Degradable biaxially oriented polylactic acid film with high peel strength and preparation method of degradable biaxially oriented polylactic acid film

Abstract

The invention discloses a degradable biaxially oriented polylactic acid film with high peel strength and a preparation method thereof. The film sequentially comprises an interface enhancement layer, a matrix layer and a heat sealing layer, the interface enhancement layer is prepared from the following components in parts by weight: 80 to 90 parts of crystalline polylactic acid, 4 to 6 parts of polyethylene glycol and 0.5 to 1 part of isocyanate additive; the interface enhancement layer is a bonding layer with the thickness of 1-2 microns; the matrix layer is prepared from 78 to 89 parts by weight of crystalline polylactic acid, 5 to 10 parts by weight of carboxylated nano cellulose, 5 to 7 parts by weight of maleic anhydride grafted crystalline polylactic acid, 6 to 8 parts by weight of organic montmorillonite, 1 to 2 parts by weight of poly (butylene adipate-co-terephthalate) and 0.03 to 0.08 part by weight of silicon dioxide; and the thickness of the matrix layer is 12-15 [mu] m. Through formula innovation and process optimization, the heat sealing temperature is reduced, meanwhile, the peel strength is improved, and the mechanical property and degradability are kept.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high peel strength biodegradable biaxially oriented polylactic acid film and its preparation method. Background Technology

[0002] Traditional packaging films pose environmental pollution problems, while pure polylactic acid (PLA) films suffer from brittleness and poor thermal stability. Existing PLA modification technologies often improve performance through blending with plasticizers or inorganic fillers, but this can lead to prolonged degradation periods or decreased mechanical properties. In some applications, the film needs to be further laminated with paper, films, or coatings, and then printed. Current PLA films exhibit poor adhesion during subsequent lamination with paper, films, or coatings, easily resulting in quality issues such as film peeling and blistering. High peel strength on the film surface is more beneficial for subsequent lamination and printing processes. Therefore, there is a need to improve existing technologies to provide a polylactic acid film with good mechanical properties and strong interfacial adhesion. Summary of the Invention

[0003] This invention provides a high peel strength biodegradable biaxially oriented polylactic acid film and its preparation method. Through formulation innovation and process optimization, the peel strength of the polylactic acid film is increased while maintaining its mechanical properties and biodegradability.

[0004] A high peel strength biodegradable biaxially oriented polylactic acid film, comprising an interface reinforcement layer, a substrate layer and a heat-sealing layer in sequence;

[0005] The interface reinforcement layer is composed of the following components: 80-90 parts by weight of crystalline polylactic acid, 4-6 parts by weight of polyethylene glycol, and 0.5-1 parts by weight of isocyanate additives; the interface reinforcement layer is an adhesive layer with a thickness of 1-2 μm.

[0006] The matrix layer comprises: 78-89 parts by weight of crystalline polylactic acid, 5-10 parts by weight of carboxylated nanocellulose, 5-7 parts by weight of maleic anhydride-grafted crystalline polylactic acid, 6-8 parts by weight of organomontmorillonite, 1-2 parts by weight of polybutylene terephthalate-adipate, and 0.03-0.08 parts by weight of silica; the thickness of the matrix layer is 12-15 μm.

[0007] The heat-sealing layer comprises: 80-90 parts by weight of amorphous polylactic acid, 9-12 parts by weight of ethylene-ethyl acrylate copolymer, 6-8 parts by weight of polycaprolactone, 4-6 parts by weight of polybutylene adipate / terephthalate, 5-8 parts by weight of tributyl citrate, 2-3 parts by weight of acetylated tributyl citrate, and 0.01-0.03 parts by weight of silica; the thickness of the heat-sealing layer is 6-9 μm.

[0008] More preferably, the molecular weight of the crystalline polylactic acid in the matrix layer and the interface reinforcement layer, as well as the amorphous polylactic acid in the heat-sealing layer, is 30,000-50,000.

[0009] More preferably, the carboxylated nanocellulose has a diameter of 4-8 nm, a length of 1-3 μm, and an aspect ratio of 1:200-300.

[0010] More preferably, the organomontmorillonite is organically treated with hexadecyltrimethylammonium bromide, and the interlayer spacing is 1-2 nm.

[0011] More preferably, the isocyanate additive is diphenylmethane diisocyanate.

[0012] More preferably, the polyethylene glycol has a molecular weight of 2000-4000.

[0013] A method for preparing a high peel strength biodegradable biaxially oriented polylactic acid film includes the following steps:

[0014] Step 1: According to the formula ratio, the components of the interface reinforcement layer, matrix layer and heat-sealing layer are put into a twin-screw extruder for melt blending and extrusion to obtain interface reinforcement layer masterbatch, matrix layer masterbatch and heat-sealing layer masterbatch respectively.

[0015] Step 2: The interface reinforcement layer masterbatch, matrix layer masterbatch, and heat-sealing layer masterbatch are fed into different extruders for melting, extrusion, and converged into the same T-die, from which the melt flows out. The melting temperature of the matrix layer extruder is 160-190℃, while the melting temperatures of the interface reinforcement layer and heat-sealing layer extruders, as well as the temperature of the T-die, are 180-210℃.

[0016] Step 3: The melt flowing out of the die head is rapidly cooled and cast into a sheet, and then subjected to biaxial stretching treatment to obtain a high peel strength biodegradable biaxially oriented polylactic acid film.

[0017] More preferably, the biaxial stretching treatment in step three includes the following steps:

[0018] a. Preheating: The casting is preheated before stretching at a temperature of 50-65℃;

[0019] b. Longitudinal stretching: The casting is stretched longitudinally at a temperature of 70-90℃ and a stretching ratio of 2-3 times.

[0020] c. Lateral stretching: After longitudinal stretching, the film is stretched laterally at a temperature of 110-120℃ and a stretching ratio of 3-4 times.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] I. Material Performance Optimization

[0023] 1. Excellent mechanical properties

[0024] The matrix layer forms a highly crystalline network structure through the synergistic effect of crystalline polylactic acid (PLA) grafted with maleic anhydride and carboxylated nanocellulose, giving the film excellent tensile strength and impact resistance; organomontmorillonite enhances the barrier properties of the matrix layer through intercalation composite.

[0025] 2. Enhanced interface integration

[0026] The interface reinforcement layer adopts a compound system of crystalline polylactic acid, polyethylene glycol, and isocyanate additives, which effectively reduces the interface energy and avoids delamination or peeling after lamination with paper, film and coating, ensuring the high compositeness of the multilayer structure.

[0027] 3. Excellent low-temperature heat-sealing performance

[0028] The heat-sealing layer uses ethylene-ethyl acrylate copolymer (EEA), which lowers the heat-sealing temperature. Combined with the plasticizing effect of tributyl citrate, this significantly reduces the brittleness and improves the flexibility of the heat-sealing layer, avoiding the problem of brittle cracking during low-temperature heat sealing. It can achieve efficient heat sealing under low-temperature conditions, avoiding material degradation or deformation caused by high-temperature heat sealing. The polycaprolactone and polybutylene adipate / terephthalate added to the heat-sealing layer further improve the flexibility and adhesive strength of the heat-sealing layer, ensuring that the sealing interface is free of bubbles and leaks.

[0029] II. Processing Technology Innovation

[0030] 1. Optimization of Biaxial Stretching Process: Through a gradient stretching process involving preheating, longitudinal stretching, and transverse stretching, the molecular chains of the film are arranged in an orderly manner along the stretching direction, significantly improving mechanical properties (such as tensile strength and elongation at break) and barrier properties. Rapid cooling casting process (quenching to room temperature) inhibits grain growth, forming a fine crystalline structure, further improving the flexibility and impact resistance of the film.

[0031] 2. Low-temperature processing compatibility avoids polylactic acid degradation caused by high temperatures, while ensuring consistent melt flow across all layers and reducing processing defects. Detailed Implementation

[0032] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0033] Example 1

[0034] A high peel strength biodegradable biaxially oriented polylactic acid film, comprising, in sequence, an interface reinforcement layer, a substrate layer, and a heat-sealing layer;

[0035] The interface reinforcement layer is composed of the following components: 90 parts by weight of crystalline polylactic acid, 6 parts by weight of polyethylene glycol, and 1 part by weight of isocyanate additives; the interface reinforcement layer is an adhesive layer with a thickness of 2 μm; the molecular weight of polyethylene glycol is 4000;

[0036] The matrix layer comprises: 89 parts by weight of crystalline polylactic acid, 10 parts by weight of carboxylated nanocellulose, 7 parts by weight of maleic anhydride-grafted crystalline polylactic acid, 8 parts by weight of organomontmorillonite, 2 parts by weight of polybutylene terephthalate-adipate, and 0.08 parts by weight of silica; the thickness of the matrix layer is 15 μm.

[0037] The heat-sealing layer comprises: 90 parts by weight of amorphous polylactic acid, 12 parts by weight of ethylene-ethyl acrylate copolymer, 8 parts by weight of polycaprolactone, 6 parts by weight of polybutylene adipate / terephthalate, 8 parts by weight of tributyl citrate, 3 parts by weight of acetylated tributyl citrate, and 0.03 parts by weight of silica; the thickness of the heat-sealing layer is 9 μm.

[0038] The molecular weight of the crystalline polylactic acid in the matrix layer and interface reinforcement layer, as well as the amorphous polylactic acid in the heat-sealing layer, is 50,000. The carboxylated nanocellulose has a diameter of 8 nm, a length of 3 μm, and an aspect ratio of 1:300. The organomontmorillonite is organically treated with hexadecyltrimethylammonium bromide, with an interlayer spacing of 2 nm. The isocyanate additive is diphenylmethane diisocyanate.

[0039] A method for preparing a high peel strength biodegradable biaxially oriented polylactic acid film includes the following steps:

[0040] Step 1: According to the formula ratio, the components of the interface reinforcement layer, matrix layer and heat-sealing layer are put into a twin-screw extruder for melt blending and extrusion to obtain interface reinforcement layer masterbatch, matrix layer masterbatch and heat-sealing layer masterbatch respectively.

[0041] Step 2: The interface reinforcement layer masterbatch, matrix layer masterbatch, and heat-sealing layer masterbatch are fed into different extruders for melting, extrusion, and converged into the same T-die, from which the melt flows out. The melting temperature of the matrix layer extruder is 170℃, while the melting temperatures of the interface reinforcement layer and heat-sealing layer extruders, as well as the temperature of the T-die, are all 200℃.

[0042] Step 3: The melt flowing from the die is rapidly cooled and cast into a sheet, which is then subjected to biaxial stretching to obtain a high peel strength biodegradable biaxially oriented polylactic acid film. The biaxial stretching process includes the following steps:

[0043] a. Preheating: The casting is preheated before stretching at a temperature of 55℃;

[0044] b. Longitudinal stretching: The casting is longitudinally stretched at a temperature of 80℃ and a stretching ratio of 2.

[0045] c. Lateral stretching: After longitudinal stretching, the film is stretched laterally at a temperature of 110℃ and a stretching ratio of 3 times.

[0046] Example 2

[0047] A high peel strength biodegradable biaxially oriented polylactic acid film, comprising an interface reinforcement layer, a substrate layer and a heat-sealing layer in sequence;

[0048] The interface reinforcement layer is composed of the following components: 80 parts by weight of crystalline polylactic acid, 4 parts by weight of polyethylene glycol, and 0.5 parts by weight of isocyanate additives; the interface reinforcement layer is an adhesive layer with a thickness of 1 μm; the polyethylene glycol has a molecular weight of 2000;

[0049] The matrix layer comprises: 78 parts by weight of crystalline polylactic acid, 5 parts by weight of carboxylated nanocellulose, 5 parts by weight of maleic anhydride-grafted crystalline polylactic acid, 6 parts by weight of organomontmorillonite, 1 part by weight of polybutylene terephthalate-adipate, and 0.03 parts by weight of silica; the thickness of the matrix layer is 12 μm.

[0050] The heat-sealing layer comprises: 80 parts by weight of amorphous polylactic acid, 9 parts by weight of ethylene-ethyl acrylate copolymer, 6 parts by weight of polycaprolactone, 4 parts by weight of polybutylene adipate / terephthalate, 5 parts by weight of tributyl citrate, 2 parts by weight of acetylated tributyl citrate, and 0.01 parts by weight of silica; the thickness of the heat-sealing layer is 6 μm.

[0051] The molecular weight of the crystalline polylactic acid in the matrix layer and the interface reinforcement layer, as well as the amorphous polylactic acid in the heat-sealing layer, is 30,000. The carboxylated nanocellulose has a diameter of 4 nm, a length of 1 μm, and an aspect ratio of 1:200. The organomontmorillonite is organically treated with hexadecyltrimethylammonium bromide, with an interlayer spacing of 1 nm. The isocyanate additive is diphenylmethane diisocyanate.

[0052] The method for preparing the thin film is the same as in Example 1.

[0053] Comparative Example 1

[0054] The interface reinforcement layer in the thin film formulation of Example 1 was removed. The rest of the formulation remained unchanged.

[0055] Comparative Example 2

[0056] The carboxylated nanocellulose, maleic anhydride-grafted crystalline polylactic acid, and organomontmorillonite in the film formulation of Example 1 were removed. The remaining formulation remained unchanged.

[0057] Comparative Example 3

[0058] The polycaprolactone, ethylene-ethyl acrylate copolymer, tributyl citrate, and acetylated tributyl citrate in the heat-sealing layer of the film formulation of Example 1 were removed. The remaining formulation remained unchanged.

[0059] The films prepared in each embodiment and comparative example were subjected to performance tests. Peel strength was tested by laminating the interfacial reinforcement layer of the film with an aluminized film. Test items and standards are shown in Table 1, and test results are shown in Table 2.

[0060] Table 1 Thin Film Test Items and Test Standards

[0061]

[0062] Table 2 Thin Film Test Results

[0063]

[0064] The film prepared in this invention exhibits good barrier properties, low-temperature heat-sealing performance, and high peel strength. The low-temperature heat-sealing performance is well-suited for packaging high-temperature sensitive foods and products, preventing the effects of high temperatures on foods and products such as cheese and chocolate. The improved peel strength provides greater possibilities for the material's applications, such as printing the coating layer and laminating with other materials (paper, film, metallized layer), making the lamination process more user-friendly and preventing interlayer delamination during film lamination. The film's biodegradable properties align with environmental trends.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high peel strength biodegradable biaxially oriented polylactic acid film, characterized in that, It consists of an interface reinforcement layer, a substrate layer, and a heat-sealing layer, in sequence. The interface reinforcement layer is composed of the following components: 80-90 parts by weight of crystalline polylactic acid, 4-6 parts by weight of polyethylene glycol, and 0.5-1 parts by weight of isocyanate additives; the interface reinforcement layer is an adhesive layer with a thickness of 1-2 μm. The matrix layer comprises: 78-89 parts by weight of crystalline polylactic acid, 5-10 parts by weight of carboxylated nanocellulose, 5-7 parts by weight of maleic anhydride-grafted crystalline polylactic acid, 6-8 parts by weight of organomontmorillonite, 1-2 parts by weight of polybutylene terephthalate-adipate, and 0.03-0.08 parts by weight of silica; the thickness of the matrix layer is 12-15 μm. The heat-sealing layer comprises: 80-90 parts by weight of amorphous polylactic acid, 9-12 parts by weight of ethylene-ethyl acrylate copolymer, 6-8 parts by weight of polycaprolactone, 4-6 parts by weight of polybutylene adipate / terephthalate, 5-8 parts by weight of tributyl citrate, 2-3 parts by weight of acetylated tributyl citrate, and 0.01-0.03 parts by weight of silica; the thickness of the heat-sealing layer is 6-9 μm.

2. The high peel strength biodegradable biaxially oriented polylactic acid film according to claim 1, characterized in that, The molecular weights of the crystalline polylactic acid in the matrix layer and the interface reinforcement layer, as well as the amorphous polylactic acid in the heat-sealing layer, are all 30,000-50,000.

3. The high peel strength biodegradable biaxially oriented polylactic acid film according to claim 1, characterized in that, The carboxylated nanocellulose has a diameter of 4-8 nm, a length of 1-3 μm, and an aspect ratio of 1:200-300.

4. The high peel strength biodegradable biaxially oriented polylactic acid film according to claim 3, characterized in that, The organomontmorillonite was organically treated with hexadecyltrimethylammonium bromide, and the interlayer spacing was 1-2 nm.

5. The high peel strength biodegradable biaxially oriented polylactic acid film according to claim 4, characterized in that, The isocyanate additive is diphenylmethane diisocyanate.

6. The high peel strength biodegradable biaxially oriented polylactic acid film according to claim 5, characterized in that, The polyethylene glycol has a molecular weight of 2000-4000.

7. A method for preparing a high peel strength biodegradable biaxially oriented polylactic acid film according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: According to the formula ratio, the components of the interface reinforcement layer, matrix layer and heat-sealing layer are put into a twin-screw extruder for melt blending and extrusion to obtain interface reinforcement layer masterbatch, matrix layer masterbatch and heat-sealing layer masterbatch respectively. Step 2: The interface reinforcement layer masterbatch, matrix layer masterbatch, and heat-sealing layer masterbatch are fed into different extruders for melting, extrusion, and converged into the same T-die, from which the melt flows out. The melting temperature of the matrix layer extruder is 160-190℃, while the melting temperatures of the interface reinforcement layer and heat-sealing layer extruders, as well as the temperature of the T-die, are 180-210℃. Step 3: The melt flowing out of the die head is rapidly cooled and cast into a sheet, and then subjected to biaxial stretching treatment to obtain a high peel strength biodegradable biaxially oriented polylactic acid film.

8. The method for preparing a high peel strength biodegradable biaxially oriented polylactic acid film according to claim 7, characterized in that, The biaxial stretching treatment in step three includes the following steps: a. Preheating: The casting is preheated before stretching at a temperature of 50-65℃; b. Longitudinal stretching: The casting is stretched longitudinally at a temperature of 70-90℃ and a stretching ratio of 2-3 times. c. Lateral stretching: After longitudinal stretching, the film is stretched laterally at a temperature of 110-120℃ and a stretching ratio of 3-4 times.

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