Preparation method and application of antibacterial polylactic acid film

Abstract

The invention relates to the technical field of food packaging materials, in particular to a preparation method and application of an antibacterial polylactic acid film. The preparation method of the antibacterial polylactic acid film comprises the following steps: step 1, putting montmorillonite into a methanol solution, ultrasonically dispersing uniformly, then adding a silane coupling agent, adjusting the pH value of a system to be acidic, performing first-stage heating, and then performing second-stage heating, centrifugal washing and vacuum drying to obtain modified montmorillonite; step 2, mixing the modified montmorillonite with shaddock peel essential oil for adsorption to obtain an antibacterial material; 3, the polylactic acid particles, N-methyl pyrrolidone and an antibacterial material are put into a double-screw extruder to be extruded and granulated, then the granules are put into a single-screw blow molding machine to be subjected to blow molding, and the antibacterial polylactic acid film is obtained. The problems that in the prior art, essential oil is fast in volatilization and uneven in dispersion, and the performance of the film is degraded due to addition of the essential oil are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, and in particular to a method for preparing an antibacterial polylactic acid film and its application. Background Technology

[0002] With the development of the food industry, consumers are increasingly demanding higher standards for food shelf life and safety, while also creating a growing need for environmentally friendly packaging materials. Polylactic acid (PLA), a biodegradable polymer synthesized from renewable biomass such as corn starch and sugarcane, has become an important alternative to traditional petroleum-based plastics due to its excellent biocompatibility and degradability, and is widely used in the food packaging field.

[0003] However, polylactic acid films have inherent defects: on the one hand, they have poor gas barrier properties and lack antibacterial activity, making it difficult to inhibit the growth of common foodborne pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa during food storage, which leads to food spoilage and shortened shelf life; on the other hand, their ultraviolet light blocking ability is insufficient, which makes food prone to oxidation, fading and other quality deterioration problems due to light exposure.

[0004] To address these issues, researchers have attempted to add antibacterial agents to polylactic acid (PLA). Grapefruit peel oil, a natural plant extract, possesses broad-spectrum antibacterial properties and safety, and is abundant and inexpensive, making it an ideal antibacterial additive. However, grapefruit peel oil is highly volatile and prone to sensory interactions with food. Direct addition to the PLA matrix can lead to unstable antibacterial effects and may affect food flavor. Furthermore, ensuring biocompatibility and original physical barrier properties while improving the antibacterial performance of PLA films remains a pressing technical challenge. Summary of the Invention

[0005] Based on the above, the present invention provides a method for preparing an antibacterial polylactic acid film and its application.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing an antibacterial polylactic acid film, comprising the following steps: Step 1: Disperse montmorillonite evenly in methanol solution by ultrasonication, then add silane coupling agent and adjust the pH of the system to acidic. Perform first-stage heating, followed by second-stage heating, centrifuge and wash, and vacuum dry to obtain modified montmorillonite. Step 2: The modified montmorillonite is mixed with grapefruit peel essential oil for adsorption to obtain an antibacterial material; Step 3: Polylactic acid granules, N-methylpyrrolidone, and antibacterial materials are fed into a twin-screw extruder for extrusion granulation, and then fed into a single-screw blow molding machine for blow molding to obtain the antibacterial polylactic acid film.

[0007] In a preferred embodiment of the present invention, in step 1, the particle size of the montmorillonite is 2000 mesh; the methanol solution is an aqueous methanol solution with a volume fraction of 85%; and the silane coupling agent is γ-aminopropyltriethoxysilane.

[0008] In a preferred embodiment of the present invention, in step 1, the ratio of the amount of montmorillonite to the amount of methanol solution and silane coupling agent is 5g:150mL:1g.

[0009] In a preferred embodiment of the present invention, step 1, adjusting the pH of the system to acidity specifically involves adjusting the pH of the system to 4-5 using glacial acetic acid.

[0010] In a preferred embodiment of the present invention, in step 1, the first stage of heating specifically involves: holding at 50°C for 1.5 hours under nitrogen protection; the second stage of heating specifically involves: holding at 85°C for 2 hours under nitrogen protection.

[0011] In a preferred embodiment of the present invention, in step 2, the mass ratio of the modified montmorillonite to the grapefruit peel essential oil is (1~3):1; the adsorption specifically involves standing for 10 days at room temperature and under vacuum conditions.

[0012] In a preferred embodiment of the present invention, in step 3, the amount of N-methylpyrrolidone added is 5-10% of the mass of the polylactic acid particles; the amount of antibacterial material added is 3% of the mass of the polylactic acid particles.

[0013] In a preferred embodiment of the present invention, in step 3, extrusion granulation is performed at a temperature of 170~180℃ and a rotation speed of 300~400 r / min; and blow molding is performed at a temperature of 180~190℃ and a rotation speed of 1000 r / min.

[0014] The second technical solution of the present invention is an antibacterial polylactic acid film prepared by the above-mentioned preparation method.

[0015] The third technical solution of the present invention is the application of the above-mentioned antibacterial polylactic acid film in the preparation of food packaging materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves efficient loading and stable sustained release of grapefruit peel essential oil in polylactic acid film through an innovative modified montmorillonite loading system and N-methylpyrrolidone-assisted dispersion-removal process, effectively solving the problems of rapid evaporation of essential oil, uneven dispersion and film performance degradation caused by the addition of essential oil in the prior art.

[0017] (2) Modified montmorillonite adsorbs grapefruit peel essential oil through its layered structure, forming a "nano container" that significantly reduces the evaporation rate of the essential oil, allowing the film to maintain continuous antibacterial activity during food storage and extending shelf life.

[0018] (3) The present invention has a high antibacterial rate against foodborne pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. The essential oil is confined between the montmorillonite layers, reducing direct contact with food and avoiding flavor migration, which meets the requirements of green food packaging.

[0019] (4) Modified montmorillonite is peeled and dispersed in polylactic acid matrix to form a maze effect, which improves the barrier properties of the film and significantly improves the mechanical properties of polylactic acid film, thus solving the problem of film embrittlement caused by the addition of traditional essential oils. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0025] Unless otherwise specified, "room temperature" in this invention refers to 20~30℃.

[0026] The first aspect of this invention provides a method for preparing an antibacterial polylactic acid film, comprising the following steps: Step 1: Disperse montmorillonite evenly in methanol solution by ultrasonication, then add silane coupling agent and adjust the pH of the system to acidic. Perform first-stage heating, followed by second-stage heating, centrifuge and wash, and vacuum dry to obtain modified montmorillonite. Step 2: The modified montmorillonite is mixed with grapefruit peel essential oil for adsorption to obtain an antibacterial material; Step 3: Polylactic acid granules, N-methylpyrrolidone, and antibacterial materials are fed into a twin-screw extruder for extrusion granulation, and then fed into a single-screw blow molding machine for blow molding to obtain the antibacterial polylactic acid film.

[0027] In a preferred embodiment of the present invention, in step 1, the particle size of the montmorillonite is 2000 mesh; the methanol solution is an aqueous methanol solution with a volume fraction of 85%; and the silane coupling agent is γ-aminopropyltriethoxysilane.

[0028] In a preferred embodiment of the present invention, in step 1, the ratio of the amount of montmorillonite to the amount of methanol solution and silane coupling agent is 5g:150mL:1g.

[0029] In a preferred embodiment of the present invention, step 1, adjusting the pH of the system to acidity specifically involves adjusting the pH of the system to 4-5 using glacial acetic acid.

[0030] In a preferred embodiment of the present invention, in step 1, the first stage of heating specifically involves: holding at 50°C for 1.5 hours under nitrogen protection; the second stage of heating specifically involves: holding at 85°C for 2 hours under nitrogen protection.

[0031] The first stage of heating enables silane to be fully hydrolyzed to generate silanol; the second stage of heating enables silanol to condense with the interlayer / surface SiOH / AlOH of montmorillonite, completing intercalation and surface covalent bonding, and achieving the final modification of montmorillonite.

[0032] This invention does not impose any particular limitations on the vacuum drying conditions, but adopts vacuum drying conditions commonly used by those skilled in the art, such as vacuum drying at 90°C for 24 hours.

[0033] In a preferred embodiment of the present invention, in step 2, the mass ratio of the modified montmorillonite to the grapefruit peel essential oil is (1~3):1; the adsorption specifically involves standing for 10 days at room temperature and under vacuum conditions.

[0034] In this invention, montmorillonite serves two purposes: firstly, as a carrier for grapefruit peel essential oil, enabling its slow release within the polylactic acid (PLA) film; and secondly, by enhancing the mechanical properties of the PLA film. This invention achieves uniform dispersion of montmorillonite in PLA through modifications to the montmorillonite. Without modification, montmorillonite would agglomerate within the PLA film, preventing uniform dispersion.

[0035] In this invention, if the ratio of montmorillonite to grapefruit peel oil is too high (i.e., increasing the amount of montmorillonite), the adsorption of grapefruit peel oil in montmorillonite will decrease, thereby affecting the antibacterial effect of the polylactic acid film prepared subsequently. If the ratio of montmorillonite to grapefruit peel oil is too low (i.e., increasing the amount of grapefruit peel oil), the grapefruit peel oil will not be able to fully enter the montmorillonite, and some grapefruit peel oil will be directly mixed into the polylactic acid film, which is highly volatile and affects the antibacterial effect of the polylactic acid film.

[0036] In a preferred embodiment of the present invention, in step 3, the amount of N-methylpyrrolidone added is 5-10% of the mass of the polylactic acid particles; the amount of the antibacterial material added is 3%.

[0037] In this invention, if the amount of antibacterial material added is too high, it will lead to agglomeration, affecting the mechanical properties, antibacterial properties and thermal stability of the prepared film; if the amount of antibacterial material added is too low, the antibacterial properties of the film will be insufficient. Therefore, the preferred method of this invention is to limit the amount of antibacterial material added to the parameters mentioned above.

[0038] In a preferred embodiment of the present invention, in step 3, extrusion granulation is performed at a temperature of 170~180℃ and a rotation speed of 300~400 r / min; and blow molding is performed at a temperature of 180~190℃ and a rotation speed of 1000 r / min.

[0039] Under the extrusion granulation temperature conditions specified in this invention, N-methylpyrrolidone has a high vapor pressure. During the twin-screw extrusion process, N-methylpyrrolidone in the mixture (polylactic acid granules + N-methylpyrrolidone + antibacterial material) can be flash-evaporated and removed, avoiding the influence of N-methylpyrrolidone on the antibacterial polylactic acid film properties during subsequent blow molding. If the extrusion granulation temperature is too low, N-methylpyrrolidone cannot be completely removed, affecting the mechanical properties of the subsequently prepared polylactic acid film; while if the extrusion granulation and blow molding temperatures are too high, it will lead to the thermal degradation of polylactic acid, affecting the mechanical properties of the prepared polylactic acid film.

[0040] In this invention, the role of N-methylpyrrolidone is to ensure uniform dispersion of the antibacterial material in polylactic acid (PLA). During extrusion granulation, N-methylpyrrolidone is uniformly dispersed in PLA before being removed. Using N-methylpyrrolidone as a dispersion medium, the modified montmorillonite is dispersed along with the uniform dispersion of N-methylpyrrolidone in PLA. Insufficient N-methylpyrrolidone will affect the uniformity of dispersion of the antibacterial material in PLA, thus affecting the antibacterial properties and mechanical properties of the prepared antibacterial PLA film. Excessive N-methylpyrrolidone will result in incomplete removal during subsequent extrusion granulation, affecting the mechanical properties of the prepared antibacterial PLA film.

[0041] This invention does not impose any particular limitation on the source of the twin-screw extruder; any twin-screw extruder with venting function that is commonly used by those skilled in the art is applicable to this invention.

[0042] A second aspect of the present invention provides an antibacterial polylactic acid film prepared by the above-described preparation method.

[0043] A third aspect of the present invention provides the application of the above-described antibacterial polylactic acid film in the preparation of food packaging materials.

[0044] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0045] The montmorillonite used in this embodiment of the invention was purchased from Shanghai Wanzhao Fine Chemical Co., Ltd., with a particle size of 2000 mesh and an effective ingredient content of ≥99%.

[0046] The silane coupling agent used in the embodiments of the present invention is γ-aminopropyltriethoxysilane (KH550).

[0047] The polylactic acid granules used in the embodiments of this invention were purchased from Dongguan Global Environmental Protection Technology Co., Ltd.

[0048] The methanol solution used in this embodiment of the invention is an 85% (v / v) methanol aqueous solution.

[0049] The grapefruit peel essential oil used in this embodiment of the invention is obtained through the following steps: Take 1 kg of fresh grapefruit peel, crush it, add 5 L of distilled water, and extract it by steam distillation for 4 h to collect crude essential oil. Add anhydrous sodium sulfate (mass ratio 1:5) to the crude essential oil, let it stand for 24 h to dehydrate, and then perform silica gel column chromatography (silica gel particle size 100~200 mesh, eluent is petroleum ether-ethyl acetate, volume ratio 95:5), collect the main peak fraction, and obtain grapefruit peel essential oil with a purity of 96%.

[0050] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1 Step 1: Add 5g of montmorillonite to 150mL of methanol solution, sonicate at room temperature for 30min (ultrasonic power of 200W), then add 1.0g of silane coupling agent, and adjust the pH to 4-5 with glacial acetic acid. Under nitrogen protection, first keep warm at 50℃ for 1.5h, then raise the temperature to 85℃ and keep warm for 2h. After that, centrifuge and wash 3 times with methanol, and dry under vacuum at 90℃ for 24h to obtain modified montmorillonite.

[0052] Step 2: Mix 4g of modified montmorillonite with 2g of grapefruit peel essential oil and let stand for 10 days at room temperature and under vacuum to obtain saturated bentonite, which is the antibacterial material.

[0053] Step 3: Polylactic acid granules, N-methylpyrrolidone, and antibacterial material are fed into a twin-screw extruder and extruded and granulated at a temperature of 180°C and a speed of 400 r / min. Then, the granules are fed into a single-screw blow molding machine and blow molded at a temperature of 190°C and a speed of 1000 r / min to obtain an antibacterial polylactic acid film with a thickness of approximately 25 μm. The amount of N-methylpyrrolidone added is 7% of the mass of the polylactic acid granules, and the amount of antibacterial material added is 3% of the mass of the polylactic acid granules.

[0054] Example 2 Step 1: Add 5g of montmorillonite to 150mL of methanol solution, sonicate at room temperature for 30min (ultrasonic power of 200W), then add 1.0g of silane coupling agent, and adjust the pH to 4-5 with glacial acetic acid. Under nitrogen protection, first keep warm at 50℃ for 1.5h, then raise the temperature to 85℃ and keep warm for 2h. After that, centrifuge and wash 3 times with methanol, and dry under vacuum at 90℃ for 24h to obtain modified montmorillonite.

[0055] Step 2: Mix 6g of modified montmorillonite with 2g of grapefruit peel essential oil and let stand for 10 days at room temperature and under vacuum to obtain saturated bentonite, which is the antibacterial material.

[0056] Step 3: Polylactic acid granules, N-methylpyrrolidone, and antibacterial material are fed into a twin-screw extruder and extruded and granulated at a temperature of 180°C and a speed of 400 r / min. Then, the granules are fed into a single-screw blow molding machine and blow molded at a temperature of 190°C and a speed of 1000 r / min to obtain an antibacterial polylactic acid film with a thickness of approximately 25 μm. The amount of N-methylpyrrolidone added is 7% of the mass of the polylactic acid granules, and the amount of antibacterial material added is 3% of the mass of the polylactic acid granules.

[0057] Example 3 Step 1: Add 5g of montmorillonite to 150mL of methanol solution, sonicate at room temperature for 30min (ultrasonic power of 200W), then add 1.0g of silane coupling agent, and adjust the pH to 4-5 with glacial acetic acid. Under nitrogen protection, first keep warm at 50℃ for 1.5h, then raise the temperature to 85℃ and keep warm for 2h. After that, centrifuge and wash 3 times with methanol, and dry under vacuum at 90℃ for 24h to obtain modified montmorillonite.

[0058] Step 2: Mix 2g of modified montmorillonite with 2g of grapefruit peel essential oil and let stand for 10 days at room temperature and under vacuum to obtain saturated bentonite, which is the antibacterial material.

[0059] Step 3: Polylactic acid granules, N-methylpyrrolidone, and antibacterial material are fed into a twin-screw extruder and extruded and granulated at a temperature of 180°C and a speed of 400 r / min. Then, the granules are fed into a single-screw blow molding machine and blow molded at a temperature of 190°C and a speed of 1000 r / min to obtain an antibacterial polylactic acid film with a thickness of approximately 25 μm. The amount of N-methylpyrrolidone added is 7% of the mass of the polylactic acid granules, and the amount of antibacterial material added is 3% of the mass of the polylactic acid granules.

[0060] Comparative Example 1 The only difference from Example 1 is that steps 1 and 2 are omitted, and the antibacterial material in step 3 is grapefruit peel essential oil.

[0061] Comparative Example 2 The only difference from Example 1 is that the addition of N-methylpyrrolidone in step 3 is omitted.

[0062] Comparative Example 3 The only difference from Example 1 is that in step 3, the amount of N-methylpyrrolidone added is 1% of the mass of the polylactic acid particles.

[0063] Comparative Example 4 The only difference from Example 1 is that in step 3, the amount of N-methylpyrrolidone added is 16% of the mass of the polylactic acid particles.

[0064] Test Example 1 The antibacterial polylactic acid films prepared in Examples 1-3 and Comparative Examples 1-4 were tested according to QB / T 8046-2024, and the results are shown in Table 1.

[0065] Table 1

[0066] Note: " / " in the table indicates that this item was not tested.

[0067] Test Example 2 The antibacterial properties of the antibacterial polylactic acid films prepared in Examples 1-3 and Comparative Examples 1-4 were tested. The test strains were Staphylococcus aureus (ATCC 25923) and Pseudomonas aeruginosa (ATCC 15692). The test method involved placing the prepared films at room temperature in an air atmosphere for 10 days, then cutting them into 1cm × 1cm samples, sterilizing them, and then reacting them with a concentration of 1 × 10⁻⁶. 6 The bacterial suspension (1 mL) with CFU / mL was incubated for 24 h (37℃). The number of viable bacteria was calculated using the plate count method. The inhibition rate was calculated as (number of viable bacteria in the blank group - number of viable bacteria in the sample group) / number of viable bacteria in the blank group × 100%. The test results are shown in Table 2.

[0068] Table 2

[0069] Test Example 3 The oxygen transmission rate (OTR) of the antibacterial polylactic acid film prepared in Example 1 was tested according to ASTM D3985 standard. The results showed that its oxygen transmission rate was 0.796 cm⁻¹. 3 ·m -2 ·day -1 ·atm -1 It has excellent oxygen barrier properties.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an antibacterial polylactic acid film, characterized by, The method comprises the following steps: Step 1, uniformly disperse the montmorillonite in a methanol solution, then add a silane coupling agent, adjust the pH of the system to be acidic, perform a first-stage heating, then perform a second-stage heating, centrifugal washing, vacuum drying, and obtain modified montmorillonite; Step 2, mix the modified montmorillonite with naringin essential oil to perform adsorption, and obtain an antibacterial material; Step 3, put polylactic acid particles, N-methyl pyrrolidone and the antibacterial material into a double-screw extruder to perform extrusion granulation, then put into a single-screw blow molding machine to perform blow molding, and obtain the antibacterial polylactic acid film.

2. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 1, the particle size of the montmorillonite is 2000 mesh; the methanol solution is a methanol aqueous solution with a volume fraction of 85%; and the silane coupling agent is γ-aminopropyl triethoxysilane.

3. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 1, the use amount ratio of the montmorillonite, the methanol solution and the silane coupling agent is 5g:150mL:1g.

4. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 1, the adjustment of the pH of the system to be acidic is specifically adjusting the pH of the system to be 4-5 by using glacial acetic acid.

5. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 1, the first-stage heating is specifically heating at 50℃ for 1.5h under nitrogen protection; and the second-stage heating is specifically heating at 85℃ for 2h under nitrogen protection.

6. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 2, the mass ratio of the modified montmorillonite to the naringin essential oil is (1-3):1; and the adsorption is specifically standing for 10d under the conditions of room temperature and vacuum.

7. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 3, the addition amount of the N-methyl pyrrolidone is 5-10% of the mass of the polylactic acid particles; and the addition amount of the antibacterial material is 3% of the mass of the polylactic acid particles.

8. The method for preparing the antibacterial polylactic acid film according to claim 1, characterized in that, In step 3, the extrusion granulation is performed under the conditions of a temperature of 170-180℃ and a rotating speed of 300-400r / min; and the blow molding is performed under the conditions of a temperature of 180-190℃ and a rotating speed of 1000r / min.

9. The antibacterial polylactic acid film prepared by the preparation method in any one of claims 1-8.

10. A food packaging material, characterized in that The main component comprises the antibacterial polylactic acid film in claim 9.

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