Antibacterial flame-retardant polylactic acid film and preparation method thereof

Abstract

The application relates to the technical field of high polymer materials, and discloses an antibacterial and flame-retardant polylactic acid film and a preparation method thereof. A quaternary ammonium cation modified polyphosphoric acid ammonium is prepared by introducing a quaternary ammonium cation substituent containing a hydroxyl group on both ends of the hydroxyl group of the polyphosphoric acid ammonium, so that the quaternary ammonium cation modified polyphosphoric acid ammonium has the effects of hydrophilicity, antibiosis, antistatic property and flame retardation. The quaternary ammonium cation modified polyphosphoric acid ammonium and polylactic acid are simultaneously high-temperature blended, melted and chemically crosslinked with diphenylmethane diisocyanate, the molecular structure of the quaternary ammonium cation modified polyphosphoric acid ammonium is firmly combined with the molecular chain of the polylactic acid through esterification crosslinking, modified polylactic acid master batches are prepared, and finally, polylactic acid film is prepared. The polylactic acid film not only has high and persistent flame-retardant performance, but also has strong and persistent hydrophilicity, antibiosis and antistatic property, the application effect of the polylactic acid film in the fields of packaging and medical treatment is improved, and the application range of the polylactic acid film is expanded.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to an antibacterial and flame-retardant polylactic acid membrane and its preparation method. Background Technology

[0002] In recent years, polylactic acid (PLA) has been widely used in biomedical and packaging fields, and as an environmentally friendly and biodegradable bio-based material, it has received increasing attention. However, current PLA materials still have some shortcomings in practical applications. For example, the limiting oxygen index (LOI) of pure PLA materials is generally around 20%–26%, classifying it as a flammable material. Solving this problem is crucial for improving its application performance in situations requiring good flame retardancy. In existing technologies, the conventional method for improving the flame retardancy of PLA substrates mainly involves blending flame retardants with the PLA substrate. However, the flame retardant and substrate are only physically bonded, and due to poor compatibility, exudation easily occurs, making it difficult to maintain a long-lasting flame retardant effect. Furthermore, excessive addition of flame retardants can degrade the mechanical and processing properties of the material. In addition, the antibacterial properties of PLA materials are limited, failing to meet the requirements of some applications with high hygiene and health requirements, such as medical dressings.

[0003] Therefore, if hydrophilic and antibacterial organic polymers are branched onto the molecular chains of flame-retardant materials to form composite antibacterial-flame-retardant additives, and then chemically bonded to polylactic acid molecular chains, polylactic acid materials will be endowed with long-lasting flame retardancy and antibacterial properties without precipitation, which is expected to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an antibacterial and flame-retardant polylactic acid (PLA) film and its preparation method. By introducing quaternary ammonium cation substituents containing hydroxyl groups to the hydroxyl ends of ammonium polyphosphate, a quaternary ammonium cation-modified polyphosphate with hydrophilic, antibacterial, antistatic, and flame-retardant effects is prepared. Then, the quaternary ammonium cation-modified polyphosphate, polylactic acid, and diphenylmethane diisocyanate are simultaneously blended and melted at high temperature and a chemical cross-linking reaction occurs. The molecular structure of the quaternary ammonium cation-modified polyphosphate is firmly bonded to the polylactic acid molecular chain through esterification cross-linking to form a modified PLA masterbatch. Finally, a PLA film is prepared. This not only endows the PLA film with high and long-lasting flame-retardant properties but also gives it strong and long-lasting hydrophilic, antibacterial, and antistatic properties, improving its application in packaging, medical, and other fields and expanding the application range of PLA films.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing an antibacterial and flame-retardant polylactic acid film includes the following steps: Step (1): Prepare quaternary ammonium cation-modified ammonium polyphosphate; 2,3-epoxypropyltrimethylammonium chloride was added to ammonium polyphosphate, premixed, and reacted. After the reaction was completed, the mixture was purified to obtain quaternary ammonium cation-modified ammonium polyphosphate. Step (2): Prepare modified polylactic acid masterbatch; Take polylactic acid, crush and grind it, add quaternary ammonium cation modified polyphosphate, mix and grind it to obtain a mixed powder; Diphenylmethane diisocyanate was added to the mixed powder, stirred evenly, melt-blended, and extruded and granulated to obtain modified polylactic acid masterbatch. Step (3): Prepare an antibacterial and flame-retardant polylactic acid membrane; The modified polylactic acid masterbatch was mixed and dissolved with a solvent, defoamed, laid into a film, scraped flat and dried, and then the film was peeled off to obtain an antibacterial and flame-retardant polylactic acid film.

[0006] Preferably, in step (1), the amount of 2,3-epoxypropyltrimethylammonium chloride added is 1-8% of the mass of ammonium polyphosphate.

[0007] Preferably, in step (1), the premixing time is 5-10 min; the reaction conditions are: stirring at 100-300 r / min for 3-6 h at a temperature of 80-110℃.

[0008] Preferably, in step (1), the purification operation includes: washing with ethanol by stirring, filtration, repeating the washing and filtration operation twice, and then drying.

[0009] Preferably, in step (2), the amount of quaternary ammonium cation modified polyphosphate added is 5-15% of the mass of polylactic acid; the amount of diphenylmethane diisocyanate added is 0.5-2.5% of the mass of polylactic acid.

[0010] Preferably, in step (2), the melt blending conditions are: melt blending at 170-210 ℃ for 10-25 min; the extrusion granulation conditions are: extrusion granulation at 170-210 ℃ at a speed of 10-50 r / min.

[0011] Preferably, in step (3), the ratio of modified polylactic acid masterbatch to solvent is 1g:15-20mL.

[0012] Furthermore, in step (3), the solvent includes any one or a mixture of two or more of dichloromethane, chloroform, acetone, tetrahydrofuran, N,N-dimethylformamide, toluene, and trifluoroethanol.

[0013] Preferably, an antibacterial and flame-retardant polylactic acid film is prepared using the method described above for preparing an antibacterial and flame-retardant polylactic acid film.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the principle that epoxy groups can undergo etherification with hydroxyl groups. 2,3-epoxypropyltrimethylammonium chloride is etherified with the terminal hydroxyl groups on the ammonium polyphosphate molecular chain, introducing quaternary ammonium cation substituents containing hydroxyl groups onto the two hydroxyl groups of the ammonium polyphosphate. This produces an organic-inorganic composite additive material, quaternary ammonium cation-modified ammonium polyphosphate, which possesses hydrophilic, antibacterial, antistatic, and flame-retardant properties. In this material, the middle structural portion provides flame retardancy, while the two end structural portions exhibit hydrophilic, antibacterial, and antistatic effects. During the preparation process, this invention employs a dry reaction method, uniformly mixing the highly reactive 2,3-epoxypropyltrimethylammonium chloride with ammonium polyphosphate before reaction. This method offers advantages such as simple process, high reaction efficiency, solvent-free operation, and low environmental pollution. Furthermore, compared to traditional wet preparation processes, it optimizes wastewater discharge.

[0015] Furthermore, this invention utilizes the principle of chemical reaction between isocyanate functional groups and polar functional groups such as hydroxyl and carboxyl groups. Quaternary ammonium cation-modified polyphosphate and polylactic acid are simultaneously blended and melted with diphenylmethane diisocyanate at high temperature. This allows the hydroxyl groups in the quaternary ammonium cation-modified polyphosphate, the hydroxyl groups and carboxyl groups in polylactic acid, and the isocyanate groups in diphenylmethane diisocyanate to undergo a chemical cross-linking reaction. This firmly binds the molecular structure of quaternary ammonium cation-modified polyphosphate with the polylactic acid molecular chain through esterification cross-linking, producing modified polylactic acid masterbatch, which is then used to produce a polylactic acid film.

[0016] The preparation method of this invention employs a method of first constructing a multifunctional antibacterial-flame retardant material, and then further firmly attaching it to the polylactic acid (PLA) molecular chain through chemical bonds. This overcomes the problem that when adding additives to PLA using conventional blending methods, the additives are hydrophilic while PLA is hydrophobic, resulting in poor compatibility and uneven dispersion of the additives in the PLA matrix. Consequently, the additives tend to precipitate and leak from the film matrix after film formation, leading to a decrease in performance (such as antibacterial and flame retardant properties). Furthermore, the introduction of positively charged hydrophilic cationic functional groups imparts hydrophilicity to the PLA membrane, optimizing its antistatic effect.

[0017] In summary, this invention not only endows polylactic acid films with high and long-lasting flame retardant properties, but also gives them strong and long-lasting hydrophilic, antibacterial, and antistatic properties, improving their application effects in packaging, medical and other fields, and expanding the application scope of polylactic acid films. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the reaction process in the preparation of antibacterial and flame-retardant polylactic acid membrane in this invention; Figure 2 This is a scanning electron microscope image of the polylactic acid membrane prepared in Example 3 of the present invention; Figure 2 In the image, a is a scanning electron microscope image at 1000x magnification, b is a scanning electron microscope image at 2000x magnification, and c is a scanning electron microscope image at 5000x magnification. Figure 3 This is an X-ray energy dispersive spectroscopy (EDS) analysis diagram of the polylactic acid membrane prepared in Example 3 of the present invention; Figure 4 These are Staphylococcus aureus colony diagrams of the polylactic acid membrane samples prepared in Examples 1-3 and Comparative Example 1 of this invention, and the blank group. Figure 4 In the diagram, a is the Staphylococcus aureus colony map of the blank group, b is the Staphylococcus aureus colony map of the polylactic acid membrane sample prepared in Comparative Example 1, c is the Staphylococcus aureus colony map of the polylactic acid membrane sample prepared in Example 1, d is the Staphylococcus aureus colony map of the polylactic acid membrane sample prepared in Example 2, and e is the Staphylococcus aureus colony map of the polylactic acid membrane sample prepared in Example 3. Figure 5 These are Escherichia coli colony diagrams of polylactic acid membrane samples prepared in Examples 1-3 and Comparative Example 1 of this invention, and the blank group. Figure 5 In the diagram, a is the E. coli colony diagram of the blank group, b is the E. coli colony diagram of the polylactic acid membrane sample prepared in Comparative Example 1, c is the E. coli colony diagram of the polylactic acid membrane sample prepared in Example 1, d is the E. coli colony diagram of the polylactic acid membrane sample prepared in Example 2, and e is the E. coli colony diagram of the polylactic acid membrane sample prepared in Example 3. Figure 6 This is a bar chart showing the antibacterial rate of polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 against Staphylococcus aureus. Figure 7 This is a bar chart showing the antibacterial rate of polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 against Escherichia coli. Figure 8 This is a combustion characteristic diagram of the polylactic acid membrane prepared in Comparative Example 1 of the present invention; Figure 8 In the image, a1 and a2 are photos of the polylactic acid membrane prepared in Comparative Example 1 when it is close to the flame, b1 and b2 are photos of the polylactic acid membrane prepared in Comparative Example 1 in the flame, c1 and c2 are photos of the polylactic acid membrane prepared in Comparative Example 1 when it leaves the flame, and d is a photo of the residue morphology of the polylactic acid membrane prepared in Comparative Example 1 after combustion. Figure 9 This is a combustion characteristic diagram of the polylactic acid membrane prepared in Example 3 of the present invention; Figure 9 In the image, a1 and a2 are photos of the polylactic acid membrane prepared in Example 3 when it is close to the flame, b1 and b2 are photos of the polylactic acid membrane prepared in Example 3 in the flame, c1 and c2 are photos of the polylactic acid membrane prepared in Example 3 when it leaves the flame, and d is a photo of the residue morphology of the polylactic acid membrane prepared in Example 3 after combustion. Figure 10This is a bar chart showing the limiting oxygen index of the polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0019] The present invention will be further illustrated below through specific embodiments. The following embodiments are specific implementations of the present invention, but the implementation of the present invention is not limited to the following embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and are included within the protection scope of the present invention.

[0020] Example 1 like Figure 1 As shown in the figure, this embodiment discloses a method for preparing an antibacterial and flame-retardant polylactic acid film, including the following steps: Step (1): Prepare quaternary ammonium cation-modified ammonium polyphosphate; 2,3-epoxypropyltrimethylammonium chloride was added to ammonium polyphosphate (purchased from Aladdin, purity: n≥1000), premixed for 5 min, and then stirred at 200 r / min for 4 h in a water bath at 95 °C. After the reaction was completed, the mixture was washed with ethanol for 15 min, filtered, and the washing and filtration were repeated twice. The mixture was then dried at 80 °C for 6 h to obtain quaternary ammonium cation modified ammonium polyphosphate. The amount of 2,3-epoxypropyltrimethylammonium chloride added is 5% of the mass of ammonium polyphosphate; Step (2): Prepare modified polylactic acid masterbatch; Take 15g of polylactic acid (PLA, purchased from Fengyuan Group, brand name FY602, specification 2) 10 5 The mixture was crushed and ground (g / mol), and 5% of PLA mass of quaternary ammonium cationic modified ammonium polyphosphate was added. After thorough mixing and grinding, the mixture was placed in an oven at 80℃ for 4 h to obtain a mixed powder. The screw extruder was preheated at 180℃. Diphenylmethane diisocyanate (MDI) was added to the mixed powder at a rate of 1% of the PLA mass. After thorough mixing, the mixture was added to the screw extruder and melt-blended at 180℃ for 15 min. The mixture was then extruded and granulated at a speed of 30 r / min to obtain modified polylactic acid masterbatch. Step (3): Prepare an antibacterial and flame-retardant polylactic acid membrane; Modified polylactic acid masterbatch and dichloromethane were added to a small beaker at a ratio of 1 g: 15 mL and sealed with plastic wrap. The mixture was magnetically stirred for 3 hours until completely dissolved. After removing air bubbles in an ultrasonic cleaner for 5 minutes, the film-forming solution was obtained. Wipe the glass plate with ethanol until it is free of water and dust, and adjust it to be level. Slowly and evenly pour the film-laying solution onto the glass plate, scrape it flat, and place it in a fume hood to dry for 12 hours. Then peel off the film to obtain an antibacterial and flame-retardant polylactic acid film, which is recorded as sample 1#.

[0021] Example 2 The difference from Example 1 is that the mass of quaternary ammonium cation modified polyphosphate added in step (2) is changed from "5% of the mass of PLA" to "10% of the mass of PLA". All other parameters and conditions are the same as in Example 1, and it is referred to as Sample 2#.

[0022] Example 3 The difference from Example 1 is that the mass of quaternary ammonium cation modified polyphosphate added in step (2) is changed from "5% of the mass of PLA" to "15% of the mass of PLA". All other parameters and conditions are the same as in Example 1, and it is referred to as sample 3#.

[0023] Comparative Example 1 This embodiment discloses a method for preparing a polylactic acid membrane, including the following steps: Polylactic acid and dichloromethane were added to a small beaker at a ratio of 1 g: 15 mL and sealed with plastic wrap. The mixture was magnetically stirred for 2-3 hours until completely dissolved. After that, air bubbles were removed in an ultrasonic cleaner for 3-5 minutes to obtain the film-forming solution. Wipe the glass plate with ethanol until it is free of water and dust, and adjust it to be level. Slowly and evenly pour the film-laying solution onto the glass plate, scrape it flat, and place it in a fume hood for 6-12 hours. Then peel off the film to obtain a polylactic acid film, which is recorded as the control sample.

[0024] Experimental data characterization and performance testing Figure 2 The polylactic acid membrane prepared in Example 3 was subjected to different magnifications (1000). 2000 5000 Scanning electron microscope image of ). Figure 2 As can be seen, the film possesses dense micropores, which impart excellent air permeability. During film preparation, the polylactic acid masterbatch was dissolved in dichloromethane and dried on a glass plate to form a film. During the drying process, the rapid volatilization of dichloromethane caused the film to form dense micropores.

[0025] Figure 3 This is an X-ray energy dispersive spectroscopy (EDS) analysis chromatogram of the polylactic acid membrane prepared in Example 3. APP (ammonium polyphosphate) contains C, O, and N elements, while polylactic acid mainly contains C and O. Figure 3It is evident that the polylactic acid modified membrane sample contains not only the aforementioned elements but also Cl ions. The presence of Cl ions in 2,3-epoxypropyltrimethylammonium chloride indicates the successful modification of APP (ammonium polyphosphate) with 2,3-epoxypropyltrimethylammonium chloride quaternary ammonium cations.

[0026] The antibacterial properties of the polylactic acid films prepared in Examples 1-3 and Comparative Example 1 were tested, and the test results are as follows: Figures 4 to 7 As shown.

[0027] The antibacterial performance test method was as follows: Using *Staphylococcus aureus* and *Escherichia coli* as experimental strains, a sufficient amount of bacteria was scraped using an inoculation loop and placed in a glass tube containing 5 mL of liquid culture medium (Broth). The bacteria were vortexed to disperse them evenly. The glass tube was then incubated in a 37 ℃ constant temperature shaker (120 r / min) for 18-24 h. After centrifugation, the bacteria were separated and isolated using 5 mL of PBS solution (Source: Shanghai Aladdin Biochemical Technology Co., Ltd.; Specification: 10×, pH 7.2-7.4, sterile, Ca-free). 2+ / Mg 2+ Wash and disperse the bacteria; finally, add 0.1 mL of the evenly dispersed bacterial / PBS suspension to a new Broth glass tube and place it in a shaker for continued incubation at a constant temperature. This is the first generation of bacteria. Propagate the above bacteria for three generations to obtain a bacterial suspension for later use. Cut the polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 into 2.5 cm × 2.5 cm samples and place them on the surface of a culture dish on a sterile operating platform. Add 25 μL of bacterial suspension; cover the sample with another sample to ensure full contact between the bacterial suspension and the sample. After 5 min, place both samples into 5 mL of PBS solution. Vortex the solution for 10 s, then continuously dilute with 100 mmol / L PBS solution and evenly add it to the surface of the solid culture dish. Incubate at a constant temperature of 37 ℃ for 24 h. Measure the colony count. The fewer the colonies, the stronger the antibacterial activity. Calculate the antibacterial rate. The test method for the blank group was as follows: a sterile glass slide (cut to 2.5 cm × 2.5 cm) was used instead of polylactic acid membrane. The sterile glass slide was placed on the surface of a culture dish on a sterile operating platform, and 25 μL of bacterial suspension was added. Another sterile glass slide was placed on top to ensure that the bacterial suspension was in full contact with the sterile glass slide. After 5 min, the two sterile glass slides were placed in 5 mL of PBS solution. After vortexing the solution for 10 s, it was continuously diluted with 100 mmol / L PBS solution and evenly added to the surface of the solid culture dish. After incubation at 37 ℃ for 24 h, the colony count was determined.

[0028] Figure 4These are Staphylococcus aureus colony diagrams of polylactic acid membrane samples prepared in Examples 1-3 and Comparative Example 1, and the blank group; Figure 5 These are Escherichia coli colony images of polylactic acid membrane samples prepared in Examples 1-3 and Comparative Example 1, and the blank group; Figure 4 and Figure 5 As can be seen, the colonies in the polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 are significantly less than the original colonies in the blank group, and the colonies in the polylactic acid membranes prepared in Examples 1-3 are less than the colonies in Comparative Example 1.

[0029] Figure 6 and Figure 7 These are the calculated antibacterial rates of the polylactic acid films prepared in Examples 1-3 and Comparative Example 1; from Figure 6 and Figure 7 As can be seen, the antibacterial rate of the polylactic acid membranes prepared in Examples 1-3 is higher than that of the polylactic acid membrane prepared in Comparative Example 1. In particular, the antibacterial rate of the polylactic acid membrane prepared in Example 3 is higher than 99% for both types of bacteria. This indicates that the introduction of cationic quaternary ammonium salt functional groups improves the antibacterial properties of polylactic acid membranes, and when the content of this functional group is high, the antibacterial rate reaches more than 99.0%.

[0030] The improved antibacterial properties of the polylactic acid (PLA) membrane are mainly attributed to the cationic quaternary ammonium salt functional groups introduced into the PLA matrix in this invention. These functional groups can inhibit bacterial growth and reproduction, thus achieving an antibacterial and bacteriostatic effect, enabling the modified PLA membrane to exhibit more outstanding antibacterial properties. In practical applications, the excellent antibacterial properties allow the PLA membrane to better meet the antibacterial requirements of some application fields.

[0031] The combustion properties of the polylactic acid films prepared in Example 3 and Comparative Example 1 were tested, and the test results are as follows: Figure 8 As shown; The combustion test method is as follows: the polylactic acid film samples prepared in Example 3 and Comparative Example 1 are held with tweezers and slowly brought close to the burning flame. The changes that occur in the samples during combustion are observed, including whether there is shrinkage when close to the flame; the color of the flame and the state of the sample during combustion; whether the sample continues to burn and emits an odor after leaving the flame; and the color of the ash after combustion.

[0032] Figure 8 and Figure 9 Combustion characteristic images of polylactic acid membranes prepared in Comparative Example 1 and Example 3, respectively. Figure 8 and Figure 9 As can be seen, the polylactic acid film melts both before and after modification, but Figure 9 The polylactic acid film prepared in Example 3 showed a lower melting tendency than... Figure 8The polylactic acid (PLA) membrane prepared in Comparative Example 1 and the PLA membrane prepared in Example 3 exhibited weaker combustion in a flame compared to the PLA membrane prepared in Comparative Example 1. The PLA membrane prepared in Comparative Example 1 continued to burn after being removed from the flame, while the PLA membrane prepared in Example 3 extinguished itself without further combustion after being removed from the flame. These experimental results demonstrate that the introduction of ammonium polyphosphate with flame-retardant properties endows the PLA membrane with excellent flame retardancy.

[0033] The limiting oxygen index of the polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1 was tested, and the test results are as follows: Figure 10 As shown; The limiting oxygen index test method is as follows: Adjust the flow rates of oxygen and nitrogen to remove air from the combustion chamber. Use the polylactic acid membranes prepared in Example 3 and Comparative Example 1 as samples. Vertically install the samples at the center of the combustion chamber, with the top of the sample at least 100 mm below the top opening of the combustion chamber and the lowest point of the sample at least 100 mm above the top surface of the gas dispersion device. Ignite the igniter and adjust the flame height to 10-20 mm. Apply the lowest part of the flame to the top surface of the sample, covering the entire top surface, but do not touch the vertical surface or edge of the sample. Continuously apply the flame for a maximum of 30 seconds. Remove the flame every 5 seconds and observe whether the sample ignites. Once the sample ignites, immediately remove the flame source and start timing. Allow the sample to continue burning until it self-extinguishes at a depth of 3-5 cm.

[0034] Figure 10 The graph shows the limiting oxygen index test results for the polylactic acid membranes prepared in Examples 1-3 and Comparative Example 1. Figure 10 It is evident that the limiting oxygen index (LOI) of the polylactic acid (PLA) film increases after modification. Furthermore, the LIOI of the PLA film gradually increases with the increase in the amount of quaternary ammonium cation-modified ammonium polyphosphate added during the preparation of the modified PLA masterbatch. To achieve immediate self-extinguishing upon removal from the flame, the LIOI of the material should be greater than 27%. The LIOI values ​​of the four PLA films prepared in this invention—the control sample, sample 1, sample 2, and sample 3—are 23.6%, 26.2%, 28.3%, and 29.7%, respectively. Therefore, samples 2 and 3 can achieve immediate self-extinguishing upon removal from the flame or with a delayed effect. A higher LIOI value indicates better flame retardancy. Therefore, the flame retardancy of the PLA film is significantly improved after modification of PLA using the preparation method of this invention.

[0035] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing an antibacterial and flame-retardant polylactic acid film, characterized in that, Includes the following steps: Step (1): Add 2,3-epoxypropyltrimethylammonium chloride to ammonium polyphosphate, premix for 5-10 min, stir at 100-300 r / min for 3-6 h at a temperature of 80-110℃, and purify to obtain quaternary ammonium cation modified ammonium polyphosphate. The amount of 2,3-epoxypropyltrimethylammonium chloride added is 1-8% of the mass of ammonium polyphosphate; Step (2): Add quaternary ammonium cation modified polyphosphate to polylactic acid, then add diphenylmethane diisocyanate, melt blend, extrude and granulate to obtain modified polylactic acid masterbatch. The amount of the quaternary ammonium cationic modified ammonium polyphosphate added is 5-15% of the mass of polylactic acid, and the amount of diphenylmethane diisocyanate added is 0.5-2.5% of the mass of polylactic acid; Step (3): Mix and dissolve the modified polylactic acid masterbatch with a solvent, and then lay the film to obtain an antibacterial and flame-retardant polylactic acid film.

2. The method for preparing the antibacterial and flame-retardant polylactic acid membrane according to claim 1, characterized in that, In step (1), the purification operation includes: washing with ethanol by stirring, filtration, repeating the washing and filtration operation twice, and then drying.

3. The method for preparing the antibacterial and flame-retardant polylactic acid membrane according to claim 1, characterized in that, In step (2), the melt blending conditions are: melt blending at 170-210 ℃ for 10-25 min.

4. The method for preparing the antibacterial and flame-retardant polylactic acid membrane according to claim 1, characterized in that, In step (2), the extrusion granulation conditions are: extrusion granulation at a temperature of 170-210 ℃ and a speed of 10-50 r / min.

5. The method for preparing the antibacterial and flame-retardant polylactic acid membrane according to claim 1, characterized in that, In step (3), the ratio of modified polylactic acid masterbatch to solvent is 1g:15-20mL; the solvent includes any one or more of dichloromethane, chloroform, acetone, tetrahydrofuran, N,N-dimethylformamide, toluene, and trifluoroethanol.

6. An antibacterial and flame-retardant polylactic acid membrane prepared by the method for preparing an antibacterial and flame-retardant polylactic acid membrane as described in any one of claims 1-5.

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