Fully biodegradable composite film and method for preparing the same

Abstract

Provided are a fully biodegradable composite film and a preparation method thereof. The fully biodegradable composite film comprises three parts of an outer layer, a middle layer and an inner layer, the outer layer comprising modified calcium carbonate, PLA, PBAT and an epoxy chain extender; the middle layer comprising modified montmorillonite, PLA, PBAT, PPC and an epoxy chain extender; and the inner layer comprising PLA, PBAT, an epoxy chain extender and an optional opening agent. The preparation method of the raw material of the middle layer comprises: (i) dividing the epoxy chain extender used in the middle layer into two parts of epoxy chain extender A and epoxy chain extender B, mixing PPC, modified montmorillonite and epoxy chain extender A to obtain a first master batch of the middle layer; (ii) mixing PLA, PBAT and epoxy chain extender B to obtain a second master batch of the middle layer; and (iii) uniformly mixing the first master batch of the middle layer and the second master batch of the middle layer, and extruding and granulating to obtain the raw material of the middle layer. The fully biodegradable composite film prepared by the method has good uniformity and quality.

Description

Technical Field

[0001] This invention belongs to the field of packaging film, specifically relating to a fully biodegradable composite film and its preparation method. Background Technology

[0002] With economic development and improved living standards, people have increasingly higher demands for goods, leading to rapid development in packaging materials, particularly demanding enhanced barrier properties. Packaging for food, pharmaceuticals, and high-tech precision instruments requires materials with good gas and moisture barrier properties. The permeation of oxygen and water vapor can affect the shelf life or usability of the product, shortening its lifespan. Furthermore, leakage can contaminate and corrode shelves, impacting consumer demand. This is especially critical in the food and pharmaceutical industries, where the entry of oxygen and water vapor poses a fatal threat to product quality and harms human health. While commonly used synthetic polymers in barrier packaging, such as polyethylene, polypropylene plastics, EVOH resin series barrier films, active barrier films, and PET bottles, offer good barrier properties against water vapor and moisture, the resulting plastic waste creates significant environmental problems alongside the convenience of these products. Therefore, developing green, healthy, sustainable, widely available, and highly biodegradable composite materials with excellent gas barrier properties is of great significance and holds immense promise.

[0003] Biodegradable plastics have achieved industrial-scale production in my country, with polylactic acid (PLA), polybutylene adipate / terephthalate (PBAT), and polypropylene carbonate (PPC) holding the largest market share. PLA has high tensile strength and elastic modulus, but it is brittle and lacks toughness, has unstable high-temperature mechanical properties, is highly sensitive to temperature changes, and has a narrow processing range. PBAT has good mechanical properties and toughness, high processing performance, and high thermal stability, but low strength. PPC has certain gas barrier properties; however, its amorphous structure, high molecular chain flexibility, and weak interaction forces result in poor thermal properties, leading to poor high-temperature dimensional stability and high brittleness at low temperatures. Therefore, its large-scale application has not yet achieved a breakthrough.

[0004] Currently, to meet various quality standards for biodegradable plastic shopping bags, film blow molding is typically performed using a blend of multiple materials. However, during the blow molding process, it has been found that the compatibility between biodegradable materials is poor, making continuous blow molding difficult. Compatibilizers are generally added to improve the compatibility and mechanical strength of the raw materials. While there are some research and applications of fully biodegradable packaging bags, compared to traditional plastic bags, they still have significant shortcomings in terms of high strength, high toughness, high barrier properties, and cost.

[0005] Chinese patent application CN100999587A discloses a fully degradable film with excellent heat resistance, anisotropic tear resistance, and flexibility, and a method for preparing the same material. The film composition mainly consists of polylactic acid and aliphatic polyester, along with corresponding plasticizers and additives. However, its drawbacks are: from the compositional perspective, polylactic acid and aliphatic polyester do not achieve good compatibility, and the resulting flexible film has poor heat resistance and puncture resistance. Furthermore, it is prone to creep deformation at high temperatures, affecting normal use.

[0006] Chinese patent application CN02801476.6 discloses a biodegradable resin polymer, a film, and an agricultural film. The polymer is composed of fatty acid polyester and polylactic acid-based polymers. Its drawback is that the polylactic acid content in the components is less than 20 parts in total, resulting in films with low mechanical strength and poor tear resistance.

[0007] Chinese patent application CN104387732A discloses a transparent, tear-resistant polylactic acid (PLA) biodegradable film and its preparation method. The mixture mainly consists of PLA, a toughening agent, a plasticizer, a lubricant, and an opening agent. Its drawbacks are: the PLA film has poor toughness and is easily brittle; the added plasticizer is a small molecule substance that easily leaks from the polymer; furthermore, the toughening agent, polybutylene carbonate, has poor thermal properties and is easily degraded during processing, resulting in reduced mechanical properties of the film and poor puncture resistance and rigidity-toughness balance.

[0008] Chinese patent application CN104893199A discloses a fully degradable plastic film with a wide operating temperature range and high toughness. Its drawbacks include: a large number of components, resulting in poor compatibility and a poor balance between strength and toughness; and the lack of specific definition for polyvinyl alcohol in the composition, leading to safety uncertainties.

[0009] Chinese patent application CN 105462124 A discloses a bio-based plastic and its preparation method. Its drawback is that the mixed solvent used contains benzene compounds, which are easily released during blow molding, thus failing to meet the requirements of green processing technology.

[0010] Chinese patent application CN 106633722 A discloses a tear-resistant, high-toughness, biodegradable material. This invention employs a two-step method to prepare PBAT / nanomaterials in a single step. Reactive plasticization is achieved in the front section of the extruder, while reactive chain extension and compatibilization are realized in the middle and later stages, resulting in a material with high tear resistance and good flexibility. Its drawbacks include: a large number of components, cumbersome processing steps, and a lack of good puncture resistance in the film.

[0011] Chinese patent application CN201611028759.6 discloses "a tear-resistant, high-toughness biodegradable material and its preparation method," which is a PLA / PBAT binary alloy material. Its tear resistance and toughness are mainly achieved through PBAT, plasticizers, and other auxiliary materials, with a significant improvement in toughness. However, its drawbacks are that the improvement in tear resistance is not significant, while the tensile strength decreases considerably.

[0012] Chinese patent application CN201510646442.8 discloses a "PLA / MMT degradable reinforcing masterbatch blended modified PLA / PBAT composite material and its preparation method." This invention uses polylactic acid (PLA), poly(terephthalic acid-adipate-butanediol) copolyester (PBAT), and PLA / MMT degradable reinforcing masterbatch as raw materials. 10-90 parts of PLA, 10-90 parts of PBAT, and 5-30 parts of PLA / MMT degradable reinforcing masterbatch are mixed evenly, and then melt-blended to modify PLA / PBAT to prepare a PLA / PBAT composite material. The PLA / MMT degradable reinforcing masterbatch is prepared by ion exchange using intercalating agents and co-intercalating agents to increase the interlayer spacing of montmorillonite. Then, monomers or polylactic acid molecular chains are intercalated into the interlayer space of montmorillonite through melt in-situ polymerization. Its drawback is that its elongation at break is 16.23%, which is unsuitable for the express packaging film field because this elongation at break is far below the requirements of this application.

[0013] Chinese patent application CN201510380483.7 discloses "a method for preparing PLA / PBAT / PPC composite modified materials by reactive extrusion". The weight ratio of PLA is 5-35, PBAT 30-55, PPC 5-15, and based on 100 parts by weight of PPC, the plasticizer content is 0.5-2 parts by weight; based on 100 parts by weight of PBAT, the initiator content is 0.01-0.08 parts by weight, the co-reactant content is 0.01-0.05 parts by weight, the grafted monomer content is 1-3 parts by weight, and the anti-aging additive content is 0.5-1.5 parts by weight. This invention uses a reactive twin-screw extruder to graft PBAT and then blend it with PLA and PPC to prepare a ternary alloy composite material. The grafted PBAT plays a compatibilizing role, and the toughness of the composite material is improved to a certain extent. Its drawbacks are that the improvement in tear resistance is not significant, and due to the low tensile strength and poor heat resistance of PPC, the tensile strength of the PLA / PBAT binary composite material is even lower, while the heat resistance is also worse.

[0014] Chinese patent application CN201310192664.8 discloses a "PLA / PBAT biodegradable composite material," which is made of 60%–75% polylactic acid, 60%–75% polybutylene adipate / terephthalate, 1%–5% polycaprolactone, 5%–15% ethylene-vinyl acetate copolymer, 1%–5% ethylene-vinyl acetate copolymer grafted with polylactic acid, and 1%–10% vegetable oil polyol. Its drawback is that ethylene-vinyl acetate copolymer is a petroleum-based material, lacking low-carbon and environmentally friendly characteristics, and is not biodegradable in the natural environment; therefore, the invention's low-carbon biodegradability is poor.

[0015] Chinese patent application CN113881110A discloses a fully biodegradable composite film, its preparation method, and a corresponding express delivery bag. Specifically, the composite film comprises a first layer, a second layer, and a third layer stacked sequentially. The first and third layers comprise: 70-90 parts by weight of plasticized starch, 5-15 parts by weight of polylactic acid, 5-15 parts by weight of polycaprolactone, and 0.02-0.1 parts by weight of a chain extender. The second layer comprises: 60-80 parts by weight of polypropylene carbonate, 5-15 parts by weight of poly(adipic acid / terephthalic acid)butylene glycolate, 5-15 parts by weight of polycaprolactone, and 0.02-0.1 parts by weight of a chain extender. Its drawback is that the first and third layers contain a large proportion of plasticized starch, resulting in poor compatibility and poor impact resistance of the film, making the prepared packaging bag prone to breakage during use.

[0016] In summary, in view of the shortcomings of existing technologies, the present invention aims to provide a fully biodegradable film with high strength, high toughness, and high barrier properties. Summary of the Invention

[0017] The primary objective of this invention is to overcome the deficiencies in the prior art and provide a fully biodegradable film composition and its preparation method that are high-strength, high-toughness, high-barrier-performance, and low-cost. The fully biodegradable film composition of this invention can be widely used in high-end packaging fields with high barrier-of-effect requirements, such as packaging for high-tech precision instruments, and the food and pharmaceutical industries.

[0018] Specifically, the present invention provides a fully biodegradable composite membrane, which comprises three parts arranged sequentially from the outside to the inside: an outer layer, a middle layer, and an inner layer, wherein the thickness ratio of the outer layer, the middle layer, and the inner layer is 1:(1-1.5):1; wherein, by weight:

[0019] The outer layer comprises: 30-40 parts modified calcium carbonate, 20-40 parts PLA, 20-50 parts PBAT, and 0.2-0.5 parts epoxy chain extender;

[0020] The middle layer comprises: 10-15 parts modified montmorillonite, 5-10 parts PLA, 10-25 parts PBAT, 45-70 parts PPC, and 0.2-0.5 parts epoxy chain extender.

[0021] The inner layer comprises: 30-45 parts PLA, 50-65 parts PBAT, and 0.2-0.5 parts epoxy chain extender; the inner layer may also include an optional opening agent, wherein the amount of the opening agent is 2-5 parts.

[0022] The method for preparing the intermediate layer raw material includes: (i) dividing the epoxy chain extender used in the intermediate layer into two parts, epoxy chain extender A and epoxy chain extender B, and preparing the first intermediate layer masterbatch by mixing PPC, modified montmorillonite and epoxy chain extender A; (ii) preparing the second intermediate layer masterbatch by mixing PLA, PBAT and epoxy chain extender B; (iii) mixing the first intermediate layer masterbatch and the second intermediate layer masterbatch evenly, extruding and granulating to obtain the intermediate layer raw material.

[0023] The total thickness of the fully biodegradable composite membrane is 30-40 μm, and the thickness ratio of the outer layer, middle layer and inner layer is 1:(1-1.5):1.

[0024] Optionally, the outer layer may also include 0 to 1.0 parts by weight of an antistatic agent, as needed.

[0025] Optionally, the middle layer may also include 0 to 2 parts by weight of color masterbatch, as needed.

[0026] Optionally, the inner layer may also include 2 to 5 parts by weight of an opening agent, SiO2, as needed.

[0027] The antistatic agents, color masterbatches, and SiO2 mentioned above are all commercially available products.

[0028] The PLA is polylactic acid with a weight-average molecular weight of 100,000 to 250,000, preferably polylactic acid with good film-forming properties, a wide processing range, and a weight-average molecular weight of 150,000 to 200,000.

[0029] Wherein, the PBAT is polybutylene adipate / terephthalate with a weight-average molecular weight of 50,000 to 100,000, preferably polybutylene adipate / terephthalate with a moderate molecular chain, a certain degree of branching, and a weight-average molecular weight of 50,000 to 75,000.

[0030] The PPC (polypropylene carbonate) has a number-average molecular weight of 30,000 to 50,000, a molecular weight distribution of 3 to 6, a carbon dioxide content greater than 40%, and a density of 1.23 to 1.32. g / cm 3 PPC with a number average molecular weight of 30,000 to 40,000 is preferred, as it can impart good barrier properties and strong adhesion properties to the packaging film.

[0031] The epoxy chain extender can be one or more copolymers of cyclohexyl acrylate, glycidyl methacrylate, and methyl methacrylate with styrene. Preferably, the epoxy chain extender is capable of reducing the regularity of PLA and increasing its branching degree; it preferably contains 7-10 active epoxy groups, has an epoxy equivalent of 300-400 g / mol, a particle size of 0.5-1.5 mm, and a weight-average molecular weight of 7000-8000; for example, BASF's ADR4468.

[0032] The modified calcium carbonate is an organically modified calcium carbonate, prepared by modifying commercially available calcium carbonate using a first organic modifier. The commercially available calcium carbonate is preferably light calcium carbonate with a particle size of 700-1000 mesh and a white color. The first organic modifier includes dioctadecyldimethylammonium chloride.

[0033] The modified montmorillonite is organically modified montmorillonite or organically activated montmorillonite, prepared by modifying commercially available bentonite using a second organic modifier. The commercially available bentonite is preferably sodium-based montmorillonite with a montmorillonite content greater than 30% by mass, a layer thickness of 0.90-1.5 nm (preferably 0.96 nm), an aspect ratio of 100-1000, and adsorbs sodium ions between its layers. The second organic modifier includes dioctadecyldimethylammonium chloride.

[0034] The present invention also provides a method for preparing the fully biodegradable film, comprising the following steps:

[0035] (1) Preparation of modified calcium carbonate: Calcium carbonate is organically modified using a first organic modifier to obtain the modified calcium carbonate;

[0036] (2) Preparation of modified montmorillonite: montmorillonite is organically modified using a second organic modifier to obtain the modified montmorillonite;

[0037] (3) Preparation of outer layer raw materials: The modified calcium carbonate, PLA, PBAT and epoxy chain extender in the outer layer formula are dried, stirred evenly, and extruded and granulated to obtain the outer layer raw materials;

[0038] (4) Preparation of middle layer raw materials:

[0039] (4.1) The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. The middle layer first masterbatch is prepared by mixing PPC, modified montmorillonite and epoxy chain extender A in the middle layer formulation.

[0040] (4.2) The second masterbatch of the middle layer was prepared by mixing PLA, PBAT and epoxy chain extender B in the middle layer formulation;

[0041] (4.3) Mix the first masterbatch and the second masterbatch of the middle layer evenly, and extrude and granulate to obtain the middle layer raw material;

[0042] (5) Preparation of inner layer raw materials: The inner layer formulation of PLA, PBAT, epoxy chain extender and optional opening agent are dried, stirred evenly, extruded and granulated to obtain the inner layer raw materials;

[0043] (6) Blown film: The outer layer material, middle layer material and inner layer material are used to perform three-layer co-extrusion blown film to obtain the fully biodegradable film.

[0044] Specifically, step (1) of preparing modified calcium carbonate includes:

[0045] (1.1) Calcium carbonate is vacuum dried to obtain dried calcium carbonate;

[0046] (1.2) Place 10-50 parts by weight of dried calcium carbonate into 100-1000 parts by weight of the first solution and mix well to obtain suspension A1;

[0047] (1.3) Dissolve 0.1-3 parts by weight of the first organic modifier in 300-1200 parts by weight of the first solution, mix well, and obtain suspension A2;

[0048] (1.4) The suspension A1 is ultrasonically dispersed, and the suspension A2 is slowly added dropwise to the suspension A1 while ultrasonically dispersing. The suspension is ultrasonically dispersed at 70-80℃ for 4-6 hours (preferably 5 hours) until it is uniformly mixed. The modified calcium carbonate is obtained by filtration, drying and pulverizing.

[0049] In step (1.1), the vacuum drying temperature is 75-90℃, the vacuum drying time is 2-6h (preferably 4h), and the vacuum degree of vacuum drying is 0.08-0.12MPa (preferably 0.10MPa). The vacuum drying can be carried out in a vacuum oven.

[0050] In steps (1.2) and (1.3), the first solution is an aqueous solution of ethylene glycol, wherein the volume ratio of ethylene glycol to deionized water is 80-90:10-20 (preferably 85:15); the mixing is performed by ultrasonic dispersion for 20-40 min (preferably 30 min).

[0051] In step (1.4), the modified calcium carbonate obtained has a particle size of 10-20 μm.

[0052] Specifically, step (2) of preparing modified montmorillonite includes:

[0053] (2.1) Purification of commercially available montmorillonite: Add 1-50 parts by weight of commercially available montmorillonite to 100-1000 parts by weight of water, stir at high speed at 50-80℃ to form a suspension system, remove the precipitate in the suspension system, add 1-20 parts by weight of trichloroacetic acid to the suspension system, stir evenly to obtain suspension B1.

[0054] (2.2) Dissolve 0.1-10 parts by weight of the second organic modifier in 20-300 parts by weight of anhydrous ethanol to form solution B2;

[0055] (2.3) Add solution B2 dropwise to suspension B1 at 70-90℃ while stirring. Control the addition time within 0.5-3h to obtain modified montmorillonite suspension. Then wash, filter, dry and pulverize it to obtain the modified montmorillonite.

[0056] In step (2.3), the modified montmorillonite obtained has a particle size of 50-150 μm.

[0057] In step (3), the drying process includes drying in a vacuum drying oven at 60-80°C (preferably 70°C) for 3-5 hours (preferably 4 hours).

[0058] In step (3), the stirring includes: stirring evenly in a low-speed mixer at a speed of 500-1000 r / min, a stirring time of 5-10 min, and a stirring temperature of 10-20℃.

[0059] In step (3), the extrusion granulation includes: using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48-52 for extrusion granulation, and the granulation temperature is 150-170℃.

[0060] Specifically, step (4.1) includes: first, vacuum drying PPC in a vacuum drying oven at 30-50℃ (preferably 40℃) for 36-60h (preferably 48h), and vacuum drying modified montmorillonite in a vacuum drying oven at 50-70℃ (preferably 60℃) for 36-60h (preferably 48h); then, mixing the dried PPC, the dried modified montmorillonite, and epoxy chain extender A in a low-speed mixer, wherein the mixing speed is 500-800r / min, the mixing time is 5-10min, and the mixing temperature is 10-20℃; finally, extruding and granulating the mixture using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48-52 to obtain the first masterbatch of the middle layer, wherein the granulation temperature is 120-140℃.

[0061] Specifically, step (4.2) includes: first, placing PLA, PBAT, and epoxy chain extender B in a vacuum drying oven at 60-80℃ (preferably 70℃) for vacuum drying for 3-5 hours (preferably 4 hours); then, mixing the dried PLA, PBAT, and epoxy chain extender B evenly in a low-speed mixer, wherein the stirring speed is 500-1000 r / min, the stirring time is 5-10 min, and the stirring temperature is 10-20℃; finally, extruding and granulating the mixture using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48-52 to obtain the second masterbatch in the middle layer, wherein the granulation temperature is 150-170℃.

[0062] Specifically, step (4.3) includes: first, placing the first intermediate layer masterbatch and the second intermediate layer masterbatch in a vacuum drying oven at 30-50℃ (preferably 40℃) and a vacuum drying oven at 60-80℃ (preferably 70℃) respectively for vacuum drying for 3-5 hours (preferably 4 hours); then, mixing the dried first intermediate layer masterbatch and the dried second intermediate layer masterbatch evenly in a low-speed mixer, wherein the mixing speed is 500-1000 r / min, the mixing time is 5-10 min, and the mixing temperature is 10-20℃; finally, extruding and granulating the intermediate layer raw material using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48-52, wherein the granulation temperature is 150-170℃.

[0063] In step (5), the drying process includes drying in a vacuum drying oven at 60-80°C (preferably 70°C) for 3-5 hours (preferably 4 hours).

[0064] In step (5), the stirring includes: stirring evenly in a low-speed mixer at a speed of 500-1000 r / min, a stirring time of 5-10 min, and a stirring temperature of 10-20℃.

[0065] In step (5), the extrusion granulation includes: using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48-52 for extrusion granulation, and the granulation temperature is 150-170℃.

[0066] Specifically, step (6) includes: passing the outer layer raw material, middle layer raw material and inner layer raw material through three extruders, plasticizing them evenly, and then entering the same three-layer blown film die head. After fusion, they are extruded through the die head to form film bubbles, thereby obtaining the fully biodegradable film.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) The present invention uses fewer types of base materials, and the resulting fully biodegradable packaging film has good uniformity and quality.

[0069] (2) In the middle layer of the present invention, the two-dimensional sheet structure of montmorillonite is fully utilized. Modified montmorillonite is prepared by cation exchange, which increases the spacing between montmorillonite sheets and improves the microenvironment within the layers. This allows the organic long-chain dioctadecyl cations entering the interlayer to effectively change the surface of the montmorillonite sheets to be oleophilic and hydrophobic, reducing the surface energy between the sheets. Consequently, PPC can be inserted between the montmorillonite sheets to react.

[0070] The PPC molecular chain contains carbonyl groups and ether bonds, exhibiting high molecular chain mobility during melting. Simultaneously, some montmorillonite acts as a nucleating agent, promoting heterogeneous nucleation of PPC, reducing spherulites, and resulting in regular, smooth grains that are regularly arranged and tightly packed within the montmorillonite layers, increasing air resistance and improving gas barrier properties. The insertion of PPC further increases the interlamellar spacing of montmorillonite, achieving effective peeling of montmorillonite lamellars, and forming a disordered "PPC-intercalated" layered structure in the middle layer of the first masterbatch.

[0071] During the preparation of the second masterbatch in the middle layer, the special epoxy functional group structure of the epoxy chain extender effectively reduces the regularity of PLA and increases the branching degree of PLA. At the same time, low molecular weight PBAT is interspersed in it to form a "networked" structure.

[0072] When the first and second masterbatches in the middle layer are melt-blended, the disordered layered structure of "PPC regularly arranged insert-type" montmorillonite is evenly distributed in the second masterbatch. The entire composite material fully combines the complementary microstructures of inorganic materials and polymers, so that the disordered "PPC regularly arranged insert-type" montmorillonite layered structure is arranged to form a dense protective layer similar to "PLA / PBAT matrix-MMT sheets-PPC regularly arranged-MMT sheets-PLA / PBAT matrix", which effectively blocks the flow of gas.

[0073] Meanwhile, the addition of chain extenders improves the compatibility between the base materials, and the cross-linked structure of PLA and PBAT also gives the composite film good impact resistance, puncture resistance and tear resistance.

[0074] (3) The outer layer is filled with inexpensive and easily modified calcium carbonate, which can improve the overall strength of the composite film and effectively improve the overall stacking performance of the composite film.

[0075] (4) The three-layer film of the present invention uses PLA and PBAT as matrix raw materials. The layers have strong adhesion. By adding different additives and fillers, the advantages of the three-layer film raw materials can be combined, and the synergistic effect of "1+1+1>>3" can be played to improve the overall performance of the film. The prepared film has strong tear resistance, good impact resistance, can meet the high and low temperature use environment, and has good rigidity and toughness balance and barrier performance.

[0076] (5) The preparation method of the present invention is simple, and the granulation and blown film of the three-layer raw materials can be completed using general extrusion equipment.

[0077] (6) The film prepared by the present invention can be made into packaging films of different thicknesses according to actual needs, which can meet the needs of high-end packaging fields such as supermarket shopping bags, express delivery bags, packaging of high-tech precision instruments, food and pharmaceutical industries. Detailed Implementation

[0078] The present invention will now be described in further detail with reference to specific embodiments. However, it should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the claims of this application.

[0079] In the following embodiments, PLA was purchased from Natureworks, Inc., USA; PBAT was purchased from Jinhui Zhaolong High-Tech Co., Ltd.; PPC was purchased from Nanyang Zhongju Tianguan Low Carbon Technology Co., Ltd.; the epoxy chain extender was ADR4468, purchased from BASF. Unless otherwise specified, other raw materials and reagents are all commercially available from conventional markets.

[0080] Examples 1-4

[0081] The fully biodegradable composite membranes of Examples 1-4 were prepared. The component ratios for each example are shown in Table 1 below, where the weight parts of each component are represented.

[0082] Modified calcium carbonate, specifically calcium carbonate modified with bis(octadecyldimethylammonium chloride), in the following tables, for example, 30 (1:100) in Example 1 means: the weight of modified calcium carbonate in Example 1 is 30, and the weight ratio of bis(octadecyldimethylammonium chloride) to calcium carbonate in the modified calcium carbonate is 1:100. Examples 2-4 are similar.

[0083] Modified montmorillonite, specifically montmorillonite modified with bis(octadecyl)dimethylammonium chloride, in subsequent tables, for example, 10 (1:50) in Example 1 means: the weight part of modified montmorillonite in Example 1 is 10, and the weight ratio of bis(octadecyl)dimethylammonium chloride to montmorillonite in modified montmorillonite is 1:50. Examples 2-4 are similar.

[0084] Table 1 Raw materials and proportions for Examples 1-4

[0085]

[0086]

[0087] The fully biodegradable composite membranes of Examples 1-4 above were prepared using the following methods:

[0088] Example 1:

[0089] (1) Preparation of organically modified calcium carbonate

[0090] Commercially available light calcium carbonate was dried in a vacuum oven at 75°C for 4 hours with a vacuum pressure of 0.10 MPa to obtain dried calcium carbonate.

[0091] Weigh 10 parts of dried calcium carbonate and place them in a 100-part mixed aqueous solution of ethylene glycol (the volume ratio of ethylene glycol to deionized water is 85:15). Disperse the mixture by ultrasonication for 30 minutes to obtain a calcium carbonate suspension A1.

[0092] Dissolve 0.1 parts of commercially available dioctadecyl dimethyl ammonium chloride in a mixture of 300 parts ethylene glycol (the volume ratio of ethylene glycol to deionized water is 85:15), and ultrasonically disperse for 30 min to obtain a suspension A2 of dioctadecyl dimethyl ammonium chloride.

[0093] Suspension A1 was further ultrasonically dispersed, and suspension A2 was slowly added dropwise to suspension A1. The mixture was ultrasonically dispersed at 70°C for 5 hours until it was homogeneous. After filtration, drying and pulverization, 10 μm organic modified calcium carbonate (dioctadecyl dimethyl ammonium chloride to calcium carbonate weight ratio of 1:100) was prepared.

[0094] (2) Preparation of modified montmorillonite:

[0095] Commercially available montmorillonite is purified and then organically activated, specifically as follows:

[0096] Add 10 parts of montmorillonite to 100 parts of deionized water and stir at high speed at 50°C to form a suspension system. Remove the precipitate and add 1 part of trichloroacetic acid to the suspension. Stir evenly to form suspension B1 for later use.

[0097] Dissolve 0.1 parts of dioctadecyldimethylammonium chloride in 20 parts of anhydrous ethanol to form solution B2;

[0098] Solution B2 was added dropwise to suspension B1 at 70℃ while stirring, and the addition time was controlled within 0.5h to obtain modified montmorillonite suspension; after washing, drying and pulverizing, 50μm modified montmorillonite (the weight ratio of dioctadecyl dimethyl ammonium chloride to montmorillonite was 1:50) was prepared.

[0099] (3) Preparation of outer layer raw materials:

[0100] According to the formulation of Example 1 shown in Table 1, modified calcium carbonate, PLA, PBAT, and chain extender ADR4468 were vacuum dried in a vacuum drying oven at 70°C for 4 hours, mixed evenly in a low-speed mixer at a stirring speed of 500 r / min for 5 min and a stirring temperature of 10°C, and extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48. The granulation temperatures in zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively, to obtain the outer layer raw material.

[0101] (4) Preparation of middle layer raw materials:

[0102] The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. PPC is placed in a vacuum drying oven at 40°C and vacuum dried for 48 hours. Modified montmorillonite is vacuum dried at 60°C for 48 hours. According to the formulation of Example 1 shown in Table 1, epoxy chain extender A, PPC, and modified montmorillonite are mixed evenly in a low-speed mixer at a stirring speed of 500 r / min, a stirring time of 5 min, and a stirring temperature of 10°C. The mixture is then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48. The granulation temperatures for zones 1-5 are 120°C, 125°C, 130°C, 135°C, and 140°C, respectively, to prepare the first masterbatch for the middle layer.

[0103] According to the formulation of Example 1 shown in Table 1, epoxy chain extender B, PLA, and PBAT were placed in a vacuum drying oven at 70°C and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 500 r / min, a stirring time of 5 min, and a stirring temperature of 10°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The middle layer second masterbatch was obtained by extrusion.

[0104] The first and second intermediate layer masterbatches were placed in a 40°C vacuum drying oven and a 70°C vacuum drying oven, respectively, and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 500 r / min for 5 min and a temperature of 10°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The intermediate layer raw material was obtained by extrusion.

[0105] (5) Preparation of inner layer raw materials:

[0106] According to the formulation of Example 1 shown in Table 1, PLA, PBAT, epoxy chain extender ADR4468, and opening agent SiO2 were vacuum dried in a vacuum drying oven at 70°C for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 500 r / min for 5 minutes and a stirring temperature of 10°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 48. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The inner layer raw material was obtained by extrusion.

[0107] (6) Thin film blowing

[0108] The outer, middle, and inner layers of raw materials were passed through three extruders and plasticized uniformly before entering the same three-layer blown film die. After fusion, they were extruded through the die to form a film bubble, thus preparing a fully biodegradable composite film with a total thickness of 30 μm and a thickness ratio of 1:1:1 for the outer, middle, and inner layers.

[0109] Example 2:

[0110] (1) Preparation of organically modified calcium carbonate

[0111] Commercially available light calcium carbonate was dried in a vacuum oven at 790℃ for 4 hours with a vacuum value of 0.10 MPa to obtain dried calcium carbonate.

[0112] Weigh 50 parts of dried calcium carbonate and place it in a mixed aqueous solution of 1000 parts of ethylene glycol (the volume ratio of ethylene glycol to deionized water is 85:15). Disperse the mixture by ultrasonication for 30 minutes to obtain a calcium carbonate suspension A1.

[0113] Dissolve 3 parts of commercially available dioctadecyl dimethyl ammonium chloride in 1200 parts of ethylene glycol mixture (ethylene glycol to deionized water volume ratio of 85:15), and ultrasonically disperse for 30 min to obtain a suspension A2 of dioctadecyl dimethyl ammonium chloride.

[0114] Suspension A1 was further ultrasonically dispersed, and suspension A2 was slowly added dropwise to suspension A1. The mixture was ultrasonically dispersed at 80°C for 5 hours until it was homogeneous. After filtration, drying and pulverization, it was made into 20μm organic modified calcium carbonate (the weight ratio of dioctadecyl dimethyl ammonium chloride to calcium carbonate was 1:200).

[0115] (2) Preparation of modified montmorillonite:

[0116] Commercially available montmorillonite is purified and then organically activated, specifically as follows:

[0117] Add 50 parts of montmorillonite to 1000 parts of deionized water and stir at high speed at 80°C to form a suspension system. Remove the precipitate and add 20 parts of trichloroacetic acid to the suspension. Stir evenly to form suspension B1 for later use.

[0118] Dissolve 10 parts of dioctadecyldimethylammonium chloride in 00 parts of anhydrous ethanol to form solution B2;

[0119] Solution B2 was added dropwise to suspension B1 at 90℃ while stirring, and the addition time was controlled within 3.0h to obtain modified montmorillonite suspension; after washing, drying and pulverizing, 150μm modified montmorillonite (the weight ratio of dioctadecyl dimethyl ammonium chloride to montmorillonite was 1:100) was prepared.

[0120] (3) Preparation of outer layer raw materials:

[0121] According to the formulation of Example 2 shown in Table 1, modified calcium carbonate, PLA, PBAT, and chain extender ADR4468 were vacuum dried in a vacuum drying oven at 70°C for 4 hours, mixed evenly in a low-speed mixer at a stirring speed of 1000 r / min for 10 min and a stirring temperature of 20°C, and extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 52. The granulation temperatures in zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively, to obtain the outer layer raw material.

[0122] (4) Preparation of middle layer raw materials:

[0123] The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. PPC is placed in a vacuum drying oven at 40°C and vacuum dried for 48 hours. Modified montmorillonite is vacuum dried at 60°C for 48 hours. According to the formulation of Example 2 shown in Table 1, epoxy chain extender A, PPC, and modified montmorillonite are mixed evenly in a low-speed mixer at a stirring speed of 800 r / min, a stirring time of 10 min, and a stirring temperature of 20°C. The mixture is then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 52. The granulation temperatures for zones 1-5 are 120°C, 125°C, 130°C, 135°C, and 140°C, respectively, to prepare the first masterbatch for the middle layer.

[0124] According to the formulation of Example 2 shown in Table 1, epoxy chain extender B, PLA, and PBAT were placed in a vacuum drying oven at 70°C and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 1000 r / min for 10 min and a temperature of 20°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 52. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The middle layer second masterbatch was obtained by extrusion.

[0125] The first and second intermediate layer masterbatches were placed in a 40°C vacuum drying oven and a 70°C vacuum drying oven, respectively, and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 1000 r / min for 10 min and a temperature of 20°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 52. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The intermediate layer raw material was obtained by extrusion.

[0126] (5) Preparation of inner layer raw materials:

[0127] According to the formulation of Example 2 shown in Table 1, PLA, PBAT, chain extender ADR4468, and opening agent SiO2 were vacuum dried in a vacuum drying oven at 70°C for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 1000 r / min for 10 min and a stirring temperature of 20°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 52. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The inner layer raw material was obtained by extrusion.

[0128] (6) Thin film blowing

[0129] The outer, middle, and inner layers of raw materials were processed by three separate extruders and plasticized uniformly before being fed into the same three-layer blown film die. After fusion, the materials were extruded through the die to form a film bubble, thus preparing a fully biodegradable composite film with a total thickness of 30 μm and a thickness ratio of 1:1.5:1 for the outer, middle, and inner layers.

[0130] Example 3:

[0131] (1) Preparation of organically modified calcium carbonate

[0132] Commercially available light calcium carbonate was dried in a vacuum oven at 80°C for 4 hours with a vacuum pressure of 0.10 MPa to obtain dried calcium carbonate.

[0133] Weigh 35 parts of dried calcium carbonate and place them in a 500-part mixed aqueous solution of ethylene glycol (the volume ratio of ethylene glycol to deionized water is 85:15). Disperse the mixture by ultrasonication for 30 minutes to obtain a calcium carbonate suspension A1.

[0134] Two parts of commercially available dioctadecyl dimethyl ammonium chloride were dissolved in a mixture of 900 parts ethylene glycol (the volume ratio of ethylene glycol to deionized water was 85:15), and the mixture was ultrasonically dispersed for 30 minutes to obtain a suspension A2 of dioctadecyl dimethyl ammonium chloride.

[0135] Suspension A1 was further ultrasonically dispersed, and suspension A2 was slowly added dropwise to suspension A1. The mixture was ultrasonically dispersed at 75°C for 5 hours until it was homogeneous. After filtration, drying and pulverization, it was made into 15μm organic modified calcium carbonate (the weight ratio of dioctadecyl dimethyl ammonium chloride to calcium carbonate was 1:150).

[0136] (2) Preparation of modified montmorillonite:

[0137] Commercially available montmorillonite is purified and then organically activated, specifically as follows:

[0138] Add 35 parts of montmorillonite to 500 parts of deionized water and stir at high speed at 65°C to form a suspension system. Remove the precipitate and add 15 parts of trichloroacetic acid to the suspension. Stir evenly to form suspension B1 for later use.

[0139] Dissolve 0.1–10 parts of dioctadecyldimethylammonium chloride in 20–300 parts of anhydrous ethanol to form solution B2;

[0140] Solution B2 was added dropwise to suspension B1 at 80℃ while stirring, and the addition time was controlled within 2.0h to obtain modified montmorillonite suspension; after washing, drying and pulverizing, 400μm modified montmorillonite (the weight ratio of dioctadecyl dimethyl ammonium chloride to montmorillonite was 1:75) was prepared.

[0141] (3) Preparation of outer layer raw materials:

[0142] According to the formulation of Example 3 shown in Table 1, modified calcium carbonate, PLA, PBAT, and chain extender ADR4468 were vacuum dried in a vacuum drying oven at 70°C for 4 hours, mixed evenly in a low-speed mixer at a stirring speed of 800 r / min for 8 min and a stirring temperature of 15°C, and extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures of zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively, to obtain the outer layer raw material.

[0143] (4) Preparation of middle layer raw materials:

[0144] The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. PPC is placed in a vacuum drying oven at 40°C and vacuum dried for 48 hours. Modified montmorillonite is vacuum dried at 60°C for 48 hours. According to the formulation of Example 3 shown in Table 1, epoxy chain extender A, PPC, and modified montmorillonite are mixed evenly in a low-speed mixer at a stirring speed of 650 r / min, a stirring time of 8 min, and a stirring temperature of 15°C. The mixture is then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 are 120°C, 125°C, 130°C, 135°C, and 140°C, respectively, to prepare the first masterbatch for the middle layer.

[0145] According to the formulation of Example 3 shown in Table 1, epoxy chain extender B, PLA, and PBAT were placed in a vacuum drying oven at 70°C and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 800 r / min, a stirring time of 8 min, and a stirring temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The middle layer second masterbatch was obtained by extrusion.

[0146] The first and second intermediate layer masterbatches were placed in a 40°C vacuum drying oven and a 70°C vacuum drying oven, respectively, and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 800 r / min for 8 min and a temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The intermediate layer raw material was obtained by extrusion.

[0147] (5) Preparation of inner layer raw materials:

[0148] According to the formulation of Example 3 shown in Table 1, PLA, PBAT, chain extender ADR4468, and opening agent SiO2 were vacuum dried in a vacuum drying oven at 70°C for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 800 r / min for 8 minutes and a stirring temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The inner layer raw material was obtained by extrusion.

[0149] (6) Thin film blowing

[0150] The outer, middle, and inner layers of raw materials were processed by three separate extruders and plasticized uniformly before being fed into the same three-layer blown film die. After fusion, the mixture was extruded through the die to form a film bubble, thus preparing a fully biodegradable composite film with a total thickness of 30 μm and a thickness ratio of 1:1.25:1 for the outer, middle, and inner layers.

[0151] Example 4:

[0152] (1) Preparation of organically modified calcium carbonate

[0153] Commercially available light calcium carbonate was dried in a vacuum oven at 80°C for 4 hours with a vacuum pressure of 0.10 MPa to obtain dried calcium carbonate.

[0154] Weigh 30 parts of dried calcium carbonate and place them in a mixed aqueous solution of 300 parts ethylene glycol (the volume ratio of ethylene glycol to deionized water is 85:15). Disperse the mixture by ultrasonication for 30 minutes to obtain a calcium carbonate suspension A1.

[0155] Dissolve 1.5 parts of commercially available dioctadecyl dimethyl ammonium chloride in a 600-part ethylene glycol mixture (ethylene glycol to deionized water volume ratio of 85:15), and ultrasonically disperse for 30 min to obtain a suspension A2 of dioctadecyl dimethyl ammonium chloride.

[0156] Suspension A1 was further ultrasonically dispersed, and suspension A2 was slowly added dropwise to suspension A1. The mixture was ultrasonically dispersed at 75°C for 5 hours until it was homogeneous. After filtration, drying and pulverization, 12 μm organic modified calcium carbonate (dioctadecyl dimethyl ammonium chloride to calcium carbonate weight ratio of 1:125) was prepared.

[0157] (2) Preparation of modified montmorillonite:

[0158] Commercially available montmorillonite is purified and then organically activated, specifically as follows:

[0159] Add 25 parts of montmorillonite to 250 parts of deionized water and stir at high speed at 60°C to form a suspension system. Remove the precipitate and add 12 parts of trichloroacetic acid to the suspension. Stir evenly to form suspension B1 for later use.

[0160] Dissolve 0.1–10 parts of dioctadecyldimethylammonium chloride in 20–300 parts of anhydrous ethanol to form solution B2;

[0161] Solution B2 was added dropwise to suspension B1 at 75℃ while stirring, and the addition time was controlled within 1.5h to obtain modified montmorillonite suspension; after washing, drying and pulverizing, 85μm modified montmorillonite (the weight ratio of dioctadecyl dimethyl ammonium chloride to montmorillonite was 1:65) was prepared.

[0162] (3) Preparation of outer layer raw materials:

[0163] According to the formulation of Example 4 shown in Table 1, modified calcium carbonate, PLA, PBAT, and chain extender ADR4468 were vacuum dried in a vacuum drying oven at 70°C for 4 hours, mixed evenly in a low-speed mixer at a stirring speed of 650 r / min for 7 min and a stirring temperature of 12°C, and extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures in zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively, to obtain the outer layer raw material.

[0164] (4) Preparation of middle layer raw materials:

[0165] The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. PPC is placed in a vacuum drying oven at 40°C and vacuum dried for 48 hours. Modified montmorillonite is vacuum dried at 60°C for 48 hours. According to the formulation of Example 4 shown in Table 1, epoxy chain extender A, PPC, and modified montmorillonite are mixed evenly in a low-speed mixer at a stirring speed of 650 r / min, a stirring time of 7 min, and a stirring temperature of 12°C. The mixture is then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 are 120°C, 125°C, 130°C, 135°C, and 140°C, respectively, to prepare the first masterbatch for the middle layer.

[0166] According to the formulation of Example 4 shown in Table 1, epoxy chain extender B, PLA, and PBAT were placed in a vacuum drying oven at 70°C and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 700 r / min, a stirring time of 7 min, and a stirring temperature of 12°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The middle layer second masterbatch was obtained by extrusion.

[0167] The first and second intermediate layer masterbatches were placed in a 40°C vacuum drying oven and a 70°C vacuum drying oven, respectively, and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 700 r / min for 7 min and a temperature of 12°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The intermediate layer raw material was obtained by extrusion.

[0168] (5) Preparation of inner layer raw materials:

[0169] According to the formulation of Example 4 shown in Table 1, PLA, PBAT, chain extender ADR4468, and opening agent SiO2 were vacuum dried in a vacuum drying oven at 70°C for 4 hours. They were then mixed evenly in a low-speed mixer at a stirring speed of 650 r / min, a stirring time of 6 min, and a stirring temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The inner layer raw material was obtained by extrusion.

[0170] (6) Thin film blowing

[0171] The outer, middle, and inner layers of raw materials were processed by three separate extruders and plasticized uniformly before being fed into the same three-layer blown film die. After fusion, the mixture was extruded through the die to form a film bubble, thus preparing a fully biodegradable composite film with a total thickness of 30 μm and a thickness ratio of 1:1.3:1 for the outer, middle, and inner layers.

[0172] Comparative Example 1

[0173] According to the raw material ratio of Example 3, except that the preparation method of the middle layer raw material is different from that of Example 3, the other steps are the same as those of Example 3, and the fully biodegradable composite membrane of Comparative Example 1 is obtained.

[0174] The preparation method of the intermediate layer raw material in Comparative Example 1 did not involve two granulation processes. Specifically, according to the intermediate layer raw material formulation of Example 3 shown in Table 1, PPC was placed in a 40℃ vacuum drying oven and vacuum dried for 48 hours. Modified montmorillonite, PLA, PBAT, and chain extender ADR4468 were placed in a 70℃ vacuum drying oven and vacuum dried for 7 hours. All raw materials were mixed evenly in a low-speed mixer at a stirring speed of 800 r / min, a stirring time of 8 min, and a stirring temperature of 15℃. Granulation was performed using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 120℃, 135℃, 140℃, 155℃, and 160℃, respectively, to obtain the intermediate layer raw material.

[0175] Comparative Example 2

[0176] According to the raw material ratio of Example 3, except for the preparation method of the middle layer raw material which is different from Example 3, the other steps are the same as in Example 3, and the fully biodegradable composite membrane of Comparative Example 2 is obtained.

[0177] In the preparation method of the intermediate layer raw material in Comparative Example 2, the organically modified montmorillonite of Example 3 was not used. Instead, commercially available montmorillonite was used directly for two-step masterbatch preparation. The specific preparation method of the intermediate layer raw material is as follows:

[0178] According to the formulation of Example 3 shown in Table 1 (except that the modified montmorillonite was replaced with commercially available montmorillonite), PPC was placed in a vacuum drying oven at 40°C and vacuum dried for 48 hours. The commercially available montmorillonite was vacuum dried at 60°C for 48 hours. The chain extender used in the middle layer was divided into two parts: chain extender A and chain extender B. Chain extender A, PPC, and commercially available montmorillonite were mixed evenly in a low-speed mixer at a stirring speed of 650 r / min, a stirring time of 8 min, and a stirring temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 120°C, 125°C, 130°C, 135°C, and 140°C, respectively, to prepare the first masterbatch for the middle layer.

[0179] Chain extender B, PLA, and PBAT were placed in a vacuum drying oven at 70℃ and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 750 r / min for 8 minutes and a temperature of 15℃. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150℃, 155℃, 160℃, 165℃, and 170℃, respectively. The middle layer second masterbatch was obtained by extrusion.

[0180] The first and second masterbatches of the intermediate layer were placed in a vacuum drying oven at 40°C and 70°C respectively, and vacuum dried for 4 hours. They were then mixed evenly in a low-speed mixer at a speed of 750 r / min, a mixing time of 8 min, and a mixing temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively, to obtain the intermediate layer raw material.

[0181] Comparative Example 3

[0182] According to the raw material ratio of Example 3, except that the preparation method of the middle layer raw material is different from that of Example 3, the other steps are the same as those of Example 3, and the fully biodegradable composite membrane of Comparative Example 3 is obtained.

[0183] In the preparation method of the intermediate layer raw material in Comparative Example 3, the timing of adding the modified montmorillonite in Example 3 was changed, and the mixing timing of other raw materials was adjusted. The specific preparation method of the intermediate layer raw material is as follows:

[0184] Weigh each raw material according to the proportions shown in Table 1 for Example 3. Place PPC in a 40℃ vacuum drying oven and vacuum dry for 48 hours. Place chain extender ADR4468, PLA, and PBAT in a 70℃ vacuum drying oven and vacuum dry for 4 hours. Mix PPC, PLA, PBAT, and chain extender evenly in a low-speed mixer at a speed of 800 r / min for 8 min and a temperature of 15℃. Extrude and granulate using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 are 120℃, 135℃, 140℃, 155℃, and 160℃, respectively, to obtain the first masterbatch in the middle layer.

[0185] The first masterbatch of the intermediate layer and the modified montmorillonite prepared in Example 3 were placed in a vacuum drying oven at 60°C and vacuum dried for 4 hours. The first masterbatch and the organic modified montmorillonite were mixed evenly in a low-speed mixer at a stirring speed of 800 r / min, a stirring time of 8 min, and a stirring temperature of 15°C. The mixture was then extruded and granulated using a twin-screw extruder with a length-to-diameter ratio (L / D) of 50. The granulation temperatures for zones 1-5 were 150°C, 155°C, 160°C, 165°C, and 170°C, respectively. The intermediate layer raw material was obtained by extrusion.

[0186] Comparative Example 4

[0187] According to the patent application CN 106633722 A entitled "A tear-resistant, high-toughness biodegradable material and its preparation method", Example 6 in the specification of CN 106633722 A is used as Comparative Example 4 of the present invention.

[0188] The specific implementation method is as follows: Accurately weigh 95 kg of carbon nanotubes CNTS-5, heat it to 80°C using a high-speed mixer, mix at high speed, and add 5 kg of KH-560 via spray. Mix for 20 minutes to obtain surface-treated carbon nanotubes CNTS-5. Accurately weigh 10 kg of the above-mentioned surface-treated carbon nanotubes CNTS-5 and 90 kg of PBAT TH801, mix them in an internal mixer at 160°C and 40 rpm for 10 minutes, and then melt-mix them using a single-screw extruder with a length-to-diameter ratio of 40:1. The extrusion temperature is 160-170°C and the screw speed is 800 rpm to obtain PBAT / CNTS-5 one-step material. Accurately weigh 40 kg of PLA 101, 30 kg of PBAT / CNTS-5 one-step feedstock, 15 kg of acetylated epoxidized vegetable oleic acid adipate glyceryl ester, 14.4 kg of talc, 0.1 kg of epoxy chain extender 4370, and 0.5 kg of antioxidant 1076. Premix the above components thoroughly, and then melt-blend them using a twin-screw extruder. The heating zone of the extruder, from the feed port to the die head, is set sequentially to 130℃, 180℃, 180℃, 180℃, 180℃, and 180℃, with a rotation speed of 200 rpm, to obtain a tear-resistant, high-toughness, biodegradable material.

[0189] The prepared tear-resistant, high-toughness, biodegradable material was vacuum dried in a vacuum drying oven at 70℃ for 4 hours. It was then extruded through a single-screw extruder with a length-to-diameter ratio of 25:1, a screw speed of 70-100 r / min, and an extrusion temperature of 150-175℃. Air was introduced into the blown film bubble at the die head to inflate it. After cooling, the film was shaped by a herringbone plate, pulled by a traction machine, and finally flattened and wound up by a winding device to prepare a 30 μm thick biodegradable plastic film, as shown in Comparative Example 4.

[0190] Comparative Example 5

[0191] According to the patent application CN 109486138 A entitled "Modified PLA / PBAT Biodegradable Resin and Preparation Method Thereof", Example 3 in the specification of CN 109486138 A is used as Comparative Example 5 of the present invention.

[0192] The specific implementation method is as follows: PHA-modified PLA / PBAT biodegradable resin is prepared from the following raw materials in parts by weight: PLA 35 parts, PBAT 35 parts, PHA 30 parts. The resin is blown into a film using a blown film machine to prepare a biodegradable plastic shopping bag of Comparative Example 5 with a thickness of 30 μm.

[0193] Comparative Example 6

[0194] According to the patent application CN113881110, "A fully biodegradable composite film, preparation method and express delivery bag thereof", Example 4 of the specification with the best test performance was selected as the comparative example 6 of the present invention.

[0195] Specifically, the composite film comprises a first layer, a second layer, and a third layer stacked sequentially; the first and third layers comprise: 70-90 parts by weight of plasticized starch, 5-15 parts by weight of polylactic acid, 5-15 parts by weight of polycaprolactone, and 0.02-0.1 parts by weight of a chain extender; the second layer comprises: 60-80 parts by weight of polypropylene carbonate, 5-15 parts by weight of poly(adipic acid / terephthalic acid)butylene glycolate, 5-15 parts by weight of polycaprolactone, and 0.02-0.1 parts by weight of a chain extender.

[0196] The prepared biodegradable material was vacuum dried in a vacuum drying oven at 70℃ for 4 hours. It was then extruded through a single screw extruder with a length-to-diameter ratio of 25:1 at a screw speed of 70-100 r / min and an extrusion temperature of 150-175℃. Air was introduced into the blown film bubble at the die head to inflate it. After cooling, the film was shaped by a herringbone plate, pulled by a traction machine, and finally flattened and wound up by a winding device to prepare a 30 μm thick biodegradable plastic film, as shown in Comparative Example 6.

[0197] Comparative Example 7

[0198] A biodegradable plastic shopping bag of a well-known brand with a thickness of 30μm was purchased as a control example 7.

[0199] Performance testing

[0200] The biodegradable films obtained in the above embodiments and comparative examples were subjected to performance tests, and the test methods are as follows:

[0201] Tensile strength, tensile yield stress, and nominal strain at break were tested according to GB / T1040.3-2006, with a tensile rate of 200 mm / min.

[0202] Elemandorf tear strength: tested according to GB / T 16578.2-2009, using rectangular specimens.

[0203] Puncture performance test: The membrane is cut into a circle with a diameter of 2.5 cm, stretched over the mouth of a small triangular flask, and the pressure that the membrane can withstand is measured using INSTRON. The pressure is expressed as the maximum pressure per unit cross-sectional area (N / mm²). 2 The drill bit diameter is 13mm, and the descent speed is 50mm / min.

[0204] Dart impact test: The dart impact test shall be carried out in accordance with the provisions of GB / T9639.1-2008A. Single specimens shall be used, and the step method shall not be used. The number of samples without breakage shall be determined by fixing the dart mass. The dart mass is 50g and the number of samples is 10.

[0205] Heat resistance test: Overlap two surfaces, apply a load of 4.9N on them, and place them in an oven at 80℃ for 1 hour. After removing them, immediately separate the two overlapping samples and check for any abnormalities such as adhesion or melting marks on the surfaces.

[0206] Cold resistance test: Take 4 samples, about 300 mm long and 20 mm wide, from the test film or bag. Place the other two samples in a constant temperature chamber at -22℃ for more than 2 hours. After taking out the samples, fold them 180° along their length and check the film surface for any damage, cracks or other abnormalities.

[0207] Lifting test: Bag fatigue testing machine, amplitude 30mm±2mm, frequency 2~3Hz. Put a simulated substance (such as sand, rice grains, etc.) equivalent to the nominal load and whose volume does not exceed two-thirds of the effective solvent of the bag into the bag, and then suspend it on the testing machine. Test 1800 times and observe the bag body and the handle for any damage. The number of tests is 3.

[0208] Drop test: Fill the bag with a simulated object (such as sand, rice grains, etc.) that is equivalent to the nominal weight and whose volume does not exceed two-thirds of the effective volume of the bag. Remove the excess air, and seal the bag opening with adhesive tape while keeping the upper bag film fully relaxed. Drop the bag freely from a height of 0.5m above the bottom. The test ground should be a smooth, flat and hard surface. Observe whether the simulated object (such as sand, rice grains, etc.) leaks out. The number of tests is 3.

[0209] Oxygen permeability: Referring to the national standard GB / T1038-2000, select film samples with intact surfaces, and use a matching film cutter to cut the four ratio films into circular samples with a diameter of 960 mm. Place them in the oxygen permeability instrument, seal them strictly, set the vacuum time to 2 h, the temperature to 23 ℃, and the pre-permeability time to 15 min. Connect the air and conduct the air permeability performance test. Perform 3 parallel tests for each type of film, and take the average as the experimental result.

[0210] Water vapor transmission rate: Referring to the national standard GB / T1037-1988, film samples with intact surfaces were selected. Using a matching film cutter, four different film ratios were cut into circular samples with a diameter of 800 mm. The samples were placed in a moisture permeability instrument with 100% humidity in the test cup and 10% humidity in the test chamber. The temperature was raised and stabilized for 3 hours. The moisture permeability test was conducted at 38℃. Three parallel tests were performed for each type of film, and the average value was taken as the experimental result.

[0211] The fully biodegradable composite membranes prepared in Examples 1-4 meet the performance requirements of GB / T38082-2019 and GB / T21661-2020. Other performance results are shown in Table 2. The performance results of the biodegradable membranes prepared in Comparative Examples 1-7 are shown in Table 3.

[0212] Table 2 Performance test results of Examples 1-4

[0213]

[0214] Table 3 Performance test results for Comparative Examples 1-7

[0215]

[0216]

[0217] A comparison of the test results from the examples and comparative examples shows that, under the same testing conditions, a standard test thickness of 30 μm is optimal for biodegradable plastic shopping bags:

[0218] (1) In Comparative Example 1, the intermediate layer material was prepared by one-step melt mixing. PPC was not effectively inserted into montmorillonite, and montmorillonite was not effectively peeled off. The intermediate layer melt mixing effect was poor, and the intermediate layer material did not form a dense protective layer. The prepared film had low physical properties and poor barrier properties.

[0219] (2) In Comparative Example 2, the middle layer raw material was prepared by adding commercially available montmorillonite in a two-step process. The montmorillonite was not modified by ion exchange with dioctadecyl dimethyl ammonium chloride, the montmorillonite was not effectively peeled off, and the PPC was not effectively inserted into the montmorillonite interlayer, resulting in the prepared film failing both the lifting and drop tests.

[0220] (3) In Comparative Example 3, PPC, PLA and PBAT were first melt-blended and modified to prepare the first masterbatch. Then, the modified montmorillonite prepared in the same way as in the Example was melt-blended in the second step. Finally, the film was blown. PPC was not effectively inserted into the montmorillonite layers, and it did not further promote the effective isolation of the montmorillonite sheets. It did not promote the formation of a dense barrier protective layer of the middle layer raw material, resulting in poor film barrier properties.

[0221] (4) Comparative Example 4 is an example in CN 106633722 A. The carbon nanotubes were pretreated using the same method as in CN 106633722 A, and qualified biodegradable material was prepared by two-step melt mixing. Biodegradable plastic shopping bags were made using the blown film process consistent with the present invention. Although the shopping bags have high tear strength and toughness, they have a lot of added components and poor puncture resistance. Cracks appeared in the cold resistance test, and damage occurred in the drop test and lifting test. At the same time, the film does not have barrier properties.

[0222] (5) Comparative Example 5 is an example in CN 109486138 A. Biodegradable plastic shopping bags were prepared using the same method as in CN 109486138 A. The raw material composition is relatively simple, the price of PHA is high, the degree of commercialization is low, and PHA has low toughness, increased brittleness, poor puncture resistance, and failed the dart impact test. The prepared biodegradable plastic shopping bags are more sensitive to changes in external temperature, and both the cold resistance test and the heat resistance test failed, resulting in poor barrier performance.

[0223] (6) Comparative Example 6 is an example in CN113881110A. A fully biodegradable composite film was prepared using the preparation method in CN113881110A. Since the first and third layers use 70-90 parts by weight of plasticized starch, which is a relatively high proportion, the prepared film is difficult to meet the requirements of the lifting test and drop test. The composite film prepared has poor adhesion between layers and poor physical properties.

[0224] (7) Comparative Example 7 is a brand-name biodegradable plastic shopping bag that has good mechanical properties, but it is not suitable for high-end packaging applications. It is prone to breakage when encountering hard objects, and the overall puncture resistance of the shopping bag is poor. In addition, its barrier properties are poor.

[0225] The intermediate layer raw material of this invention fully utilizes the two-dimensional lamellar structure of montmorillonite. Modified montmorillonite is prepared through cation exchange, increasing the interlayer spacing of montmorillonite while improving the microenvironment within the layers. This allows the organic long-chain dioctadecyl cations entering the interlayers to effectively change the surface of the montmorillonite layers to be oleophilic and hydrophobic, reducing the surface energy between the layers. This allows PPC to insert into the montmorillonite layers for reaction. The PPC molecular chain contains carbonyl groups and ether bonds, exhibiting high molecular chain mobility during melting. Simultaneously, some montmorillonite can act as a nucleating agent, promoting heterogeneous nucleation of PPC, reducing spherulites, and resulting in regular, smooth grains that are regularly arranged and tightly packed between the montmorillonite layers, increasing air resistance and improving gas barrier properties. The insertion of PPC further increases the interlayer spacing of montmorillonite, achieving effective peeling of the montmorillonite layers. The first masterbatch in the intermediate layer forms a disordered "PPC regularly arranged inserted" montmorillonite layered structure. In the second step of preparing the intermediate layer masterbatch, the specific epoxy functional group structure of the chain extender effectively reduces the regularity of PLA and increases its branching degree. Simultaneously, low-molecular-weight PBAT is interspersed within, forming a "networked" structure. The two masterbatches from the first and second steps are melt-blended in the intermediate layer. The "regularly arranged intercalated" montmorillonite layered structure of the intermediate layer is uniformly distributed into the second masterbatch. The entire composite material fully integrates the complementary microstructures of inorganic materials and polymers, arranging the disordered "regularly arranged intercalated" montmorillonite layered structure to form a dense protective layer similar to "PLA / PBAT matrix - MMT sheets - regularly arranged PPC - MMT sheets - PLA / PBAT matrix," effectively blocking gas flow. Furthermore, the addition of the chain extender ensures good compatibility between the matrix materials, and the cross-networked structure of PLA and PBAT also gives the composite film good impact resistance, puncture resistance, and tear resistance. The outer layer material uses inexpensive and easily modified calcium carbonate as a filler, which reduces the production cost of the composite film while improving its overall physical properties, stacking performance, and impact resistance. In this embodiment of the invention, all three layers use PLA and PBAT as matrix materials, exhibiting strong adhesion between layers. By adding different additives and fillers, the advantages of the three film materials are combined to achieve a synergistic effect of "1+1+1>>3," improving the overall performance of the film. The resulting film exhibits strong tear resistance, good impact resistance, and can meet the requirements of high and low temperature operating environments, demonstrating a good balance of rigidity and toughness, as well as barrier properties.

[0226] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0227] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

[0228] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A fully biodegradable composite membrane, comprising an outer layer, a middle layer, and an inner layer arranged sequentially from the outside to the inside, wherein the thickness ratio of the outer layer, the middle layer, and the inner layer is 1:(1~1.5):1; wherein, By weight: The outer layer comprises: 30-40 parts modified calcium carbonate, 20-40 parts PLA, 20-50 parts PBAT, and 0.2-0.5 parts epoxy chain extender; The middle layer comprises: 10-15 parts modified montmorillonite, 5-10 parts PLA, 10-25 parts PBAT, 45-70 parts PPC, and 0.2-0.5 parts epoxy chain extender. The inner layer comprises: 30-45 parts PLA, 50-65 parts PBAT, and 0.2-0.5 parts epoxy chain extender; The method for preparing the intermediate layer raw material includes: (i) dividing the epoxy chain extender used in the intermediate layer into two parts, epoxy chain extender A and epoxy chain extender B, and preparing the first intermediate layer masterbatch by mixing PPC, modified montmorillonite and epoxy chain extender A; (ii) preparing the second intermediate layer masterbatch by mixing PLA, PBAT and epoxy chain extender B; (iii) mixing the first intermediate layer masterbatch and the second intermediate layer masterbatch evenly, extruding and granulating to obtain the intermediate layer raw material. The modified calcium carbonate is prepared by modifying commercially available calcium carbonate using a first organic modifier, which includes bis(octadecyl)dimethylammonium chloride. The modified montmorillonite is prepared by modifying commercially available bentonite using a second organic modifier, which includes dioctadecyldimethylammonium chloride.

2. The fully biodegradable composite membrane as described in claim 1, wherein, The total thickness of the fully biodegradable composite membrane is 30–40 μm, and the thickness ratio of the outer layer, middle layer and inner layer is 1:(1–1.5):

1.

3. The fully biodegradable composite membrane as described in claim 1, wherein, The PLA is polylactic acid with a weight-average molecular weight of 100,000 to 250,000; the PBAT is polybutylene adipate / terephthalate with a weight-average molecular weight of 50,000 to 100,000; the PPC has a number-average molecular weight of 30,000 to 50,000, a molecular weight distribution between 3 and 6, a carbon dioxide content greater than 40%, and a density of 1.23 to 1.32 g / cm³. 3 .

4. The fully biodegradable composite membrane as described in claim 1, wherein, The epoxy chain extender is one or more copolymers of cyclohexyl acrylate, glycidyl methacrylate, and methyl methacrylate with styrene.

5. A method for preparing the fully biodegradable composite membrane as described in any one of claims 1-4, comprising the steps of: (1) Preparation of modified calcium carbonate: Calcium carbonate is organically modified using a first organic modifier to obtain the modified calcium carbonate; (2) Preparation of modified montmorillonite: montmorillonite is organically modified using a second organic modifier to obtain the modified montmorillonite; (3) Preparation of outer layer raw materials: The modified calcium carbonate, PLA, PBAT and chain extender of the outer layer formula are dried, stirred evenly, and extruded and granulated to obtain the outer layer raw materials; (4) Preparation of intermediate layer raw materials: (4.1) The epoxy chain extender used in the middle layer is divided into two parts: epoxy chain extender A and epoxy chain extender B. The middle layer first masterbatch is prepared by mixing PPC, modified montmorillonite and epoxy chain extender A in the middle layer formulation. (4.2) The second masterbatch of the middle layer was prepared by mixing PLA, PBAT and epoxy chain extender B in the middle layer formulation; (4.3) Mix the first masterbatch and the second masterbatch of the middle layer evenly, and extrude and granulate to obtain the middle layer raw material; (5) Preparation of inner layer raw materials: The inner layer formulation of PLA, PBAT and epoxy chain extender is dried, stirred evenly, extruded and granulated to obtain the inner layer raw materials; (6) Blowing film: using the outer layer material, middle layer material and inner layer material to perform three-layer co-extrusion blown film to obtain the fully biodegradable composite film.

6. The method for preparing the fully biodegradable composite membrane as described in claim 5, wherein, The preparation of modified calcium carbonate in step (1) specifically includes: (1.1) Calcium carbonate is vacuum dried to obtain dried calcium carbonate; (1.2) Place 10-50 parts by weight of dried calcium carbonate into 100-1000 parts by weight of the first solution and mix them evenly to obtain suspension A1; the first solution is an aqueous solution of ethylene glycol, wherein the volume ratio of ethylene glycol to deionized water is 80-90:10-20. (1.3) Dissolve 0.1-3 parts by weight of the first organic modifier in 300-1200 parts by weight of the first solution, mix well, and obtain suspension A2; (1.4) The suspension A1 is ultrasonically dispersed, and the suspension A2 is slowly added dropwise to the suspension A1 while ultrasonically dispersing. The suspension is ultrasonically dispersed at 70-80℃ for 4-6 hours until it is uniformly mixed. The modified calcium carbonate is obtained by filtration, drying and pulverizing.

7. The method for preparing the fully biodegradable composite membrane as described in claim 5, wherein, The preparation of modified montmorillonite in step (2) specifically includes: (2.1) Purification of commercially available montmorillonite: Add 1-50 parts by weight of commercially available montmorillonite to 100-1000 parts by weight of water, stir at high speed at 50-80℃ to form a suspension system, remove the precipitate in the suspension system, and then add 1-20 parts by weight of trichloroacetic acid to the suspension system and stir evenly to obtain suspension B1. (2.2) Dissolve 0.1-10 parts by weight of the second organic modifier in 20-300 parts by weight of anhydrous ethanol to form solution B2; (2.3) Add solution B2 dropwise to suspension B1 at 70-90℃ while stirring. The addition time is controlled within 0.5-3h to obtain modified montmorillonite suspension. Then wash, filter, dry and crush it to obtain the modified montmorillonite.

8. The method for preparing the fully biodegradable composite membrane according to any one of claims 5-7, wherein, The modified montmorillonite has a particle size of 50-150 micrometers, and the modified calcium carbonate has a particle size of 10-20 micrometers.

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