High-toughness polylactic acid packaging film and preparation method thereof

Abstract

The invention discloses a high-toughness polylactic acid packaging film and a preparation method thereof, belongs to the technical field of packaging film preparation, and aims at solving the technical problems that in the prior art, a polylactic acid packaging film with high degradability is low in toughness and poor in thermal stability and cannot meet the requirement for high toughness of polylactic acid in the fields of high-end packaging materials and the like. The preparation method of the high-toughness polylactic acid packaging film comprises the following steps: carrying out melt extrusion on polylactic acid master batches, reinforcing filler, a modified plasticizer and poly (butylene succinate) to obtain modified polylactic acid master batches; adding the modified polylactic acid master batch into a film blowing machine for extrusion and film blowing to obtain the high-toughness polylactic acid packaging film. The preparation method comprises the following steps: carrying out reaction on trimellitic anhydride, citric acid, 1, 3-propylene glycol and trimellitic anhydride to obtain elastomer polyester; reacting the elastomer polyester with epoxidized soybean oil to synthesize a modified plasticizer; and reacting the anhydride-modified silane coupling agent with an inorganic filler to prepare the reinforced filler. The polylactic acid packaging film prepared by the invention has the advantages of high toughness, high degradation rate and high thermal stability.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging film preparation, and in particular to a high-toughness polylactic acid packaging film and a preparation method thereof. Background Art

[0002] Plastics are used to make disposable products such as takeout containers, cups, cutlery, straws, wrapping paper, and shopping bags. They are ubiquitous synthetic polymers in our daily lives. General-purpose plastics such as polyethylene, polypropylene, and polystyrene undergo a long aging period when landfilled, forming microplastics. These microplastics can pollute marine ecosystems such as oceans, rivers, and waterways, creating an environmental crisis that affects the normal growth and reproduction of organisms and poses potential risks to human health. New biodegradable materials, such as polylactic acid (PLA) and its derivatives, have attracted widespread attention due to their non-irritating, non-toxic, and biodegradable properties. However, pure PLA suffers from high brittleness, low toughness, and poor thermal stability in actual use. High-end food packaging and medical packaging require even higher toughness levels for PLA-based packaging films.

[0003] Patent application CN105462196A discloses a method for preparing a polylactic acid composite film. The method involves dissolving polylactic acid, polylactic acid grafted with maleic anhydride, polycaprolactone, and maleic anhydride-isobutyl grafted POSS in a dichloromethane solution, introducing electrospun nanofibers, and casting the resulting polylactic acid composite film. However, many components in the polylactic acid composite film exhibit limited compatibility with the polylactic acid matrix, failing to meet the high-toughness performance requirements of polylactic acid films in the high-end packaging material market.

[0004] In order to further improve the toughness of the prepared polylactic acid composite film, an appropriate amount of plasticizer is often added to the polylactic acid composite film; however, when using organic small molecule plasticizers such as polyols and citrates, the small molecule plasticizer is not only easy to volatilize during the melt processing but also easy to precipitate during the aging process, thereby causing the prepared polylactic acid to become brittle again.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing high-toughness polylactic acid packaging film, which is used to solve the technical problem that the polylactic acid packaging film with high degradability in the prior art has low toughness and poor thermal stability, and cannot meet the high toughness requirements of polylactic acid in high-end packaging materials and other fields.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preparing a high-toughness polylactic acid packaging film comprises the following steps:

[0009] S1. According to parts by weight, 80-90 parts of polylactic acid masterbatch, 5-10 parts of reinforcing filler, 3-10 parts of modified plasticizer and 3-5 parts of polybutylene succinate are added to an extruder for melt extrusion to obtain modified polylactic acid masterbatch;

[0010] S2. The modified polylactic acid masterbatch is added into a film blowing machine for extrusion and film blowing to obtain a high-toughness polylactic acid packaging film.

[0011] Furthermore, the preparation method of the modified plasticizer comprises the following steps:

[0012] A1. Blend citric acid, 1,3-propylene glycol, trimellitic anhydride, and a polymerization inhibitor, place the mixture under an inert gas atmosphere, heat to 170-175°C, stir and melt for 20-30 minutes, then cool to 140-150°C, evacuate, and continue prepolymerization for 2-3 hours, then cool to 110-120°C and continue polymerization for 5-10 hours to obtain an elastomeric polyester;

[0013] Citric acid, 1,3-propylene glycol, and trimellitic anhydride are used as monomers to synthesize the elastomer polyester as follows:

[0014]

[0015] A2. Add the elastomer polyester into a torque rheometer and heat until it is melted. Then add the epoxy soybean oil, mix, and naturally cool to room temperature to prepare a modified plasticizer.

[0016] The elastomer polyester can undergo a cross-linking reaction with epoxidized soybean oil under heating and melting conditions to synthesize a modified plasticizer.

[0017] Furthermore, in step A1, the amount ratio of citric acid, 1,3-propylene glycol, trimellitic anhydride and polymerization inhibitor is 1.92-3.84g:1.52-3.04g:1.92-3.84g:0.0055-0.011g, and the vacuum degree is 0.1-0.2MPa; in step A2, the weight ratio of elastomer polyester and epoxy soybean oil is 20-30:5-10, the heating and melting temperature is 170-175°C, and the mixing temperature is 140-150°C.

[0018] Furthermore, the preparation method of the reinforcing filler comprises the following steps:

[0019] B1, carbon nanotubes, citric acid and deionized water are mixed to obtain a mixture; the mixture is reacted at 60-80°C for 2-3 hours, and then centrifuged and filtered to obtain a solid; the solid is washed until neutral to obtain acidified carbon nanotubes;

[0020] Citric acid is used as an organic acid to acidify the carbon nanotubes, thereby introducing carboxyl groups into the multi-walled carbon nanotubes to obtain acidified carbon nanotubes.

[0021] B2. 3-aminopropyltriethoxysilane and DMF were mixed to prepare a coupling agent solution; 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added to DMF and completely dissolved, and the coupling agent solution was then added dropwise to obtain a reaction system after the addition was complete; the reaction system was reacted at 35-45° C. for 3-4 hours to obtain a coupling agent mixture;

[0022] Using DMF as solvent, 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 3-aminopropyltriethoxysilane undergo a nucleophilic addition-elimination reaction, the reaction formula of which is as follows:

[0023]

[0024] B3. Adding the acidified carbon nanotubes and nano-silica to the coupling agent mixture, ultrasonically dispersing the mixture to obtain a mixture; reacting the mixture at 75-85° C. for 20-24 hours to obtain a reaction solution; filtering the reaction solution using a 0.25-0.3 μm microporous filter membrane, and then vacuum drying to obtain a reinforcing filler.

[0025] Furthermore, in step B1, the mass ratio of carbon nanotubes, citric acid and deionized water is 1-2:5-10:50.

[0026] Furthermore, in step B2, the ratio of 3-aminopropyltriethoxysilane to DMF is 15-25 g:50 g, and the ratio of the mixed solution of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, DMF and coupling agent is 8-16 g:200-250 mL:55-60 mL.

[0027] Furthermore, in step B3, the ratio of the acidified carbon nanotubes, nano-silica and coupling agent mixture is 5-10 g:5-10 g:150-200 mL.

[0028] Furthermore, in step S1, the four temperature zones of the extruder are set to 140-150°C, 160°C, 170°C and 180-185°C respectively; in step S2, the four temperature zones of the film blowing machine are set to 150°C, 160°C, 165-170°C and 145°C respectively.

[0029] As another aspect of the present invention, a method for preparing a high-toughness polylactic acid packaging film provides a high-toughness polylactic acid packaging film.

[0030] The present invention has the following beneficial effects:

[0031] 1. Citric acid, 1,3-propylene glycol, and trimellitic anhydride are reacted as monomers to produce an elastomeric polyester. The active functional groups in the elastomeric polyester are reacted with epoxidized soybean oil to produce a modified plasticizer. Compared to polyols such as 1,3-propylene glycol and small organic molecule plasticizers such as citrate esters, the modified plasticizer is less likely to volatilize at high temperatures during the melt extrusion and blown film processes of synthesizing polylactic acid films, and is less likely to precipitate during film aging. Furthermore, the modified plasticizer can improve the poor compatibility and propensity for phase separation between epoxidized soybean oil and polylactic acid. Furthermore, the modified plasticizer allows for the compounding of multiple plasticizers to form a plasticizer compound system, achieving multi-dimensional plasticization, enhancing the plasticizing effect of the prepared packaging film, and improving the tensile strength and elongation at break of the resulting synthetic packaging film.

[0032] 2. To further enhance the degradability of the packaging film, the present invention primarily uses polylactic acid as the matrix to synthesize the packaging film material. However, a single polylactic acid matrix has poor mechanical properties. The present invention uses carbon nanotubes and nano-silica as reinforcing fillers to improve the mechanical properties of the polylactic acid matrix. Filling the polylactic acid with nano-scale inorganic materials forms a dense filler network within the matrix, enhancing the thermal stability of the polylactic acid packaging film. In order to improve the drawbacks of uneven distribution and easy agglomeration of nano-inorganic materials in a polylactic acid matrix, the present invention uses a coupling agent mixture to modify acidified carbon nanotubes and nano-silica; the coupling agent mixture is obtained by hydrolyzing 3-aminopropyltriethoxysilane modified with 3,3',4,4'-dibenzophenonetetracarboxylic dianhydride as an anhydride; the multi-phenyl ring structure in the coupling agent mixture can further enhance the mechanical properties of the inorganic filler; in addition, the anhydride structure in the coupling agent mixture, the carboxyl groups of the acidified carbon nanotubes, and the hydrophilic hydroxyl groups rich in the surface of the nano-silica can all undergo secondary cross-linking with polylactic acid, thereby improving the mechanical properties of the synthetic polylactic acid matrix from both physical and chemical perspectives. In addition, the amount of the reinforcing filler added is small, ensuring the overall degradation efficiency of the polylactic acid packaging film.

[0033] 3. During the melt extrusion and film blowing process of the polylactic acid matrix, a small amount of polybutylene succinate is added. As a toughening polymer, polybutylene succinate significantly improves the toughness of the synthesized polylactic acid matrix. Furthermore, polybutylene succinate itself is an aliphatic, biodegradable polyester. The additives added to the polylactic acid packaging film prepared by the present invention are mostly biodegradable, resulting in a high degradation rate, excellent thermal stability, and high toughness of the synthesized polylactic acid packaging film. DETAILED DESCRIPTION

[0034] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] The epoxidized soybean oil used in Examples 1-3 of the present invention was purchased from Shandong Changhui Chemical Co., Ltd., with a single product number of A0367; the carbon nanotubes used in Examples 4-6 of the present invention are specifically multi-walled carbon nanotubes, purchased from Shanghai Naio Nano Technology Co., Ltd., with a particle size of 10 nm; the nano-silicon dioxide used in Examples 4-6 of the present invention was purchased from Jiangsu Tianxing New Materials Co., Ltd., with a product number of H10, a model of TSP-H10, a particle size of 20 nm, and a specific surface area of 200 m 2 / g; the polybutylene succinate used in Examples 7-9 of the present invention was purchased from Shanghai Aoji Chemical Co., Ltd., model 345345, item number 2323424; the polylactic acid masterbatch used in Examples 7-9 of the present invention was purchased from Shanghai Hongyuanda Plastic Technology Co., Ltd., brand INGEO, brand INGEO 4060D.

[0036] Example 1

[0037] This embodiment provides a method for preparing a modified plasticizer for high-toughness polylactic acid packaging film, comprising the following steps:

[0038] A1. Add 1.92 g of citric acid, 1.52 g of 1,3-propylene glycol, 1.92 g of trimellitic anhydride and 0.0055 g of polymerization inhibitor p-hydroxyanisole into a three-necked flask. Place the flask in a nitrogen atmosphere, first heat it to 170°C, melt-stir for 20 min, then cool the flask to 140°C and evacuate to continue prepolymerization for 2 h at a vacuum degree of 0.1 MPa; then cool the flask to 110°C and continue polymerization for 5 h to obtain an elastomeric polyester.

[0039] A2. Add 20 parts by weight of polyester elastomer to a torque rheometer and heat until melted. The temperature of the torque rheometer is set to 170°C. Then add 5 parts of epoxidized soybean oil and continue mixing at 140°C at 50 r / min for 20 minutes. Then naturally cool to room temperature to obtain the prepared modified plasticizer.

[0040] Example 2

[0041] This embodiment provides a method for preparing a modified plasticizer for high-toughness polylactic acid packaging film, comprising the following steps:

[0042] A1. Add 2.8 g of citric acid, 2.3 g of 1,3-propylene glycol, 2.8 g of trimellitic anhydride and 0.0066 g of polymerization inhibitor p-hydroxyanisole into a three-necked flask. Place the flask in a nitrogen atmosphere, first heat to 172°C and stir to melt for 22 min, then cool to 143°C and evacuate to continue prepolymerization for 2.5 h at a vacuum degree of 0.2 MPa, then cool the flask to 115°C and continue polymerization for 8 h to obtain an elastomeric polyester.

[0043] A2. Add 25 parts by weight of polyester elastomer to a torque rheometer and heat until melted. The temperature of the torque rheometer is set to 172°C. Then add 8 parts of epoxidized soybean oil. Mix at 145°C and 100 r / min for 22 minutes. Then cool naturally to room temperature to obtain the prepared modified plasticizer.

[0044] Example 3

[0045] This embodiment provides a method for preparing a modified plasticizer for high-toughness polylactic acid packaging film, comprising the following steps:

[0046] A1. Add 3.84 g of citric acid, 3.04 g of 1,3-propylene glycol, 3.84 g of trimellitic anhydride and 0.011 g of polymerization inhibitor p-hydroxyanisole into a three-necked flask. Place the flask in a nitrogen atmosphere, first heat it to 175°C and stir and melt for 30 min. Then cool the flask to 150°C and evacuate to continue prepolymerization for 3 h at a vacuum degree of 0.2 MPa. Then cool it to 120°C and continue polymerization for 10 h to obtain an elastomeric polyester.

[0047] A2. Add 30 parts by weight of polyester elastomer to a torque rheometer and heat until melted. The temperature of the torque rheometer is set to 175°C. Then add 10 parts of epoxidized soybean oil. Mix at 150°C and 150 r / min for 30 minutes. Then cool naturally to room temperature to obtain the prepared modified plasticizer.

[0048] Example 4

[0049] This embodiment provides a method for preparing a reinforcing filler for a high-toughness polylactic acid packaging film, comprising the following steps:

[0050] B1. Mix carbon nanotubes, citric acid, and deionized water in a mass ratio of 1:5:50 to obtain a mixture; place the mixture in a constant temperature heated magnetic stirrer and react at 60°C for 2 hours, then centrifuge at a speed of 8000 r / min for 5 minutes, and filter to obtain a solid; wash the solid with deionized water until neutral to obtain acidified carbon nanotubes.

[0051] B2. 15 g of 3-aminopropyltriethoxysilane and 50 g of DMF were mixed to obtain a coupling agent solution; a 500 mL four-necked flask equipped with a stirrer, a nitrogen tube, a thermometer and a dropping funnel was selected, and after replacing the air in the four-necked flask with nitrogen, 8 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 200 mL of DMF were added in sequence. After 3,3',4,4'-benzophenone tetracarboxylic dianhydride was completely dissolved in DMF, the four-necked flask was placed in an ice bath at a temperature of 0°C; 55 mL of the coupling agent mixture was then added dropwise into the four-necked flask at a dropping rate of 1 mL / min. After the dropwise addition was completed, a reaction system was obtained; the reaction system was continued to stir and react at room temperature at 100 r / min for 3 h to obtain a coupling agent mixture.

[0052] B3. Add 5 g of acidified carbon nanotubes and 5 g of nanosilica to 150 mL of the coupling agent mixture and disperse them evenly by ultrasonication at a frequency of 20 kHz for 5 minutes to obtain a mixture. Heat the mixture to 75°C in an oil bath and reflux with mechanical stirring at 100 rpm for 20 hours to obtain a reactant. Filter the reactant through a 0.25 μm microporous filter membrane and vacuum dry at 75°C for 1 hour to obtain a reinforcing filler.

[0053] Example 5

[0054] This embodiment provides a method for preparing a reinforcing filler for a high-toughness polylactic acid packaging film, comprising the following steps:

[0055] B1. Mix carbon nanotubes, citric acid, and deionized water in a mass ratio of 2:8:50 to obtain a mixture; place the mixture in a constant temperature heated magnetic stirrer and react at 70°C for 2.2 hours, then centrifuge at a speed of 8600 r / min for 2 minutes, and filter to obtain a solid; wash the solid with deionized water until it is neutral to obtain acidified carbon nanotubes.

[0056] B2. Mix 20g of 3-aminopropyltriethoxysilane and 50g of DMF to prepare a coupling agent solution. In a 500mL four-necked flask equipped with a stirrer, nitrogen gas tube, thermometer, and dropping funnel, replace the air in the flask with nitrogen. Then, add 12g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 220g of DMF sequentially. After the 3,3',4,4'-benzophenonetetracarboxylic dianhydride is completely dissolved in DMF, yielding reactant A. Place the four-necked flask in an ice bath at -2°C. Then, add 58mL of the coupling agent mixture dropwise to the flask at a rate of 2mL / min. After complete addition, a reaction system is obtained. The reaction system is heated to 40°C and stirred at 150 rpm for 3.5 hours to yield a coupling agent mixture.

[0057] B3. Add 8 g of acidified carbon nanotubes and 8 g of nano-silica to 180 mL of the coupling agent mixture and disperse them evenly by ultrasonication at a frequency of 26 kHz for 8 minutes to obtain a mixture. Heat the mixture to 80°C in an oil bath and reflux with mechanical stirring at 120 rpm for 22 hours to obtain a reaction solution. Filter the reaction solution through a 0.25 μm microporous filter membrane and vacuum dry it at 77°C for 1.5 hours to obtain a reinforcing filler.

[0058] Example 6

[0059] This embodiment provides a method for preparing a reinforcing filler for a high-toughness polylactic acid packaging film, comprising the following steps:

[0060] B1. Mix carbon nanotubes, citric acid, and deionized water in a mass ratio of 2:10:50 to obtain a mixture; place the mixture in a constant temperature heated magnetic stirrer and react at 80°C for 3 hours, then centrifuge at a speed of 9000 r / min for 10 minutes, and filter to obtain a solid; wash the solid with deionized water until neutral to obtain acidified carbon nanotubes.

[0061] B2. Mix 25g of 3-aminopropyltriethoxysilane and 50g of DMF to prepare a coupling agent solution. A 500mL four-necked flask equipped with a stirrer, nitrogen tube, thermometer, and dropping funnel was prepared. After replacing the air in the flask with nitrogen, 16g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 250mL of DMF were added sequentially. After the 3,3',4,4'-benzophenonetetracarboxylic dianhydride was completely dissolved in the DMF, the four-necked flask was placed in an ice bath at -5°C. 60mL of the coupling agent mixture was then added dropwise to the four-necked flask at a rate of 2mL / min. After the addition was complete, a reaction system was obtained. The reaction system was stirred at 200 rpm at room temperature for 4 hours to obtain a coupling agent mixture.

[0062] B3. Add 10 g of acidified carbon nanotubes and 10 g of nanosilica to 200 mL of the coupling agent mixture and disperse them evenly by ultrasonication at a frequency of 30 kHz for 10 minutes to obtain a mixture. Heat the mixture to 85°C in an oil bath and reflux with mechanical stirring at 200 rpm for 24 hours to obtain a reactant. Filter the reactant through a 0.3 μm microporous filter membrane and vacuum dry at 80°C for 2 hours to obtain a reinforcing filler.

[0063] Example 7

[0064] This embodiment provides a method for preparing a high-toughness polylactic acid packaging film, comprising the following steps:

[0065] S1. The polylactic acid masterbatch was dried in a vacuum drying oven at 50°C for 6 hours to obtain dried polylactic acid masterbatch; 80 parts of the dried polylactic acid masterbatch, 5 parts of the reinforcing filler prepared in Example 4, 3 parts of the modified plasticizer prepared in Example 1, and 3 parts of polybutylene succinate were added to a single-screw extruder for melt extrusion, and the four temperature zones of the extruder were set to 140°C, 160°C, 170°C and 180°C, respectively, to obtain modified polylactic acid masterbatch.

[0066] S2. Add the modified polylactic acid masterbatch into the film blowing machine to extrude the film, wherein the four temperature zones of the film blowing machine are set to 150°C, 160°C, 165°C and 145°C respectively, and the film thickness is 30 μm to obtain a high-toughness polylactic acid packaging film.

[0067] Example 8

[0068] This embodiment provides a method for preparing a high-toughness polylactic acid packaging film, comprising the following steps:

[0069] S1. The polylactic acid masterbatch was dried in a vacuum drying oven at 55°C for 7 hours to obtain the dried polylactic acid masterbatch; 85 parts of the dried polylactic acid masterbatch, 8 parts of the reinforcing filler prepared in Example 5, 6 parts of the modified plasticizer prepared in Example 2, and 4 parts of polybutylene succinate were added to a single-screw extruder for melt extrusion, and the four temperature zones of the extruder were set to 145°C, 160°C, 170°C and 182°C, respectively, to obtain the modified polylactic acid masterbatch.

[0070] S2. Add the modified polylactic acid masterbatch into the film blowing machine to extrude the film, wherein the four temperature zones of the film blowing machine are set to 150°C, 160°C, 168°C and 145°C respectively, and the film thickness is 40 μm to obtain a high-toughness polylactic acid packaging film.

[0071] Example 9

[0072] This embodiment provides a method for preparing a high-toughness polylactic acid packaging film, comprising the following steps:

[0073] S1. The polylactic acid masterbatch was dried in a vacuum drying oven at 60°C for 8 hours to obtain the dried polylactic acid masterbatch; 90 parts of the dried polylactic acid masterbatch, 10 parts of the reinforcing filler prepared in Example 6, 10 parts of the modified plasticizer prepared in Example 3, and 5 parts of polybutylene succinate were added to a single-screw extruder for melt extrusion, and the four temperature zones of the extruder were set to 150°C, 160°C, 170°C and 185°C, respectively, to obtain the modified polylactic acid masterbatch.

[0074] S2. Add the modified polylactic acid masterbatch into the film blowing machine to extrude the film, wherein the four temperature zones of the film blowing machine are set to 150°C, 160°C, 170°C and 145°C respectively, and the film thickness is 50 μm to obtain a high-toughness polylactic acid film.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 9 is that, when preparing the reinforcing filler, the carbon nanotubes are not acidified with organic acid.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 9 is that the method for preparing the reinforcing filler is different, as follows:

[0079] B1. Mix carbon nanotubes, citric acid, and deionized water in a mass ratio of 2:10:50 to obtain a mixture; place the mixture in a constant temperature heated magnetic stirrer and react at 80°C for 3 hours, then centrifuge at a speed of 9000 r / min for 10 minutes, and filter to obtain a solid; wash the solid with deionized water until neutral to obtain acidified carbon nanotubes.

[0080] B2. Mix 25 g of 3-aminopropyltriethoxysilane and 50 mL of DMF to obtain a coupling agent solution.

[0081] B3. Add 10 g of modified multi-walled carbon nanotubes and 10 g of nano-silica to 200 mL of the coupling agent solution and disperse them evenly by ultrasonication at a frequency of 30 kHz for 10 minutes to obtain a mixture. Heat the mixture to 85°C in an oil bath and reflux with mechanical stirring at 200 rpm for 24 hours to obtain a reaction solution. Filter the reaction solution through a 0.3 μm microporous filter membrane and vacuum dry it at 80°C for 2 hours to obtain a reinforcing filler.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 9 is that when preparing the modified polylactic acid masterbatch, polybutylene succinate is not added in step S1.

[0084] Performance testing:

[0085] 1. According to GB / T1040.2-2006 “Determination of Tensile Properties of Plastics”, an electronic tensile testing machine was used to test the elongation at break and tensile strength of the high-toughness polylactic acid prepared in Examples 7-9 and Comparative Examples 1-3.

[0086] 2. According to GBT1843-2008 "Determination of Izod Impact Strength of Plastics", the high-toughness polylactic acid packaging films prepared in Examples 7-9 and Comparative Examples 1-3 were cut into 80 mm × 10 mm × 4 mm strips, and then notched impact tests were performed on an impact tester.

[0087] 3. Weigh 10 mg of the high-toughness polylactic acid prepared in Examples 7-9 and Comparative Examples 1-3 and put it into a crucible. In a nitrogen atmosphere, heat it to 300° C. at a heating rate of 10° C. / min, and test its maximum decomposition temperature.

[0088] 4. According to GB / T19277.1-2011 "Testing the Biodegradability of Materials under Controlled Composting Conditions," the degradation performance of the high-toughness polylactic acid prepared in Examples 7-9 and Comparative Examples 1-3 was tested using the composting degradation test method, and the degradation rates after 144 hours were recorded. Specific test results are shown in Table 1:

[0089] Table 1. Sample performance test data

[0090]

[0091] Data analysis: The high-toughness polylactic acid prepared in Examples 7-9 of the present invention all have excellent mechanical properties, which are manifested in high tensile strength and elongation at break values; in Comparative Example 1, when synthesizing the reinforcing filler, the carbon nanotubes were not acidified with citric acid; this resulted in poor compatibility between the prepared reinforcing filler and the polylactic acid matrix, which was manifested in reduced toughness of the synthesized polylactic acid packaging film (small notched impact strength value), reduced tensile strength values, and reduced elongation at break values; in addition, organic acid acidification can further enhance the degradation performance of the synthetic packaging film, which is manifested in a reduced degradation rate value.

[0092] The high-toughness polylactic acid prepared in Examples 7-9 of the present invention exhibits strong thermal stability, as evidenced by a high maximum decomposition temperature. The modified aminosilane coupling agent not only possesses a polyphenyl ring structure, further enhancing the mechanical properties of the polylactic acid packaging film, but also contains anhydride functional groups in the coupling agent mixture, which can form a two-layer cross-linked structure with the polylactic acid matrix, thereby improving its thermal stability. However, in Comparative Example 2, when the reinforcing filler was prepared using a hydrolyzed solution of 3-aminopropyltriethoxysilane instead of the coupling agent mixture, thermal stability decreased, with a lower maximum decomposition temperature.

[0093] No polybutylene succinate is added to the high-toughness polylactic acid prepared in Comparative Example 3 of the present invention; compared with a single polylactic acid matrix, compounding with an organic body can not only enhance its own degradability, but also improve the various properties of the synthetic packaging film in multiple dimensions; this is manifested in that the tensile strength value, elongation at break, maximum decomposition temperature and degradation rate of the polylactic acid packaging film prepared in Comparative Example 3 are all reduced.

[0094] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0095] Throughout this specification, references to terms such as "one embodiment," "example," and "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0096] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high-toughness polylactic acid packaging film, characterized in that: The preparation method comprises the following steps: S1. According to parts by weight, 80-90 parts of polylactic acid masterbatch, 5-10 parts of reinforcing filler, 3-10 parts of modified plasticizer and 3-5 parts of polybutylene succinate are added to an extruder for melt extrusion to obtain modified polylactic acid masterbatch; S2. The modified polylactic acid masterbatch is added into a film blowing machine for extrusion and film blowing to obtain a high-toughness polylactic acid packaging film.

2. The method for preparing a high-toughness polylactic acid packaging film according to claim 1, characterized in that: The preparation method of the modified plasticizer comprises the following steps: A1. Blend citric acid, 1,3-propylene glycol, trimellitic anhydride, and a polymerization inhibitor, place the mixture under an inert gas atmosphere, heat to 170-175°C, stir and melt for 20-30 minutes, then cool to 140-150°C, evacuate, and continue prepolymerization for 2-3 hours, then cool to 110-120°C and continue polymerization for 5-10 hours to obtain an elastomeric polyester; A2. Add the elastomer polyester into a torque rheometer and heat until it is melted. Then add the epoxy soybean oil, mix, and naturally cool to room temperature to prepare a modified plasticizer.

3. The method for preparing a high-toughness polylactic acid packaging film according to claim 2, characterized in that: In step A1, the ratio of citric acid, 1,3-propylene glycol, trimellitic anhydride and polymerization inhibitor is 1.92-3.84 g:1.52-3.04 g:1.92-3.84 g:0.0055-0.011 g, and the vacuum degree is 0.1-0.2 MPa. In step A2, the weight ratio of elastomer polyester and epoxy soybean oil is 20-30:5-10, the heating and melting temperature is 170-175°C, and the mixing temperature is 140-150°C.

4. The method for preparing a high-toughness polylactic acid packaging film according to claim 1, characterized in that: The preparation method of the reinforcing filler comprises the following steps: B1, carbon nanotubes, citric acid and deionized water are mixed to obtain a mixture; the mixture is reacted at 60-80°C for 2-3 hours, and then centrifuged and filtered to obtain a solid; the solid is washed until neutral to obtain acidified carbon nanotubes; B2. 3-aminopropyltriethoxysilane and DMF were mixed to prepare a coupling agent solution; 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added to DMF and completely dissolved, and the coupling agent solution was then added dropwise to obtain a reaction system after the addition was complete; the reaction system was reacted at 35-45° C. for 3-4 hours to obtain a coupling agent mixture; B3. Adding the acidified carbon nanotubes and nano-silica to the coupling agent mixture, ultrasonically dispersing the mixture to obtain a mixture; reacting the mixture at 75-85° C. for 20-24 hours to obtain a reaction solution; filtering the reaction solution using a 0.25-0.3 μm microporous filter membrane, and then vacuum drying to obtain a reinforcing filler.

5. The method for preparing a high-toughness polylactic acid packaging film according to claim 4, characterized in that: In step B1, the mass ratio of carbon nanotubes, citric acid and deionized water is 1-2:5-10:

50.

6. The method for preparing a high-toughness polylactic acid packaging film according to claim 4, characterized in that: In step B2, the ratio of 3-aminopropyltriethoxysilane to DMF is 15-25 g:50 g, and the ratio of the mixed solution of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, DMF and coupling agent is 8-16 g:200-250 mL:55-60 mL.

7. The method for preparing a high-toughness polylactic acid packaging film according to claim 4, characterized in that: In step B3, the ratio of the acidified carbon nanotubes, nano-silica and coupling agent mixture is 5-10 g:5-10 g:150-200 mL.

8. The method for preparing a high-toughness polylactic acid packaging film according to claim 1, characterized in that: In step S1, the four temperature zones of the extruder are set to 140-150°C, 160°C, 170°C and 180-185°C respectively; in step S2, the four temperature zones of the film blowing machine are set to 150°C, 160°C, 165-170°C and 145°C respectively.

9. A high-toughness polylactic acid packaging film, characterized in that: The high-toughness polylactic acid packaging film is prepared by the preparation method of a high-toughness polylactic acid packaging film according to any one of claims 1 to 8.

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