A transparent heat-resistant, rollable polylactic acid film and its preparation method

Abstract

This invention discloses a transparent, heat-resistant, flexible polylactic acid (PLA) film and its preparation method, relating to the field of polymer packaging materials technology. The preparation method provided by this invention includes: uniformly mixing a nucleating agent, modified zinc oxide whiskers, and PLA resin; granulating the mixture to obtain a PLA composite resin masterbatch; casting the PLA composite resin masterbatch to obtain a film preform; stretching the film preform at a preset temperature and then shaping it to obtain the PLA film product; the modified zinc oxide whiskers are obtained by surface plasma treatment of zinc oxide whiskers. This PLA film product exhibits high transparency and excellent heat-resistant, flexible properties. The preparation method of the transparent, heat-resistant, flexible PLA film of this invention is simple, uses readily available raw materials, is low in cost, and produces a product with excellent performance. The transparent, heat-resistant, flexible PLA film of this invention exhibits high transparency and excellent heat-resistant, flexible properties.

Description

Technical Field

[0001] This invention relates to the field of polymer packaging materials technology, and in particular to a transparent heat-resistant, rollable polylactic acid film and its preparation method. Background Technology

[0002] Polylactic acid (PLA) resin is a biodegradable polyester polymer obtained by polymerizing lactic acid as the main raw material. PLA is currently the biodegradable polymer material with the largest production capacity and the most widespread application. PLA can be prepared into products for different purposes through various processing technologies such as injection molding, casting, and spinning. In addition to being biodegradable, the products obtained also have good biocompatibility, mechanical properties, transparency, and texture.

[0003] Because polylactic acid (PLA) crystallizes very slowly and hardly crystallizes during processing, the resulting products are often amorphous PLA, leading to poor dimensional stability. Its heat distortion temperature is typically only 55-60℃. Due to residual stress within PLA during processing, especially in film packaging products, curling and other heat deformations easily occur after exceeding the heat distortion temperature, significantly impacting its practical applications. Improving the dimensional stability of PLA at higher temperatures is currently a research hotspot in PLA application research.

[0004] Patent CN102206406A discloses a method for preparing a transparent, heat-resistant polylactic acid modified material. This method utilizes a chain extender, polymethyl methacrylate (PMMA)-coated chitin whiskers, and a PMMA composite material blended with phosphite to improve the thermal stability of the PMMA system. The PMMA-coated chitin whiskers used in this method require free radical polymerization initiated by an initiator in an aqueous solution system. The free radical polymerization reaction is quite vigorous and difficult to control, easily causing the PMMA to polymerize and agglomerate in the aqueous system, thus failing to effectively coat the chitin whiskers and resulting in an unstable product.

[0005] Patent CN118386581A discloses a high-transmittance biaxially oriented polylactic acid (PLA) film, its preparation method, and its applications. The method involves biaxially stretching a three-layer PLA film (surface melt, middle melt, and inner melt) to obtain a high-thermal-stability PLA film. The three melt layers are: a surface melt composed of modified PLA and PBAT; a middle melt composed of hydroxyl-terminated PLA, amino-terminated liquid nitrile butadiene rubber, and diphenyl dihydrazide sebacate; and an inner melt composed of hydroxyl-terminated PLA and amino-terminated liquid nitrile butadiene rubber. Furthermore, the surface-modified PLA requires aldehyde and amino modification in solvents such as dichloromethane, making the entire process cumbersome and complex, and involving the extensive use of highly toxic organic solvents such as dichloromethane and trichloromethane.

[0006] Patent CN111548617A discloses a biodegradable polylactic acid (PLA) material, its preparation method, and its applications. The method utilizes a PLA film modified with diatomaceous earth, toughening agents, and plasticizers. While the PLA film prepared by this method improves both the toughness and heat resistance of PLA, the increase in its heat distortion temperature is limited. In a comparative example, the PLA film's heat distortion temperature only increased from 53°C to 63°C, which is still far from meeting the requirements of some applications with high heat resistance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that current polylactic acid film materials are prone to deformation and curling under high temperature conditions.

[0008] To address the above problems, the present invention proposes the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a transparent, heat-resistant, curlable polylactic acid film, comprising the following steps:

[0010] S1. Mix the nucleating agent, modified zinc oxide whiskers and polylactic acid resin evenly, granulate, and obtain polylactic acid composite resin masterbatch.

[0011] S2. The polylactic acid composite resin masterbatch is cast into a film preform.

[0012] S3. The film preform is stretched and shaped at a preset temperature to obtain a polylactic acid film product.

[0013] The modified zinc oxide whiskers are obtained by surface plasma treatment of zinc oxide whiskers.

[0014] A further technical solution is that the zinc oxide whiskers are tetraneedle-shaped zinc oxide whiskers.

[0015] Tetranephrite zinc oxide whiskers are single whiskers with a unique three-dimensional structure. Due to their unique three-dimensional tetranephrite structure, they possess excellent properties such as high strength, high modulus, wear resistance, antibacterial properties, and antistatic properties, and are widely used as reinforcing materials. However, zinc oxide whiskers have high surface activity and poor interfacial compatibility with low surface energy polymer materials. They are prone to agglomeration during blending with resin materials such as polylactic acid, making it difficult for them to effectively reinforce the resin matrix.

[0016] The modified zinc oxide whiskers of this invention employ plasma treatment technology to modify the surface of zinc oxide whiskers, which can effectively increase the surface roughness of zinc oxide whiskers without damaging the integrity of the whiskers. It can effectively increase the content of functional groups on the surface, thereby improving the interfacial bonding strength between zinc oxide whiskers and polylactic acid resin.

[0017] A further technical solution is that the power of the surface plasma treatment is 100-1200W, and the treatment time is 10-120s.

[0018] A further technical solution is that the surface plasma treatment includes air plasma treatment, oxygen plasma treatment, ammonia plasma treatment, and nitrogen plasma treatment.

[0019] A further technical solution is that the size of the whisker needles has a crucial impact on the properties of polylactic acid resin. In order to provide the tensile strength and heat resistance of the polylactic acid film, the size of the zinc oxide whiskers in this invention is 1-50 micrometers.

[0020] A further technical solution is that, in step S1, the ratio of the nucleating agent, modified zinc oxide whiskers, and polylactic acid resin is 0.05-1:0.2-2:100.

[0021] A further technical solution is that the nucleating agent includes one or more of the following: silicon dioxide, calcium carbonate, mica, talc, hydrotalcite, ethylene bis-stearamide, sebacate diphenyl dihydrazide, octanoic acid dibenzoyl hydrazide, zinc citrate, and copper citrate.

[0022] A further technical solution is that, in step S3, the preset temperature is 90-150℃.

[0023] A further technical solution is that, in step S3, the elongation of the film preform during stretching is 1%-100%.

[0024] In a second aspect, the present invention provides a transparent heat-resistant and flexible polylactic acid film, which is prepared by the method for preparing the transparent heat-resistant and flexible polylactic acid film described in the first aspect.

[0025] Compared with the prior art, the technical effects achieved by the present invention include:

[0026] The present invention provides a method for preparing a transparent, heat-resistant, and curlable polylactic acid (PLA) film. The method involves blending and granulating a nucleating agent, modified zinc oxide whiskers, and PLA resin to ensure uniform dispersion of each component with the PLA resin, resulting in a PLA composite resin masterbatch. The PLA composite resin masterbatch is then cast to form the film body, which is subsequently stretched and induced to crystallize, yielding the final film product. This PLA film product exhibits high transparency and excellent heat-resistant curling properties, effectively solving the problem of PLA film materials easily deforming and curling under high-temperature conditions.

[0027] The preparation method of the transparent heat-resistant rollable polylactic acid film of the present invention is simple, the raw materials are readily available, the cost is low, and the product performance is excellent.

[0028] The transparent heat-resistant and curlable polylactic acid film of the present invention has high transparency and excellent heat-resistant and curlable properties. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a photograph of zinc oxide whiskers used in Example 1 of the present invention.

[0031] Figure 2 This is a photograph of zinc oxide whiskers used in Example 2 of the present invention.

[0032] Figure 3 This is a photograph of the thin film preform obtained in Example 1 of the present invention.

[0033] Figure 4 This is a photograph of the transparent heat-resistant, rollable polylactic acid film prepared in Example 1 of the present invention.

[0034] Figure 5 The graph shows the heat resistance test results at 90°C for the film preform and the transparent heat-resistant rollable polylactic acid film prepared in Example 1 of this invention.

[0035] Figure 6 The graph shows the results of high-temperature resistance tests on the polylactic acid film product obtained in Example 2 of the present invention and the polylactic acid film product obtained in Comparative Example 2. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0038] It should also be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] Example 1

[0040] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0041] Zinc oxide whiskers with needle-like dimensions of approximately 30 micrometers (microstructure as shown) Figure 1 Modified zinc oxide whiskers were obtained by treating the mixture with oxygen plasma at a power of 800W for 30s.

[0042] The above-mentioned 1g modified zinc oxide whiskers, 0.2g hydrotalcite, 0.1g zinc citrate and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0043] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0044] The obtained polylactic acid film preform with high transparency (such as...) Figure 3 The product is placed in a 110°C oven and heated to 110°C before being stretched to an elongation of 50%. After stretching, it is quickly removed and rapidly cooled to room temperature to obtain a polylactic acid film product with a thickness of approximately 50 mm. μm .

[0045] contrast Figure 3 and Figure 4 As can be seen from the photos, the polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 92.7% after measurement.

[0046] Temperature resistance test: The polylactic acid film product and the unstretched film preform were placed together in an 85°C oven. After 1 hour, the unstretched film preform curled and deformed (see...). Figure 5 PLA film (marked in Chinese), after being stretched, showed no significant deformation when placed in an 85°C oven for 24 hours (see...). Figure 5 Modified PLA film with Chinese marking).

[0047] The above test results indicate that the transparent heat-resistant curable polylactic acid film provided by the present invention contains modified zinc oxide whiskers, which can significantly improve the dimensional stability of the polylactic acid film under high temperature environment after stretching treatment.

[0048] Example 2

[0049] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0050] Zinc oxide whiskers with needle-like dimensions of approximately 10 micrometers (microstructure as shown) Figure 2 Modified zinc oxide whiskers were obtained by treating the mixture with ammonia plasma at a power of 500W for 60 seconds.

[0051] The above-mentioned 0.6g modified zinc oxide whiskers, 0.1g silicon dioxide, 0.1g talc powder and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0052] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0053] The obtained highly transparent polylactic acid (PLA) film was heated to 130°C in an oven and then stretched to an elongation of 75%. It was then quickly removed and rapidly cooled to room temperature. After stretching, the film was again quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0054] The polylactic acid film product prepared in the example maintained high transparency after stretching. The light transmittance of the final polylactic acid film product reached 93.1% as measured.

[0055] Comparative Example 1

[0056] To better illustrate the effect of adding zinc oxide whiskers on the final film product, this comparative example is based on the formulation of Example 2, but the modified zinc oxide whiskers are replaced with the same mass of silicon dioxide. Other processes and treatments are the same as in Example 2, resulting in the polylactic acid film product of Comparative Example 1 without the addition of zinc oxide whiskers.

[0057] According to the temperature resistance test, the polylactic acid film product without zinc oxide whiskers obtained in Comparative Example 1 showed obvious curling and deformation after being placed in a 90℃ oven for 1 hour.

[0058] Comparative Example 2

[0059] To better illustrate the effect of plasma-treated modified zinc oxide whiskers on the final film product, this comparative example replaces the modified zinc oxide whiskers in the formulation of Example 2 with untreated zinc oxide whiskers. Other processes and treatment procedures are the same as in Example 2, resulting in the untreated polylactic acid film product of Comparative Example 2.

[0060] The polylactic acid film product obtained in Example 2 and the polylactic acid film product obtained in Comparative Example 2 were subjected to high temperature resistance tests.

[0061] Test method: The polylactic acid film product obtained in Example 2 and the untreated polylactic acid film product from Comparative Example 2 were placed together in a 90°C oven for 2 hours. Figure 6 The results show that, compared with Comparative Example 2, the polylactic acid film prepared under the same process conditions with added zinc oxide without plasma surface treatment (see...) Figure 6 The untreated film (marked in the middle) showed slight curling at the edges after being placed at 90°C for 2 hours. Its heat-resistant curling performance was improved to some extent compared to the polylactic acid film without zinc oxide whiskers in Comparative Example 1, but slight curling at the edges still remained. The final transparent heat-resistant polylactic acid film product obtained in Example 2 of this invention (see...) Figure 6 The surface-treated film (marked in the middle) was placed at 90°C for 2 hours. No obvious curling occurred in the whole film or in any part of it, indicating that the transparent anti-curling polylactic acid film obtained in the embodiment of the present invention has good anti-heat curling properties.

[0062] Example 3

[0063] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0064] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of approximately 50 micrometers with air plasma at a power of 1200W for 10 seconds.

[0065] The above-mentioned 2g modified zinc oxide whiskers, 0.05g talc powder and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0066] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0067] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 150°C oven and heated to 150°C before stretching to 100% elongation. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0068] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 90.3% after measurement.

[0069] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0070] Example 4

[0071] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0072] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of about 5 micrometers with nitrogen plasma at a power of 300W for 120s.

[0073] The above-mentioned 0.3g modified zinc oxide whiskers, 0.1g talc, 0.5g ethylene bis-stearamide and 1000g polylactic acid were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0074] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0075] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 90°C oven and heated to 90°C, then stretched with an elongation of 10%. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0076] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 93.5% after measurement.

[0077] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0078] Example 5

[0079] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0080] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of approximately 1.2 micrometers with oxygen plasma at a power of 100W for 120 seconds.

[0081] The above-mentioned 0.2g modified zinc oxide whiskers, 0.5g calcium carbonate, 0.5g copper citrate and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0082] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0083] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 115°C oven and heated to 115°C before stretching to an elongation of 25%. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0084] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 92.1% after measurement.

[0085] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0086] Example 6

[0087] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0088] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of approximately 20 micrometers with oxygen plasma at a power of 500W for 60 seconds.

[0089] After simple mixing of 0.5g modified zinc oxide whiskers, 0.1g hydrotalcite, 0.1g mica and 1000g polylactic acid resin, the mixture was extruded and granulated using a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0090] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0091] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 120°C oven and heated to 120°C before stretching to 100% elongation. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0092] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 90.3% after measurement.

[0093] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0094] Example 7

[0095] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0096] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of about 10 micrometers with oxygen plasma at a power of 300W for 100s.

[0097] The above-mentioned 0.6g modified zinc oxide whiskers, 0.1g talc, 0.1g dibenzoyl hydrazine octanoate and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0098] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0099] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 105°C oven and heated to 105°C before stretching to an elongation of 60%. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0100] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 92.7% after measurement.

[0101] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0102] Example 8

[0103] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0104] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of approximately 20 micrometers with oxygen plasma at a power of 800W for 30 seconds.

[0105] The above-mentioned 1.5g modified zinc oxide whiskers, 0.5g talc, 0.25g zinc citrate and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0106] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0107] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 125°C oven and heated to 125°C, then stretched to an elongation of 50%. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0108] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 90.8% after measurement.

[0109] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0110] Example 9

[0111] This embodiment provides a transparent heat-resistant, rollable polylactic acid film and its preparation method, the specific steps of which are as follows:

[0112] Modified zinc oxide whiskers were obtained by treating zinc oxide whiskers with needle-like structures of about 10 micrometers with oxygen plasma at a power of 1000W for 100s.

[0113] The above-mentioned 1.2g modified zinc oxide whiskers, 0.1g silicon dioxide, 0.7g dibenzoyl succinate and 1000g polylactic acid resin were simply stirred and mixed, and then extruded and granulated by a twin-screw extruder to obtain a uniformly mixed polylactic acid composite resin masterbatch.

[0114] The obtained polylactic acid composite resin masterbatch was cast into a film preform with uniform thickness using a casting machine.

[0115] The obtained highly transparent polylactic acid (PLA) film preform was placed in a 110°C oven and heated to 110°C before stretching to an elongation of 80%. After stretching, it was quickly removed and rapidly cooled to room temperature to obtain the PLA film product with a thickness of approximately 50 mm. μm .

[0116] The polylactic acid film product prepared in this embodiment still maintains high transparency after stretching. The light transmittance of the final polylactic acid film product reached 91.1% after measurement.

[0117] After temperature resistance testing, the transparent heat-resistant polylactic acid film product obtained in this embodiment did not exhibit significant edge curling after being placed at 90°C for 2 hours, indicating that the transparent heat-resistant polylactic acid film obtained in this embodiment has good heat resistance properties.

[0118] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0119] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a transparent, heat-resistant, curlable polylactic acid film, characterized in that, Includes the following steps: S1. Mix the nucleating agent, modified zinc oxide whiskers and polylactic acid resin evenly, granulate, and obtain polylactic acid composite resin masterbatch. S2. The polylactic acid composite resin masterbatch is cast into a film preform. S3. The film preform is stretched and shaped at a preset temperature to obtain a polylactic acid film product. The modified zinc oxide whiskers are obtained by surface plasma treatment of zinc oxide whiskers; In step S1, the ratio of the nucleating agent, modified zinc oxide whiskers, and polylactic acid resin is as follows: 0.05-1：0.2-2：100； The nucleating agents include one or more of the following: silicon dioxide, calcium carbonate, mica, talc, hydrotalcite, ethylene bis-stearamide, sebacate diphenyl dihydrazide, octanoic acid dibenzoyl hydrazide, zinc citrate, and copper citrate. The needle-like size of the zinc oxide whiskers is 1-50 micrometers.

2. The method for preparing the transparent heat-resistant, curlable polylactic acid film as described in claim 1, characterized in that, The zinc oxide whiskers are tetraneedle-shaped zinc oxide whiskers.

3. The method for preparing the transparent, heat-resistant, curlable polylactic acid film as described in claim 1, characterized in that, The surface plasma treatment has a power of 100-1200W and a treatment time of 10-120s.

4. The method for preparing the transparent heat-resistant, curlable polylactic acid film as described in claim 1, characterized in that, The surface plasma treatment includes air plasma treatment, oxygen plasma treatment, ammonia plasma treatment, and nitrogen plasma treatment.

5. The method for preparing the transparent heat-resistant, curlable polylactic acid film as described in claim 1, characterized in that, In step S3, the preset temperature is 90-150℃.

6. The method for preparing the transparent heat-resistant, curlable polylactic acid film as described in claim 1, characterized in that, In step S3, the elongation of the film preform during stretching is 1%-100%.

7. A transparent, heat-resistant, rollable polylactic acid film, characterized in that, The transparent heat-resistant, rollable polylactic acid film is prepared by the method described in any one of claims 1-6.

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