A biodegradable film with improved adhesion and a method for preparing the same

Abstract

The application relates to a biodegradable film with improved adhesion and a preparation method thereof, the biodegradable film comprising a heat-pressed composite polyglycolic acid film layer and a biodegradable polyester film layer; wherein the crystallinity of the polyglycolic acid film layer is 9-40%. In the application, the adhesion between the high-melting-point polyglycolic acid film layer and the biodegradable polyester film layer can be obviously enhanced by controlling the crystallinity of the polyglycolic acid film layer and selecting a heat-pressing process.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification and preparation, and more specifically, to a biodegradable film and its preparation method. Background Technology

[0002] Polyglycolic acid (PGA), also known as polyhydroxyacetic acid, is the simplest linear aliphatic polyester and is widely used as a biodegradable material. It is a typical highly crystalline polymer with a stable crystal lattice and a high melting point. PGA possesses excellent biodegradability, rapid degradation, good biocompatibility, good bioreabsorption, and high mechanical strength (some indicators are comparable to engineering plastics). It is mainly used in medical sutures, drug delivery systems, fracture fixation materials, tissue engineering scaffolds, reinforcing materials, and oilfield applications. However, PGA's rapid crystallization and high crystallinity result in insufficient toughness. Furthermore, the rapid degradation of PGA leads to a short shelf life, severely limiting its everyday applications.

[0003] Currently, researchers utilize the high barrier and biodegradable properties of PGA (polyvinyl chloride) by incorporating it as one layer in a multilayer co-extrusion process to improve the overall mechanical properties of the film and obtain a high-barrier film with biodegradable characteristics. However, in the preparation of PGA multilayer co-extruded films, due to the weak interaction between the PGA layer and other polyester resin layers, an adhesive layer is usually required for tight bonding. Generally, the adhesive layer is a resin grafted with groups that can react with PGA. Furthermore, because the adjacent resins in the composite with PGA vary, obtaining an adhesive layer that matches PGA requires customization and is not readily available on the market. At the same time, most adhesive layers are modified by grafting with multifunctional compounds such as maleic acid, and the impact of this modification on the overall biodegradability of the multilayer composite film remains to be discussed.

[0004] To address the issues of poor interlayer bonding and large melting point temperature differences between existing high-melting-point polyglycolic acid films and other low-melting-point biodegradable polyester films, and their susceptibility to degradation above the melting point, this invention aims to eliminate the uncertain influence of the adhesive layer on the overall biodegradability of the multilayer composite film. The invention provides a composite method for different types of biodegradable multilayer films with significantly different melting points, which effectively improves the interlayer bonding strength between the two types of biodegradable resins with different melting points. Summary of the Invention

[0005] This invention aims to develop a biodegradable film with high adhesion and its preparation method. The interlayer bonding force between the polyglycolic acid film layer and the biodegradable polyester film layer of the biodegradable film is improved. By controlling the crystallinity of the polyglycolic acid film layer and using a simple hot-pressing process, this invention can significantly improve the thermal bonding force between the polyglycolic acid film layer and the biodegradable polyester film layer without adding an adhesive layer, thus obtaining a biodegradable film with tight bonding.

[0006] In a first aspect, the present invention relates to a biodegradable film comprising a hot-pressed composite polyglycolic acid film layer and a biodegradable polyester film layer; wherein the crystallinity of the polyglycolic acid film layer is 9-40%.

[0007] Secondly, the present invention relates to a method for preparing a biodegradable thin film, the method comprising the following steps:

[0008] S1. Polyglycolic acid resin is used to prepare a polyglycolic acid film layer, wherein the crystallinity of the polyglycolic acid film layer is controlled at 9-40%;

[0009] S2. Prepare a biodegradable polyester film from biodegradable polyester;

[0010] S3. The polyglycolic acid film layer and the biodegradable polyester film layer are stacked and then hot-pressed together to form a biodegradable film.

[0011] This invention proposes a method to improve the interlayer bonding between the polyglycolic acid (PGA) film layer and the biodegradable polyester film layer by controlling the crystallinity of the PGA film layer in a biodegradable film without adding an adhesive layer. This method allows for direct hot-pressing lamination to obtain a tightly bonded biodegradable film. Compared with existing technologies, this method significantly improves the heat-sealing strength between the PGA film layer and the biodegradable polyester film layer without adding an adhesive layer. Simultaneously, the step-by-step hot-pressing process reduces degradation damage to the biodegradable polyester film caused by direct co-extrusion with a high-melting-point PGA layer. Detailed Implementation

[0012] The present invention will be further illustrated below by means of embodiments. However, it should be noted that the scope of protection of the present invention is not limited by these embodiments, but is determined by the claims.

[0013] It should be noted that the two or more aspects (or embodiments) disclosed in the context of this specification can be arbitrarily combined with each other, and the resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0014] The "polyglycolic acid" (PGA) described in this invention, also known as polyglycolic acid or polyhydroxyacetic acid, is the simplest linear aliphatic polyester. PGA can be prepared by melt polycondensation of glycolic acid or ring-opening polymerization of glycolide. PGA is a typical highly crystalline polymer with a stable crystal lattice and a high melting point. The rapid crystallization rate and high crystallinity of PGA result in high brittleness and high modulus, but low impact strength, making its products extremely brittle and limiting its applications. PGA possesses excellent biodegradability, allowing it to enter the human circulatory system for in vivo degradation and excretion, as well as degrading in the in vitro environment. It is mainly used in medical sutures, drug delivery systems, fracture fixation materials, tissue engineering scaffolds, and reinforcing materials. Through solution spinning and melt spinning, PGA can be processed into surgical sutures with high tensile strength that can be maintained for a sufficient time, making it suitable for suturing deep tissue wounds.

[0015] This invention relates to a biodegradable film, comprising a hot-pressed composite polyglycolic acid film layer and a biodegradable polyester film layer; wherein the crystallinity of the polyglycolic acid film layer is 9-40%. Specifically, in this invention, the biodegradable film can be formed by controlling the crystallinity of the polyglycolic acid film layer and hot-pressing it with the biodegradable polyester film layer.

[0016] According to some embodiments of the present invention, the crystallinity of the polyglycolic acid film layer is 9-15%.

[0017] According to some embodiments of the present invention, the melting point of the polyglycolic acid film layer is at least 20°C higher than the melting point of the biodegradable polyester film layer.

[0018] According to some embodiments of the present invention, the polyglycolic acid film layer is made of polyglycolic acid resin, for example, by a casting process. Specifically, a melt blending reactive extrusion casting process is used, in which polyglycolic acid resin is added to a single-screw extruder for extrusion, and the material is drawn to a cooling roller and a calendering roller for winding after entering the film.

[0019] More specifically, the polyglycolic acid resin is extruded and cast using a single screw extruder at a speed of 100-200 rpm, more preferably 150-200 rpm. The extrusion temperature is 180°C to 260°C, more preferably 200°C to 250°C. The material is wound up after the cooling roller at the extruder nozzle, with the cooling roller temperature being 10-60°C, more preferably 10-40°C.

[0020] According to some embodiments of the present invention, the polyglycolic acid resin has an intrinsic viscosity of 1.0-1.4 dl / g and / or a melting point range of 205-235°C.

[0021] According to some embodiments of the present invention, the thickness of the polyglycolic acid film layer is 70-150 micrometers, preferably 70-110 micrometers.

[0022] According to some embodiments of the present invention, the biodegradable polyester film is prepared from biodegradable polyester, for example by blown film or cast film, preferably by blown film.

[0023] According to some embodiments of the present invention, the biodegradable polyester is selected from one or more of polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), carbon dioxide-based biodegradable plastics (PPC), and diacid-diol copolyesters; preferably, the biodegradable polyester is a diacid-diol copolyester.

[0024] Further, the diacid-based diol copolyester is selected from one or more of polybutylene adipate / terephthalate (PBAT), polybutylene succinate-co-butylene terephthalate (PBST), polybutylene succinate-butylene adipate (PBSA), and polybutylene succinate (PBS); preferably, the diacid-based diol copolyester is polybutylene adipate / terephthalate (PBAT).

[0025] According to some embodiments of the present invention, the biodegradable polyester has a melt index of 2-20 g / 10 min under test conditions of 190°C and 2.16 kg.

[0026] According to some embodiments of the present invention, the melting point of the biodegradable film layer is ≤185°C.

[0027] According to some embodiments of the present invention, the thickness of the biodegradable polyester film layer is 8-40 micrometers; preferably 8-15 micrometers; more preferably 10 micrometers.

[0028] According to some embodiments of the present invention, the hot-pressing composite is carried out under the following conditions: temperature of 80°C to 160°C, more preferably 100°C to 130°C; time of 1 min to 5 min, more preferably 2 min to 3 min; and pressure of 8-200 kPa, more preferably 10-100 kPa.

[0029] The present invention also relates to a method for preparing the above-mentioned biodegradable film, the method comprising the following steps:

[0030] S1. Polyglycolic acid resin is used to prepare a polyglycolic acid film layer, wherein the crystallinity of the polyglycolic acid film layer is controlled at 9-40%;

[0031] S2. Prepare a biodegradable polyester film from biodegradable polyester;

[0032] S3. The polyglycolic acid film layer and the biodegradable polyester film layer are stacked and then hot-pressed together to form a biodegradable film.

[0033] According to some embodiments of the present invention, polyglycolic acid resin is melt-blended and extruded, with an extrusion speed of 100-200 rpm, more preferably 150-200 rpm. The extrusion temperature is 180°C to 260°C, more preferably 200°C to 250°C. The material is wound up after the cooling roller at the extruder nozzle, with the cooling roller temperature being 10-60°C, more preferably 10-40°C.

[0034] According to some embodiments of the present invention, the polyglycolic acid resin has an intrinsic viscosity of 1.0-1.4 dl / g and a melting point range of 205-235℃.

[0035] According to some embodiments of the present invention, the thickness of the polyglycolic acid film layer is 70-150 micrometers, preferably 70-110 micrometers.

[0036] According to some embodiments of the present invention, the biodegradable polyester film is prepared by blown film or cast film from biodegradable polyester, preferably, the biodegradable polyester film is prepared by blown film.

[0037] According to some embodiments of the present invention, the biodegradable polyester is selected from one or more of polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), carbon dioxide-based biodegradable plastics (PPC), and diacid-diol copolyesters; preferably, the biodegradable polyester is a diacid-diol copolyester.

[0038] Further, the diacid-based diol copolyester is selected from one or more of polybutylene adipate / terephthalate (PBAT), polybutylene succinate-co-butylene terephthalate (PBST), polybutylene succinate-butylene adipate (PBSA), and polybutylene succinate (PBS); preferably, the diacid-based diol copolyester is polybutylene adipate / terephthalate (PBAT).

[0039] According to some embodiments of the present invention, the biodegradable polyester has a melt index of 2-20 g / 10 min under test conditions of 190°C and 2.16 kg.

[0040] According to some embodiments of the present invention, the thickness of the biodegradable polyester film layer is 8-40 micrometers; preferably 8-15 micrometers; more preferably 10 micrometers.

[0041] According to some embodiments of the present invention, the polyglycolic acid film layer and the biodegradable polyester film layer are stacked in an ABA or BAB manner and placed in a vacuum hot press.

[0042] According to some embodiments of the present invention, hot pressing can be performed using equipment such as vacuum hot presses and flat vulcanizing machines.

[0043] Furthermore, the hot pressing is performed under the following conditions: temperature of 80°C to 160°C, more preferably 100°C to 130°C; time of 1 min to 5 min, more preferably 2 min to 3 min; and pressure of 8-200 kPa, more preferably 10-100 kPa.

[0044] Experimental materials :

[0045] The polyglycolic acid (PGA) used in this invention is manufactured by Corbion Purac, and its brand name is [brand name missing]. PG S. The polybutylene adipate / terephthalate (PBAT) used was manufactured by BASF in Germany, and its brand name is [brand name missing]. F C-1200. Polylactic acid (PLA) is 4370D manufactured by NatureWorks, USA.

[0046] Test methods and equipment :

[0047] Heat seal strength test: The test was conducted according to OB / T 2358-98 standard using an INSTRON 3344 film product testing machine with Bluehill version 2.31 software. The film was cut to Type 2 as per ISO 527-2 standard and placed in a Bluepard BPS-100CB constant temperature and humidity chamber (23°C, 50% relative humidity) at Shanghai Yiheng Scientific Instruments Co., Ltd. for 24 hours. During testing, the initial clamp spacing was 50 mm, and the tensile rate was 300 mm / min. Centered on the heat-sealed area, the upper film was peeled to the same position, opened 180°, and the two ends of the sample were clamped onto the two clamps of the testing machine, with the lower ends of the sample extending by the same length. Each sample was tested 5 times, and the average value was recorded. The maximum load at which the sample broke was read.

[0048] Thin film crystallinity testing: The crystallization thermodynamic parameters of PGA thin films were determined using a differential scanning calorimeter (DSC) from TA Instruments (USA). Approximately 4-8 mg of PGA thin film sample was added to the DSC sample cell and heated to 250°C at a rate of 10°C / min, held at that temperature for 2 min to eliminate thermal history. Then, the sample was cooled to -50°C at a rate of 10°C / min, and the cooling crystallization DSC spectrum was recorded. The sample was then heated to 250°C again at a rate of 10°C / min, and the crystallization melting DSC spectrum was recorded. Processing the two DSC curves yielded the crystallization thermodynamic parameters of the PGA thin film, including crystallization temperature, melting point, and heat of fusion. Among these, the crystallinity of the PGA thin film (X...)... c Calculate according to the following formula:

[0049]

[0050] In the formula, X c Crystallinity, %; ΔH m The enthalpy of melting is ΔH, J / g. m100 The enthalpy of melting endothermic reaction during complete crystallization of PGA is 191.32 J / g.

[0051] Biodegradable film: The two biodegradable films with different melting points were placed in the hot press chamber using a LABPRO 600 vacuum hot press from Fontijne Grotnes, Inc. in the Netherlands. The temperature, hot pressing time and pressure were set and then hot pressed. After hot pressing, the composite film was taken out and weighed down with a heavy object to keep the film flat.

[0052] Example

[0053] Example 1

[0054] The brand name is FC-1200 poly(butylene adipate) terephthalate (PBAT) granules were blown into film using a HAAKE™ Rheomex OS single-screw extrusion blown film extruder manufactured by Thermo Fisher Scientific Inc. in the USA. This extruder has a screw diameter of 19 mm, an aspect ratio of 25, and is equipped with a 3:1 standard metering screw. The feeder enters the extruder, which is heated to the following temperatures: 120°C, 120°C, 130°C, 130°C, 140°C, 140°C, 130°C, 130°C, 120°C, and 120°C. The screw speed is set to a stable 200 rpm, with a torque range of 10-50%. The extruder uses a 19.5 mm diameter circular die (0.5 mm gap). After extrusion, the melt undergoes cooling, setting, traction, and winding to form a film. By controlling the draw ratio and winding speed, the PBAT film thickness is controlled to approximately 10 μm.

[0055] Example 2

[0056] 20 parts by weight of fully dried polylactic acid (NatureWorks 4370D) and 80 parts by weight of PBAT ( After thorough premixing with FC-1200, the extruder feeds the sample into a PolyLab HAAKE™ Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16mm, L / D=40) from Thermo Fisher Scientific, USA, via a volumetric feeder for granulation. The extruder has 11 sections from the feed inlet to the die, numbered 1-11. Section 1 only serves as the feeder and does not provide heating. The temperatures of sections 2-11 are 160℃, 160℃, 170℃, 170℃, 180℃, 180℃, 170℃, 170℃, 160℃, and 160℃, respectively, with the screw speed set at 200 rpm. During stable operation, the torque ranges from 20-60%. The extruder is equipped with a 3mm diameter circular die. After extrusion and air cooling, the sample is cut into approximately 3mm cylindrical particles using a pelletizer. Collect the particles, dry them in a vacuum drying oven at 60°C for 4 hours, and then package them for later use.

[0057] Fully dried PLA / PBAT particles were blown into film using a HAAKE™ Rheomex OS single-screw extrusion blown film extruder manufactured by Thermo Fisher Scientific Inc. in the USA. This extruder has a screw diameter of 19 mm, an L / D ratio of 25, and is equipped with a 3:1 standard metering screw. The material enters the extruder via a feeder. The extruder's heating temperatures are: 130°C, 130°C, 140°C, 140°C, 150°C, 150°C, 140°C, 140°C, 130°C, and 120°C. The screw speed is set to a stable 200 rpm, with a torque range of 10-50%. The extruder is equipped with a 19.5 mm diameter circular nozzle (0.5 mm gap). After extrusion, the melt undergoes cooling, setting, traction, and winding to form a film. By controlling the draw ratio and winding speed, the PLA / PBAT film thickness is controlled to approximately 10 μm.

[0058] Example 3

[0059] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. After exiting the PGA film, it was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set at 20℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 9.9%. Next, the PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were hot-pressed in a vacuum hot press with an ABA structure. The hot-pressing temperature was set at 120℃, and the film was held at 100kPa for 3 minutes before being removed and cooled to room temperature. A weight was then applied to maintain the film's flatness.

[0060] Example 4

[0061] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set at 30℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 13.3%. Next, the PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were hot-pressed in an ABA structure in a vacuum hot press. The hot-pressing temperature was set at 120℃, and the film was held at 100kPa for 3 minutes before being removed and cooled to room temperature. A weight was then applied to maintain the film's flatness.

[0062] Example 5

[0063] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200 rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 60℃, and the winding speed was 1.6 m / min. DSC testing showed that the crystallinity of the obtained PGA film was 28.8%. Next, the PGA film prepared above is used as the inner layer "B" and the 10mm thick PLA / PBAT film is used as the "A" layer. The two layers are hot-pressed in a vacuum hot press with an ABA structure. The hot pressing temperature is set to 120℃. After holding at 100kPa pressure for 3 minutes, the film is taken out and cooled to room temperature. A heavy object is then pressed on the film to keep it flat.

[0064] Example 6

[0065] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200 rpm. During stable operation, the torque ranged from 20-50%. After exiting the extruder, the PGA film was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 20℃, and the winding speed was 1.6 m / min. DSC testing showed that the crystallinity of the obtained PGA film was 9.9%. Next, the PGA film prepared above is used as the inner layer "B" and the 10mm thick PLA / PBAT film is used as the "A" layer. The two layers are hot-pressed in a vacuum hot press with an ABA structure. The hot pressing temperature is set to 120℃. After holding at 100kPa pressure for 3 minutes, the film is taken out and cooled to room temperature. A heavy object is then pressed on the film to keep it flat.

[0066] Comparative Example 1

[0067] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 80℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 37%. Next, the prepared PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were hot-pressed in an ABA structure in a vacuum hot press at 120℃ and 6kPa pressure for 3 minutes. The film was then removed, cooled to room temperature, and weighted to maintain its flatness.

[0068] Comparative Example 2

[0069] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 60℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 28.2%. Next, the prepared PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were hot-pressed in an ABA structure in a vacuum hot press at 120℃ and 6kPa pressure for 3 minutes. The film was then removed, cooled to room temperature, and weighted to maintain its flatness.

[0070] Comparative Example 3

[0071] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 80℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 37%. The PGA film prepared above was then used as the inner layer "B" and a 10μm thick PBAT film as the "A" layer. These layers were then hot-pressed in an ABA structure in a vacuum hot press at 120℃ and 8kPa pressure for 3 minutes. After cooling to room temperature, a weight was applied to maintain the film's flatness.

[0072] Comparative Example 4

[0073] The temperatures of sections 2-11 of the machine are 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200 rpm. During stable operation, the torque range is 20-50%. After exiting the PGA film, it is cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature is set at 80℃, and the winding speed is 1.6 m / min. After DSC testing, the crystallinity of the obtained PGA film is 37%. Next, the PGA film prepared above is used as the inner layer "B" and a 10 μm thick PBAT film is used as the "A" layer. The film is hot-pressed in an ABA structure in a vacuum hot press at a temperature of 120℃ and a pressure of 10 kPa for 3 minutes. After cooling to room temperature, a heavy object is placed on top to keep the film flat.

[0074] Comparative Example 5

[0075] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 60℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 28.2%. The prepared PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were then hot-pressed in an ABA structure in a vacuum hot press at 140℃ and 6kPa pressure for 3 minutes. The film was then removed, cooled to room temperature, and weighted to maintain its flatness.

[0076] Comparative Example 6

[0077] The temperatures of sections 2-11 of the machine are 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200 rpm. During stable operation, the torque range is 20-50%. After exiting the PGA film, it is cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature is set at 60℃, and the winding speed is 1.6 m / min. After DSC testing, the crystallinity of the obtained PGA film is 28.2%. Next, the PGA film prepared above is the inner layer film "B" and the 10 μm thick PBAT film is the "A" layer. They are hot-pressed in an ABA structure in a vacuum hot press at a temperature of 180℃ and a pressure of 6 kPa for 3 minutes. After that, the film is removed and cooled to room temperature, and a heavy object is placed on it to keep the film flat.

[0078] Comparative Example 7

[0079] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. The PGA film exiting the extruder was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set at 15℃, and the winding speed at 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 9.9%. Next, the PGA film (inner layer "B") and a 10μm thick PBAT film (layer "A") were hot-pressed in an ABA structure in a vacuum hot press at 120℃ and 6kPa pressure for 3 minutes. The film was then removed, cooled to room temperature, and weighted to maintain its flatness.

[0080] Comparative Example 8

[0081] 100g of PGA particles were cast using a Collin single-screw extruder. During the experiment, the screw temperatures in sections 2-11 of the extruder were 200℃, 220℃, 230℃, 230℃, 240℃, 250℃, 250℃, 240℃, 230℃, and 220℃, respectively, with the screw speed set at 200rpm. During stable operation, the torque ranged from 20-50%. After exiting the PGA film, it was cooled by a cooling roller and then wound up by a calendering roller. The cooling roller temperature was set to 80℃, and the winding speed was 1.6m / min. DSC testing showed that the crystallinity of the obtained PGA film was 37%. Next, the prepared PGA film (inner layer "B") and a 10μm thick PLA / PBAT film (layer "A") were hot-pressed in a vacuum hot press with an ABA structure at 120℃ and 100kPa pressure for 3 minutes. The film was then removed, cooled to room temperature, and weighed down to maintain its flatness.

[0082] Thermal bonding strength test

[0083] The 10 multilayer composite films prepared in Examples 3-6 and Comparative Examples 1-8 were first placed in a constant temperature and humidity environment of 23°C and 50%RH for 24 hours for pretreatment. The thermal bonding performance of the samples was measured according to the steps described above, and the values ​​are listed in Table 1.

[0084] Table 1. Thermal strength of specimens from Examples 3-6 and Comparative Examples 1-8

[0085]

[0086]

[0087] By controlling the temperature of the casting cooling roller, PGA films with different crystallinities were obtained. Using PGA films of different crystallinities as the inner layer "B" and PBAT and PLA / PBAT as the outer layers, a three-layer composite film could be obtained through hot pressing. Heat-sealing strength tests revealed that, regardless of whether a single PBAT layer or a PLA / PBAT blend film was used as the outer layer, controlling the crystallinity of the inner PGA film and selecting appropriate hot-pressing conditions (120℃, 100kPa, 3min) significantly enhanced the bonding force between the inner and outer layers (Examples 3-5). Analysis of Examples 3, 7, 1, and 8 showed that the bonding force between PGA and the outer layer was significantly improved under 100kPa pressure. Comparative Examples 2-4 indicated that 120℃ was the most suitable hot-pressing temperature.

[0088] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0089] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A biodegradable film, comprising a hot-pressed composite polyglycolic acid film layer and a biodegradable polyester film layer; wherein, The crystallinity of the polyglycolic acid film layer is 9-13.3%. The biodegradable polyester film layer is made of biodegradable polyester, which is a diacid-diol copolyester, specifically poly(adipate / butylene terephthalate). The method for preparing the biodegradable film includes the following steps: S1. Prepare a polyglycolic acid film layer from polyglycolic acid resin; S2. Prepare a biodegradable polyester film from biodegradable polyester; S3. The polyglycolic acid film layer and the biodegradable polyester film layer are stacked and then hot-pressed together to form a biodegradable film. The hot-pressing composite is performed under the following conditions: temperature from 80°C to 160°C. The polyglycolic acid resin has a melting point range of 205~235℃; the biodegradable polyester has a melting point ≤185℃.

2. The biodegradable film according to claim 1, characterized in that, The melting point of the polyglycolic acid film is at least 20°C higher than that of the biodegradable polyester film.

3. The biodegradable film according to claim 1, characterized in that, The intrinsic viscosity of the polyglycolic acid resin is 1.0-1.4 dl / g, and the thickness of the polyglycolic acid film is 70-150 micrometers.

4. The biodegradable film according to claim 3, characterized in that, The thickness of the polyglycolic acid film is 70-110 micrometers.

5. The biodegradable film according to any one of claims 1-4, characterized in that, The biodegradable polyester exhibits a melt index of 2-20 g / 10 min under test conditions of 190°C and 2.16 kg; and / or The thickness of the biodegradable polyester film is 8-40 micrometers.

6. The biodegradable film according to claim 5, characterized in that, The thickness of the biodegradable polyester film is 8-15 micrometers.

7. The biodegradable film according to claim 6, characterized in that, The thickness of the biodegradable polyester film is 10 micrometers.

8. The biodegradable film according to any one of claims 1-4, characterized in that, The hot-pressing composite is carried out under the following conditions: time is 1 min to 5 min; pressure is 8-200 kPa.

9. The biodegradable film according to claim 8, characterized in that, The hot-pressing composite is carried out under the following conditions: temperature 100ºC to 130ºC; time 2 min to 3 min; pressure 10-100 kPa.

10. A method for preparing a biodegradable film as described in any one of claims 1-9, the method comprising the following steps: S1. A polyglycolic acid film is prepared from polyglycolic acid resin, wherein the crystallinity of the polyglycolic acid film is controlled at 9-13.3%; S2. Prepare a biodegradable polyester film from biodegradable polyester; S3. The polyglycolic acid film layer and the biodegradable polyester film layer are stacked and then hot-pressed together to form a biodegradable film. The polyglycolic acid film layer is prepared by casting polyglycolic acid resin, which is melt-extruded, cooled, and wound up; wherein the cooling temperature is 10-60℃, and the extrusion temperature is 180℃-260℃.

11. The method according to claim 10, characterized in that, The cooling temperature is 10-40℃.

12. The method according to claim 10, characterized in that, The extrusion speed is 100-200 rpm.

13. The method according to claim 12, characterized in that, The extrusion temperature is 200℃-250℃; and / or the extrusion speed is 150-200 rpm.

14. The method according to any one of claims 10-13, characterized in that, The biodegradable polyester film is prepared by blowing or casting biodegradable polyester.

15. The method according to claim 14, characterized in that, The biodegradable polyester film is prepared by blown film.

16. The method according to any one of claims 10-13, characterized in that, The polyglycolic acid film layer and the biodegradable polyester film layer are stacked and hot-pressed using an ABA or BAB method, respectively.

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