Biodegradable barrier composite film and preparation method thereof
By using PBAT as the main raw material, a three-layer structure design and physicochemical modification were employed to prepare a biodegradable barrier composite film with excellent barrier properties. This solved the problems of narrow thermoplastic windows and poor heat resistance of existing materials, enabling economical and efficient packaging applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Shuangzhi Packaging (Foshan) Co., Ltd.
- Filing Date
- 2026-02-05
- Publication Date
- 2026-05-12
AI Technical Summary
Existing biodegradable barrier film materials such as PHA and PPC have problems such as narrow thermoplastic windows, high processing difficulty, and poor heat resistance, making it difficult to meet the needs of packaging applications.
Using PBAT as the main raw material, a three-layer barrier composite membrane was prepared through physicochemical modification, including a water-blocking layer, an oxygen-blocking layer, and a water-blocking layer. The oxygen-blocking effect was improved by using PBAT-b-PA block copolymer, and the water-blocking performance was improved by combining hydrophobically modified PBAT.
A balance between barrier properties, biodegradability, and economy has been achieved, resulting in a biodegradable barrier composite film with good mechanical strength and flexibility, suitable for packaging applications, and capable of large-scale production using conventional equipment.
Smart Images
Figure CN122008601A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of functional plastic composite film technology, and in particular to a biodegradable barrier composite film and its preparation method. Background Technology
[0002] Barrier films are functional films with low water vapor and oxygen permeability, commonly used in packaging to significantly inhibit gas exchange between the packaged contents and the external environment, thus extending shelf life and preserving food flavor. They are widely used in pharmaceuticals, food, and electronics. These films are generally used in fast-moving consumer goods (FMCG) and are mostly single-use, posing a significant environmental burden in the long run. Using biodegradable materials to prepare barrier films offers a win-win solution. Currently, biodegradable materials used to prepare barrier films typically include polyhydroxyalkanoates (PHA) and polypropylene carbonate (PPC). PHA has excellent oxygen and carbon dioxide barrier properties, while PPC offers superior water vapor barrier performance.
[0003] However, the drawbacks of the two materials mentioned above limit their applications. For example, PHA has a narrow thermoplastic window and is difficult to process; currently, it relies on microbial fermentation for production, resulting in low yield and high price. PPC has poor heat resistance and is easily deformed when heated, making it difficult to meet the needs of packaging applications. Therefore, how to prepare biodegradable barrier films using simple and easy methods remains a problem that needs to be overcome. Summary of the Invention
[0004] This invention overcomes the shortcomings of the prior art and provides a biodegradable barrier composite membrane and its preparation method. Using low-cost PBAT as the main raw material, it achieves a balance of barrier properties, biodegradability and economy through physicochemical modification, and is easy to scale up for production.
[0005] A method for preparing a biodegradable barrier composite membrane includes the following steps:
[0006] (1) Preparation of oxygen barrier layer masterbatch: PBAT, alkaline catalyst and diisocyanate are mixed and melt-reacted at 150-220℃ to react the terminal hydroxyl groups of PBAT with isocyanate to obtain PBAT prepolymer with isocyanate groups at the end; then caprolactam and its polymerization catalyst are added to the reaction system and melt-polymerized at 220-260℃ to allow caprolactam to undergo ring-opening polymerization initiated by the isocyanate groups at the end of the PBAT prepolymer. After the reaction is completed, granulation is performed to obtain PBAT-b-PA block copolymer masterbatch;
[0007] (2) Preparation of water barrier layer masterbatch: PBAT is mixed with hydrophobic modified PBAT, melt extruded and granulated to obtain water barrier layer masterbatch; the hydrophobic modified PBAT is a product of grafting long-chain alkanes with 1-30 carbon atoms onto the PBAT molecular chain.
[0008] (3) Co-extrusion film formation: The water barrier layer masterbatch obtained in step (2) is used as the outer layer raw material, and the PBAT-b-PA masterbatch obtained in step (1) is used as the middle layer raw material. They are put into a multi-layer co-extrusion equipment and melt-cast or blow-molded at 200-250℃ and cooled to obtain a biodegradable barrier composite film with a three-layer structure.
[0009] Furthermore, in step (1), the diisocyanate is isoflurone diisocyanate; the alkaline catalyst is sodium hydroxide; and the polymerization catalyst for caprolactam is sodium caprolactam salt.
[0010] Furthermore, in step (1), by mass, the PBAT is 100 parts, the diisocyanate is 1-6 parts, and the caprolactam is 40-220 parts.
[0011] Furthermore, in step (2), the amount of hydrophobic modified PBAT used is 40-80 parts by weight, based on 100 parts by weight of PBAT.
[0012] Furthermore, in step (2), the long-chain alkane has 10-20 carbon atoms, and the hydrophobically modified PBAT is obtained by graft polymerization of octadecyl acrylate in the presence of PBAT.
[0013] Furthermore, in step (2), when preparing the water-blocking layer masterbatch, the mixed raw materials also contain 0-10 parts by weight of filler and / or 0-5 parts by weight of functional additives; the filler is selected from at least one of calcium carbonate, talc, and montmorillonite; the functional additive is selected from at least one of antioxidants, ultraviolet absorbers, and opening agents.
[0014] Furthermore, in step (3), the co-extrusion film forming process parameters are controlled so that the total thickness of the final composite film is 0.01-0.30 mm, and the total thickness of the two water-blocking layers accounts for 60%-96% of the total film thickness, and the thickness of the oxygen-blocking layer accounts for 4%-40% of the total film thickness.
[0015] Furthermore, in step (3), the cooling temperature is 20-40°C.
[0016] A biodegradable barrier composite membrane is obtained directly by any of the preparation methods described above.
[0017] Furthermore, the composite membrane includes at least a first water-blocking layer, an oxygen-blocking layer, and a second water-blocking layer stacked sequentially; the oxygen-blocking layer includes a PBAT-b-PA block copolymer, and both the first water-blocking layer and the second water-blocking layer include PBAT and hydrophobically modified PBAT.
[0018] The first water-blocking layer and / or the second water-blocking layer further include 0-10 parts by weight of filler and / or 0-5 parts by weight of functional additives.
[0019] The present invention provides a biodegradable barrier composite membrane comprising at least three layers, which, from top to bottom, are a first water-blocking layer, an oxygen-blocking layer, and a second water-blocking layer.
[0020] The thickness of the biodegradable barrier composite film is 0.01-0.30 mm, preferably 0.03-0.20 mm. Within this thickness range, the composite film has good mechanical strength, meeting the requirements of practical packaging applications, while maintaining good flexibility without being too costly. The biodegradable barrier composite film has a biodegradability rate of ≥90%.
[0021] The first and second water-blocking layers of the biodegradable barrier composite membrane are located on both sides of the oxygen barrier layer, respectively, and serve to block water vapor. Their thickness accounts for 30-48% of the overall film thickness. The thickness of the first and second water-blocking layers can be the same or different.
[0022] The first water-blocking layer and the second water-blocking layer comprise the following components (in weight proportions):
[0023] Polybutylene terephthalate-adipate (PBAT) 100 copies Hydrophobic modified PBAT 40-80 servings filler 0-10 copies Functional additives 0-5 copies
[0024] The aforementioned PBAT resin is the main component of the water-blocking layer, serving as its mechanical support and meeting the requirements for biodegradability. Its melt flow index (190℃, 2.16kg) is 1-40g / 10min, which meets the flowability requirements of conventional processing equipment. The PBAT resin can be obtained commercially through conventional means.
[0025] The aforementioned hydrophobically modified PBAT is prepared by grafting long-chain alkanes onto the PBAT molecular chain. Its main function is to reduce the water vapor absorption and permeability of the water-blocking layer. The long-chain alkanes can be saturated or unsaturated hydrocarbon groups, with saturated hydrocarbon groups being preferred for better aging resistance. The long-chain alkanes can be straight-chain or branched, with 1-30 carbon atoms, preferably 10-20. Within this carbon atom range, the product exhibits good water-blocking properties and good compatibility with PBAT. The hydrophobically modified PBAT can be synthesized using existing publicly available techniques. For example, a typical synthesis method involves uniformly mixing 100g of dry PBAT resin, 3g of octadecyl acrylate, and 0.05g of dicumyl peroxide, then melt-extruding the mixture in a twin-screw extruder at a processing temperature of 160-190℃. The product is then air-cooled and pelletized.
[0026] The aforementioned fillers are not essential. Their addition can alter the film's appearance, color, transparency, and flexibility, and can also serve as a means of cost reduction. The fillers can be inorganic fillers, such as calcium carbonate, wollastonite, talc, silicon dioxide, alumina, and montmorillonite; or color fillers, such as titanium dioxide, carbon black, or one or more combinations thereof.
[0027] The aforementioned functional additives are not essential; their addition can introduce additional functionality. These functional additives can be selected from one or more of the following: antioxidants, UV absorbers, antistatic agents, antifogging agents, and opening agents.
[0028] The components contained in the first water-blocking layer and the second water-blocking layer may be the same or different.
[0029] The preparation method of the first and second water-blocking layers is as follows: Fully dried metered raw materials are added to a high-speed mixer and mixed evenly. Then, the mixture is fed into a twin-screw extruder for melt mixing and extrusion. The product is then air-cooled and pelletized to obtain the water-blocking layer material for later use. The melt processing temperature is 140-200℃.
[0030] The biodegradable barrier composite membrane has an oxygen barrier layer positioned between the first and second water barrier layers, serving to block oxygen. Its thickness accounts for 4-40% of the overall film thickness. This oxygen barrier layer is composed of a block copolymer of PBAT and polyamide (PA) (PBAT-b-PA). PBAT-b-PA is obtained by introducing isocyanate groups at the molecular ends of PBAT and then polymerizing the polyamide molecular chains in situ. Specifically, it can be prepared through the following steps.
[0031] 100 parts of fully dried PBAT resin, 0.2-2 parts of sodium hydroxide, and 1-6 parts of isoflurane diisocyanate (IPDI) are added to a high-speed mixer and mixed evenly. The mixture is then fed into a twin-screw extruder for the first-stage reaction at a temperature of 150-220°C. 40-220 parts of fully dried caprolactam and 4-20 parts of sodium caprolactam salt are pre-mixed and added through a side feed port to the twin-screw extruder for the second-stage reaction at a temperature of 220-260°C. The extruded product is then air-cooled and pelletized to obtain the PBAT-b-PA product.
[0032] In the first stage of the reaction, due to the significant difference in activity between the two isocyanate groups on the straight chain and alicyclic ring of IPDI, under these reaction conditions, the terminal hydroxyl groups of PBAT can selectively react with the isocyanate groups on the straight chain, thereby introducing isocyanate at the end of the PBAT molecular chain. Subsequently, in the second stage of the reaction, the isocyanate at the end of PBAT can initiate in-situ ring-opening polymerization of caprolactam under the catalysis of sodium caprolactam, thereby obtaining the PBAT-b-PA copolymer.
[0033] The second aspect of this invention is a method for preparing a biodegradable barrier composite film. Specifically, the raw materials for the first water-barrier layer, the oxygen-barrier layer, and the second water-barrier layer are respectively fed into the corresponding channels of a multilayer melt co-extrusion processing equipment. The film is formed by melt casting or melt blow molding, followed by cooling, winding, and slitting. The processing temperature is 200-250°C, and the cooling temperature is 20-40°C.
[0034] Compared with the prior art, the beneficial effects of the present invention are:
[0035] (1) This invention employs a three-layer composite structure formed in one step using conventional co-extrusion equipment. The water-blocking layer contains PBAT resin and hydrophobically modified PBAT. The former provides mechanical support, while the latter combines the biodegradability of PBAT with the water-blocking properties of long-chain alkanes, thereby preparing the outer water-blocking layer. The water-blocking layer protects the inner oxygen barrier layer from moisture damage on the one hand, and provides the composite membrane with good water-blocking properties on the other.
[0036] (2) The intermediate oxygen barrier layer is composed of PBAT-b-PA copolymer, which overcomes the problem of poor compatibility between PBAT and PA. PA segments form a dense structure through intermolecular hydrogen bonding, thereby providing good oxygen barrier effect. PBAT-b-PA and the water barrier layers on both sides have good interlayer bonding force, so there is no need to introduce additional adhesives, and it does not affect the biodegradability of the composite membrane.
[0037] (3) The long-chain alkane segments on the hydrophobically modified PBAT in the outer water-blocking layer are non-polar substances, while the PA segments on the PBAT-b-PA copolymer in the middle oxygen-blocking layer are polar substances. During the co-extrusion process, due to the large difference in polarity between the two, the long-chain alkane segments will spontaneously permeate and migrate to both sides of the composite membrane, increasing the density of hydrophobic segments on the surface of the composite membrane and further improving the water-blocking performance of the composite membrane.
[0038] (4) Compared with the use of expensive biodegradable raw materials such as PHA and PPC in existing technologies, this invention uses common PBAT resin as the main component, which has a wide range of raw material sources and low cost. Through physical and chemical modification treatment, combined with a unique three-layer structure design, a biodegradable composite film with excellent barrier properties is obtained. This invention can be produced using conventional thermoplastic processing equipment, can be mass-produced, is easy to promote, and has good market prospects. Attached Figure Description
[0039] The accompanying drawings are provided to further illustrate the invention and are used together with the embodiments of the invention to explain the invention. They do not constitute a limitation of the invention. In the drawings:
[0040] Figure 1 This is a schematic diagram of the structure of a biodegradable barrier composite membrane.
[0041] Figure 2 This is a schematic diagram of the first-stage synthesis reaction of the PBAT-b-PA block copolymer.
[0042] Figure 3 This is a schematic diagram of the second-stage synthesis reaction of the PBAT-b-PA block copolymer.
[0043] In the diagram: 1. First water barrier layer; 2. Oxygen barrier layer; 3. Second water barrier layer. Detailed Implementation
[0044] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0045] Example 1
[0046] like Figures 1 to 3 As shown, this embodiment provides a biodegradable barrier composite membrane, which is prepared according to the following steps:
[0047] (1) Preparation of the first water-blocking layer 1:
[0048] 100 parts of fully dried PBAT resin (melt index 5.0 g / 10 min), 50 parts of hydrophobically modified PBAT, 5 parts of nano-calcium carbonate, and 0.3 parts of opening agent were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 175°C. After extrusion, the product was air-cooled and pelletized to obtain the first water-blocking layer 1 material of this embodiment.
[0049] (2) Preparation of the second water-blocking layer 3:
[0050] The first water-blocking layer 1 is the same as in this embodiment.
[0051] (3) Preparation of oxygen barrier layer 2:
[0052] 100 parts of fully dried PBAT resin (melt index 20.0 g / 10 min), 0.8 parts of sodium hydroxide, and 4 parts of IPDI were added to a high-speed mixer and mixed evenly. The mixture was then fed into a twin-screw extruder for the first-stage reaction at 175°C. 160 parts of fully dried caprolactam and 15 parts of sodium caprolactam were pre-mixed and added to the twin-screw extruder through a side feed port for the second-stage reaction at 250°C. The extruded product was then air-cooled and pelletized to obtain the oxygen barrier layer 2 material of this embodiment.
[0053] (4) Preparation of biodegradable barrier composite membranes:
[0054] The raw materials for the first water-barrier layer 1, oxygen-barrier layer 2, and second water-barrier layer 3 are respectively fed into the corresponding channels of a multi-layer melt co-extrusion casting equipment. The layers are then melt-cast, cooled, wound, and slit to obtain the final product. The processing temperature is 230°C, and the cooling temperature is 20°C.
[0055] The biodegradable barrier composite membrane of this embodiment has a thickness of 0.14 mm, as tested. The first water-blocking layer 1 accounts for 40% of the total membrane thickness; the second water-blocking layer 3 accounts for 40% of the total membrane thickness; and the oxygen-blocking layer 2 accounts for 20% of the total membrane thickness.
[0056] Example 2
[0057] This embodiment provides a biodegradable barrier composite membrane, which is prepared according to the following steps:
[0058] (1) Preparation of the first water-blocking layer 1:
[0059] 100 parts of fully dried PBAT resin (melt index 30.0 g / 10 min), 40 parts of hydrophobically modified PBAT, and 0.2 parts of antioxidant were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 160°C. After extrusion, the product was air-cooled and pelletized to obtain the first water-blocking layer 1 material of this embodiment.
[0060] (2) Preparation of the second water-blocking layer 3:
[0061] 100 parts of fully dried PBAT resin (melt index 18.0 g / 10 min), 80 parts of hydrophobically modified PBAT, and 0.2 parts of antioxidant were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 160°C. After extrusion, the product was air-cooled and pelletized to obtain the second water-blocking layer 3 material of this embodiment.
[0062] (3) Preparation of oxygen barrier layer 2:
[0063] 100 parts of fully dried PBAT resin (melt index 3.0 g / 10 min), 2 parts of sodium hydroxide, and 2 parts of IPDI were added to a high-speed mixer and mixed evenly. The mixture was then fed into a twin-screw extruder for the first-stage reaction at a temperature of 195°C. 100 parts of fully dried caprolactam and 7 parts of sodium caprolactam salt were pre-mixed and added to the twin-screw extruder through a side feed port for the second-stage reaction at a temperature of 240°C. The extruded product was then air-cooled and pelletized to obtain the oxygen barrier layer 2 material of this embodiment.
[0064] (4) Preparation of biodegradable barrier composite membranes:
[0065] The raw materials for the first water-barrier layer 1, oxygen-barrier layer 2, and second water-barrier layer 3 are respectively fed into the corresponding channels of a multi-layer melt co-extrusion casting equipment. The layers are then melt-cast, cooled, wound, and slit to obtain the final product. The processing temperature is 245°C, and the cooling temperature is 25°C.
[0066] Testing showed that the thickness of the biodegradable barrier composite membrane in this embodiment is 0.05 mm. The first water-blocking layer 1 accounts for 45% of the total membrane thickness; the second water-blocking layer 3 accounts for 30% of the total membrane thickness; and the oxygen-blocking layer 2 accounts for 25% of the total membrane thickness.
[0067] Example 3
[0068] This embodiment provides a biodegradable barrier composite membrane, which is prepared according to the following steps:
[0069] (1) Preparation of the first water-blocking layer 1:
[0070] 100 parts of fully dried PBAT resin (melt index 25.0 g / 10 min), 65 parts of hydrophobically modified PBAT, 0.5 parts of UV absorber, and 0.2 parts of opening agent were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 140°C. After extrusion, the product was air-cooled and pelletized to obtain the first water-blocking layer 1 material of this embodiment.
[0071] (2) Preparation of the second water-blocking layer 3:
[0072] 100 parts of fully dried PBAT resin (melt index 25.0 g / 10 min), 45 parts of hydrophobically modified PBAT, 10 parts of nano-hydrotalcite filler, 0.2 parts of antioxidant, and 0.2 parts of opening agent were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 200°C. After extrusion, the product was air-cooled and pelletized to obtain the second water-blocking layer 3 material of this embodiment.
[0073] (3) Preparation of oxygen barrier layer 2:
[0074] 100 parts of fully dried PBAT resin (melt index 32.0 g / 10 min), 0.2 parts of sodium hydroxide, and 1 part of IPDI were added to a high-speed mixer and mixed evenly. The mixture was then fed into a twin-screw extruder for the first-stage reaction at 180°C. 40 parts of fully dried caprolactam and 4 parts of sodium caprolactam salt were pre-mixed and added to the twin-screw extruder through a side feed port for the second-stage reaction at 230°C. The extruded product was then air-cooled and pelletized to obtain the oxygen barrier layer 2 material of this embodiment.
[0075] (4) Preparation of biodegradable barrier composite membranes:
[0076] The raw materials for the first water-barrier layer 1, oxygen-barrier layer 2, and second water-barrier layer 3 are respectively fed into the corresponding channels of a multi-layer melt co-extrusion casting equipment. The layers are then melt-cast, cooled, wound, and slit to obtain the final product. The processing temperature is 235°C, and the cooling temperature is 40°C.
[0077] Testing showed that the thickness of the biodegradable barrier composite membrane in this embodiment is 0.20 mm. The first water-blocking layer 1 accounts for 30% of the overall membrane thickness; the second water-blocking layer 3 accounts for 30% of the overall membrane thickness; and the oxygen-blocking layer 2 accounts for 40% of the overall membrane thickness.
[0078] Example 4
[0079] This embodiment provides a biodegradable barrier composite membrane, which is prepared according to the following steps:
[0080] (1) Preparation of the first water-blocking layer 1:
[0081] 100 parts of fully dried PBAT resin (melt index 2.0 g / 10 min), 70 parts of hydrophobically modified PBAT, 5 parts of nano-calcium carbonate, and 0.2 parts of antioxidant were mixed in a high-speed mixer. The mixture was then fed into a twin-screw extruder at a processing temperature of 185°C. After extrusion, the product was air-cooled and pelletized to obtain the first water-blocking layer 1 material of this embodiment.
[0082] (2) Preparation of the second water-blocking layer 3:
[0083] The first water-blocking layer 1 is the same as in this embodiment.
[0084] (3) Preparation of oxygen barrier layer 2:
[0085] 100 parts of fully dried PBAT resin (melt index 20.0 g / 10 min), 1.2 parts of sodium hydroxide, and 6 parts of IPDI were added to a high-speed mixer and mixed evenly. The mixture was then fed into a twin-screw extruder for the first-stage reaction at 220°C. 40 parts of fully dried caprolactam and 4 parts of sodium caprolactam salt were pre-mixed and added to the twin-screw extruder through a side feed port for the second-stage reaction at 260°C. The extruded product was then air-cooled and pelletized to obtain the oxygen barrier layer 2 material of this embodiment.
[0086] (4) Preparation of biodegradable barrier composite membranes:
[0087] The raw materials for the first water-barrier layer 1, oxygen-barrier layer 2, and second water-barrier layer 3 are respectively fed into the corresponding channels of a multi-layer melt co-extrusion casting equipment. The layers are then melt-cast, cooled, wound, and slit to obtain the final product. The processing temperature is 250°C, and the cooling temperature is 25°C.
[0088] Testing showed that the thickness of the biodegradable barrier composite membrane in this embodiment is 0.08 mm. The first water-blocking layer 1 accounts for 48% of the total membrane thickness; the second water-blocking layer 3 accounts for 48% of the total membrane thickness; and the oxygen-blocking layer 2 accounts for 4% of the total membrane thickness.
[0089] The aforementioned PBAT refers to polybutylene terephthalate (PET).
[0090] Specifically, a method for preparing a biodegradable barrier composite membrane includes the following steps:
[0091] (1) Preparation of oxygen barrier layer masterbatch:
[0092] In a high-speed mixer, add 100 parts by weight of PBAT, 0.5 parts by weight of sodium hydroxide powder, and 3 parts by weight of isoflurane diisocyanate, and mix thoroughly. Feed the mixture into a twin-screw extruder and react at a melting temperature of 180°C for approximately 2 minutes, allowing the terminal hydroxyl groups of PBAT to react with IPDI to generate a PBAT prepolymer with terminal -NCO groups.
[0093] At the middle feed inlet of the extruder, a molten mixture of 80 parts by mass of caprolactam and 1 part by mass of sodium caprolactam salt is injected into the melt containing the PBAT prepolymer. The material continues to react in the rear section of the extruder, where the temperature is set to 240°C, allowing caprolactam to undergo ring-opening polymerization initiated by the -NCO groups at the end of the prepolymer, generating PA6 segments. The total melt reaction time is approximately 5 minutes. Finally, the melt is extruded, water-cooled, and pelletized to obtain PBAT-b-PA6 block copolymer masterbatch (denoted as MB-O1).
[0094] (2) Preparation of water-blocking layer masterbatch:
[0095] 100 parts by weight of PBAT and 60 parts by weight of hydrophobic modified PBAT were premixed in a high-speed mixer. Then, 3 parts by weight of light calcium carbonate and 1 part by weight of antioxidant 1010 were added. After uniform mixing, the mixture was fed into another twin-screw extruder and melt-blended, extruded, water-cooled, and pelletized at 170-190°C to obtain the hydrophobic modified water-blocking layer masterbatch (denoted as MB-W1).
[0096] (3) Co-extrusion film formation:
[0097] The water-blocking layer masterbatch was added to the upper and lower hoppers of the three-layer co-extrusion casting film equipment, while the PBAT-b-PA6 block copolymer masterbatch was added to the middle hopper. The processing temperatures for each zone were set as follows: zone 1 200℃, zone 2 210℃, zone 3 220℃, zone 4 225℃, connector 225℃, and die 230℃. The extrusion speed of the three layers was adjusted to achieve a thickness ratio of 85:15 between the water-blocking layer masterbatch layer and the PBAT-b-PA6 block copolymer masterbatch layer, meaning the total thickness of the two water-blocking layers accounted for 85%, and the intermediate oxygen barrier layer accounted for 15%. The molten material was co-extruded through a T-die and cast onto a cooling roller with a surface temperature of 30℃ for cooling and shaping. It was then drawn and wound to obtain a biodegradable barrier composite film with a total thickness of approximately 0.05 mm.
[0098] Comparative Example 1
[0099] Referring to Example 1, the difference is that neither the first nor the second water-blocking layer contains hydrophobically modified PBAT, while the remaining components and preparation process parameters are the same as in Example 1. This yields the biodegradable barrier composite membrane of this comparative example.
[0100] Comparative Example 2
[0101] Referring to Example 1, the difference is that IPDI is not added to the oxygen barrier layer, while the remaining components and preparation process parameters are the same as in Example 1. This yields the biodegradable barrier composite membrane of this comparative example.
[0102] Comparative Example 3
[0103] Referring to Example 1, the difference lies in the preparation method of the oxygen barrier layer: 100 parts each of fully dried PBAT resin and nylon 6 resin are added to a high-speed mixer and mixed evenly, then fed into a twin-screw extruder for melt extrusion at an extrusion temperature of 250°C. After extrusion, the product is air-cooled and pelletized to obtain the oxygen barrier layer material of this comparative example.
[0104] The remaining components and preparation process parameters are the same as in Example 1. This yields the biodegradable barrier composite membrane of this comparative example.
[0105] The following performance evaluations were conducted on samples from Examples 1-4 and Comparative Examples 1-3:
[0106] (1) Appearance evaluation. Used to evaluate the appearance of the product. The test method is as follows: visual evaluation is used. The film surface should be flat and smooth, without visible pores, crystal points and foreign matter. If the requirements are met, it is recorded as qualified.
[0107] (2) Oxygen Transmission Rate (OTR): The test was conducted according to the test method of the national standard GB / T19789-2021. The test temperature was 23℃ and the relative humidity was 0. Five different areas of the sample were selected for testing and the average value was taken. The lower the OTR value, the better the barrier performance.
[0108] (3) Water vapor transmission rate (WVTR): The test was conducted according to the test method of national standard GB / T26253-2010. The test temperature was 23℃ and the relative humidity was 50%. Five different areas of the sample were selected for testing and the average value was taken. The lower the WVTR value, the better the barrier performance.
[0109] The performance evaluation results of the samples in Examples 1-4 and Comparative Examples 1-3 are listed in Table 1.
[0110] Table 1. Test results of Examples 1-4 and Comparative Examples 1-3
[0111] sample Appearance <![CDATA[OTR(cm 3 ·m -2 ·24h -1 )]]> <![CDATA[WVTR(g·m -2 ·24h -1 )]]> Example 1 qualified 5.33 20.75 Example 2 qualified 5.66 24.32 Example 3 qualified 3.72 15.22 Example 4 qualified 7.23 21.34 Comparative Example 1 qualified 85.04 230.16 Comparative Example 2 Unqualified, contains a large number of crystal points 109.45 32.65 Comparative Example 3 Unqualified, with obvious holes and cracks. Exceeding the detection limit Exceeding the detection limit
[0112] As can be seen from the test results in Table 1, compared with Examples 1-4, Comparative Example 1, lacking hydrophobically modified PBAT, has a water-blocking layer equivalent to ordinary PBAT material, exhibiting poor water vapor barrier performance and a large WVTR. Furthermore, a large amount of water vapor entering the intermediate oxygen barrier layer causes the PA segments to absorb water, thus deteriorating the oxygen barrier effect. Therefore, the barrier effect of Comparative Example 1 is unsatisfactory.
[0113] Compared with Examples 1-4, Comparative Example 2 shows that because IPDI was not added to the oxygen barrier layer material, PBAT could not react directly with the caprolactam monomer, resulting in a large amount of monomer remaining in the film, which manifested as numerous crystal points in the sample. Since the caprolactam monomer was not polymerized, the oxygen barrier layer had no oxygen barrier effect, leading to a higher OTR; the high hygroscopicity of the caprolactam monomer also contributed to an increase in WVTR.
[0114] Compared with Comparative Example 3 and Examples 1-4, because PBAT and nylon 6 in the oxygen barrier layer were simply melt-blended, their compatibility was poor, resulting in significant phase separation during film formation. This manifested macroscopically as noticeable pores and cracks in the film, leading to an unsatisfactory appearance. Phase separation caused damage to the film, rendering it ineffective as a barrier.
[0115] In summary, Examples 1-4 employ a three-layer composite design consisting of a first water-blocking layer 1, an oxygen-blocking layer 2, and a second water-blocking layer 3. The water-blocking layer primarily utilizes PBAT and hydrophobically modified PBAT, providing excellent water-blocking performance. In the oxygen-blocking layer 2, isocyanate functional groups are introduced at the ends of the PBAT molecular chains, subsequently initiating caprolactam monomer polymerization to obtain a PBAT-b-PA copolymer. This overcomes the compatibility issues between PBAT and PA and also improves the oxygen-blocking effect. The resulting biodegradable composite membrane exhibits good appearance and barrier properties and can be mass-produced using conventional thermoplastic processing equipment, demonstrating promising application prospects.
[0116] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a biodegradable barrier composite membrane, characterized in that, Includes the following steps: (1) Preparation of oxygen barrier layer masterbatch: PBAT, alkaline catalyst and diisocyanate are mixed and melt-reacted at 150-220℃ to react the terminal hydroxyl groups of PBAT with isocyanate to obtain PBAT prepolymer with isocyanate groups at the end; then caprolactam and its polymerization catalyst are added to the reaction system and melt-polymerized at 220-260℃ to allow caprolactam to undergo ring-opening polymerization initiated by the isocyanate groups at the end of the PBAT prepolymer. After the reaction is completed, granulation is performed to obtain PBAT-b-PA block copolymer masterbatch; (2) Preparation of water barrier layer masterbatch: PBAT is mixed with hydrophobic modified PBAT, melt extruded and granulated to obtain water barrier layer masterbatch; the hydrophobic modified PBAT is a product of grafting long-chain alkanes with 1-30 carbon atoms onto the PBAT molecular chain. (3) Co-extrusion film formation: The water barrier layer masterbatch obtained in step (2) is used as the outer layer raw material, and the PBAT-b-PA masterbatch obtained in step (1) is used as the middle layer raw material. They are put into a multi-layer co-extrusion equipment and melt-cast or blow-molded at 200-250℃ and cooled to obtain a biodegradable barrier composite film with a three-layer structure.
2. The preparation method according to claim 1, characterized in that, In step (1), the diisocyanate is isoflurone diisocyanate; the alkaline catalyst is sodium hydroxide; and the polymerization catalyst for caprolactam is sodium caprolactam salt.
3. The preparation method according to claim 1 or 2, characterized in that, In step (1), by mass, the PBAT is 100 parts, the diisocyanate is 1-6 parts, and the caprolactam is 40-220 parts.
4. The preparation method according to claim 1, characterized in that, In step (2), the amount of hydrophobic modified PBAT used is 40-80 parts by weight, based on 100 parts by weight of PBAT.
5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the long-chain alkane has 10-20 carbon atoms, and the hydrophobically modified PBAT is obtained by graft polymerization of octadecyl acrylate in the presence of PBAT.
6. The preparation method according to claim 1, characterized in that, In step (2), when preparing the water-blocking layer masterbatch, the mixed raw materials also contain 0-10 parts by weight of filler and / or 0-5 parts by weight of functional additives; the filler is selected from at least one of calcium carbonate, talc, and montmorillonite; the functional additive is selected from at least one of antioxidants, ultraviolet absorbers, and opening agents.
7. The preparation method according to claim 1, characterized in that, In step (3), the co-extrusion film forming process parameters are controlled so that the total thickness of the final composite film is 0.01-0.30 mm, and the total thickness of the two water-blocking layers accounts for 60%-96% of the total film thickness, and the thickness of the oxygen-blocking layer accounts for 4%-40% of the total film thickness.
8. The preparation method according to any one of claims 1-7, characterized in that, In step (3), the cooling temperature is 20-40℃.
9. A biodegradable barrier composite membrane, characterized in that, It is obtained directly by the preparation method according to any one of claims 1 to 8.
10. The biodegradable barrier composite membrane according to claim 9, characterized in that, The composite membrane includes at least a first water-blocking layer, an oxygen-blocking layer, and a second water-blocking layer stacked sequentially; the oxygen-blocking layer includes a PBAT-b-PA block copolymer, and both the first water-blocking layer and the second water-blocking layer include PBAT and hydrophobically modified PBAT. The first water-blocking layer and / or the second water-blocking layer further include 0-10 parts by weight of filler and / or 0-5 parts by weight of functional additives.