Food-grade packaging film and preparation method thereof

Abstract

The invention relates to a food-grade packaging film and a preparation method thereof, and belongs to the technical field of packaging materials. The food-grade packaging film is prepared by using waste PET, adipic acid, 1, 4-butanediol, a catalyst, a modifier and a heat stabilizer as raw materials, the adipic acid and the 1, 4-butanediol are subjected to esterification polymerization under the action of the catalyst to obtain PBA, then the waste PET and the modifier are subjected to transesterification with the 1, 4-butanediol under the action of the catalyst to obtain modified PBT, and the modified PBT is subjected to heat treatment under the action of the catalyst to obtain the food-grade packaging film. According to the food-grade packaging film, the waste PET is reasonably recycled, the consumption of the raw material terephthalic acid is reduced, the food-grade packaging film is green and environmentally friendly, the cost is reduced, and the food-grade packaging film is suitable for large-scale industrial production. And the film has good gas barrier property and antibacterial property, and can be widely applied to the field of food packaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of packaging materials, and in particular, relates to a food-grade packaging film and a preparation method thereof. Background Art

[0002] PBAT (polyethylene terephthalate-co-caprolactone) is a fully biodegradable plastic, a polymer compound synthesized from fossil fuels, with high elongation at break and strong toughness. This material has undergone many years of research and development and application since it began large-scale production in the 1990s. PBAT has corresponding applications in the field of food packaging films due to its unique biodegradability and physical properties, good flexibility, ductility and heat resistance, but the molecular chain structure of PBAT is relatively loose, and the gaps between molecules are large, which also leads to poor gas barrier properties of PBAT, so it cannot effectively isolate external gases, which will make the food inside the package easily affected by the external environment, resulting in a decrease in the packaging effect. Based on this, the present invention provides a food-grade packaging film and a preparation method thereof. Summary of the invention

[0003] The object of the present invention is to provide a food-grade packaging film and a preparation method thereof, so as to solve the problems mentioned in the above background technology.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A food-grade packaging film, comprising the following raw materials: waste PET, adipic acid, 1,4-butanediol, a catalyst, a modifier, and a thermal stabilizer;

[0006] A method for preparing a food-grade packaging film comprises the following steps:

[0007] The first step is to add adipic acid, 1,4-butanediol and a catalyst into a stainless steel reactor protected by nitrogen, raise the system temperature to 130-150°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 220-240°C and react for another 4 hours to obtain PBA;

[0008] Step 2: Add waste PET, modifier, 1,4-butanediol and catalyst into a stainless steel reactor protected by nitrogen, raise the system temperature to 210-230°C, and react for 3 hours to obtain modified PBT;

[0009] Step 3: Add modified PBT, PBA, catalyst and thermal stabilizer into a stainless steel reactor protected by nitrogen, raise the system temperature to 230-250°C, and react for 4 hours to obtain modified PBAT;

[0010] The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

[0011] Furthermore, the catalyst is one of tetrabutyl titanate and tetraisopropyl titanate.

[0012] Furthermore, the heat stabilizer is one of trimethyl phosphate and phosphorous acid.

[0013] Furthermore, in terms of mass fractions, the mass fraction ratio of adipic acid, 1,4-butanediol and catalyst used in the first step is 146 parts: 90-100 parts: 1-1.2 parts.

[0014] Furthermore, in terms of mass fractions, the mass fractions of the waste PET, modifier, 1,4-butanediol and catalyst used in the second step are 190-210 parts: 27-30 parts: 145-160 parts: 1.8-2 parts.

[0015] Furthermore, in terms of mass fractions, the modified PBT, PBA, catalyst, and heat stabilizer used in the third step are used in a ratio of 240 parts: 210-220 parts: 0.6-0.8 parts: 0.06-0.08 parts.

[0016] Further, the modifier is prepared by the following steps:

[0017] Step 1, 3,4,5-trihydroxybenzaldehyde, dimethyl malonate, tetrahydropyrrole and anhydrous ethanol were mixed in a three-necked flask, magnetic stirring was turned on, and the mixture was reacted at room temperature for 2-3 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0018] Step 2, mix the intermediate 1, diethylamine and ethanol in a three-necked flask, install a condenser and a thermometer, start magnetic stirring, and react at a temperature of 40-50°C for 2h. After the reaction is completed, the reaction solution is spin-dried to obtain the intermediate 2;

[0019] Step 3, the intermediate 2, tetradecane bromide and acetonitrile are mixed in a three-necked flask, a condenser and a thermometer are installed, magnetic stirring is turned on, and the reaction is carried out at a temperature of 80° C. for 24 hours. After the reaction is completed, the solvent is removed by rotary evaporation, and then the excess tetradecane bromide is removed by filtration. The remaining solid is washed with deionized water and dried to obtain the enhancer.

[0020] Furthermore, the dosage ratio of 3,4,5-trihydroxybenzaldehyde, dimethyl malonate, tetrahydropyrrole and anhydrous ethanol used in step 1 is 0.1 mol: 0.1-0.12 mol: 0.02 mol: 60-80 mL.

[0021] Furthermore, the usage ratio of intermediate 1, diethylamine and ethanol used in step 2 is 0.08 mol: 0.08-0.1 mol: 40-60 mL.

[0022] Furthermore, the amount ratio of intermediate 2, bromotetradecane and acetonitrile used in step 3 is 0.06 mol: 0.08-0.1 mol: 60-80 mL.

[0023] Beneficial effects of the present invention:

[0024] 1) The present invention uses waste PET, adipic acid, 1,4-butanediol, a catalyst, a modifier, and a heat stabilizer as raw materials to prepare a food-grade packaging film. The present invention first performs esterification polymerization of adipic acid and 1,4-butanediol under the action of a catalyst to obtain PBA, then performs an ester exchange reaction between the waste PET and the modifier and 1,4-butanediol under the action of a catalyst to obtain a modified PBT, then polymerizes the modified PBT and PBA under the action of a catalyst and a heat stabilizer to obtain a modified PBAT, and finally blows the modified PBAT into a film after plasticizing to obtain a food-grade packaging film. The food-grade packaging film of the present invention reasonably recycles the waste PET, reduces the consumption of the raw material terephthalic acid, and the prepared food-grade packaging film can be degraded, which is green and environmentally friendly.

[0025] 2) The present invention uses 3,4,5-trihydroxybenzaldehyde and dimethyl malonate as raw materials, utilizes the aldehyde group of 3,4,5-trihydroxybenzaldehyde and the active methylene group of dimethyl malonate to undergo Knoevenagel reaction to obtain intermediate 1, then uses intermediate 1 and diethylamine as raw materials, utilizes the double bond of intermediate 1 and the imino group of diethylamine to undergo Michael addition reaction to obtain intermediate 2, finally uses intermediate 2 and tetradecane bromide as raw materials, utilizes the tertiary amine structure of intermediate 2 and the bromine atom of tetradecane bromide to undergo quaternary ammonium salt reaction to obtain a modifier, the modifier of the present invention contains two ester groups, can undergo ester exchange reaction with 1,4-butanediol and be combined in PBT to modify PBAT, the modifier contains a large amount of phenolic hydroxyl groups, can form a stable hydrogen bond network to improve the gas barrier property of PBAT, and the modifier also has a quaternary ammonium salt structure of a long-chain alkyl group, has a good inhibitory effect on a variety of bacteria and fungi, and can give PBAT good antibacterial properties.

[0026] 3) The food-grade packaging film of the present invention is green and environmentally friendly, and has good gas barrier properties and antibacterial properties, and can be widely used in the field of food packaging. DETAILED DESCRIPTION

[0027] The following will be combined with 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.

[0028] Example 1

[0029] A modifier is prepared by the following steps:

[0030] Step 1, 0.1 mol 3,4,5-trihydroxybenzaldehyde, 0.1 mol dimethyl malonate, 0.02 mol tetrahydropyrrole, and 60 mL anhydrous ethanol were mixed in a three-necked flask, magnetic stirring was turned on, and the reaction was carried out at room temperature for 2 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0031] Step 2, 0.08 mol intermediate 1, 0.08 mol diethylamine, and 40 mL ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 40°C for 2 hours. After the reaction was completed, the reaction solution was spin-dried to obtain intermediate 2;

[0032] Step 3, 0.06 mol intermediate 2, 0.08 mol tetradecane bromide, and 60 mL acetonitrile were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 80° C. for 24 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and then the excess tetradecane bromide was removed by filtration. The remaining solid was washed with deionized water and dried to obtain the enhancer.

[0033] Example 2

[0034] A modifier is prepared by the following steps:

[0035] Step 1, 0.1 mol 3,4,5-trihydroxybenzaldehyde, 0.11 mol dimethyl malonate, 0.02 mol tetrahydropyrrole, and 70 mL anhydrous ethanol were mixed in a three-necked flask, magnetic stirring was turned on, and the reaction was carried out at room temperature for 2.5 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0036] Step 2, 0.08 mol intermediate 1, 0.09 mol diethylamine, and 50 mL ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 45°C for 2 hours. After the reaction was completed, the reaction solution was spin-dried to obtain intermediate 2;

[0037] Step 3, 0.06 mol intermediate 2, 0.09 mol tetradecane bromide, and 70 mL acetonitrile were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 80° C. for 24 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and then the excess tetradecane bromide was removed by filtration. The remaining solid was washed with deionized water and dried to obtain the enhancer.

[0038] Example 3

[0039] A modifier is prepared by the following steps:

[0040] Step 1, 0.1 mol 3,4,5-trihydroxybenzaldehyde, 0.12 mol dimethyl malonate, 0.02 mol tetrahydropyrrole, and 80 mL anhydrous ethanol were mixed in a three-necked flask, magnetic stirring was turned on, and the reaction was carried out at room temperature for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and the remaining solid was washed with deionized water and dried to obtain intermediate 1;

[0041] Step 2, 0.08 mol intermediate 1, 0.1 mol diethylamine, and 60 mL ethanol were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 50°C for 2 hours. After the reaction was completed, the reaction solution was spin-dried to obtain intermediate 2;

[0042] Step 3, 0.06 mol intermediate 2, 0.1 mol tetradecane bromide, and 80 mL acetonitrile were mixed in a three-necked flask, a condenser and a thermometer were installed, magnetic stirring was turned on, and the reaction was carried out at a temperature of 80° C. for 24 hours. After the reaction was completed, the solvent was removed by rotary evaporation, and then the excess tetradecane bromide was removed by filtration. The remaining solid was washed with deionized water and dried to obtain the enhancer.

[0043] Example 4

[0044] A food-grade packaging film, comprising the following raw materials: waste PET, adipic acid, 1,4-butanediol, tetraisopropyl titanate, the modifier obtained in Example 1, and phosphorous acid;

[0045] A method for preparing a food-grade packaging film comprises the following steps:

[0046] The first step is to add 146 parts of adipic acid, 90 parts of 1,4-butanediol and 1 part of tetraisopropyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 130°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 220°C and react for another 4 hours to obtain PBA;

[0047] Step 2: 190 parts of waste PET, 27 parts of the modifier obtained in Example 1, 145 parts of 1,4-butanediol, and 1.8 parts of tetraisopropyl titanate were added into a stainless steel reactor protected by nitrogen, the system temperature was raised to 210° C., and the reaction was carried out for 3 hours to obtain modified PBT;

[0048] Step 3: Add 240 parts of modified PBT, 210 parts of PBA, 0.6 parts of tetraisopropyl titanate, and 0.06 parts of phosphorous acid into a stainless steel reactor protected by nitrogen, raise the system temperature to 230°C, and react for 4 hours to obtain modified PBAT;

[0049] The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

[0050] Example 5

[0051] A food-grade packaging film, comprising the following raw materials: waste PET, adipic acid, 1,4-butanediol, tetraisopropyl titanate, the modifier obtained in Example 2, and phosphorous acid;

[0052] A method for preparing a food-grade packaging film comprises the following steps:

[0053] The first step is to add 146 parts of adipic acid, 95 parts of 1,4-butanediol and 1.1 parts of tetraisopropyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 140°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 230°C and react for another 4 hours to obtain PBA;

[0054] Step 2: 200 parts of waste PET, 28.5 parts of the modifier obtained in Example 2, 152.5 parts of 1,4-butanediol, and 1.9 parts of tetraisopropyl titanate were added into a stainless steel reactor protected by nitrogen, the system temperature was raised to 220°C, and the reaction was carried out for 3 hours to obtain modified PBT;

[0055] Step 3: Add 240 parts of modified PBT, 215 parts of PBA, 0.7 parts of tetraisopropyl titanate, and 0.07 parts of phosphorous acid into a stainless steel reactor protected by nitrogen, raise the system temperature to 240°C, and react for 4 hours to obtain modified PBAT;

[0056] The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

[0057] Example 6

[0058] A food-grade packaging film, comprising the following raw materials: waste PET, adipic acid, 1,4-butanediol, tetrabutyl titanate, the modifier obtained in Example 3, and trimethyl phosphate;

[0059] A method for preparing a food-grade packaging film comprises the following steps:

[0060] The first step is to add 146 parts of adipic acid, 100 parts of 1,4-butanediol and 1.2 parts of tetrabutyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 150°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 240°C and react for another 4 hours to obtain PBA;

[0061] Step 2: Add 210 parts of waste PET, 30 parts of the modifier obtained in Example 3, 160 parts of 1,4-butanediol, and 2 parts of tetrabutyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 230°C, and react for 3 hours to obtain modified PBT;

[0062] Step 3: Add 240 parts of modified PBT, 220 parts of PBA, 0.8 parts of tetrabutyl titanate, and 0.08 parts of trimethyl phosphate into a stainless steel reactor protected by nitrogen, raise the system temperature to 250°C, and react for 4 hours to obtain modified PBAT;

[0063] The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

[0064] Comparative Example 1

[0065] A food-grade packaging film, comprising the following raw materials: waste PET, adipic acid, 1,4-butanediol, tetrabutyl titanate, and trimethyl phosphate;

[0066] A method for preparing a food-grade packaging film comprises the following steps:

[0067] The first step is to add 146 parts of adipic acid, 100 parts of 1,4-butanediol and 1.2 parts of tetrabutyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 150°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 240°C and react for another 4 hours to obtain PBA;

[0068] Step 2: Add 210 parts of waste PET, 160 parts of 1,4-butanediol and 2 parts of tetrabutyl titanate into a stainless steel reactor protected by nitrogen, raise the system temperature to 230°C, and react for 3 hours to obtain modified PBT;

[0069] Step 3: Add 240 parts of modified PBT, 220 parts of PBA, 0.8 parts of tetrabutyl titanate, and 0.08 parts of trimethyl phosphate into a stainless steel reactor protected by nitrogen, raise the system temperature to 250°C, and react for 4 hours to obtain modified PBAT;

[0070] The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

[0071] Comparative Example 2

[0072] This comparative example is a commercially available food-grade antibacterial packaging film.

[0073] The food-grade packaging films in Examples 4-6 and Comparative Example 1 and the commercially available food-grade antibacterial packaging film in Comparative Example 2 were respectively subjected to performance tests, and the gas barrier properties were tested with reference to the national standard GB / T 19789-2005 "Oxygen permeability test for plastic films and sheets for packaging materials - Coulometric test method", and the food-grade packaging film obtained in Comparative Example 1 was used as a control, and the antibacterial rates against Escherichia coli and Staphylococcus aureus were tested with reference to GB / T 31402-2023 "Determination of antibacterial activity on the surface of plastics and other non-porous materials", and the test results are shown in Table 1:

[0074] Table 1

[0075]

[0076]

[0077] It can be seen from Table 1 that the oxygen permeability of the food-grade packaging film of the present invention in Examples 4-6 is much lower than that of the commercially available food-grade antibacterial packaging film, and the antibacterial rates against Escherichia coli and Staphylococcus aureus are both above 99%, indicating that the food-grade packaging film of the present invention has good gas barrier properties and antibacterial properties, and can be widely used in the field of food packaging.

[0078] A food-grade packaging film and a preparation method thereof provided by the present invention are described in detail above. 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 enables any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combination method. It should be pointed out that for ordinary technicians in the technical field, the present invention can also be improved and modified without departing from the principle of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention can be used in combination with each other in any way. The fact that these combinations are not exhaustively described in this specification is only for the purpose of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A food-grade packaging film, characterized in that: Including the following raw materials: waste PET, adipic acid, 1,4-butanediol, catalyst, modifier, thermal stabilizer; Wherein, the modifier is prepared by the following steps: Step 1, 3,4,5-trihydroxybenzaldehyde, dimethyl malonate, tetrahydropyrrole and anhydrous ethanol are mixed in a container, stirred evenly, and reacted at room temperature for 2-3 hours to obtain intermediate 1; Step 2, intermediate 1, diethylamine and ethanol are mixed in a container, stirred evenly, and reacted at a temperature of 40-50° C. for 2 h to obtain intermediate 2; Step 3: Mix the intermediate 2, tetradecane bromide and acetonitrile in a container, stir evenly, and react at 80° C. for 24 hours to obtain the enhancer.

2. A food-grade packaging film according to claim 1, characterized in that: The amount ratio of 3,4,5-trihydroxybenzaldehyde, dimethyl malonate, tetrahydropyrrole and anhydrous ethanol used in step 1 is 0.1 mol: 0.1-0.12 mol: 0.02 mol: 60-80 mL.

3. A food-grade packaging film according to claim 1, characterized in that: The usage ratio of intermediate 1, diethylamine and ethanol used in step 2 is 0.08 mol: 0.08-0.1 mol: 40-60 mL.

4. A food-grade packaging film according to claim 1, characterized in that: The amount ratio of intermediate 2, bromotetradecane and acetonitrile used in step 3 is 0.06 mol: 0.08-0.1 mol: 60-80 mL.

5. A method for preparing a food-grade packaging film according to any one of claims 1 to 4, characterized in that: The following steps are involved: The first step is to add adipic acid, 1,4-butanediol and a catalyst into a nitrogen-protected reaction vessel, raise the system temperature to 130-150°C, and then stir and react for 2 hours. After the reaction is completed, raise the system temperature to 220-240°C and react for another 4 hours to obtain PBA; Step 2: Add waste PET, modifier, 1,4-butanediol and catalyst into a nitrogen-protected reaction vessel, raise the system temperature to 210-230°C, and react for 3 hours to obtain modified PBT; Step 3: Add modified PBT, PBA, catalyst and thermal stabilizer into a nitrogen-protected reaction vessel, raise the system temperature to 230-250°C, and react for 4 hours to obtain modified PBAT; The fourth step is to add the modified PBAT into a twin-screw extruder, plasticize and blow mold it into a film, and obtain a food-grade packaging film.

6. The method for preparing a food-grade packaging film according to claim 5, characterized in that: The catalyst is one of tetrabutyl titanate and tetraisopropyl titanate.

7. The method for preparing a food-grade packaging film according to claim 5, characterized in that: The heat stabilizer is one of trimethyl phosphate and phosphorous acid.

8. The method for preparing a food-grade packaging film according to claim 5, characterized in that: In terms of mass fractions, the mass fraction ratio of adipic acid, 1,4-butanediol and catalyst used in the first step is 146 parts: 90-100 parts: 1-1.2 parts.

9. The method for preparing a food-grade packaging film according to claim 5, characterized in that: Calculated by mass, the mass ratio of the waste PET, modifier, 1,4-butanediol and catalyst used in the second step is 190-210 parts: 27-30 parts: 145-160 parts: 1.8-2 parts.

10. The method for preparing a food-grade packaging film according to claim 5, characterized in that: The usage ratio of modified PBT, PBA, catalyst and heat stabilizer used in the third step is 240 parts: 210-220 parts: 0.6-0.8 parts: 0.06-0.08 parts.

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