High-transparency and high-strength biodegradable film as well as preparation method and application thereof

Abstract

The invention discloses a high-transparency and high-strength biodegradable film and a preparation method and application thereof.The high-transparency and high-strength biodegradable film is of a three-layer co-extrusion integrated structure and is composed of an outer layer film, a middle layer film and an inner layer film; the outer layer film and the inner layer film are prepared from the following raw materials in parts by weight: 65 to 85 parts of polylactic acid, 15 to 35 parts of poly (butylene adipate-co-terephthalate), 0.5 to 5 parts of epoxidized vegetable oil, 0.1 to 0.5 part of antioxidant, 0.1 to 0.5 part of anti-hydrolysis agent, 0.5 to 1.5 parts of anti-blocking agent and 0.5 to 2 parts of dispersing agent; the middle layer film is prepared from the following raw materials in parts by weight: 80 to 95 parts of poly (butylene adipate-co-terephthalate), 5 to 20 parts of polylactic acid, 0.1 to 2 parts of an anti-hydrolysis agent, 0.1 to 0.5 part of an antioxidant, 0.5 to 1.5 parts of an anti-blocking agent and 0.5 to 2 parts of a dispersing agent. The three-layer co-extrusion film blowing technology is adopted, through the unique structural design, the brittleness problem of the polylactic acid film is solved, high transparency and high strength of the film are kept, and the use requirements of the packaging field for film materials are met.

Description

Technical Field

[0001] This invention relates to the field of biodegradable packaging film technology, specifically to a highly transparent, high-strength biodegradable film, its preparation method, and its applications. Background Technology

[0002] With the acceleration of global industrialization, the widespread use of plastic packaging materials has led to an increasingly serious problem of "white pollution." Waste plastics are difficult to degrade in the natural environment, and long-term accumulation not only damages soil structure and pollutes water bodies but also threatens the balance of ecosystems. Controlling plastic pollution has become a global consensus, and developing efficient and biodegradable packaging materials has become a core development direction for the industry. Against this backdrop, polylactic acid (PLA) and polybutylene terephthalate (PBAT) have become mainstream choices in the field of biodegradable materials due to their respective excellent properties.

[0003] PLA, derived from renewable plant resources such as corn and cassava, boasts outstanding optical transparency, good tensile strength, and printability, aligning with the development concept of green materials. However, PLA inherently suffers from high brittleness and poor thermal stability, resulting in insufficient impact resistance, limiting its application in packaging scenarios requiring flexibility and weather resistance. PBAT, while petroleum-based, possesses biodegradability. Its flexibility, elongation at break, and film-forming properties are close to traditional low-density polyethylene (LDPE), exhibiting excellent impact resistance. However, PBAT has relatively low mechanical strength and insufficient modulus, resulting in poor light transmittance under normal conditions, making it difficult to meet the visual and aesthetic requirements of highly transparent packaging.

[0004] To address the performance deficiencies of single-material formulations, the industry often employs blending modification techniques. Patent CN 104387732 A discloses a transparent, tear-resistant polylactic acid (PLA) biodegradable film and its preparation method. It uses polybutyl carbonate as a toughening agent for PLA and poly(1,2-propanediol adipate) as a plasticizer. With increasing toughening agent content, the film's elongation at break increases, while its tensile strength, tear strength, light transmittance, and haze increase. Based on these findings, there is an urgent need to develop a film that combines high transparency with excellent mechanical properties to meet the requirements of the transparent packaging industry for film materials. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a highly transparent, high-strength biodegradable film, its preparation method, and its applications.

[0006] (II) Technical Solution A highly transparent, high-strength biodegradable film, comprising an outer layer, a middle layer, and an inner layer: The outer and inner membranes comprise the following raw materials in parts by weight: PLA 65-85 parts, PBAT 15-35 parts, epoxidized vegetable oil 0.5-5 parts, antioxidant 0.1-0.5 parts, anti-hydrolysis agent 0.1-0.5 parts, opening agent 0.5-1.5 parts, and dispersant 0.5-2 parts. The intermediate layer membrane comprises the following raw materials in parts by weight: 80-95 parts PBAT, 5-20 parts PLA, 0.1-2 parts anti-hydrolysis agent, 0.1-0.5 parts antioxidant, 0.5-1.5 parts opening agent, and 0.5-2 parts dispersant.

[0007] Furthermore, the epoxidized vegetable oil is epoxidized soybean oil. The epoxidized vegetable oil undergoes a ring-opening reaction with the terminal hydroxyl and carboxyl groups of PLA and PBAT through epoxy groups, which increases the molecular chain of the polymer, reduces phase separation, and improves the relevant mechanical properties of the composite material, thus acting as a compatibilizer.

[0008] Furthermore, the antioxidant is one or more of antioxidant 1010 and antioxidant 168, and the antioxidant can slow down the oxidation rate of the film.

[0009] Furthermore, the anti-hydrolysis agent is one or more of monomeric carbodiimide and polymeric carbodiimide. The polymeric carbodiimide can react with the end groups of PLA and PBAT, causing the molecular chain of the polymer to grow, thereby playing a role in chain extension and promoting compatibility.

[0010] Furthermore, the opening agent is pentaerythritol stearate, which can create unevenness on the surface of the biodegradable film to reduce the negative pressure between the films and cause them to separate, thus solving the adhesion problem of biodegradable films during manufacturing, processing and use.

[0011] Furthermore, the dispersant is white oil.

[0012] Furthermore, a method for preparing a highly transparent, high-strength biodegradable film includes the following steps: S1: Weigh the raw materials according to the raw material ratio of the outer membrane, the middle membrane and the inner membrane, and add them to the high-speed mixer in the order of particles-liquid-powder for mixing. S2: The uniformly mixed film materials are extruded, cooled (air-cooled), and pelletized through a twin-screw extruder to obtain modified materials for each film layer; S3: Modified materials are used to plasticize, blown, drawn, and wound through a three-layer co-extrusion blown film machine to form a highly transparent and high-strength biodegradable film.

[0013] Furthermore, the processing temperature of the modified material for the outer and inner layers is 120~185 ℃, and the screw speed is 200~300 r / min; the processing temperature of the modified material for the intermediate layer is 100~175 ℃, and the screw speed is 200~300 r / min.

[0014] Furthermore, the parameters of the outer and inner extruders of the three-layer co-extrusion blown film machine are set as follows: extrusion temperature of 160~180 ℃ and extrusion speed of 30~50 Hz; the parameters of the middle extruder of the three-layer co-extrusion blown film machine are set as follows: extrusion temperature of 150~170 ℃ and extrusion speed of 25~35 Hz; and the winding speed of the three-layer co-extrusion blown film machine is 20~30 r / min.

[0015] (iii) Beneficial technical effects The beneficial effects of this invention are: 1. Through a three-layer co-extrusion structure design and formulation control, the complementary optimization of the functions of each layer is achieved, effectively solving the inherent defects of PLA's high brittleness and PBAT's insufficient transparency and strength. The formulations of the inner and outer film layers focus on strengthening mechanical support and transparency, giving the film as a whole high transparency and excellent tensile strength; the formulation of the middle film layer focuses on improving impact resistance and flexibility, with visual effects that meet the requirements of high-transparency packaging, and mechanical properties that can adapt to various external forces during packaging, transportation, and use.

[0016] 2. The film has stable performance, a wider range of applications, and higher practical value. It can effectively replace traditional petrochemical plastic films and promote the transformation of the packaging industry towards green and environmentally friendly directions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the highly transparent and high-strength biodegradable film structure proposed in this invention; Figure 2 This is a flowchart illustrating the preparation process of a highly transparent and high-strength biodegradable film proposed in this invention. Figure 3 These are the tensile properties and light transmittance curves of Examples 1-6; Figure 4 This is a diagram showing the actual application of the biodegradable film produced in Example 8; Reference numerals: 1. Outer membrane, made of PLA / PBAT / ESO material; 2. Middle membrane, made of PBAT / PLA material; 3. Inner membrane, made of PLA / PBAT / ESO material. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments. However, those skilled in the art should understand that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations on the present invention.

[0019] Unless otherwise specified, all materials mentioned in the following examples are commercially available.

[0020] Raw material preparation: Polylactic acid (PLA): Number average molecular weight is 200,000; Polybutylene terephthalate (PBAT): Number average molecular weight is 80,000; Epoxidized vegetable oil: Epoxidized soybean oil, purity ≥98%.

[0021] Example 1 90 parts PLA, 10 parts PBAT, 0.5 parts epoxidized soybean oil, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.2 parts monomeric anti-hydrolysis agent, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil were added stepwise to a high-speed mixer in the order of granules-liquid-powder and mixed. The uniformly mixed raw materials were extruded through a twin-screw extruder (temperatures of each zone: zone 1 120 ℃, zone 2 140 ℃, zone 3 160 ℃, zones 4~11 185 ℃, zone 12 175 ℃, screen changing 165 ℃, screw speed 200 r / min), air-cooled, and pelletized to obtain ESO modified PLA / PBAT granules. ESO-modified PLA / PBAT granules were added to a blown film extruder (extrusion temperature 160~180 ℃, extrusion speed 30 Hz) for plasticization, and then wound up at a winding speed of 28 r / min to obtain ESO-modified PLA / PBAT film.

[0022] Example 2 The difference between this embodiment and Embodiment 1 is that the number of PLA copies has been reduced from 90 to 85, and the number of PBAT copies has been reduced from 10 to 15.

[0023] Example 3 The difference between this embodiment and Embodiment 1 is that the number of PLA copies has been reduced from 90 to 80, and the number of PBAT copies has been reduced from 10 to 20.

[0024] Example 4 The difference between this embodiment and Embodiment 1 is that the number of PLA copies is reduced from 90 to 70, and the number of PBAT copies is reduced from 10 to 30.

[0025] Example 5 The difference between this embodiment and Embodiment 2 is that the amount of epoxidized soybean oil is changed from 0.5 parts to 1 part.

[0026] Example 6 The difference between this embodiment and Embodiment 2 is that the amount of epoxidized soybean oil is changed from 0.5 parts to 2 parts.

[0027] Example 7 The outer and inner membranes consist of the following raw materials in parts by weight: 85 parts PLA, 15 parts PBAT, 1 part epoxidized soybean oil, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.2 parts monomeric anti-hydrolysis agent, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil. These are added stepwise to a high-speed mixer in the order of granules-liquid-powder for mixing. The uniformly mixed raw materials are then extruded through a twin-screw extruder (zone temperatures are: zone 1 120 ℃, zone 2 140 ℃, zone 3 160 ℃, zones 4~11 185 ℃, zone 12 175 ℃, screen changing 165 ℃, screw speed 200 r / min), air-cooled, and pelletized to obtain the materials for the outer and inner membranes.

[0028] The interlayer membrane comprises the following raw materials in parts by weight: 95 parts PBAT, 5 parts PLA, 0.5 parts polymeric anti-hydrolysis agent, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil. These are added stepwise to a high-speed mixer in the order of granules-liquid-powder for mixing. The uniformly mixed raw materials are extruded through a twin-screw extruder (temperatures in each zone are: zone 1 100 ℃, zone 2 130 ℃, zone 3 160 ℃, zones 4~11 175 ℃, zone 12 165 ℃, screen changing 160 ℃, screw speed 200 r / min), air-cooled, and pelletized to obtain the interlayer membrane material.

[0029] The film materials for each layer are added to the outer, middle, and inner extruders of a three-layer co-extrusion blown film mill for plasticization. The extrusion temperature of the outer and inner extruders is 160~180 ℃ and the extrusion speed is 27.5 Hz; the extrusion temperature of the middle extruder is 150~170 ℃ and the extrusion speed is 45 Hz; the film is then wound up at a winding speed of 25 r / min to obtain a biodegradable film.

[0030] Example 8 The difference between this embodiment and embodiment 7 is as follows: The outer and inner membranes comprise the following raw materials in parts by weight: 85 parts PLA, 15 parts PBAT, 1 part epoxidized soybean oil, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.2 parts monomeric anti-hydrolysis agent, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil; The intermediate layer membrane comprises the following raw materials in parts by weight: 90 parts PBAT, 10 parts PLA, 0.5 parts polymeric anti-hydrolysis agent, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil.

[0031] Example 9 The difference between this embodiment and embodiment 7 is as follows: The outer and inner membranes comprise the following raw materials in parts by weight: 85 parts PLA, 15 parts PBAT, 1 part epoxidized soybean oil, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.2 parts monomeric anti-hydrolysis agent, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil; The interlayer membrane comprises the following raw materials in parts by weight: 80 parts PBAT, 20 parts PLA, 0.5 parts polymeric anti-hydrolysis agent, 0.2 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.8 parts pentaerythritol stearate, and 0.3 parts white oil.

[0032] Example 10 The difference between this embodiment and embodiment 7 is as follows: The extrusion speed of the outer and inner layer extruders is 25 Hz; the extrusion speed of the middle layer extruder is 50 Hz.

[0033] Example 11 The difference between this embodiment and embodiment 7 is as follows: The extrusion speed of the outer and inner layer extruders is 30 Hz; the extrusion speed of the middle layer extruder is 40 Hz.

[0034] The biodegradable films prepared in Examples 1-11 above were subjected to performance tests (thickness: tested according to GB / T6672-2001 test method; tensile properties: tested according to GB / T 1040.3-2006 test method; right-angle tear strength: tested according to QB / T 1130-1991 test method; light transmittance & haze: tested according to GB / T 2410-2008 test method), and the test results are shown in […]. Figure 1 Table 1.

[0035] Table 1. Performance test results of biodegradable films

[0036] This invention achieves full-chain innovation through "three-layer co-extrusion blown film technology + precise formulation synergy + process parameter optimization." Leveraging a gradient formulation design of "high PLA in the inner / outer film + high PBAT in the middle film," the complementary functions of each layer—with PLA as the primary component to enhance support in the inner / outer film and PBAT as the core component to improve flexibility in the middle film—along with a compatibilizer eliminating interface defects between PLA and PBAT, address the core challenge of balancing transparency and mechanical properties in biodegradable films. The film exhibits longitudinal and transverse tensile strengths of 39.57 MPa and 27.87 MPa, longitudinal and transverse elongation at break of 158.32% and 199.44%, respectively, haze of only 12.16%, and light transmittance of 87.21%, meeting the visual requirements of highly transparent packaging.

[0037] Comparative examples 1-4 show that as the amount of PLA decreases and the amount of PBAT increases, the tensile strength decreases, the elongation at break increases, and the light transmittance decreases. This is because PBAT acts as a toughening material for PLA, and the ring-opening reaction of the ESO epoxy groups jointly improves the brittleness of PLA, resulting in a decrease in the tensile strength and an increase in the elongation at break of the film. Furthermore, since the dispersed phase PBAT toughens the continuous phase PLA, the difference in refractive index between the two materials leads to a decrease in light transmittance. Comparative examples 2, 5, and 6 show that as the amount of ESO increases, the tensile strength and light transmittance of the film first increase and then decrease. When the ESO content is 1%, the tensile strength and light transmittance of the film reach their maximum, at 45.4 MPa and 92.2%, respectively. This is because the epoxy functional groups in ESO undergo a ring-opening reaction with the terminal hydroxyl and carboxyl groups of the PLA and PBAT blend system, achieving a chain extension effect. Further addition of ESO leads to a decrease in the tensile strength and light transmittance of the film. This is because excessive ESO can disrupt the process of PLA and PBAT molecular chains forming a polymer structure, weakening the interactions between PLA and PBAT molecular chains. Conversely, with increasing ESO content, the film's elongation at break gradually increases. This is because the epoxy functional groups of ESO undergo an effective chain extension reaction with the end groups (-OH, -COOH) of PLA and PBAT, promoting the compatibility of PLA and PBAT. Simultaneously, the insertion of small-molecule ESO between polymer molecular chains weakens the stress between them, increases the mobility of polymer molecular chains, thereby increasing the plasticity of the polymer and improving the film's elongation at break.

[0038] refer to Figure 3 The biodegradable film produced in Example 8 is shown in the actual product images of being processed into self-adhesive bags and used as office supplies and clothing packaging, as well as processed into square-bottomed flat bags and bags for plush toys. The items can be clearly seen, indicating that the biodegradable film has high transparency.

[0039] The applicant declares that this application illustrates the detailed method of this application through the above embodiments, but this application is not limited to the above detailed method, that is, it does not mean that this application must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials of this application's product, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A high transparent, high strength, biodegradable film, characterized by: The high-transparency and high-strength biodegradable film is composed of an outer film, an intermediate film and an inner film. The outer film and the inner film comprise the following raw materials in parts by weight: 65-85 parts of polylactic acid, 15-35 parts of polybutylene adipate terephthalate, 0.5-5 parts of epoxy vegetable oil, 0.1-0.5 parts of antioxidant, 0.1-0.5 parts of hydrolysis-resistant agent, 0.5-1.5 parts of opening agent and 0.5-2 parts of dispersing agent. The intermediate film comprises the following raw materials in parts by weight: 80-95 parts of polybutylene adipate terephthalate, 5-20 parts of polylactic acid, 0.1-2 parts of hydrolysis-resistant agent, 0.1-0.5 parts of antioxidant, 0.5-1.5 parts of opening agent and 0.5-2 parts of dispersing agent.

2. The biodegradable film of claim 1, wherein: The epoxy vegetable oil is epoxy soybean oil.

3. The highly transparent and high-strength biodegradable film according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 1010 and antioxidant 168.

4. The biodegradable film of claim 1, wherein: The hydrolysis-resistant agent is one or more of monomeric carbodiimide and polymeric carbodiimide.

5. The biodegradable film of claim 1, wherein: The opening agent is pentaerythritol stearate.

6. The biodegradable film of claim 1, wherein: The dispersing agent is white oil.

7. The high transparent, high strength biodegradable film according to claim 1, wherein: The method comprises the following steps: S1: the raw materials of the outer film, the intermediate film and the inner film according to the raw material ratio of claim 1 are weighed, and are added to a high-speed mixer in the order of granules-liquids-powders for mixing; S2: the mixed material of each film layer is extruded, cooled (air-cooled) and granulated by a double-screw extruder to obtain modified material for each film layer; S3: the modified material for each film layer is plasticized, blown, pulled and wound by a three-layer co-extrusion film blowing machine to form a high-transparency and high-strength biodegradable film.

8. The biodegradable film according to claim 7, wherein: The processing temperature of the modified material for the outer film and the inner film is 120-185 ℃, and the screw rotation speed is 200-300 r / min; the processing temperature of the modified material for the intermediate film is 100-175 ℃, and the screw rotation speed is 200-300 r / min.

9. The biodegradable film according to claim 7, wherein: The parameters of the outer and inner extruders of the three-layer co-extrusion film blowing machine are set as follows: the extrusion temperature is 160-180 ℃, and the extrusion speed is 30-50 Hz; the parameters of the intermediate extruder of the three-layer co-extrusion film blowing machine are set as follows: the extrusion temperature is 150-170 ℃, and the extrusion speed is 25-35 Hz; and the winding speed of the three-layer co-extrusion film blowing machine is 20-30 r / min.

10. A biodegradable film having high transparency and high strength, characterized by comprising a poly (lactic acid) resin and a poly (hydroxyalkanoate) resin. The high-transparency and high-strength biodegradable film is produced by the method of any one of claims 7-9.

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