Highly permeable and highly barrier degradable film and method of making the same

Abstract

The application discloses a high-transparency and high-barrier degradable film and a preparation method thereof, and relates to the technical field of degradable films. The outer layer is crosslinked by an initiator and a crosslinking agent to crosslink PLA and flexible PPC, compatibility of the outer layer is enhanced, and the outer layer has better mechanical properties; the intermediate layer is made of flexible PPCU with excellent water resistance and PGA with excellent gas resistance, modified nano montmorillonite is directionally intercalated in the PPCU / PGA matrix, and a three-dimensional barrier network is formed through crosslinking of isocyanate, so that the intermediate layer has better mechanical properties and barrier properties; the inner layer is crosslinked by an initiator and a crosslinking agent to crosslink PLA and PBAT, compatibility of the two is increased, and finally, the high-transparency and high-barrier degradable film with better toughness is prepared.

Description

Technical Field

[0001] This invention relates to the field of biodegradable film technology, specifically to a high-transmittance, high-barrier biodegradable film and its preparation method. Background Technology

[0002] With increasing environmental awareness, the environmental problems of traditional petroleum-based plastic films are becoming increasingly prominent. Materials such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and nylon (PA), while having long dominated core applications in food preservation, pharmaceutical packaging, electronic product protection, and industrial product storage due to their excellent mechanical strength, ease of processing, low cost, and specific barrier properties (such as PE's water vapor resistance and PET / PA's oxygen barrier properties), have become a major source of "white pollution" because their degradation cycle in the natural environment can take decades or even centuries.

[0003] These types of plastic waste not only damage soil structure and clog waterways, leading to ecosystem imbalance, but also break down into microplastics, which accumulate in the food chain and ultimately threaten human health. Therefore, developing biodegradable and compliant alternative materials has become an urgent need for the industry.

[0004] Current biodegradable film solutions on the market still face significant technical bottlenecks. For example, Chinese invention patent CN119039648A discloses a biodegradable transparent high-barrier film and its preparation method. Although it uses biodegradable substrates such as PLA (polylactic acid) and PBAT (polybutylene terephthalate), and employs vacuum deposition (SiO2)... x or AlO x While coating processes can achieve high barrier properties and transparency, this technology has two major drawbacks: First, the process is complex, requiring additional steps such as coating and curing, which not only increases equipment investment costs but also extends the production cycle, making it difficult to meet the needs of large-scale industrial mass production. Second, the interfacial bonding between the coating layer and the substrate is weak, making it prone to delamination and cracking during subsequent film processing or use, resulting in a sharp drop in barrier performance and failing to meet the "long-term preservation" requirements of food packaging.

[0005] Furthermore, the performance limitations of existing single biodegradable materials (such as pure PLA and pure PPC) restrict their applications. While pure PLA films offer high transparency and are fully biodegradable, they are brittle, have poor hydrolysis resistance, and are prone to degradation and failure in humid environments. Pure PPC films exhibit excellent flexibility but poor gas barrier properties, failing to meet the demands of high-barrier applications. PBAT films, while possessing outstanding toughness, suffer from low transparency and poor water resistance, making it difficult to achieve both high transparency and high barrier properties when used alone. Therefore, developing a biodegradable film with a simple process, controllable cost, and the ability to simultaneously achieve high transparency, high barrier properties, and excellent mechanical properties has become a key direction for overcoming current technological bottlenecks. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a high-transparency and high-barrier biodegradable film and its preparation method. The outer layer uses an initiator and a crosslinking agent to crosslink PLA with flexible PPC, enhancing their compatibility and giving the outer layer better mechanical properties. The middle layer uses flexible PPCU with excellent water resistance and PGA with excellent gas resistance, and modified nano-montmorillonite is directionally intercalated into the PPCU / PGA matrix. Then, a three-dimensional barrier network is formed through the crosslinking effect of isocyanate, giving the middle layer better mechanical and barrier properties. The inner layer uses an initiator and a crosslinking agent to crosslink PLA and PBAT, increasing their compatibility, and finally obtaining a high-transparency and high-barrier biodegradable film with better toughness.

[0007] The technical solution of this invention is as follows:

[0008] On the one hand, the present invention provides a high-transmittance, high-barrier biodegradable film, wherein the biodegradable film is a three-layer co-extruded film, and the formulation of each layer is as follows:

[0009] The inner layer is composed of 70-90 parts PLA, 10-30 parts PBAT, 0.1-0.5 parts initiator, 0.1-1.5 parts crosslinking agent, and 0.5-1 parts anti-hydrolysis agent; wherein the mass ratio of initiator to crosslinking agent is 1:(1-3).

[0010] The intermediate layer consists of 75-90 parts PPCU (carbon dioxide-based thermoplastic polyurethane elastomer), 10-25 parts PGA (polyglycolic acid), 0.5-2 parts modified nano-montmorillonite, and 0.1-2 parts isocyanate; wherein, the modified nano-montmorillonite is nano-montmorillonite modified with a silane coupling agent.

[0011] The outer layer is composed of 70-90 parts PLA, 10-30 parts PPC (polymethyl ethylene carbonate), 0.1-0.5 parts initiator, and 0.1-1.5 parts crosslinking agent; wherein the mass ratio of initiator to crosslinking agent is 1:(1-5).

[0012] Preferably, the initiator is dicumyl peroxide (DCP).

[0013] Preferably, the crosslinking agent is urea triallyl isocyanate (TAIC), with the following structure:

[0014] .

[0015] Preferably, the anti-hydrolysis agent is polycarbodiimide.

[0016] Preferably, the isocyanate is toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isoflurone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), phenylmethylene diisocyanate (XDI), or tetramethyl-isophenylmethylene diisocyanate (TMXDI).

[0017] Preferably, the silane coupling agent is KH550.

[0018] Preferably, the inner layer accounts for 15-30% of the total film thickness, the middle layer accounts for 40-70% of the total film thickness, and the outer layer accounts for 15-30% of the total film thickness.

[0019] On the other hand, the present invention provides a method for preparing the above-mentioned high-transparency and high-barrier biodegradable film. The biodegradable film is first granulated by twin-screw extrusion according to the formulation of each layer, and then subjected to three-layer co-extrusion blow molding to obtain the high-transparency and high-barrier biodegradable film.

[0020] Preferably, the extrusion granulation temperature is 130-220℃.

[0021] Preferably, the molding temperature is 130-220℃.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention achieves a "functional complementarity and performance synergy" effect through differentiated formulation design of the outer, middle, and inner layers. The outer layer uses PLA as the substrate, and through the cross-linking effect of initiators and cross-linking agents, PLA is tightly bonded to PPC with excellent flexibility, effectively solving the problem of PLA's high brittleness. The middle layer innovatively adopts a composite system of "PPCU + PGA + modified nano-montmorillonite + isocyanate", where PPCU provides flexibility and water resistance, PGA provides excellent gas barrier properties, and modified nano-montmorillonite is oriented and intercalated into the matrix, forming a three-dimensional barrier network with the cross-linking effect of isocyanate. This significantly reduces the water vapor permeability of the middle layer compared to pure PPCU, and also significantly reduces the oxygen permeability compared to pure PGA, becoming the core guarantee for the film's high barrier properties. The inner layer uses PLA / PBAT as the substrate, and improves compatibility through cross-linking agents and initiators. At the same time, an anti-hydrolysis agent is added, which not only improves the toughness of the inner layer, but also solves the problem of PBAT's poor hydrolysis resistance, ensuring the film's long-term stable use in humid packaging scenarios (such as fresh and cooked food).

[0024] 2. All raw materials used in this invention are fully biodegradable: PLA, PBAT, PPC, PPCU, and PGA can be decomposed into carbon dioxide and water by microorganisms within 6-12 months in natural environments (soil, seawater, composting conditions), leaving no residual pollutants; modified nano-montmorillonite is a natural clay mineral that can be absorbed by the soil and will not cause secondary pollution; the amount of initiators, crosslinking agents, anti-hydrolysis agents, and other additives added is extremely small, and they can be metabolized into harmless small molecules by microorganisms during the degradation process. Therefore, the biodegradable film of this invention can completely replace traditional petroleum-based plastic films, solving the problem of "white pollution" at its source.

[0025] 3. This invention employs an integrated process of "twin-screw extrusion granulation + three-layer co-extrusion blow molding," eliminating the need for additional complex processes such as coating and plating, thus shortening the production process and reducing equipment investment costs. Simultaneously, the process parameters are highly controllable, with extrusion granulation and molding temperatures both controlled within 130-220℃, making it compatible with existing plastic processing equipment (without requiring large-scale production line modifications). Furthermore, the high uniformity of raw material mixing across each layer meets the demands of industrial mass production for "high efficiency, stability, and low cost," giving it a strong competitive edge in the market.

[0026] 4. This invention uses highly transparent PLA and PPCU as the main substrates, and no light-blocking additives (such as talc or calcium carbonate) are added to the formulation of each layer. Through cross-linking process and optimized blending ratio, interfacial scattering is further reduced, improving the light transmittance of the film and reducing haze. Its high transparency makes it suitable for scenarios with high demands for "visual packaging," such as food (e.g., baked goods, fruits) and pharmaceuticals (e.g., capsules, tablets), allowing consumers to directly observe the contents and enhancing product shelf appeal.

[0027] 5. Through the optimization of cross-linking processes and composition of each layer, the mechanical properties of the film of this invention have been comprehensively improved. It can withstand the external forces during processing and use, such as folding and stretching, and is not easily damaged. It can be widely used in various scenarios such as fresh food preservation, cooked food packaging, pharmaceutical inner packaging, and moisture-proof packaging for electronic products, solving the problem of "poor mechanical properties and limited application scenarios" of existing biodegradable films. Attached Figure Description

[0028] Figure 1 These are haze and transmittance test graphs of the biodegradable films of Examples 1-8 of the present invention.

[0029] Figure 2 These are haze and transmittance test charts of the films of Comparative Examples 1-10 of this invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0031] The sources of some of the raw materials in the following examples are as follows:

[0032] PPC, Nanyang Zhongju Tianguan Low Carbon Technology Co., Ltd.

[0033] PPCU, Jiangsu Zhongke Jinlong Environmental Protection New Materials Co., Ltd.

[0034] PGA, Kureha Japan Co., Ltd.

[0035] The biodegradable films prepared in the following examples and comparative examples all have a thickness of 100 μm.

[0036] Example 1

[0037] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0038] Preparation of S1 outer layer material: 70 parts PLA, 30 parts PPC, 0.3 parts DCP and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0039] Preparation of S2 intermediate layer material: 80 parts PPCU, 20 parts PGA, 1.5 parts HDI and 1.2 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 210℃, 200℃ and 200℃.

[0040] Preparation of S3 inner layer material: 80 parts PLA, 20 parts PBAT, 0.5 parts polycarbodiimide, 0.4 parts DCP, and 1.2 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0041] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0042] Example 2

[0043] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0044] Preparation of S1 outer layer material: 90 parts PLA, 10 parts PPC, 0.5 parts DCP and 1.5 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0045] Preparation of S2 intermediate layer material: 90 parts PPCU, 10 parts PGA, 2 parts TDI and 2 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 200℃ and 200℃.

[0046] Preparation of S3 inner layer material: 90 parts PLA, 10 parts PBAT, 1 part polycarbodiimide, 0.5 parts DCP, and 1.5 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0047] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 30μm, and the thickness of the middle layer was 40μm.

[0048] Example 3

[0049] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0050] Preparation of S1 outer layer material: 80 parts PLA, 20 parts PPC, 0.2 parts DCP and 0.5 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0051] Preparation of S2 intermediate layer material: 80 parts PPCU, 20 parts PGA, 1 part MDI and 1 part modified nano montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 200℃ and 200℃.

[0052] Preparation of S3 inner layer material: 80 parts PLA, 20 parts PBAT, 0.7 parts polycarbodiimide, 0.4 parts DCP, and 0.8 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0053] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0054] Example 4

[0055] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0056] Preparation of S1 outer layer material: 70 parts PLA, 30 parts PPC, 0.3 parts DCP and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0057] Preparation of S2 intermediate layer material: 80 parts PPCU, 20 parts PGA, 1.2 parts HMDI and 1 part modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 200℃ and 200℃.

[0058] Preparation of S3 inner layer material: 80 parts PLA, 20 parts PBAT, 0.5 parts polycarbodiimide, 0.4 parts DCP, and 1.2 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0059] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0060] Example 5

[0061] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0062] Preparation of S1 outer layer material: 70 parts PLA, 30 parts PPC, 0.1 parts DCP and 0.1 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0063] Preparation of S2 intermediate layer material: 75 parts PPCU, 25 parts PGA, 0.1 parts HDI and 0.5 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 210℃, 200℃ and 200℃.

[0064] Preparation of S3 inner layer material: 70 parts PLA, 30 parts PBAT, 0.5 parts polycarbodiimide, 0.1 parts DCP, and 0.1 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0065] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 15μm, and the thickness of the middle layer was 70μm.

[0066] Example 6

[0067] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0068] Preparation of S1 outer layer material: 70 parts PLA, 30 parts PPC, 0.3 parts DCP and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0069] Preparation of S2 intermediate layer material: 90 parts PPCU, 10 parts PGA, 1.2 parts TMXDI and 1.5 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 210℃, 200℃ and 200℃.

[0070] Preparation of S3 inner layer material: 70 parts PLA, 30 parts PBAT, 1 part polycarbodiimide, 0.4 parts DCP, and 1.2 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0071] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0072] Example 7

[0073] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0074] Preparation of S1 outer layer material: 80 parts PLA, 20 parts PPC, 0.3 parts DCP and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0075] Preparation of S2 intermediate layer material: 75 parts PPCU, 25 parts PGA, 1.2 parts XDI and 1.8 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 210℃, 200℃ and 200℃.

[0076] Preparation of S3 inner layer material: 70 parts PLA, 30 parts PBAT, 0.5 parts polycarbodiimide, 0.4 parts DCP, and 1.2 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0077] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0078] Example 8

[0079] The high-transparency, high-barrier biodegradable film in this embodiment is a three-layer co-extruded film, and its preparation method is as follows:

[0080] Preparation of S1 outer layer material: 70 parts PLA, 30 parts PPC, 0.3 parts DCP and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃ and 185℃.

[0081] Preparation of S2 intermediate layer material: 75 parts PPCU, 25 parts PGA, 1.2 parts IPDI and 2 parts modified nano-montmorillonite were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 140℃, 160℃, 190℃, 210℃, 210℃, 200℃ and 200℃.

[0082] Preparation of S3 inner layer material: 90 parts PLA, 10 parts PBAT, 0.5 parts polycarbodiimide, 0.3 parts DCP, and 0.9 parts TAIC are mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 130℃, 145℃, 180℃, 195℃, 195℃, 195℃, 190℃, and 185℃.

[0083] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder. The screw temperatures for the outer layer were 170℃, 180℃, 195℃, 195℃, and 195℃; for the middle layer, they were 180℃, 190℃, 210℃, 210℃, and 210℃; and for the inner layer, they were 170℃, 180℃, 195℃, 195℃, and 195℃. The die temperature was 200℃. The thickness of the outer and inner layers was 20μm, and the thickness of the middle layer was 60μm.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that neither DCP nor TAIC is added to the outer layer material or the inner layer material, and neither HDI nor modified nano-montmorillonite is added to the middle layer material.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that neither DCP nor TAIC is added to the outer layer material or the inner layer material.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that no DCP is added to either the outer or inner layer material.

[0090] Comparative Example 4

[0091] The difference from Example 1 is that no TAIC is added to either the outer or inner layer material.

[0092] Comparative Example 5

[0093] The difference from Example 1 is that the amount of DCP added in the outer layer material is 1.8 parts, and the amount of DCP added in the inner layer material is 1.8 parts.

[0094] Comparative Example 6

[0095] The difference from Example 1 is that no HDI is added to the intermediate layer material.

[0096] Comparative Example 7

[0097] The difference from Example 1 is that no modified nano-montmorillonite is added to the intermediate layer material.

[0098] Comparative Example 8

[0099] The difference from Example 1 is that an equal amount of PPCU is used instead of PGA.

[0100] Comparative Example 9

[0101] The difference from Example 1 is that an equal amount of PGA is used instead of PPCU.

[0102] Comparative Example 10

[0103] The biodegradable film of Comparative Example 10 is a three-layer co-extruded film, and its preparation method is as follows:

[0104] Preparation of S1 outer layer material: 100 parts PBAT, 0.5 parts polycarbodiimide, 0.4 parts light stabilizer 944, and 0.7 parts tristearate were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 180℃, 170℃, and 160℃.

[0105] Preparation of S2 intermediate layer material: 45 parts of PPC-TPU, 54.2 parts of PPCP and 0.8 parts of MDI were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 180℃, 170℃ and 160℃.

[0106] Preparation of S3 inner layer material: 10 parts PLA, 90 parts PBAT, 1.1 parts polycarbodiimide, 1 part talc, and 3.5 parts nano zinc oxide were mixed evenly and then melt-blended in a twin-screw extruder at temperatures of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 180℃, 170℃, and 160℃.

[0107] Preparation of S4 biodegradable film: The outer layer, middle layer, and inner layer materials were blow-molded into a film using a three-layer co-extrusion extruder with screw temperatures of 120℃, 140℃, 170℃, 150℃, and 150℃. The outer and inner layers were both 20μm thick, and the middle layer was 60μm thick.

[0108] The barrier properties and mechanical properties of the biodegradable films from Examples 1-8 and Comparative Examples 1-10 were tested using the following methods: oxygen permeability was tested according to GB / T 1038.1-2022 "Test Methods for Gas Permeability of Plastic Films and Sheets Part 1: Differential Pressure Method"; water vapor permeability was tested according to GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Weight Gain and Loss Method"; tensile strength and elongation at break were tested according to GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics Part 2: Test Conditions for Molded and Extruded Plastics". The test results are shown in Table 1.

[0109] Table 1 Performance test results of the biodegradable films of Examples 1-8 and Comparative Examples 1-10

[0110]

[0111] As can be seen from the above data, compared with Example 1, Comparative Example 1 has no physical barrier of modified nano-montmorillonite in the middle layer and no HDI to improve the compatibility of PPCU and PGA. The inner and outer layers are not cross-linked, and the molecular chains are loosely stacked, resulting in extremely poor film barrier properties. The inner layer PLA / PBAT and the outer layer PLA / PPC are only simple physical blends with poor compatibility and fragile phase interfaces. The middle layer PPCU / PGA also has poor compatibility and cannot effectively transfer stress, resulting in poor mechanical properties.

[0112] Compared with Example 1, the modified nano-montmorillonite in the middle layer of Comparative Example 2 provides partial barrier, and HDI improves the compatibility of PPCU and PGA. However, there is no cross-linking in the inner and outer layers, and PLA / PBAT is only a simple physical blend with poor compatibility, which affects the interlayer bonding and causes a deterioration in barrier properties and mechanical properties.

[0113] Compared with Example 1, Comparative Example 3 only added TAIC to the outer and inner layers without adding DCP. TAIC could not effectively initiate cross-linking between PLA / PPC / PBAT molecular chains. The cross-linking reaction was weak and no effective cross-linking network was formed, which led to a deterioration in the mechanical and barrier properties of the film.

[0114] Compared with Example 1, Comparative Example 4 only added DCP without TAIC to the outer and inner layers, which may cause degradation of the matrix such as PLA or limited free radical reactions, but cannot form a multifunctional cross-linked network, and may even lead to a decrease in molecular weight due to degradation, which is not as stable as simple blending.

[0115] Compared with Example 1, Comparative Example 5 had too much crosslinking agent added, which resulted in an overly dense network structure between polymer molecular chains, restricting the movement of chain segments. Excessive crosslinking caused the material to become brittle and the elongation at break to plummet.

[0116] Compared with Example 1, Comparative Example 6 has no HDI in the intermediate layer. The PPCU / PGA / modified nano-montmorillonite in the intermediate layer is mainly a simple physical blend with poor compatibility, which reduces the mechanical properties and barrier properties of the film.

[0117] Modified nano-montmorillonite sheets are key to constructing the "zigzag path" barrier effect. In Comparative Example 7, no modified nano-montmorillonite was added, resulting in a reduction in the oxygen barrier capacity of the film.

[0118] Compared with Example 1, Comparative Example 8 uses PPCU instead of PGA in the intermediate layer. Since PGA has excellent gas barrier properties, its absence significantly reduces the barrier ability of the film. PPCU is a flexible polyurethane material, which makes the film exceptionally flexible, but the strength will be reduced.

[0119] Compared with Example 1, Comparative Example 9 uses PGA instead of PPCU in the intermediate layer. Although PGA itself has good barrier properties, it is brittle and prone to microcracks or defects during processing and film formation. The actual barrier effect of the film is not as good as that of the PPCU / PGA blend system. Moreover, the PGA layer is brittle, which makes the film brittle overall and deteriorates its mechanical properties.

[0120] Compared with Example 1, the inner and outer layers of Comparative Example 10 are mainly composed of flexible PBAT, lacking rigid components and effective cross-linking reinforcement, resulting in low overall strength; it also lacks efficient oxygen barrier fillers like modified nano-montmorillonite and high-barrier resins like PGA, ultimately leading to poor oxygen barrier performance of the film.

[0121] The haze and light transmittance of the biodegradable films of Examples 1-8 and Comparative Examples 1-10 were tested according to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics". The test results are as follows: Figure 1-2 As shown in the figure:

[0122] Compared with Example 1, the inner PLA / PBAT, outer PLA / PPC, and middle PPCU / PGA layers in Comparative Example 1 are all simple physical blends with extremely poor compatibility, resulting in severe phase separation and the formation of numerous microscopic phase interfaces, which strongly scatter light. The middle layer is unmodified nano-montmorillonite, which reduces filler scattering, but severe phase separation is the dominant factor, leading to a decrease in the light transmittance and an increase in haze of the film.

[0123] Compared with Example 1, Comparative Example 2 has HDI and modified nano-montmorillonite in the middle layer, which has better compatibility. However, the inner and outer layers are not cross-linked, and there is still obvious phase separation between PLA and PPC / PBAT, resulting in higher haze and lower light transmittance of the film than in Example 1.

[0124] Compared with Example 1, Comparative Example 3 only added TAIC, which as a compatibilizer may have improved the interfacial compatibility between PLA and PPC / PBAT to some extent and reduced the degree of phase separation, but there is no effective cross-linking network and the uniformity is still not as good as Example 1.

[0125] Compared with Example 1, Comparative Example 4 only added DCP, which may cause degradation of the matrix such as PLA, resulting in a wider molecular weight distribution or the generation of a small number of small molecules, increasing the heterogeneity of the system, and may even exacerbate phase separation, thus resulting in higher film haze.

[0126] Compared to Example 1, the excessive DCP in Comparative Example 5 leads to over-crosslinking, which may cause the following problems: (1) the crosslinking density is too high and too fast, resulting in the phase separation kinetics being locked and forming a more significant heterogeneous structure; (2) it may be accompanied by severe degradation reactions, producing bubbles or impurities. Both greatly increase light scattering, thereby reducing the transmittance of the film and increasing the haze.

[0127] Compared with Example 1, in Comparative Example 6, the interfacial compatibility between the intermediate layer PPCU / PGA and the modified nano-montmorillonite is worse due to the lack of HDI compatibilizer. The modified nano-montmorillonite may agglomerate, and the number of phase interfaces increases, resulting in increased light scattering, increased haze of the film and decreased light transmittance.

[0128] The refractive index difference between the nanosheets and the polymer matrix, as well as the potential for some agglomeration, remain the main sources of light scattering. Therefore, in Comparative Example 7, without the addition of modified nano-montmorillonite, the intermediate layer becomes a homogeneous PPCU / PGA / HDI system (with good compatibility), which greatly reduces the number of scattering points, resulting in low haze and high transmittance of the film.

[0129] PGA is a highly crystalline polymer, and the refractive index difference between its grains and amorphous regions is the main source of scattering. Therefore, in Comparative Example 8, after replacing PGA with completely amorphous or low-crystallinity PPCU, the crystallinity of the intermediate layer was significantly reduced, resulting in excellent optical uniformity of the material. Consequently, the film exhibited low haze and high transmittance.

[0130] PGA layers have high crystallinity and fast crystallization speed, easily forming large spherulites, which cause strong light scattering. However, at the same time, single PGA materials are brittle and may generate more internal stress or micro-defects during film processing, resulting in poor light transmittance of the film in Comparative Example 9.

[0131] Compared with Example 1, Comparative Example 10 has PBAT as the main component in both the outer and inner layers (amorphous, with good light transmittance), but the inner layer contains inorganic fillers such as talc and nano zinc oxide. These fillers are the main sources of light scattering, resulting in a significantly higher haze of the film than in Example 1.

Claims

1. A highly transparent and highly barrier biodegradable film, characterized in that, The biodegradable film is a three-layer co-extruded film, and the formulation of each layer is as follows: The inner layer is composed of 70-90 parts PLA, 10-30 parts PBAT, 0.1-0.5 parts initiator, 0.1-1.5 parts crosslinking agent, and 0.5-1 parts anti-hydrolysis agent; wherein the mass ratio of initiator to crosslinking agent is 1:(1-3). The intermediate layer consists of 75-90 parts of carbon dioxide-based thermoplastic polyurethane elastomer, 10-25 parts of PGA, 0.5-2 parts of modified nano-montmorillonite, and 0.1-2 parts of isocyanate; wherein, the modified nano-montmorillonite is nano-montmorillonite modified with a silane coupling agent. The outer layer is composed of 70-90 parts PLA, 10-30 parts PPC, 0.1-0.5 parts initiator, and 0.1-1.5 parts crosslinking agent; wherein the mass ratio of initiator to crosslinking agent is 1:(1-5). Preparation method of high-transparency and high-barrier biodegradable film: The biodegradable film is first granulated by twin-screw extrusion according to the formula of each layer, and then co-extruded and blow-molded in three layers to obtain a high-transparency and high-barrier biodegradable film; the extrusion granulation temperature is 130-220℃; the molding temperature is 130-220℃.

2. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The initiator is dicumyl peroxide.

3. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The crosslinking agent is triallyl isocyanate urea.

4. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The anti-hydrolysis agent is polycarbodiimide.

5. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The isocyanate is toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, phenylmethylene diisocyanate, or tetramethyl isophenylmethylene diisocyanate.

6. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The silane coupling agent is KH550.

7. The high-transmittance, high-barrier biodegradable film as described in claim 1, characterized in that, The inner layer accounts for 15-30% of the total film thickness, the middle layer accounts for 40-70% of the total film thickness, and the outer layer accounts for 15-30% of the total film thickness.

Images