Biodegradable environment-friendly food preservative film and manufacturing method thereof

Abstract

The invention relates to the technical field of fresh-keeping films, and discloses a biodegradable environment-friendly food fresh-keeping film and a manufacturing method thereof.The food fresh-keeping film is manufactured by taking polyadipic acid / butylene terephthalate as a base material and taking a polylactic acid compound, a biological antibacterial agent and the like as auxiliary materials through mixing, extrusion and film blowing processes. The polylactic acid compound is a grafted product of palm fibers and polylactic acid, the reinforcing effect of the palm fibers can be efficiently exerted, transmission and diffusion of stress loads are achieved, and therefore the mechanical property of the preservative film is effectively improved. According to the preservative film, the biological antibacterial agent can participate in a subsequent expansion reaction, so that the biological antibacterial agent enters a preservative film base body, the structure of the preservative film is more compact, the porosity is lower, food spoilage caused by oxygen entering is prevented, in addition, the residence time of the natural antibacterial agent caffeic acid in the preservative film can be effectively prolonged, and the antibacterial durability of the preservative film is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of cling film, in particular to a biodegradable and environment-friendly food cling film and a manufacturing method thereof. Background Art

[0002] In modern life, food cling film is a common packaging material widely used in food preservation, transportation and sales. However, traditional petroleum-based plastic cling films such as polyethylene are gradually being eliminated by the market due to their difficult-to-degrade properties. Among them, polybutylene adipate / terephthalate (PBAT) and polylactic acid (PLA), as two important environmentally friendly and degradable materials, have shown broad application prospects in the field of food cling film.

[0003] Due to the high price of polylactic acid, it is generally not used directly as the base material of cling film at this stage. It can be added as an auxiliary material by blending with PBAT. Compared with traditional polyethylene-based cling film, the strength of PBAT-based cling film is relatively low. In addition, since PBAT itself does not have antibacterial properties, the antibacterial properties of PBAT-based cling film are poor, which is very unfavorable for food preservation. Therefore, there are still major problems in practical applications.

[0004] The invention patent with publication number CN106751568B discloses an antibacterial PBAT / PLA composite film and a preparation method thereof. By designing and synthesizing an antibacterial bulking agent, the composite film is endowed with good comprehensive properties such as antibacterial properties. Therefore, various properties of PBAT can be improved by adding functional additives. However, conventional quaternary ammonium salt small molecule antibacterial agents have poor stability and are easy to volatilize and migrate, resulting in the inability to ensure the antibacterial durability of the material. Based on this, the present invention provides a biodegradable and environmentally friendly food preservative film with good antibacterial and other functional properties, which can solve the problems existing in the prior art. 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 biodegradable and environment-friendly food preservative film and a manufacturing method thereof.

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

[0007] A method for manufacturing a biodegradable and environment-friendly food preservative film, characterized in that the food preservative film is made of raw materials including the following parts by weight:

[0008] Polybutylene adipate / terephthalate 55-65 parts;

[0009] 5-12 parts of polylactic acid compound;

[0010] 2.5-4 parts of biological antibacterial agent;

[0011] Chain extender 0.5-1 part;

[0012] Lubricant 0.5-1.5 parts;

[0013] Antioxidant 0.5-1 part;

[0014] The manufacturing 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 polybutylene adipate / terephthalate, polylactic acid composite and bioantibacterial agent into the mixing kettle, control the stirring rate to 1000-1200r / min, mechanically stir and mix for 30-60min, then add chain extender, lubricant and antioxidant into the mixing kettle, continue mechanical stirring for 20-30min, discharge and form a premix;

[0017] The third step is to feed the premix into the extruder, control the extruder temperature to 160-180°C, and after the melt extrusion process, blow mold it into a film.

[0018] As a further embodiment of the present invention, the specific preparation method of the polylactic acid composite is as follows:

[0019] Step 1: adding alkalized palm fiber to tetrahydrofuran, uniformly dispersing by ultrasonication, and then adding isocyanate monomer to the formed dispersion. After the addition is completed, stirring at room temperature for 4-6 hours, discharging the material, and centrifuging the solid material to obtain functionalized palm fiber;

[0020] Step 2: Disperse the functionalized palm fiber evenly in toluene, then add the terminal hydroxyl polylactic acid and the catalyst, gradually increase the temperature to 60-70°C, keep the temperature for 6-8 hours, separate the material, and obtain the polylactic acid composite.

[0021] As a further embodiment of the present invention, in step 1, the isocyanate monomer is selected from 4-isocyanobenzoyl chloride or 3-isocyanatobenzoyl chloride.

[0022] As a further scheme of the present invention, in step 1, the preparation method of the alkalized palm fiber is: immersing the palm fiber in a sodium hydroxide solution with a mass fraction of 5-20%, controlling the temperature to 50-60°C, taking it out after 0.5-1.5h, washing it to neutrality, and then drying it.

[0023] As a further embodiment of the present invention, in step 2, the catalyst is selected from stannous octoate or dibutyltin dilaurate.

[0024] In the above technical scheme, the palm fiber is firstly subjected to an alkalization treatment so that a large number of active hydroxyl functional groups can be exposed on its surface, and then an isocyanate monomer is used to modify the surface of the alkalized palm fiber by utilizing the active acyl chloride substituents in the isocyanate monomer structure to obtain palm fiber modified with isocyanate active substituents, thereby obtaining functionalized palm fiber. Subsequently, under the action of a catalyst, terminal hydroxyl polylactic acid is used to further graft with the functionalized palm fiber to obtain palm fiber grafted polylactic acid, i.e., a polylactic acid complex.

[0025] As a further solution of the present invention, the specific preparation method of the biological antibacterial agent is as follows:

[0026] Caffeic acid and dimethyl sulfoxide are mixed, mechanically stirred evenly, and then the composite catalyst is added. After the addition, the temperature is increased to 40-50°C, and the mixture is stirred for 1-2 hours to form an activation solution. Then, guar gum is added to the activation solution. After the addition is completed, the mixture is stirred at room temperature for 8-12 hours and the bioantimicrobial agent is obtained.

[0027] As a further solution of the present invention, the composite catalyst is a mixture of 4-dimethylaminopyridine and dicyclohexylcarbodiimide in a mass ratio of 1:3-4.

[0028] As a further embodiment of the present invention, the mass ratio of caffeic acid to guar gum is 0.2-0.3:1.

[0029] In the above technical scheme, the active carboxyl substituents in the caffeic acid structure are firstly activated by a composite catalyst, and then esterified and condensed with the active hydroxyl substituents in the guar gum structure to obtain a guar gum derivative containing the natural antibacterial agent caffeic acid in its structure, i.e., a biological antibacterial agent.

[0030] As a further embodiment of the present invention, the chain extender is chain extender KL-E, the lubricant is selected from stearic acid, paraffin or polyethylene wax; and the antioxidant is selected from antioxidant 1010 or antioxidant 168.

[0031] A biodegradable and environment-friendly food preservative film is prepared by the above-mentioned manufacturing method.

[0032] Beneficial effects of the present invention:

[0033] (1) The polylactic acid composite prepared by the present invention is a grafted product of palm fiber and polylactic acid. The interfacial compatibility between the palm fiber and the material matrix can be greatly improved by chemical bonding, and the palm fiber can exist in the material matrix in the form of a chemically cross-linked core, forming a mechanical connection structure similar to a "snap", thereby enabling the reinforcing effect of the palm fiber to be efficiently exerted, realizing the transmission and diffusion of stress loads, thereby effectively improving the mechanical properties of the cling film.

[0034] (2) The biological antibacterial agent prepared by the present invention is a guar gum derivative containing a natural antibacterial agent, caffeic acid, in its structure. Since the guar gum structure contains a large number of active hydroxyl substituents, they can participate in the chain extension reaction in the subsequent chain extension process, thereby entering the plastic wrap matrix. On the one hand, this chain extension method can transform PBAT from a linear structure to a three-dimensional network structure, making the structure of the plastic wrap more compact and the porosity lower, thereby preventing oxygen from entering and causing food corruption. In addition, it can also effectively prolong the retention time of the natural antibacterial agent caffeic acid in the plastic wrap, thereby ensuring the antibacterial durability of the plastic wrap.

[0035] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is the FT-IR graph of the biological antibacterial agent. DETAILED DESCRIPTION

[0038] 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.

[0039] Preparation Example 1

[0040] Preparation of polylactic acid composites:

[0041] Step 1: immerse 5g of palm fiber in a sodium hydroxide solution with a mass fraction of 10%, control the temperature to 55°C, take it out after 1 hour, wash it to neutrality, and then dry it to obtain alkalized palm fiber;

[0042] Step 2: Add 3.5 g of alkalized palm fiber to tetrahydrofuran, disperse uniformly by ultrasonication, then add 0.6 g of 4-isocyanobenzoyl chloride to the formed dispersion, stir at room temperature for 6 h, discharge, centrifuge the solid material, and obtain functionalized palm fiber;

[0043] According to the hydrochloric acid-di-n-butylamine titration test method, the functionalized palm fiber was tested to test the percentage of isocyanate on its surface. 0.1g of functionalized palm fiber was used as the titration sample and 0.5mol / L hydrochloric acid was used as the standard solution. The titration test results showed that the percentage of isocyanate was 4.147%.

[0044] Step 3: Evenly disperse 2.6 g of functionalized palm fiber in toluene, then add 12 g of terminal hydroxyl polylactic acid and 0.1 g of dibutyltin dilaurate. After the addition, gradually increase the temperature to 65°C, keep the temperature for 6 hours, separate the material, and obtain the polylactic acid composite.

[0045] 0.1 g of the polylactic acid complex was taken again as a titration test sample, and the same titration test as in step 2 was performed. The result showed that the percentage of isocyanate was 0.381%, indicating that a large amount of isocyanate groups were consumed during the reaction with the terminal hydroxyl polylactic acid.

[0046] Preparation Example 2

[0047] Preparation of biological antibacterial agents:

[0048] 0.8 g of caffeic acid was mixed with dimethyl sulfoxide, and after mechanical stirring, 0.1 g of 4-dimethylaminopyridine and 0.3 g of dicyclohexylcarbodiimide were added. After the addition, the temperature was raised to 40°C, and the mixture was stirred for 2 h to form an activation solution. Then 3 g of guar gum was added to the activation solution. After the addition was completed, the mixture was stirred at room temperature for 9 h and the bioantibacterial agent was obtained.

[0049] The biological antibacterial agent was made into potassium bromide tablets and subjected to infrared analysis test. The results are shown in Figure 1 ,like Figure 1 As shown, 3308cm -1 The characteristic absorption peak at 3000-3100cm is the characteristic absorption peak of the hydroxyl group in the guar gum structure that does not participate in the reaction. -1 The characteristic absorption peak at 1725cm is the characteristic absorption peak of the carbon and hydrogen of the benzene ring. -1 The characteristic absorption peak at 1088 cm is the characteristic absorption peak of the carbon-oxygen double bond of the ester group produced by the esterification condensation reaction. -1 The characteristic absorption peak that appears at is the characteristic absorption peak of the ether bond.

[0050] Example 1

[0051] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0052] Polybutylene adipate / terephthalate 55 parts;

[0053] 5 parts of polylactic acid compound;

[0054] 2.5 parts of biological antibacterial agent;

[0055] Chain extender KL-E 0.5 part;

[0056] 0.5 parts of stearic acid;

[0057] Antioxidant 1010 0.5 parts;

[0058] The manufacturing method comprises the following steps:

[0059] The first step is to weigh each raw material according to the formula and set aside;

[0060] Step 2: Add polybutylene adipate / terephthalate, polylactic acid composite and bioantibacterial agent into the mixing kettle, control the stirring rate to 1000r / min, mechanically stir and mix for 60min, then add chain extender KL-E, stearic acid and antioxidant 1010 into the mixing kettle, continue mechanical stirring for 30min, discharge and form a premix;

[0061] The third step is to feed the premix into the extruder, control the extruder temperature to 160°C, and after the melt extrusion process, blow mold it into a film.

[0062] The preparation method of the polylactic acid composite is shown in Preparation Example 1; the preparation method of the biological antibacterial agent is shown in Preparation Example 2, and the same is true for the following.

[0063] Example 2

[0064] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0065] Polybutylene adipate / terephthalate 62 parts;

[0066] 9 parts of polylactic acid composite;

[0067] 3 parts of biological antibacterial agent;

[0068] Chain extender KL-E 0.6 parts;

[0069] 1 part of polyethylene wax;

[0070] Antioxidant 168 0.8 parts;

[0071] The manufacturing method comprises the following steps:

[0072] The first step is to weigh each raw material according to the formula and set aside;

[0073] Step 2: Add polybutylene adipate / terephthalate, polylactic acid composite and bioantibacterial agent into the mixing kettle, control the stirring rate to 1200r / min, mechanically stir and mix for 40min, then add chain extender KL-E, polyethylene wax and antioxidant 168 into the mixing kettle, continue mechanical stirring for 20min, discharge and form a premix;

[0074] The third step is to feed the premix into the extruder, control the extruder temperature to 170°C, and after the melt extrusion process, blow mold it into a film.

[0075] Example 3

[0076] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0077] Polybutylene adipate / terephthalate 65 parts;

[0078] 12 parts of polylactic acid compound;

[0079] 4 parts of biological antibacterial agent;

[0080] Chain extender KL-E 1 part;

[0081] 1.5 parts of paraffin;

[0082] Antioxidant 168 1 part;

[0083] The manufacturing method comprises the following steps:

[0084] The first step is to weigh each raw material according to the formula and set aside;

[0085] Step 2: Add polybutylene adipate / terephthalate, polylactic acid composite and bioantibacterial agent into the mixing kettle, control the stirring rate to 1200r / min, mechanically stir and mix for 30min, then add chain extender KL-E, paraffin wax and antioxidant 168 into the mixing kettle, continue mechanical stirring for 20min, discharge and form a premix;

[0086] The third step is to feed the premix into the extruder, control the extruder temperature to 180°C, and after the melt extrusion process, blow mold it into a film.

[0087] Comparative Example 1

[0088] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0089] Polybutylene adipate / terephthalate 62 parts;

[0090] 9 parts of palm fiber;

[0091] 3 parts of biological antibacterial agent;

[0092] Chain extender KL-E 0.6 parts;

[0093] 1 part of polyethylene wax;

[0094] Antioxidant 168 0.8 parts;

[0095] The manufacturing method comprises the following steps:

[0096] The first step is to weigh each raw material according to the formula and set aside;

[0097] Step 2: Add polybutylene adipate / terephthalate, palm fiber and bioantibacterial agent into the mixing kettle, control the stirring rate to 1200r / min, mechanically stir and mix for 40min, then add chain extender KL-E, polyethylene wax and antioxidant 168 into the mixing kettle, continue mechanical stirring for 20min, discharge and form a premix;

[0098] The third step is to feed the premix into the extruder, control the extruder temperature to 170°C, and after the melt extrusion process, blow mold it into a film.

[0099] Comparative Example 2

[0100] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0101] Polybutylene adipate / terephthalate 62 parts;

[0102] 9 parts of polylactic acid composite;

[0103] 3 parts of caffeic acid;

[0104] Chain extender KL-E 0.6 parts;

[0105] 1 part of polyethylene wax;

[0106] Antioxidant 168 0.8 parts;

[0107] The manufacturing method comprises the following steps:

[0108] The first step is to weigh each raw material according to the formula and set aside;

[0109] Step 2: Add polybutylene adipate / terephthalate, polylactic acid composite and caffeic acid into the mixing kettle, control the stirring rate to 1200r / min, mechanically stir and mix for 40min, then add chain extender KL-E, polyethylene wax and antioxidant 168 into the mixing kettle, continue mechanical stirring for 20min after addition, discharge and form a premix;

[0110] The third step is to feed the premix into the extruder, control the extruder temperature to 170°C, and after the melt extrusion process, blow mold it into a film.

[0111] Comparative Example 3

[0112] A biodegradable and environment-friendly food preservative film is made from the following raw materials in parts by weight:

[0113] Polybutylene adipate / terephthalate 62 parts;

[0114] 9 parts of polylactic acid composite;

[0115] Chain extender KL-E 0.6 parts;

[0116] 1 part of polyethylene wax;

[0117] Antioxidant 168 0.8 parts;

[0118] The manufacturing method comprises the following steps:

[0119] The first step is to weigh each raw material according to the formula and set aside;

[0120] Step 2: Add polybutylene adipate / terephthalate and polylactic acid composite into the mixing kettle, control the stirring rate to 1200r / min, mechanically stir and mix for 40min, then add chain extender KL-E, polyethylene wax and antioxidant 168 into the mixing kettle, continue mechanical stirring for 20min, discharge and form a premix;

[0121] The third step is to feed the premix into the extruder, control the extruder temperature to 170°C, and after the melt extrusion process, blow mold it into a film.

[0122] Test Case

[0123] The cling film in the embodiment and the comparative example was made into various test samples, and various performance tests were performed. The test results are recorded in Table 1:

[0124] Table 1 - Performance test results

[0125] The tensile performance test reference standard is GB / T 1040.3-2006; the oxygen permeability test method reference standard is GB / T 1038.1-2022; the antibacterial rate test reference standard is based on standard QB / T 2591-2003, and the test time is after the sample is placed at room temperature for 2 months.

[0126] From the analysis and test results, it can be seen that by using the polylactic acid composite in Preparation Example 1 of the present invention and the biological antibacterial agent in Preparation Example 2 as additives, a PBAT-based food preservative film with excellent mechanical properties, low air permeability and strong antibacterial properties can be prepared.

[0127] After replacing the polylactic acid composite with palm fiber, it is obvious that due to the interface problem, the reinforcing effect of the palm fiber cannot be fully exerted, so the mechanical properties show a significant decline.

[0128] After the biological antimicrobial agent was replaced with caffeic acid, the antimicrobial properties of the cling film showed a significant downward trend, possibly due to the volatilization migration phenomenon during storage. In addition, due to the loss of the cross-linking effect of guar gum, the cross-linking density of the cling film decreased, which directly affected the mechanical properties and oxygen barrier properties of the cling film. After the biological antimicrobial agent was completely removed, the antimicrobial properties were further reduced.

[0129] 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.

[0130] 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 producing a biodegradable and environment-friendly food preservative film, characterized in that: The food preservative film is made of the following raw materials in parts by weight: Polybutylene adipate / terephthalate 55-65 parts; 5-12 parts of polylactic acid compound; 2.5-4 parts of biological antibacterial agent; Chain extender 0.5-1 part; Lubricant 0.5-1.5 parts; Antioxidant 0.5-1 part; The manufacturing method comprises the following steps: The first step is to weigh each raw material according to the formula and set aside; Step 2: Add polybutylene adipate / terephthalate, polylactic acid composite and bioantibacterial agent into the mixing kettle, control the stirring rate to 1000-1200r / min, mechanically stir and mix for 30-60min, then add chain extender, lubricant and antioxidant into the mixing kettle, continue mechanical stirring for 20-30min, discharge and form a premix; The third step is to feed the premix into the extruder, control the extruder temperature to 160-180°C, and after the melt extrusion process, blow mold it into a film.

2. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 1, characterized in that: The specific preparation method of the polylactic acid composite is as follows: Step 1: using isocyanate monomer to graft modify alkalized palm fiber to obtain functionalized palm fiber; Step 2: Using toluene as a medium and in the presence of a catalyst, the terminal hydroxyl polylactic acid and the functionalized palm fiber are further reacted to obtain a polylactic acid composite.

3. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 2, characterized in that: In step 1, the isocyanate monomer is selected from 4-isocyanobenzoyl chloride or 3-isocyanatobenzoyl chloride.

4. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 2, characterized in that: In step 1, the preparation method of the alkalized palm fiber is: immerse the palm fiber in a sodium hydroxide solution with a mass fraction of 5-20%, control the temperature to 50-60° C., take it out after 0.5-1.5 hours, wash it to neutrality, and then dry it.

5. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 2, characterized in that: In step 2, the catalyst is selected from stannous octoate or dibutyltin dilaurate.

6. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 1, characterized in that: The specific preparation method of the biological antibacterial agent is as follows: Caffeic acid and dimethyl sulfoxide are mixed, mechanically stirred evenly, and then the composite catalyst is added. After the addition, the temperature is increased to 40-50°C, and the mixture is stirred for 1-2 hours to form an activation solution. Then, guar gum is added to the activation solution. After the addition is completed, the mixture is stirred at room temperature for 8-12 hours and the bioantimicrobial agent is obtained.

7. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 6, characterized in that: The composite catalyst is a mixture of 4-dimethylaminopyridine and dicyclohexylcarbodiimide, with a mass ratio of 1:3-4.

8. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 6, characterized in that: The mass ratio of caffeic acid to guar gum is 0.2-0.3:

1.

9. The method for manufacturing a biodegradable and environment-friendly food preservative film according to claim 1, characterized in that: The chain extender is chain extender KL-E, the lubricant is selected from stearic acid, paraffin or polyethylene wax; and the antioxidant is selected from antioxidant 1010 or antioxidant 168.

10. A biodegradable and environment-friendly food preservative film, characterized in that: The method is prepared by the manufacturing method according to any one of claims 1 to 9.

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