the tensile strength and toughness of the composite film. The components also work synergistically to increase the gas passage path, thereby helping to improve the barrier performance.

[0029] 4. By adding a first adhesive layer and a second adhesive layer with specific components, the present invention can form a cross-linking effect with the adjacent interface during the melt extrusion process, resulting in strong interfacial bonding and helping to improve the mechanical properties and barrier properties of the composite film. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] An embodiment of the present invention provides a composite film based on polypropylene carbonate, the composite film based on polypropylene carbonate comprising a PBAT heat-sealing layer, a modified PPC layer and a PLA layer, wherein the PBAT heat-sealing layer and the modified PPC layer are bonded together by a first adhesive layer, and the modified PPC layer and the PLA layer are bonded together by a second adhesive layer.

[0033] The PBAT heat-sealing layer comprises the following raw materials in parts by weight: 100-110 parts PBAT, 7-12 parts heat stabilizer, 1-5 parts lubricant, and 5-15 parts antioxidant.

[0034] The modified PPC layer comprises the following raw materials in parts by weight: 100-120 parts PPC, 15-25 parts chain extender, 1-10 parts modified composite filler, and 1-7 parts plasticizer A.

[0035] The PLA layer comprises the following raw materials in parts by weight: 80-100 parts PLA, 10-15 parts ethylene-acrylic acid copolymer, 1-5 parts antioxidant, and 1-5 parts plasticizer B;

[0036] Both the first adhesive layer and the second adhesive layer comprise the following raw materials in parts by weight: 30 to 45 parts of polyvinyl alcohol, 25 to 35 parts of maleic anhydride-grafted ethylene polymer, and 1 to 5 parts of compatibilizer.

[0037] In one embodiment, the heat stabilizer is prepared by mixing dioctyltin dilaurate and zinc stearate in a mass ratio of 1:(1-3).

[0038] In one embodiment, the lubricant is at least one selected from stearic acid, aluminum stearate, calcium stearate, and zinc stearate.

[0039] In one embodiment, the compatibilizer is at least one of PP-g-MAH and ethylene-methyl acrylate copolymer.

[0040] In one embodiment, the chain extender is at least one selected from isocyanate-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and hexamethylene diisocyanate.

[0041] In one embodiment, the modified composite filler is obtained by mixing calcium carbonate and lignin cellulose in a mass ratio of (1-5):1, followed by modification with a silane coupling agent.

[0042] In one embodiment, the modification treatment is as follows: calcium carbonate and lignocellulose are mixed and ball-milled, and then a silane coupling agent is added at a ratio of 1g / 10mL, and the mixture is stirred at 65℃~75℃ for 30min~60min.

[0043] In one embodiment, the plasticizer A is at least one of poly(1,2-propanediol succinate), glycerol, and pentaerythritol.

[0044] In one embodiment, the antioxidant is one or a mixture of two of antioxidant 1076 and antioxidant 168.

[0045] In one embodiment, the plasticizer B is at least one of tributyl citrate, acetylated triethyl citrate, and acetylated tributyl citrate.

[0046] In addition, the present invention also provides a method for preparing a composite film based on polypropylene carbonate, the preparation method comprising the following steps:

[0047] PBAT, heat stabilizer, lubricant and antioxidant are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 5 min to 10 min at 100℃ to 125℃ to obtain mixed raw material A for preparing PBAT heat seal layer;

[0048] Chain extender was added to PPC, heated to 120℃~130℃, and reacted for 20min~30min. Then chloroform was added and ethanol was used for precipitation to remove small molecules. Modified composite filler and plasticizer A were added in sequence, and the mixture was treated at 100℃~120℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material B for preparing modified PPC layer.

[0049] PLA, ethylene-acrylic acid copolymer, antioxidant and plasticizer B are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 15 min to 20 min at 100℃ to 125℃ to obtain mixed raw material C for preparing PLA layer;

[0050] Polyvinyl alcohol, maleic anhydride-grafted ethylene polymer and compatibilizer are added to a mixer and treated at 100℃~115℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer.

[0051] The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 85℃~180℃. After stepwise biaxial stretching and heat treatment, a composite film based on polypropylene carbonate is obtained.

[0052] In one embodiment, the heat treatment temperature is 90°C to 135°C.

[0053] The above solution optimizes the raw materials and their proportions for the preparation of the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer, and the PLA layer, thereby increasing the compatibility between the raw materials. The composite film exhibits excellent high barrier properties, thermal stability, and mechanical properties, and is biodegradable, making it well-suited for application in the field of environmentally friendly functional packaging.

[0054] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0055] Example 1:

[0056] A method for preparing a composite film based on polypropylene carbonate, the method comprising the following steps:

[0057] According to the weight ratio, 100 parts of PBAT, 8 parts of heat stabilizer (dioctyltin dilaurate and zinc stearate in a mass ratio of 1:3), 3 parts of stearic acid and 5 parts of antioxidant 1076 were added to the mixer in sequence and treated at 150 r / min for 10 min at 100℃ to obtain mixed raw material A for preparing PBAT heat seal layer;

[0058] By weight ratio, 20 parts of isocyanate-maleic anhydride copolymer were added to 100 parts of PPC, heated to 120°C, and reacted for 30 min. Then, chloroform was added and ethanol was used for precipitation to remove small molecules. Next, 7 parts of modified composite filler and 5 parts of poly(1,2-propanediol succinate) were added sequentially, and the mixture was treated at 105°C with a stirring speed of 150 r / min for 15 min to obtain mixed raw material B for preparing the modified PPC layer. In this embodiment, the modified composite filler was obtained by ball milling calcium carbonate and lignin cellulose at a mass ratio of 3:1, adding silane coupling agent at a material-to-liquid ratio of 1 g / 10 mL, and modifying the mixture at 65°C for 30 min.

[0059] According to the weight ratio, 100 parts of PLA, 15 parts of ethylene-acrylic acid copolymer, 3 parts of antioxidant 168 and 5 parts of tributyl citrate were added to the mixer in sequence and treated at 150 r / min for 15 min at 100℃ to obtain mixed raw material C for preparing PLA layer.

[0060] According to the weight ratio, 40 parts of polyvinyl alcohol, 30 parts of maleic anhydride grafted ethylene polymer and 3 parts of ethylene-methyl acrylate copolymer were added to a mixer and treated at 150 r / min for 15 min at 100°C to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer.

[0061] The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer, and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 120℃. After stepwise biaxial stretching and heat treatment at 95℃, a composite film based on polypropylene carbonate is obtained.

[0062] Example 2:

[0063] A method for preparing a composite film based on polypropylene carbonate, the method comprising the following steps:

[0064] According to the weight ratio, 100 parts of PBAT, 8 parts of heat stabilizer (dioctyltin dilaurate and zinc stearate in a mass ratio of 1:3), 3 parts of aluminum stearate and 10 parts of antioxidant 1076 were added to the mixer in sequence and treated at 110°C and a stirring speed of 150 r / min for 10 min to obtain mixed raw material A for preparing PBAT heat seal layer;

[0065] By weight ratio, 25 parts of styrene-maleic anhydride copolymer were added to 100 parts of PPC, heated to 125°C, and reacted for 25 min. Then, chloroform was added and ethanol was used for precipitation to remove small molecules. Next, 8 parts of modified composite filler and 4 parts of glycerol were added sequentially. The modified composite filler was obtained by ball milling calcium carbonate and lignin cellulose at a mass ratio of 3:1, adding silane coupling agent at a material-to-liquid ratio of 1 g / 10 mL, and stirring at 70°C for 45 min. The mixture was then stirred at 150 r / min at 100°C for 15 min to obtain mixed raw material B for preparing the modified PPC layer.

[0066] According to the weight ratio, 100 parts of PLA, 12 parts of ethylene-acrylic acid copolymer, 3 parts of antioxidant 168 and 5 parts of triethyl acetyl citrate were added to the mixer in sequence and treated at 115°C and 150 r / min for 20 min to obtain mixed raw material C for preparing PLA layer.

[0067] According to the weight ratio, 42 parts of polyvinyl alcohol, 30 parts of maleic anhydride grafted ethylene polymer and 5 parts of PP-g-MAH were added to a mixer and treated at 105°C and a stirring speed of 150 r / min for 15 min to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer.

[0068] The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 120℃. After stepwise biaxial stretching and heat treatment at 90℃~100℃, a composite film based on polypropylene carbonate is obtained.

[0069] Example 3:

[0070] A method for preparing a composite film based on polypropylene carbonate, the method comprising the following steps:

[0071] According to the weight ratio, 100 parts of PBAT, 12 parts of heat stabilizer (dioctyltin dilaurate and zinc stearate in a mass ratio of 1:3), 5 parts of calcium stearate and 7 parts of antioxidant 1076 were added to the mixer in sequence and treated at 125°C and a stirring speed of 150 r / min for 10 min to obtain mixed raw material A for preparing PBAT heat seal layer;

[0072] By weight ratio, 25 parts of isocyanate-maleic anhydride copolymer were added to 100 parts of PPC, heated to 120°C, and reacted for 30 min. Then, chloroform was added and ethanol was used for precipitation to remove small molecules. Next, 9 parts of modified composite filler and 5 parts of poly(1,2-propanediol succinate) were added sequentially. The modified composite filler was obtained by ball milling calcium carbonate and lignin cellulose at a mass ratio of 3:1, adding silane coupling agent at a material-to-liquid ratio of 1 g / 10 mL, and stirring at 70°C for 45 min. The mixture was then stirred at 150 r / min at 120°C for 20 min to obtain mixed raw material B for preparing the modified PPC layer.

[0073] According to the weight ratio, 100 parts of PLA, 12 parts of ethylene-acrylic acid copolymer, 4 parts of antioxidant 168 and 5 parts of acetylated tributyl citrate were added to the mixer in sequence and treated at 120°C and 150 r / min for 20 min to obtain mixed raw material C for preparing PLA layer.

[0074] According to the weight ratio, 45 parts of polyvinyl alcohol, 35 parts of maleic anhydride grafted ethylene polymer and 5 parts of ethylene-methyl acrylate copolymer were added to a mixer and treated at 110°C and a stirring speed of 150 r / min for 15 min to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer.

[0075] The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer, and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 120℃. After stepwise biaxial stretching and heat treatment at 95℃, a composite film based on polypropylene carbonate is obtained.

[0076] Comparative Example 1:

[0077] The difference between Comparative Example 1 and Example 3 is that no heat stabilizer was added in Comparative Example 1, while the rest is the same as in Example 3.

[0078] Comparative Example 2:

[0079] The difference between Comparative Example 2 and Example 3 is that no isocyanate-maleic anhydride copolymer (chain extender) was added in Comparative Example 2, while the rest was the same as in Example 3.

[0080] Comparative Example 3:

[0081] The difference between Comparative Example 3 and Example 3 is that no modified filler was added in Comparative Example 3, while the rest is the same as Example 3.

[0082] Comparative Example 4:

[0083] The difference between Comparative Example 4 and Example 3 is that Comparative Example 4 includes a composite filler (calcium carbonate and lignin cellulose ball-milled and mixed in a mass ratio of 3:1), meaning the composite filler was not modified. Otherwise, it is the same as Example 3.

[0084] Comparative Example 5:

[0085] The difference between Comparative Example 5 and Example 3 is that Comparative Example 5 added only calcium carbonate, that is, lignin cellulose was not added, while the rest was the same as Example 3.

[0086] Comparative Example 6:

[0087] The difference between Comparative Example 6 and Example 3 is that Comparative Example 6 contains a single lignin fiber, i.e., calcium carbonate is not added, while the rest is the same as Example 3.

[0088] Comparative Example 7:

[0089] The difference between Comparative Example 7 and Example 3 is that epoxy resin was used as the raw material for preparing the first adhesive layer and the second adhesive layer in Comparative Example 7, while the rest is the same as in Example 3.

[0090] Comparative Example 8:

[0091] The difference between Comparative Example 8 and Example 3 is that in Comparative Example 8, all the raw materials were added to a mixer in sequence and stirred at 150 r / min for 20 min at 120°C. Then, the mixture was melt-cast to obtain a single-layer composite film.

[0092] The composite membrane samples prepared in Examples 1-3 and the comparative composite membrane samples prepared in Comparative Examples 1-8 were subjected to performance tests. Mechanical properties were tested according to GB / T1040.3; heat sealing strength was tested according to GB / T10004-2008; moisture permeability was tested according to GB1037 "Test Method for Water Vapor Permeability of Plastic Films and Sheets - Cup Method", using a W3 / 031 water vapor transmission rate tester for 24 hours at a test pressure of 0.1 MPa; air permeability was tested according to GB1038 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method", using a Classic2016 differential pressure gas permeameter for 24 hours; and heat shrinkage was tested according to STMD1204 standard at a test temperature of 150℃ for 30 minutes. The results are shown in Tables 1 and 2 below.

[0093] Table 1: Performance Test Results

[0094]

[0095]

[0096] As can be seen from the data analysis in Table 1, by optimizing the composition and process of the composite membrane, the present invention can ensure the mechanical properties of the composite membrane, thus meeting the application requirements.

[0097] Table 2: Performance Test Results

[0098]

[0099] Analysis of the data in Table 2 shows that the composite film prepared in this application exhibits excellent heat-sealing strength and thermal stability, and demonstrates superior barrier properties. The difference between Comparative Example 1 and Example 3 is that no heat stabilizer was added in Comparative Example 1. While the heat-sealing strength and barrier properties were good, they were still inferior to those of Example 3, and the thermal stability was significantly worse. This indicates that the addition of a heat stabilizer helps improve the overall thermal stability of the composite film. The difference between Comparative Example 2 and Example 3 is that no isocyanate-maleic anhydride copolymer (chain extender) was added in Comparative Example 2. The heat-sealing strength and barrier properties were significantly worse than those of Example 3, and the thermal stability was also worse. This indicates that the addition of isocyanate-maleic anhydride copolymer (chain extender) helps improve the crosslinking of the composite film and enhance its overall performance. The interaction between the components of the membrane promotes its barrier properties. The difference between Comparative Examples 3-6 and Example 3 lies in the use of modified composite fillers. It can be seen that the addition of modified composite fillers also has a synergistic effect, promoting the mechanical and barrier properties of the composite membrane. The difference between Comparative Example 7 and Example 3 is that epoxy resin was used as the raw material for preparing the first and second adhesive layers in Comparative Example 7. It can be seen that the heat-sealing strength of the composite membrane decreased significantly, and the barrier properties also deteriorated significantly, indicating that the raw materials for preparing the first and second adhesive layers also significantly promote the barrier properties of the composite membrane. In Comparative Example 8, the raw materials of this application were sequentially added to a mixer for melt casting to obtain a single-layer membrane. However, its barrier properties were worse than those of the multi-layer composite membrane in Example 3, indicating that this application has also optimized the structure of the composite membrane. Under the condition of component interaction, the interaction of different membrane layer structures further promotes the barrier properties of the composite membrane, making it more suitable for market use.

[0100] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0101] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite film based on polypropylene carbonate, characterized in that, The polypropylene carbonate-based composite film includes a PBAT heat-sealing layer, a modified PPC layer, and a PLA layer, wherein the PBAT heat-sealing layer and the modified PPC layer are bonded together by a first adhesive layer, and the modified PPC layer and the PLA layer are bonded together by a second adhesive layer. The PBAT heat-sealing layer comprises the following raw materials in parts by weight: 100-110 parts PBAT, 7-12 parts heat stabilizer, 1-5 parts lubricant, and 5-15 parts antioxidant. The modified PPC layer comprises the following raw materials in parts by weight: 100-120 parts PPC, 15-25 parts chain extender, 1-10 parts modified composite filler, and 1-7 parts plasticizer A; The heat stabilizer is prepared by mixing dioctyltin dilaurate and zinc stearate in a mass ratio of 1:(1~3); The chain extender is at least one of isocyanate-maleic anhydride copolymer, styrene-maleic anhydride copolymer and hexamethylene diisocyanate; The modified composite filler is prepared by mixing calcium carbonate and lignin cellulose in a mass ratio of (1~5):1 and ball milling them, then adding silane coupling agent at a material-to-liquid ratio of 1g / 10mL, and stirring at 65℃~75℃ for 30min~60min. The PLA layer comprises the following raw materials in parts by weight: 80-100 parts PLA, 10-15 parts ethylene-acrylic acid copolymer, 1-5 parts antioxidant, and 1-5 parts plasticizer B; Both the first adhesive layer and the second adhesive layer comprise the following raw materials in parts by weight: 30 to 45 parts of polyvinyl alcohol, 25 to 35 parts of maleic anhydride-grafted ethylene polymer, and 1 to 5 parts of compatibilizer.

2. The composite membrane based on polypropylene carbonate according to claim 1, characterized in that, The lubricant is at least one of stearic acid, aluminum stearate, calcium stearate, and zinc stearate.

3. The composite membrane based on polypropylene carbonate according to claim 1, characterized in that, The compatibilizer is at least one of PP-g-MAH and ethylene-methyl acrylate copolymer.

4. The composite membrane based on polypropylene carbonate according to claim 1, characterized in that, The plasticizer A is at least one of poly(1,2-propanediol succinate), glycerol, and pentaerythritol.

5. The composite membrane based on polypropylene carbonate according to claim 1, characterized in that, The antioxidant is one or a mixture of two of antioxidants 1076 and antioxidant 168.

6. The composite membrane based on polypropylene carbonate according to claim 1, characterized in that, The plasticizer B is at least one of tributyl citrate, acetylated triethyl citrate, and acetylated tributyl citrate.

7. A method for preparing a composite film based on polypropylene carbonate, characterized in that, The preparation method is used to prepare the polypropylene carbonate-based composite film as described in any one of claims 1 to 6, and the preparation method includes the following steps: PBAT, heat stabilizer, lubricant and antioxidant are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 5 min to 10 min at 100℃ to 125℃ to obtain mixed raw material A for preparing PBAT heat seal layer; Chain extender was added to PPC, heated to 120℃~130℃, and reacted for 20min~30min. Then chloroform was added and ethanol was used for precipitation to remove small molecules. Modified composite filler and plasticizer A were added in sequence, and the mixture was treated at 100℃~120℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material B for preparing modified PPC layer. PLA, ethylene-acrylic acid copolymer, antioxidant and plasticizer B are added to a mixer in sequence and treated at 150 r / min to 200 r / min for 15 min to 20 min at 100℃ to 125℃ to obtain mixed raw material C for preparing PLA layer; Polyvinyl alcohol, maleic anhydride-grafted ethylene polymer and compatibilizer are added to a mixer and treated at 100℃~115℃ with a stirring speed of 150r / min~200r / min for 10min~20min to obtain mixed raw material D for preparing the first adhesive layer and the second adhesive layer. The mixed raw materials corresponding to the PBAT heat-sealing layer, the first adhesive layer, the modified PPC layer, the second adhesive layer, and the PLA layer are heated and melted in an extruder, and then extruded and cast through a T-die. The extrusion temperature is set to 85℃~180℃. After stepwise biaxial stretching and heat treatment, a composite film based on polypropylene carbonate is obtained.

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