An oriented polycaprolactone / polylactic acid blend film and a method for preparing the same

Abstract

The application belongs to the technical field of polymer materials, and particularly relates to an oriented polycaprolactone / polylactic acid blend film and a preparation method thereof. The preparation method of the oriented polycaprolactone / polylactic acid blend film provided by the application comprises the following steps: S1, preparing an oriented polyethylene film by using a melt stretching method; S2, spin coating a polycaprolactone / polylactic acid / trichloromethane solution on a silicon wafer to obtain a polycaprolactone / polylactic acid blend film; S3, covering the oriented polyethylene film prepared in the step S1 on the polycaprolactone / polylactic acid blend film prepared in the step S2, and performing heat treatment, and finally removing the upper oriented polyethylene film to obtain the oriented polycaprolactone / polylactic acid blend film. The blend film prepared by the application has excellent orientation, and a method for regulating the orientation structure morphology of the oriented polycaprolactone / polylactic acid blend film is provided.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to an oriented polycaprolactone / polylactic acid blend film and its preparation method. Background Technology

[0002] As is well known, the physical and chemical structure of a material determines its properties and applications. For semi-crystalline polymers, crystallization and orientation are important means of controlling polymer properties.

[0003] Due to the long-chain structure of polymer molecules, during polymer molding and processing, with the help of an external force field, polymer chains, segments, or crystallites will align in an orderly manner along the direction of the force, a process known as polymer orientation. Oriented polymer materials outperform isotropic materials in many properties. For example, the mechanical, electrical, and thermal conductivity of oriented polymer materials can be improved by a factor of one hundred, and the orientation morphology has a significant impact on the material properties.

[0004] Therefore, how to control the orientation structure of materials has always been a research hotspot in the materials science field.

[0005] Epiphytic crystallization is an important means of controlling material structure, enabling the manipulation of crystal form and orientation. Epiphytic crystallization refers to the oriented crystallization of a crystalline substance on a different substrate; essentially, it is an orientation-induced crystallization phenomenon. A unique interaction exists between the epiphytic substrate and the epiphytic material, leading to the formation of oriented structures and unusual morphologies. Therefore, epiphytic crystallization is often used as an effective method for controlling the morphology and structure of materials.

[0006] Polylactic acid (PLA) materials possess excellent plasticity, thermoformability, and biocompatibility, but also suffer from brittleness and fragility. Polycaprolactone (PVC), on the other hand, exhibits good flexibility and processability. Blending the two can mutually improve their properties. However, current methods for preparing PVC / PLA oriented films involve spin-coating a PVC / PLA solution onto an oriented polyethylene film followed by recrystallization, resulting in PVC / PLA films with poor orientation.

[0007] Therefore, there is a need to provide a method for preparing highly oriented polycaprolactone / polylactic acid blend films that can effectively control their orientation structure morphology. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide an oriented polycaprolactone / polylactic acid (PVC) blend film and its preparation method. The present invention provides an oriented PVC / PVC blend film and its preparation method, which involves coating an oriented polyethylene film onto a PVC / PVC blend film, followed by heat treatment, and finally removing the oriented polyethylene film. The blend film prepared using the method provided by the present invention exhibits excellent orientation properties. Furthermore, a method for controlling the orientation structure morphology of the oriented PVC / PVC blend film is provided.

[0009] The technical solution of this invention is:

[0010] A method for preparing an oriented polycaprolactone / polylactic acid blend film includes the following steps:

[0011] S1. Preparation of oriented polyethylene film: Oriented polyethylene film is prepared by melt stretching method;

[0012] S2. Preparation of polycaprolactone / polylactic acid blend film: spin-coating a polycaprolactone / polylactic acid / chloroform solution onto a silicon wafer to obtain a polycaprolactone / polylactic acid blend film.

[0013] S3. Preparation of oriented polycaprolactone / polylactic acid blend film: The oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and heat treatment is performed to crystallize polylactic acid and polycaprolactone. Finally, the upper oriented polyethylene film is peeled off to obtain the oriented polycaprolactone / polylactic acid blend film.

[0014] Further, the heat treatment process in step S3 is as follows: the oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and the film is kept at 80-130°C for 3.5-4.5 hours to allow polylactic acid to crystallize, and then kept at 30-50°C for 3-5 hours to ensure polycaprolactone crystallization.

[0015] Furthermore, the preparation method of the polycaprolactone / polylactic acid / chloroform solution in step S2 is as follows:

[0016] Polycaprolactone and polylactic acid are dissolved in chloroform at a weight ratio of 20 / 80 to 80 / 20 to prepare a polycaprolactone / polylactic acid / chloroform solution of 2 to 15 mg / mL.

[0017] Furthermore, the weight ratio of polycaprolactone to polylactic acid is 40 / 60.

[0018] Furthermore, the specific steps for preparing oriented polyethylene film by melt stretching in step S1 are as follows:

[0019] High-density polyethylene is added to xylene solvent and heated to 190–210°C. The mixture is stirred until the polyethylene is completely dissolved, preparing a polyethylene / xylene solution of 5–20 mg / mL. The prepared polyethylene / xylene solution is dropped onto a glass plate preheated to 125–140°C and spread evenly. After the solvent in the polyethylene / xylene solution on the glass plate evaporates, an electric roller with a rotation speed of 4–20 cm / s is used to lift the polyethylene on the glass plate. During the lifting process, the polyethylene in the supercooled melt state is stretched and pulled by the roller to obtain an oriented polyethylene film.

[0020] Furthermore, the concentration of the polyethylene / xylene solution is 5 mg / mL.

[0021] Furthermore, the thickness of the oriented polyethylene film obtained in step S1 is 40–60 nm.

[0022] Furthermore, the thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 is 20–100 nm.

[0023] The present invention also provides an oriented polycaprolactone / polylactic acid blend film prepared by the above-mentioned method.

[0024] Furthermore, the present invention also provides a method for controlling the orientation structure morphology of oriented polycaprolactone / polylactic acid blend films, comprising the following steps:

[0025] S1. Preparation of oriented polyethylene film: Oriented polyethylene film is prepared by melt stretching method;

[0026] S2. Preparation of polycaprolactone / polylactic acid blend film: spin-coating a polycaprolactone / polylactic acid / chloroform solution onto a silicon wafer to obtain a polycaprolactone / polylactic acid blend film.

[0027] S3. Preparation of oriented polycaprolactone / polylactic acid blend film: The oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and heat treatment is performed to crystallize polylactic acid and polycaprolactone. Finally, the upper oriented polyethylene film is peeled off to obtain the oriented polycaprolactone / polylactic acid blend film.

[0028] Furthermore, the method for controlling the orientation structure morphology of polycaprolactone / polylactic acid blend films provided by the present invention is mainly carried out by controlling the thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 and the heat treatment conditions in step S3.

[0029] Polycaprolactone crystals belong to the orthorhombic crystal system, with cell parameters a = 0.747 nm, b = 0.498 nm, and c = 1.705 nm. Polyethylene also belongs to the orthorhombic crystal system, with cell parameters a = 0.74 nm, b = 0.494 nm, and c = 0.253 nm. The (hk0) crystal planes of the two exhibit perfect lattice matching. For example, the mismatch rate of the (010) crystal plane is only 0.8%, while the mismatch rate of the (100) crystal plane is 0.9%. Moreover, the interatomic spacing along the chain axis of polycaprolactone is 0.122 nm, and the interatomic spacing along the chain axis of polyethylene is 0.123 nm, which matches well. Therefore, the polycaprolactone molecular chains can be arranged parallel to the polyethylene molecular chains to form an oriented structure. In oriented polyethylene, oriented lamellar and amorphous regions alternate, forming nanoscale grooves on the film. The direction of these grooves is perpendicular to the direction of the molecular chains in the film. These grooves on the surface of the oriented film can induce polylactic acid to align along the groove direction. The polylactic acid molecular chains are perpendicular to the direction of the polyethylene molecular chains. The uncrystallized polylactic acid molecular chains are aligned parallel to the spiral path of the polylactic acid parallel lamellar crystals, forming lamellar crystals tilted to the direction of the polyethylene molecular chains.

[0030] To prepare highly oriented polycaprolactone / polylactic acid (PLA) blend films, this invention first prepares a highly oriented polyethylene film using a melt stretching method. Then, a PLA / PLA / chloroform blend solution is prepared, and a PLA / PLA blend film of a specific thickness is prepared using a spin-coating method. The oriented polyethylene film is then coated onto the PLA / PLA blend film, followed by heat treatment. First, the PLA is cold-crystallized, and then the PLA is melt-recrystallized to obtain the highly oriented PLA / PLA blend film. Furthermore, the preparation method provided by this invention allows for effective control of the orientation structure morphology of the obtained oriented PLA / PLA blend film by adjusting the heat treatment temperature and the thickness of the PLA / PLA blend film.

[0031] Compared with the prior art, the method for preparing oriented polycaprolactone / polylactic acid blend films provided by the present invention has the following advantages:

[0032] The present invention provides a simple method for preparing oriented polycaprolactone / polylactic acid blend films, producing films with extremely high orientation. Furthermore, by controlling the heat treatment temperature or the thickness of the polycaprolactone / polylactic acid blend film during the preparation process, the morphology of the oriented polycaprolactone / polylactic acid blend film can be effectively controlled. Attached Figure Description

[0033] Figure 1(a) is an atomic force microscopy (AFM) phase diagram of the oriented polycaprolactone / polylactic acid (PLA) blend film prepared in Example 1 of the present invention; (b) is an AFM phase diagram of the oriented PLA / PLA blend film prepared in Example 1 when heated to 75°C; (c) is an AFM phase diagram of the oriented PLA / PLA blend film prepared in Example 1 when heated to 75°C and then directly cooled to 20°C.

[0034] Figure 2 (a) and (b) are atomic force microscopy phase diagrams of the oriented polycaprolactone / polylactic acid blend films prepared in Examples 2 and 3 of this invention, respectively.

[0035] Figure 3 This is an atomic force microscopy phase image of the polycaprolactone / polylactic acid blend thin film prepared in Comparative Example 1 of this invention;

[0036] Figure 4 (a) is an atomic force microscopy phase diagram of the polycaprolactone / polylactic acid blend thin film prepared in Comparative Example 2 of the present invention, and (b) is a partial magnified view of (a). Detailed Implementation

[0037] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0038] Unless otherwise specified, the reagents used in the following examples and comparative examples are conventional reagents, all of which can be purchased from conventional reagent manufacturers and distributors. Unless otherwise specified, the methods used are existing technologies. Information on some raw material manufacturers is as follows:

[0039] High-density polyethylene (M w =9.9×10 4 g / mol), purchased from Lanzhou Petrochemical Company;

[0040] Polylactic acid (M) w =2.4×10 5 g / mol), purchased from Nature Works;

[0041] Polycaprolactone (M) n =8×10 4 g / mol), purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0042] Example 1: A method for preparing an oriented polycaprolactone / polylactic acid blend film

[0043] The method for preparing the oriented polycaprolactone / polylactic acid blend film includes the following steps:

[0044] S1. Preparation of oriented polyethylene film by melt stretching method: High-density polyethylene is added to xylene solvent, heated to 200℃, and stirred to completely dissolve the polyethylene, preparing a polyethylene / xylene solution with a concentration of 5 mg / mL; the polyethylene / xylene solution is taken with a dropper and dropped onto a glass plate preheated to 132℃, and the solution is spread evenly with a glass rod; after the solvent in the polyethylene / xylene solution evaporates, an electric roller with a rotation speed of 20 cm / s is used to pull the polyethylene on the glass plate. During the pulling process, the polyethylene in the supercooled melt state is stretched and pulled by the roller to obtain an oriented polyethylene film with a thickness of 50 nm.

[0045] S2. Preparation of polycaprolactone / polylactic acid blend film: Polycaprolactone and polylactic acid were dissolved in chloroform at a mass ratio of 40 / 60 to prepare a 10 mg / mL polycaprolactone / polylactic acid / chloroform solution; the prepared polycaprolactone / polylactic acid / chloroform solution was spin-coated onto a silicon wafer using a spin coater for 60 s to obtain a 70 nm thick polycaprolactone / polylactic acid film;

[0046] S3. Preparation of oriented polycaprolactone / polylactic acid blend film: Cover the polycaprolactone / polylactic acid blend film obtained in step S2 with the oriented polyethylene film obtained in step S1, and then place it at 100°C for 4 hours to allow polylactic acid to crystallize. Then place it at 45°C for 4 hours to ensure polycaprolactone crystallization. Finally, peel off the upper oriented polyethylene film to obtain the oriented polycaprolactone / polylactic acid blend film.

[0047] Example 2: A method for preparing an oriented polycaprolactone / polylactic acid blend film

[0048] Compared with Example 1, the difference in Example 2 is that the thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 is 30 nm, while other parameters and operations are the same as in Example 1.

[0049] Example 3: A method for preparing an oriented polycaprolactone / polylactic acid blend film.

[0050] Compared with Example 1, the difference in Example 3 is that the thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 is 30 nm, and the heat treatment process in step S3 is as follows: the oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and then it is placed at 120°C for 4 hours to allow polylactic acid to crystallize, and then at 45°C for 4 hours to ensure polycaprolactone crystallization. Other parameters and operations are the same as in Example 1.

[0051] Comparative Example 1: A method for preparing a polycaprolactone / polylactic acid blend film

[0052] Compared with Example 1, the difference in Comparative Example 1 is that step S1 (not preparing an oriented polyethylene film) is omitted, and the obtained polycaprolactone / polylactic acid blend film is directly subjected to heat treatment. Other parameters and operations are the same as in Example 1.

[0053] Comparative Example 2: A method for preparing a polycaprolactone / polylactic acid blend film

[0054] The method for preparing the oriented polycaprolactone / polylactic acid blend film includes the following steps:

[0055] S1. Preparation of oriented polyethylene film by melt stretching method: High-density polyethylene is added to xylene solvent, heated to 200℃, and stirred to completely dissolve the polyethylene, preparing a polyethylene / xylene solution with a concentration of 5 mg / mL; the polyethylene / xylene solution is taken with a dropper and dropped onto a glass plate preheated to 132℃, and the solution is spread evenly with a glass rod; after the solvent in the polyethylene / xylene solution evaporates, an electric roller with a rotation speed of 20 cm / s is used to pull the polyethylene on the glass plate. During the pulling process, the polyethylene in the supercooled melt state is stretched and pulled by the roller to obtain an oriented polyethylene film with a thickness of 50 nm.

[0056] S2. Preparation of oriented polycaprolactone / polylactic acid blend film: Polycaprolactone and polylactic acid were dissolved in chloroform at a mass ratio of 40 / 60 to prepare a 10 mg / mL polycaprolactone / polylactic acid / chloroform solution. Using the oriented polyethylene film obtained in step S1 as a substrate, the polycaprolactone / polylactic acid / chloroform solution was spin-coated onto the oriented polyethylene film using a spin coater for 60 s. The thickness of the spin-coated polycaprolactone / polylactic acid blend film was 70 nm. The spin-coated polycaprolactone / polylactic acid / polyethylene sample was then placed at 100°C for 4 h to allow polylactic acid crystallization, and then at 45°C for 4 h to ensure polycaprolactone crystallization.

[0057] Experimental Example 1: Orientation Structure Analysis of the Oriented Polycaprolactone / Polylactic Acid Blend Film Prepared in Example 1 of the Present Invention

[0058] The crystal morphology of polymers was studied using an Agilent 5500 atomic force microscope. During the experiment, the atomic force microscope was used in tapping scan mode with a scan rate of 0.8 μm / s. The resonant frequency used for the test was 320–350 kHz, the elastic constant of the probe cantilever was 20–30 N / m, and the pixel size of the acquired image was 512 × 512.

[0059] The orientation structure of the oriented polycaprolactone / polylactic acid blend film prepared in Example 1 of this invention was analyzed, and the results were obtained. Figure 1 Wherein (a) is an atomic force microscopy phase image of the oriented polycaprolactone / polylactic acid blend film prepared in Example 1. Figure 1 In (a), the arrows indicate the direction of the oriented polyethylene molecular chains. It can be observed that when an oriented polyethylene film is covered on the surface of a polycaprolactone / polylactic acid blend film, and then heat-treated and the oriented polyethylene film is removed, the polycaprolactone molecular chains are oriented parallel to the direction of the polyethylene molecular chains, while some of the polylactic acid molecular chains are perpendicular to the direction of the polyethylene molecular chains, and some are at a certain angle to the polyethylene molecular chains. Figure 1 The results in (a) demonstrate that a highly oriented polycaprolactone / polylactic acid blend film can be obtained by covering the surface of the polycaprolactone / polylactic acid blend film with an oriented polyethylene film and then subjecting it to heat treatment.

[0060] Figure 1 (b) An atomic force microscopy phase image of the oriented polycaprolactone / polylactic acid blend film prepared in Example 1 when heated to 75°C (i.e., Figure 1 (a) The oriented polycaprolactone / polylactic acid blend film was observed after being heated to 75°C. Since the melting point of polycaprolactone is approximately 60°C and that of polylactic acid is approximately 175°C, when the oriented polycaprolactone / polylactic acid blend film prepared in Example 1 was heated to 75°C, the polycaprolactone in the blend film melted. Scanning the sample at this point yielded a sample morphology containing only polylactic acid. This demonstrates that the molten lamellar crystals with molecular chains parallel to the polyethylene molecular chain direction are polycaprolactone, and the unmelted portion is polylactic acid.

[0061] Figure 1 (c) An atomic force microscopy phase diagram of the oriented polycaprolactone / polylactic acid blend film prepared in Example 1, after being heated to 75°C and then directly cooled to 20°C (i.e.,...). Figure 1 (b) When the sample was cooled to 20°C, the polycaprolactone crystallized during the cooling process. Since it was not covered by an oriented polyethylene film, it could be seen that the polycaprolactone no longer had an oriented structure, which also proved that the oriented polyethylene film had a strong inducing orientation effect on it.

[0062] Example 2: Atomic force microscopy (AFM) images of the oriented polycaprolactone / polylactic acid blend film prepared according to the present invention. Figure 1 Experimental materials: Polycaprolactone / polylactic acid blend films prepared in Examples 2-3 and Comparative Examples 1-2 of this invention.

[0063] 2. Test methods:

[0064] In the experiment, an Agilent 5500 atomic force microscope was used to study the crystal morphology of the polymer. During the experiment, the atomic force microscope was used in tapping scan mode with a scan rate of 0.8 μm / s. The resonant frequency used for the test was 320–350 kHz, the elastic constant of the probe cantilever was 20–30 N / m, and the pixel size of the acquired image was 512 × 512.

[0065] 3. The test results are from Figures 2-4 As shown.

[0066] Figure 2 Figures (a) and (b) are atomic force microscopy phase images of the oriented polycaprolactone / polylactic acid blend films prepared in Examples 2 and 3, respectively. The thickness of the polycaprolactone / polylactic acid blend films prepared in (a) and (b) is 30 nm. The heat treatment process in (a) is to hold at 100°C for 4 hours, followed by holding at 45°C for 4 hours; the heat treatment process in (b) is to hold at 120°C for 4 hours, followed by holding at 45°C for 4 hours.

[0067] It can be seen that the 30nm polycaprolactone / polylactic acid film can form an oriented structure under heat treatment at both 100℃ and 120℃. However, at the high temperature of 120℃, the polylactic acid molecular chains have strong mobility and are prone to aggregation, resulting in more obvious phase separation and partitioning. At the low temperature of 100℃, the polylactic acid molecular chains have weak mobility and are less prone to aggregation, thus the phase separation size is smaller than that of the sample heat-treated at 120℃. It can be seen that the heat treatment temperature in the preparation method of the oriented polycaprolactone / polylactic acid blend film provided by this invention can affect the morphology of its oriented structure.

[0068] Atomic force microscopy phase images of the oriented polycaprolactone / polylactic acid blend films prepared in Examples 1 and 2 of this invention (respectively) Figure 1 (a) and Figure 2 As shown in (a)), the only difference between Example 1 and Example 2 is the thickness of the polycaprolactone / polylactic acid blend film. Both 30 nm and 70 nm thick polycaprolactone / polylactic acid blend films can form oriented structures, but the phase separation size of polycaprolactone and polylactic acid in the 30 nm thick film is smaller than that in the 70 nm thick sample. This is because when the thickness of the nanofilm is larger, the fixation effect of the substrate on the film is reduced, the molecular chain mobility is stronger, and phase separation is more likely to occur. Therefore, the phase separation size of the 70 nm thick polycaprolactone / polylactic acid film is larger than that of the 30 nm thick film. It can be seen that the thickness of the polycaprolactone / polylactic acid blend film affects the morphology of its oriented structure.

[0069] Figure 3The image shows the atomic force microscopy phase diagram of the polycaprolactone / polylactic acid blend film prepared in Comparative Example 1. Because the polycaprolactone / polylactic acid blend film was not covered with an oriented polyethylene film during preparation and was directly heat-treated, from... Figure 3 As can be seen from the results, neither polycaprolactone nor polylactic acid in the blend film prepared in Comparative Example 1 is oriented.

[0070] Figure 4 (a) is an atomic force microscopy phase diagram of the polycaprolactone / polylactic acid blend film prepared in Comparative Example 2, and (b) is a magnified view of (a). When the polycaprolactone / polylactic acid blend solution is spin-coated onto an oriented polyethylene film and then subjected to heat treatment, it can be seen that when the heat treatment temperature is 100°C, the polycaprolactone melts, and the polycaprolactone / polylactic acid film is very prone to agglomeration, exposing the bottom oriented polyethylene substrate, which affects its orientation crystallization on the polyethylene substrate and forms a non-oriented morphological structure.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing an oriented polycaprolactone / polylactic acid blend film, characterized in that: Includes the following steps: S1. Preparation of oriented polyethylene film: Oriented polyethylene film is prepared by melt stretching method; S2. Preparation of polycaprolactone / polylactic acid blend film: spin-coating a polycaprolactone / polylactic acid / chloroform solution onto a silicon wafer to obtain a polycaprolactone / polylactic acid blend film. S3. Preparation of oriented polycaprolactone / polylactic acid blend film: The oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and heat treatment is performed to crystallize polylactic acid and polycaprolactone. Finally, the upper oriented polyethylene film is peeled off to obtain the oriented polycaprolactone / polylactic acid blend film. The heat treatment process in step S3 is as follows: the oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and the film is kept at 80~130 ºC for 3.5~4.5 h, and then kept at 30~50 ºC for 3~5 h. The weight ratio of polycaprolactone to polylactic acid is 40 / 60.

2. The method for preparing the oriented polycaprolactone / polylactic acid blend film according to claim 1, characterized in that, The specific steps for preparing oriented polyethylene film by melt stretching in step S1 are as follows: High-density polyethylene (HDPE) is added to xylene solvent and heated to 190–210 °C. The mixture is stirred until the polyethylene is completely dissolved, preparing a 5–20 mg / mL polyethylene / xylene solution. The prepared polyethylene / xylene solution is dropped onto a glass plate preheated to 125–140 °C and spread evenly. After the solvent in the polyethylene / xylene solution on the glass plate evaporates, an electric roller with a rotation speed of 4–20 cm / s is used to lift the polyethylene on the glass plate. During the lifting process, the polyethylene in a supercooled melt state is stretched and pulled by the roller to obtain an oriented polyethylene film.

3. The method for preparing the oriented polycaprolactone / polylactic acid blend film according to claim 2, characterized in that, The concentration of the polyethylene / xylene solution is 5 mg / mL; the thickness of the oriented polyethylene film obtained in step S1 is 40~60 nm.

4. The method for preparing the oriented polycaprolactone / polylactic acid blend film according to claim 3, characterized in that, The thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 is 20~100 nm.

5. An oriented polycaprolactone / polylactic acid blend film prepared by the method for preparing an oriented polycaprolactone / polylactic acid blend film according to any one of claims 1 to 4.

6. A method for controlling the orientation structure morphology of oriented polycaprolactone / polylactic acid blend films, characterized in that, Includes the following steps: S1. Preparation of oriented polyethylene film: Oriented polyethylene film is prepared by melt stretching method; S2. Preparation of polycaprolactone / polylactic acid blend film: spin-coating a polycaprolactone / polylactic acid / chloroform solution onto a silicon wafer to obtain a polycaprolactone / polylactic acid blend film. S3. Preparation of oriented polycaprolactone / polylactic acid blend film: The oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and heat treatment is performed to crystallize polylactic acid and polycaprolactone. Finally, the upper oriented polyethylene film is peeled off to obtain the oriented polycaprolactone / polylactic acid blend film. The heat treatment process in step S3 is as follows: the oriented polyethylene film obtained in step S1 is covered on the polycaprolactone / polylactic acid blend film obtained in step S2, and the film is kept at 80~130 ºC for 3.5~4.5 h, and then kept at 30~50 ºC for 3~5 h. The weight ratio of polycaprolactone to polylactic acid is 40 / 60; The control is achieved by adjusting the thickness of the polycaprolactone / polylactic acid blend film obtained in step S2 and the heat treatment conditions in step S3.

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