Preservative film for food storage and preparation method thereof

Abstract

The invention relates to the technical field of materials, and discloses a preservative film for food storage and a preparation method thereof.The preservative film is prepared by taking polylactic acid as a matrix and compounding an antibacterial modifier, a functional chain extender and other additives through mixing, extrusion and blow molding processes, the preservative film is endowed with excellent antibacterial performance, is non-toxic and harmless, and can guarantee food safety, the functional chain extender can realize chain extension connection of polylactic acid, polylactic acid is converted into a three-dimensional cross-linked structure from a straight-chain structure, the cross-linking density of a polylactic acid molecular chain is further improved, and the service life of the preservative film is prolonged. The movement of a polylactic acid molecular chain under a high-temperature condition is hindered, so that the heat resistance of the preservative film is improved. In addition, the POSS skeleton contains a large number of silicon-oxygen bonds with high bond energy, so that the heat resistance of the preservative film can be further improved.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a fresh-keeping film for food storage and a preparation method thereof. Background Art

[0002] Although traditional cling film materials such as polyethylene and polyvinyl chloride have excellent performance, their non-degradability has brought great pressure to the environment. Therefore, finding alternative materials has become a hot topic in industry research. Polylactic acid, as a new type of biodegradable material, is gradually emerging in the field of food cling film.

[0003] Polylactic acid is a bio-based polymer material synthesized from natural lactic acid as the main raw material. It has good biocompatibility and biodegradability. Its degradation products are water and carbon dioxide, without secondary pollution, so it is considered to be one of the ideal materials to replace traditional plastics. In the field of food wrap, the application of polylactic acid not only meets consumers' demand for food safety, but also significantly reduces the generation of plastic waste.

[0004] Polylactic acid cling film is widely used in the packaging of candies, fruits and vegetables due to its excellent transparency, glossiness and printing adaptability. Although PLA cling film has many advantages, it still has some shortcomings in practical applications, such as poor flexibility and lower tensile properties than commonly used resins, which to a certain extent limits its application in certain packaging fields. In addition, polylactic acid has poor heat resistance and low heat deformation temperature, which is not suitable for use in high temperature environments. In addition, polylactic acid itself does not have antibacterial properties, which is very unfavorable for food preservation. Therefore, it is of great significance to develop polylactic acid cling film with strong toughness, good heat resistance and good antibacterial properties. Summary of the invention

[0005] In order to solve the problems mentioned in the background technology, the object of the present invention is to provide a fresh-keeping film for food storage and a preparation method thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a fresh-keeping film for food storage, wherein the fresh-keeping film is made of the following raw materials in parts by weight:

[0008] Polylactic acid 30-45 parts;

[0009] PBAT 20-35 parts;

[0010] 3-4.5 parts of antibacterial modifier;

[0011] 5-10 parts of functional chain extender;

[0012] 0.5-1.5 parts of antioxidant;

[0013] 1-2 parts of lubricant;

[0014] The preparation method comprises the following steps:

[0015] The first step is to weigh each raw material according to the formula and set aside;

[0016] Step 2: Add polylactic acid, PBAT, antibacterial modifier, functional chain extender, antioxidant and lubricant into a mixer, control the temperature to 80-100°C, the speed to 1000-1500r / min, and mechanically stir for 20-40min to form a mixed material;

[0017] The third step is to feed the mixed material into a twin-screw extruder, control the temperature of the front end of the screw to 180±5℃, the temperature of the middle end to 175±5℃, and the temperature of the rear end to 160±5℃, perform melt extrusion, and then undergo a blow molding process to obtain a cling film.

[0018] As a further embodiment of the present invention, the preparation method of the antibacterial modifier comprises the following steps:

[0019] Step A, adding sepiolite to tetrahydrofuran, ultrasonically dispersing for 20-30 minutes to form a uniform dispersion, then adding an anhydride modifier, after the addition, raising the temperature to 50-60° C., keeping warm and stirring for 6-9 hours, centrifuging the solid product, washing and vacuum drying to obtain a modified sepiolite;

[0020] Step B, dispersing the modified sepiolite in toluene, adding active macromolecular antibacterial agent and catalyst, stirring evenly, gradually raising the temperature to 90-95°C, keeping the temperature for 6-9 hours, centrifuging the product, washing and drying, and obtaining the antibacterial modifier.

[0021] As a further embodiment of the present invention, in step A, the anhydride modifier is selected from any one of succinic anhydride, glutaric anhydride or maleic anhydride.

[0022] As a further embodiment of the present invention, in step B, the catalyst is selected from aminosulfonic acid or trifluoromethanesulfonic acid.

[0023] As a further embodiment of the present invention, in step B, the active macromolecular antibacterial agent is selected from ε-polylysine with a number average molecular weight of 3600-4300.

[0024] As a further solution of the present invention, the preparation method of the functional chain extender is as follows:

[0025] Mix phenylamine POSS and acetone, stir to form a uniform mixture, and then place in an ice bath environment, then add the end group modifier to the mixture, after the addition is complete, remove the ice bath, and then add the acid binding agent to the mixture. After the addition is complete, stir at room temperature for 4-6 hours to obtain a functional chain extender.

[0026] As a further embodiment of the present invention, the terminal group modifier is selected from 4-isocyanatobenzoyl chloride or 3-isocyanatobenzoyl chloride.

[0027] As a further embodiment of the present invention, the acid binding agent is selected from triethylamine or pyridine.

[0028] As a further embodiment of the present invention, the antioxidant is a mixture of lignin and antioxidant 168, with a mass ratio of 1:0.2-0.4; and the lubricant is selected from any one of polyethylene wax, stearic acid or magnesium stearate.

[0029] A fresh-keeping film for food storage, characterized in that it is made by adopting the above-mentioned preparation method.

[0030] Beneficial effects of the present invention:

[0031] (1) The present invention uses ε-polylysine to modify the surface of sepiolite to obtain an antibacterial modifier, which is used as an additive. On the one hand, the presence of the organic phase ε-polylysine is equivalent to forming a "transition" layer between the sepiolite and the polylactic acid matrix, which can greatly improve the compatibility between them, so that the sepiolite can effectively play its own reinforcing role, improve the mechanical properties of polylactic acid, and then enable the prepared cling film to exhibit good tensile properties. In addition, ε-polylysine itself has a spectrum antibacterial effect, which can give the cling film excellent antibacterial properties, and ε-polylysine is non-toxic and harmless, which can ensure food safety.

[0032] (2) The present invention prepares a modified POSS having multiple isocyanate substituents as a functional chain extender. During the melt extrusion process, the isocyanate groups can interact with the active end groups in the polylactic acid molecular chain to achieve chain extension connection of the polylactic acid. Due to the presence of multiple isocyanate substituents, the polylactic acid can be converted from a linear structure to a three-dimensional cross-linked structure, thereby increasing the cross-linking density of the polylactic acid molecular chain, resulting in the movement of the polylactic acid molecular chain under high temperature conditions being hindered, thereby improving the heat resistance of the cling film. In addition, the POSS skeleton contains a large number of high-energy silicon-oxygen bonds, which can further improve the heat resistance of the cling film. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0034] Figure 1 is the infrared spectra of sepiolite and antibacterial modifier; Figure 2 This is the infrared spectrum of the functional chain extender. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Preparation Example 1

[0038] Preparation of the antibacterial modifier:

[0039] Step A, adding 2.5 g of sepiolite to tetrahydrofuran, ultrasonically dispersing for 30 min to form a uniform dispersion, then adding 6 g of succinic anhydride, after the addition, raising the temperature to 60° C., keeping warm and stirring for 8 h, centrifuging out the solid product to obtain a modified sepiolite;

[0040] Step B: Disperse 1.8 g of modified sepiolite in toluene, add 3.5 g of ε-polylysine with a number average molecular weight of 4300 and 0.1 g of trifluoromethanesulfonic acid, stir evenly mechanically, gradually increase the temperature to 90°C, keep warm for 9 hours, centrifuge the product, wash and dry it, and then obtain the antibacterial modifier.

[0041] 0.5 g of the antibacterial modifier was weighed as a test sample, and the percentage of organic elements in the sample was analyzed using an organic element analyzer. The test results showed that the carbon content in the sample was 19.41%, and the nitrogen content was 7.05%. It can be inferred that succinic anhydride has high activity and can interact with the hydroxyl groups on the surface of sepiolite to modify the active carboxyl substituents on the surface of sepiolite to form a sepiolite modifier, which is then catalyzed by trifluoromethanesulfonic acid to further interact with the amino group in the ε-polylysine structure, thereby obtaining a sepiolite-based antibacterial modifier with a surface modified with ε-polylysine macromolecules.

[0042] Figure 1This is the infrared analysis test diagram of sepiolite and antibacterial modifier. It can be seen from the figure that compared with sepiolite, the antibacterial modifier has a higher infrared spectroscopy at 3487cm -1 The hydroxyl absorption peak at 3253 cm -1 The characteristic absorption peak of NH appeared at 2800-3000cm -1 The characteristic absorption peak of CH in methylene appeared at 1746 cm -1 The C=O characteristic absorption peak of the ester group appeared at 1690 cm -1 The C=O characteristic absorption peak of the amide group appeared at .

[0043] Preparation Example 2

[0044] Preparation of functional chain extender:

[0045] Mix 0.5 g of phenylamine POSS and acetone, stir to form a uniform mixture, and then place in an ice bath. Then add 0.6 g of 4-isocyanobenzoyl chloride to the mixture. After the addition, remove the ice bath, and then add 0.05 g of pyridine to the mixture. After the addition is complete, stir at room temperature for 6 hours to obtain a functional chain extender.

[0046] The functional chain extender was made into potassium bromide tablets and subjected to infrared analysis test. The results are shown in Figure 2 , of which 3201cm -1 The absorption peak at 3000-3100cm is the characteristic absorption peak of NH. -1 The absorption peak at 1670 cm is the characteristic absorption peak of carbon and hydrogen in the benzene ring skeleton. -1 The absorption peak at 1059 cm is the characteristic absorption peak of C=O in the amide group. -1 The absorption peak appearing at is the characteristic absorption peak of silicon and oxygen in the POSS skeleton.

[0047] It can be speculated that phenylamine POSS has an amino-terminated structure. Using 4-isocyanobenzoyl chloride as a capping modifier, under the catalytic action of pyridine, the acyl chloride group in the 4-isocyanobenzoyl chloride structure undergoes an amidation reaction with the capped amino group of phenylamine POSS to obtain a functional chain extender with an isocyanate group at the end of the structure.

[0048] Example 1

[0049] A fresh-keeping film for food storage is made from the following raw materials in parts by weight:

[0050] 30 parts of polylactic acid;

[0051] PBAT 20 copies;

[0052] 3 parts of antimicrobial modifier;

[0053] 5 parts of functional chain extender;

[0054] 0.5 parts of antioxidant;

[0055] 1 part of polyethylene wax;

[0056] The preparation method of the fresh-keeping film comprises the following steps:

[0057] The first step is to weigh each raw material according to the formula and set aside;

[0058] Step 2: Add polylactic acid, PBAT, antibacterial modifier, functional chain extender, antioxidant and polyethylene wax into a mixer, control the temperature to 80°C, the speed to 1000r / min, and mechanically stir for 40min to form a mixed material;

[0059] The third step is to feed the mixed material into a twin-screw extruder, control the temperature of the front end of the screw to 180°C, the temperature of the middle end to 175°C, and the temperature of the rear end to 160°C, perform melt extrusion, and then undergo a blow molding process to produce a fresh-keeping film.

[0060] The preparation method of the antibacterial modifier is shown in Preparation Example 1; the preparation method of the functional chain extender is shown in Preparation Example 2; the antioxidant is a mixture of lignin and antioxidant 168, with a mass ratio of 1:0.3; the following are the same.

[0061] Example 2

[0062] A fresh-keeping film for food storage is made from the following raw materials in parts by weight:

[0063] 40 parts of polylactic acid;

[0064] PBAT 25 copies;

[0065] 4 parts of antimicrobial modifier;

[0066] 6 parts of functional chain extender;

[0067] 1 part antioxidant;

[0068] 1.5 parts of stearic acid;

[0069] The preparation method of the fresh-keeping film comprises the following steps:

[0070] The first step is to weigh each raw material according to the formula and set aside;

[0071] Step 2: Add polylactic acid, PBAT, antibacterial modifier, functional chain extender, antioxidant and stearic acid into a mixer, control the temperature to 90°C, the speed to 1200r / min, and mechanically stir for 30 minutes to form a mixed material;

[0072] The third step is to feed the mixed material into a twin-screw extruder, control the temperature of the front end of the screw to 180°C, the temperature of the middle end to 175°C, and the temperature of the rear end to 160°C, perform melt extrusion, and then undergo a blow molding process to produce a fresh-keeping film.

[0073] Example 3

[0074] A fresh-keeping film for food storage is made from the following raw materials in parts by weight:

[0075] 45 parts of polylactic acid;

[0076] PBAT 35 copies;

[0077] 4.5 parts of antibacterial modifier;

[0078] 10 parts of functional chain extender;

[0079] 1.5 parts of antioxidant;

[0080] 2 parts of stearic acid;

[0081] The preparation method of the fresh-keeping film comprises the following steps:

[0082] The first step is to weigh each raw material according to the formula and set aside;

[0083] Step 2: Add polylactic acid, PBAT, antibacterial modifier, functional chain extender, antioxidant and stearic acid into a mixer, control the temperature to 100°C, the speed to 1500r / min, and mechanically stir for 20min to form a mixed material;

[0084] The third step is to feed the mixed material into a twin-screw extruder, control the temperature of the front end of the screw to 180°C, the temperature of the middle end to 175°C, and the temperature of the rear end to 160°C, perform melt extrusion, and then undergo a blow molding process to produce a fresh-keeping film.

[0085] Comparative Example 1

[0086] A fresh-keeping film for food storage, which is different from Example 2 in that the antibacterial modifier is replaced by sepiolite, and the rest remains unchanged.

[0087] Comparative Example 2

[0088] A fresh-keeping film for food storage, which is different from Example 2 in that the antibacterial modifier is replaced by ε-polylysine, and the rest remains unchanged.

[0089] Comparative Example 3

[0090] A fresh-keeping film for food storage, which is different from Example 2 in that the functional chain extender is removed and the rest remains unchanged.

[0091] Test Case

[0092] The cling films in Examples 1 to 3 and Comparative Examples 1 to 3 were tested for various properties, and the results are recorded in Table 1:

[0093] Table 1 - Performance test results Tensile strength / MPa Elongation at break / % Antibacterial rate / % Heat deformation temperature / ℃ Example 1 35.1 560 99.5 92 Example 2 35.4 580 99.8 93 Example 3 35.0 560 99.8 90 Comparative Example 1 29.8 470 56.7 89 Comparative Example 2 24.5 310 98.3 86 Comparative Example 3 34.7 550 99.5 75

[0094] Note: According to the standard GB / T 1040-2008, the tensile properties are tested; according to the standard QB / T 2591-2003, the antibacterial rate is tested, and the test bacteria is Escherichia coli; according to the standard GB / T 1634-2019, the heat deformation temperature is tested.

[0095] Analysis of the test data in Table 1 shows that the cling film prepared by adding antibacterial modifiers and functional chain extenders has excellent tensile properties and antibacterial properties, and has a high heat deformation temperature, showing good heat resistance. However, after the antibacterial modifier is replaced by sepiolite, due to the large compatibility problem with the polylactic acid matrix, its own advantages cannot be fully utilized, so the tensile properties are reduced, and the antibacterial properties are significantly reduced due to the absence of ε-polylysine.

[0096] When the antimicrobial modifier was replaced with ε-polylysine, the advantages of sepiolite could not be utilized, and thus the tensile properties were further reduced.

[0097] After removing the functional chain extender, polylactic acid cannot form a cross-linked network structure and does not contain a POSS skeleton, so its heat resistance is greatly reduced.

[0098] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

[0099] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fresh-keeping film for food storage, characterized in that: The fresh-keeping film is made of the following raw materials in parts by weight: Polylactic acid 30-45 parts; PBAT 20-35 parts; 3-4.5 parts of antibacterial modifier; 5-10 parts of functional chain extender; 0.5-1.5 parts of antioxidant; 1-2 parts of lubricant; The preparation method comprises the following steps: The first step is to weigh each raw material according to the formula and set aside; Step 2: Add polylactic acid, PBAT, antibacterial modifier, functional chain extender, antioxidant and lubricant into a mixer, control the temperature to 80-100°C, the speed to 1000-1500r / min, and mechanically stir for 20-40min to form a mixed material; The third step is to feed the mixed material into a twin-screw extruder, control the temperature of the front end of the screw to 180±5°C, the temperature of the middle end to 175±5°C, and the temperature of the rear end to 160±5°C, perform melt extrusion, and then perform a blow molding process to obtain a fresh-keeping film; The antibacterial modifier is sepiolite with ε-polylysine macromolecules modified on the surface; The functional chain extender is a POSS derivative with an isocyanate group at the structural end.

2. The method for preparing a fresh-keeping film for food storage according to claim 1, characterized in that: The preparation method of the antibacterial modifier comprises the following steps: Step A, adding sepiolite to tetrahydrofuran, ultrasonically dispersing for 20-30 minutes to form a uniform dispersion, then adding anhydride modifier, after the addition, raising the temperature to 50-60° C., keeping warm and stirring for 6-9 hours, centrifuging out the solid product to obtain a modified sepiolite; Step B: Under the catalytic action of a catalyst, an active macromolecular antibacterial agent is used to further graft-modify the sepiolite modifier to obtain an antibacterial modifier.

3. The method for preparing a fresh-keeping film for food storage according to claim 2, characterized in that: In step A, the anhydride modifier is selected from any one of succinic anhydride, glutaric anhydride or maleic anhydride.

4. The method for preparing a fresh-keeping film for food storage according to claim 2, characterized in that: In step B, the catalyst is selected from aminosulfonic acid or trifluoromethanesulfonic acid.

5. The method for preparing a fresh-keeping film for food storage according to claim 2, characterized in that: In step B, the active macromolecular antibacterial agent is selected from ε-polylysine with a number average molecular weight of 3600-4300.

6. The method for preparing a fresh-keeping film for food storage according to claim 1, characterized in that: The preparation method of the functional chain extender is as follows: Mix phenylamine POSS and acetone, stir to form a uniform mixture, and then place in an ice bath environment, then add the end group modifier to the mixture, after the addition is complete, remove the ice bath, and then add the acid binding agent to the mixture. After the addition is complete, stir at room temperature for 4-6 hours to obtain a functional chain extender.

7. The method for preparing a fresh-keeping film for food storage according to claim 6, characterized in that: The end group modifier is selected from 4-isocyanatobenzoyl chloride or 3-isocyanatobenzoyl chloride.

8. The method for preparing a fresh-keeping film for food storage according to claim 6, characterized in that: The acid binding agent is selected from triethylamine or pyridine.

9. The method for preparing a fresh-keeping film for food storage according to claim 1, characterized in that: The antioxidant is a mixture of lignin and antioxidant 168, with a mass ratio of 1:0.2-0.4; the lubricant is selected from any one of polyethylene wax, stearic acid or magnesium stearate.

10. A fresh-keeping film for food storage, characterized in that: The method is prepared according to any one of claims 1 to 9.

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