A three-layer co-extruded biodegradable food preservation film and its preparation method

Abstract

This invention discloses a three-layer co-extruded biodegradable food preservation film and its preparation method. The film uses hydrophobically modified PBAT / modified starch as the outer and inner layers and high-barrier PVA / starch as the middle layer. The three-layer biodegradable food preservation film is prepared by three-layer co-extrusion blow molding. It has excellent mechanical properties, a smooth and flat appearance, low moisture absorption, high stability, high gas barrier properties and excellent biodegradability. In addition, it has low cost and meets the requirements for food preservation packaging.

Description

Technical fields:

[0001] This invention relates to the field of biodegradable materials technology, specifically to a three-layer co-extruded biodegradable food preservation film and its preparation method. Background technology:

[0002] In recent years, research on food preservation technology has become increasingly popular. The essence of preservation is to use different methods to regulate the physiological characteristics of products with different physiological features, in order to maintain their original quality characteristics as much as possible. With the development of scientific agriculture, more and more preservation methods are being used in the market. Among them, using high-performance biodegradable materials for fresh food packaging not only meets people's pursuit of safe, nutritious, and healthy diets, but also conforms to the concept of green environmental protection. PBAT (terephthalic acid-adipic acid-butanediol copolyester) is currently the mainstream biodegradable plastic in the Chinese environmental protection market. This is because PBAT's processing performance is similar to LDPE, allowing for blow molding; PBAT has good elasticity, is waterproof and tear-resistant, and can come into contact with food; it also has excellent mechanical properties, with good ductility and impact resistance.

[0003] The preservation effect of a film requires that its permeability be compatible with the respiration rate of fruits and vegetables. Its preservation principle involves selectively allowing gases to pass through the film, creating a low-O2, high-CO2 environment inside the packaging to inhibit the respiration metabolism of fruits and vegetables and maintain their initial quality. However, PBAT film has poor gas barrier properties and tends to stick together due to its self-adhesive nature. Therefore, it must be blended and modified with other materials before use as a preservation film material. Furthermore, PBAT has high production costs, limiting its development and application. Therefore, blending and modifying it with inexpensive biodegradable materials with good gas barrier properties is the best choice. PVA (polyvinyl alcohol) and starch are two biodegradable materials with extremely low COD (chemical oxygen demand) and BOD (biochemical oxygen demand), which can give the composite film strong oxygen barrier properties, and they are relatively inexpensive, but both have poor moisture barrier properties. In addition, natural starch, due to its microcrystalline and granular structure, lacks thermoplastic processing properties. PVA has strong hydrogen bonding between and within molecules, and its melting point and decomposition temperature are very close, making it difficult to thermoplastic process. This greatly limits the application and promotion of PVA and starch in preservation and other fields. Summary of the Invention:

[0004] The purpose of this invention is to provide a three-layer co-extruded biodegradable food preservation film and its preparation method. The film uses hydrophobically modified PBAT / modified starch as the outer and inner layers, and high-barrier PVA / starch as the middle layer. The three-layer biodegradable food preservation film is prepared by three-layer co-extrusion blow molding, exhibiting excellent mechanical properties, a smooth and flat appearance, low moisture absorption, high stability, high gas barrier properties, and excellent biodegradability. Furthermore, it is low in cost, meets the requirements for food preservation packaging, and solves the problems existing in the prior art.

[0005] This invention is achieved through the following technical solutions:

[0006] A three-layer co-extruded biodegradable food preservation film, comprising, in sequence, a PBAT / modified starch layer, a PVA / starch layer, and a PBAT / modified starch layer, wherein the PVA / starch layer is the middle layer;

[0007] The PBAT / modified starch layer comprises the following components in parts by weight: 60-90 parts PBAT, 10-40 parts modified starch, 0.5-1 part compatibilizer, 0.5-1 part hydrophobic modifier, 0.1-1 part antioxidant, 0.5-1 part opening agent, 1-5 parts PLA (polylactic acid), and 1-5 parts inorganic filler. The modified starch is glycerol-plasticized modified starch, prepared as follows: starch is placed in a high-speed mixer, glycerol is slowly added, and stirring continues after addition is complete to obtain glycerol-plasticized modified starch. The powder contains starch and glycerol in a mass ratio of 10:(2-4); the compatibilizer is an aromatic compound containing polyepoxy functional groups, selected from any one of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether, 9,9-bis[(2,3-epoxypropoxy)phenyl]fluorene, 9,9-bis(4-epoxypropyloxy-3-tolyl)fluorene, triglycidylaminom-cresol, triglycidyl-p-aminophenol, or triglycidyl-m-aminophenol; the hydrophobic modifier is an alkyl ketene dimer.

[0008] The PVA / starch layer comprises the following components in parts by weight: 60-90 parts PVA, 10-40 parts starch, 20-40 parts compound plasticizer composed of glycerol and polyethylene glycol or polypropylene glycol with a molecular weight of less than 600, 0.1-1 parts antioxidant, 0.5-1 parts opening agent, 0.5-2 parts talc, and 1-5 parts processing lubricant.

[0009] The opening agent is any one of erucamide, oleamide, or hard amide.

[0010] The inorganic filler is activated talc, calcium carbonate, or silica, with a fineness ≥2000 mesh.

[0011] The processing lubricant is one or more of polyethylene glycol 2000, polyethylene glycol 4000, polyethylene glycol 6000, polyethylene glycol 8000, or polyethylene glycol 10000.

[0012] The preparation method of the aforementioned three-layer co-extruded biodegradable food preservation film includes the following steps:

[0013] (1) Preparation of PBAT / modified starch blown film granules: Modified starch is placed in a high-speed mixer and PBAT, compatibilizer, hydrophobic modifier, antioxidant, opening agent, PLA and inorganic filler are added in sequence according to the metered components. After stirring evenly, the mixture is discharged and then extruded and granulated by a twin-screw extruder to obtain PBAT / modified starch blown film granules.

[0014] (2) Preparation of PVA / starch blown film granules: PVA, starch, antioxidant, opening agent, talc powder, and processing lubricant are placed in a high-speed mixer according to the metered components and mixed evenly. Then the temperature is raised to 80°C and stirring is continued. Glycerin and a compound plasticizer composed of polyethylene glycol or polypropylene glycol with a molecular weight of less than 600 are slowly added. After the addition is completed, stirring is continued for 10 to 20 minutes. Then the material is discharged and extruded and granulated by a twin-screw extruder to obtain PVA / starch blown film granules.

[0015] (3) PBAT / modified starch blown film granules and PVA / starch blown film granules are fed to a three-layer co-extrusion blown film unit and blown into shape to prepare a three-layer co-extruded biodegradable preservation film.

[0016] The modified starch is prepared as follows: starch is placed in a high-speed mixer, glycerol is slowly added, and stirring is continued after the addition is complete to obtain glycerol plasticized modified starch, wherein the mass ratio of starch to glycerol is 10:4 to 10:2.

[0017] This invention also protects the application of three-layer co-extruded biodegradable preservation film in food preservation packaging.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The outer and inner layers of the film provided by this invention are PBAT / modified starch layers, and the middle layer is PVA / starch layer. Each layer contains starch, which reduces the content of PBAT and thus significantly reduces the cost of the film. Moreover, the preparation method is simple, easy to industrialize and mass-produce, and has strong market competitiveness.

[0020] 2. This invention improves the compatibility between PBAT and starch by using a compatibilizer containing polyepoxy functional groups, and the addition of alkyl ketene dimer hydrophobic modifier reduces the hygroscopicity of the PBAT / starch layer. At the same time, all three layers of the film contain starch to ensure compatibility between the layers, thereby improving the mechanical properties of the biodegradable film.

[0021] 3. This invention innovatively utilizes a three-layer co-extrusion technology, using PBAT-based material with good heat-sealing and water resistance as the inner and outer layers, and PVA-based biodegradable thermoplastic material with excellent gas barrier properties as the middle layer. The two work together to ensure that the biodegradable film has excellent barrier properties.

[0022] 4. The main components of the biodegradable film of the present invention, PBAT, starch and PVA, are all completely biodegradable, and thus belong to biodegradable materials.

[0023] In summary, the three-layer biodegradable preservation film prepared by this invention has excellent mechanical properties, a smooth and flat appearance, low moisture absorption, high stability, high gas barrier properties, and excellent biodegradability. In addition, it is low in cost, meets the requirements for food preservation packaging, and has broad application prospects in fruit and vegetable preservation packaging. Detailed implementation method:

[0024] The following is a further description of the invention, but not a limitation thereof.

[0025] Example 1: Preparation of a three-layer co-extruded biodegradable food preservation film

[0026] The three-layer co-extruded biodegradable food preservation film consists of a PBAT / modified starch layer, a PVA / starch layer, and a PBAT / modified starch layer, with the PVA / starch layer serving as the middle layer.

[0027] (1) Preparation of PBAT / modified starch blown film granules: 1 kg of starch was placed in a high-speed mixer, and 300 g of glycerol was slowly added. After the addition was completed, the mixture was stirred for 10 min to obtain glycerol plasticized modified starch. Then, 8.7 kg of PBAT, 60 g of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether compatibilizer, 50 g of alkyl ketene dimer hydrophobic modifier, 30 g of antioxidant 1010, 20 g of antioxidant 168, 50 g of erucamide opening agent, 500 g of PLA, and 500 g of activated calcium carbonate (above 2000 mesh) were added in sequence. After stirring evenly, the mixture was discharged and then extruded and granulated by a twin-screw extruder to obtain PBAT / modified starch blown film granules.

[0028] (2) Preparation of PVA / starch blown film granules: 9kg PVA, 1kg dry starch, 30g antioxidant 1098, 20g antioxidant 168, 50g erucamide opening agent, 100g talc powder, and 500g polyethylene glycol 4000 processing lubricant are placed in a high-speed mixer and mixed evenly. Then the temperature is raised to 80℃ and stirring is continued. 3.5kg compound plasticizer (composed of 2kg glycerin and 1kg polyethylene glycol 200 or polypropylene glycol 200 and 0.5kg polyethylene glycol 400 or polypropylene glycol 400) is slowly added. After the addition is completed, stirring is continued for 10-20 minutes. Then the material is discharged and granulated by a twin-screw extruder to obtain PVA / starch blown film granules.

[0029] (3) PBAT / modified starch blown film granules and PVA / starch blown film granules are fed to a three-layer co-extrusion blown film unit and blown into shape to prepare a three-layer co-extruded biodegradable preservation film.

[0030] Example 2

[0031] Referring to Example 1, the difference is that in step (1), the amount of dried starch is 2 kg, the amount of glycerol is 600 g, and the amount of PBAT is 7.4 kg; in step (2), the amount of PVA is 8 kg and the amount of dried starch is 2 kg.

[0032] Example 3

[0033] Referring to Example 1, the difference is that in step (1), the amount of dried starch is 3 kg, the amount of glycerol is 900 g, and the amount of PBAT is 6.1 kg; in step (2), the amount of PVA is 7 kg and the amount of dried starch is 3 kg.

[0034] Example 4

[0035] Referring to Example 1, the difference is that in step (1), the dry starch is 3 kg, glycerol is 900 g, PBAT is 6.1 kg, and compatibilizer is 60 g of triglycidyl-p-aminophenol; in step (2), PVA is 7 kg and dry starch is 3 kg.

[0036] Example 5

[0037] Referring to Example 1, the difference is that in step (1), the dry starch is 3 kg, glycerol is 900 g, PBAT is 6.1 kg, and the compatibilizer is 60 g of triglycidyl-m-aminophenol; in step (2), PVA is 7 kg and dry starch is 3 kg.

[0038] Example 6

[0039] Referring to Example 1, the difference is that in step (1), the dry starch is 3 kg, the glycerol is 900 g, the PBAT is 6.1 kg, and the compatibilizer is 60 g of triglycidylaminom-cresol; in step (2), the PVA is 7 kg and the dry starch is 3 kg.

[0040] Comparative Example 1:

[0041] Referring to Example 6, the difference is that there is no PVA / starch layer, only a PBAT / modified starch layer.

[0042] Comparative Example 2:

[0043] Referring to Example 6, the difference is that only the PVA / starch layer is present.

[0044] Comparative Example 3:

[0045] Referring to Example 6, the difference is that in step (1), PBAT is replaced with PBS (polybutylene succinate).

[0046] Comparative Example 4:

[0047] Referring to Example 6, the difference is that the dried starch in steps (1) and (2) is replaced with PBS, and no compatibilizer is added in step (1).

[0048] Comparative Example 5:

[0049] Referring to Example 6, the difference is that in step (2), PVA is replaced with PVAc (polyvinyl acetate).

[0050] Comparative Example 6: Refer to Example 6, except that no hydrophobic modifier was added in step (1).

[0051] The performance test results of the three-layer co-extruded biodegradable food preservation films obtained in Examples 1-6 and Comparative Examples 1-6 are shown in Table 1-3:

[0052] Table 1. Test results of food preservation film performance.

[0053]

[0054] Table 2 Results of performance tests on food preservation film

[0055]

[0056] Table 3. Performance test results of food preservation film

[0057]

[0058] As shown in Tables 1-3, the three-layer co-extruded biodegradable food preservation films produced in Examples 1-6 exhibit tensile strength exceeding 19 MPa, elongation at break exceeding 650%, and tear strength exceeding 120 N / mm, demonstrating excellent mechanical properties. They also possess a smooth and superior appearance, a moisture absorption rate of less than 2.1% in water, high stability with a water immersion residue exceeding 98%, and a tolerance to oxygen levels below 122 cc·μm / (m²). 2 Transmission rate (24h), water vapor permeability below 1250 g·mm / (m 2 Transmittance of carbon dioxide below 2600 cc·μm / (m·24h) 2 With a permeability of 24h, high gas barrier properties, and excellent biodegradability, it fully meets the requirements for food preservation packaging and can be widely promoted and applied.

[0059] Compared with Comparative Examples 1 and 2, Special Example 6 shows that the PBAT / modified starch layer and PVA / starch layer of the present invention work synergistically, significantly reducing the O2 permeability coefficient (see Table 3). This may be because the exposed PVA / starch layer in Comparative Example 2 easily absorbs water and swells, leading to increased thickness and high measured water vapor, oxygen, and carbon dioxide permeability. However, as an intermediate layer, it exerts a synergistic effect, further reducing the permeability of each gas. Comparative Examples 1 and 2 produce single-layer PBAT / starch films. Due to insufficient preservation performance, the PBAT / starch films have high water vapor and oxygen permeability, while the PVA / starch films, lacking the protection of the PBAT / starch film layer, more easily absorb moisture from the environment, resulting in a decrease in oxygen permeability. This does not meet the requirements for conventional fruit and vegetable preservation packaging applications. Comparative Example 3, which uses PBS instead of PBAT, and Comparative Example 4, which uses PBS instead of dry starch without adding a compatibilizer, have poor mixing effects, are prone to phase separation, and are easily delaminated under stress. Comparative Example 4 also has high oxygen permeability. These shortcomings prevent it from being used for preservation. The film produced by Comparative Example 5, which used PVAc instead of PVA, could not meet the high barrier properties for oxygen and carbon dioxide, thus making it unsuitable for use in food preservation packaging.

Claims

1. A three-layer co-extruded biodegradable food preservation film, characterized in that, The mixture consists of three layers: a PBAT / modified starch layer, a PVA / starch layer, and a PBAT / modified starch layer, with the PVA / starch layer serving as the intermediate layer. The PBAT / modified starch layer comprises the following components in parts by weight: 60-90 parts PBAT, 10-40 parts modified starch, 0.5-1 part compatibilizer, 0.5-1 part hydrophobic modifier, 0.1-1 part antioxidant, 0.5-1 part opening agent, 1-5 parts PLA, and 1-5 parts inorganic filler. The modified starch is glycerol-plasticized modified starch, prepared by placing starch in a high-speed mixer and slowly adding glycerol. After addition, stirring continues to obtain glycerol-plasticized modified starch, with a starch-to-glycerol mass ratio of 10:(2-4). The compatibilizer is an aromatic compound containing polyepoxy functional groups, selected from N,N,N',N'-tetraglycidyl-4,4 The PVA / starch layer comprises any one of the following components by weight: '-diaminodiphenyl ether, 9,9-bis[(2,3-epoxypropoxy)phenyl]fluorene, 9,9-bis(4-epoxypropyloxy-3-tolyl)fluorene, triglycidylaminom-cresol, triglycidylp-aminophenol, or triglycidylm-aminophenol; the hydrophobic modifier is an alkyl ketone dimer; the PVA / starch layer comprises the following components in parts by weight: 60-90 parts PVA, 10-40 parts starch, 20-40 parts compound plasticizer composed of glycerol and polyethylene glycol or polypropylene glycol with a molecular weight of less than 600, 0.1-1 parts antioxidant, 0.5-1 part opening agent, 0.5-2 parts talc, and 1-5 parts processing lubricant; the opening agent is any one of erucamide, oleamide, or hard amide; the preparation method of the three-layer co-extruded biodegradable preservation film includes the following steps: (1) Preparation of PBAT / modified starch blown film granules: Modified starch is placed in a high-speed mixer, and PBAT, compatibilizer, hydrophobic modifier, antioxidant, opening agent, PLA and inorganic filler are added in sequence according to the metered components. After stirring evenly, the mixture is discharged and then extruded and granulated by a twin-screw extruder to obtain PBAT / modified starch blown film granules. (2) Preparation of PVA / starch blown film granules: PVA, starch, antioxidant, opening agent, talc powder, and processing lubricant are placed in a high-speed mixer according to the metered components and mixed evenly. Then the temperature is raised to 80°C and stirring is continued. Glycerin and a compound plasticizer composed of polyethylene glycol or polypropylene glycol with a molecular weight of less than 600 are slowly added. After the addition is completed, stirring is continued for 10 to 20 minutes. Then the material is discharged and extruded and granulated by a twin-screw extruder to obtain PVA / starch blown film granules. (3) PBAT / modified starch blown film granules and PVA / starch blown film granules are fed to a three-layer co-extrusion blown film unit and blown into shape to prepare a three-layer co-extruded biodegradable preservation film.

2. The three-layer co-extruded biodegradable preservation film according to claim 1, characterized in that, The inorganic filler is activated talc, calcium carbonate, or silica, with a fineness ≥2000 mesh.

3. The three-layer co-extruded biodegradable preservation film according to claim 1, characterized in that, The processing lubricant is one or more of polyethylene glycol 2000, polyethylene glycol 4000, polyethylene glycol 6000, polyethylene glycol 8000, or polyethylene glycol 10000.

4. The application of the three-layer co-extruded biodegradable preservation film of claim 1 in the preservation packaging of food.

5. The application of the three-layer co-extruded biodegradable preservative film according to claim 4 in food preservation packaging, characterized in that, It is used in fruit and vegetable preservation packaging.

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