A biodegradable antibacterial food packaging bag and a preparation method thereof

Abstract

The application discloses a biodegradable antibacterial food packaging bag and a preparation method thereof, and belongs to the technical field of food packaging. The preparation method comprises the following steps: reacting carboxymethyl chitosan and N-isopropyl acrylamide to prepare carboxymethyl chitosan graft copolymer; taking the carboxymethyl chitosan graft copolymer as wall material and taking epsilon-polylysine as core material, and then reacting to prepare modified chitosan microcapsules; and then melting and blending the modified chitosan microcapsules with raw materials such as citric acid modified nanocellulose and polylactic acid, extruding and granulating, and blow molding to prepare the biodegradable antibacterial food packaging bag. The epsilon-polylysine is stably embedded and slowly released through microencapsulation, and the long-lasting antibacterial performance of the packaging bag is enhanced; the modified chitosan microcapsules and the citric acid modified nanocellulose can synergistically enhance the mechanical performance of the packaging bag; the prepared packaging bag has excellent mechanical strength, biodegradability and long-acting antibacterial performance, and can meet the multifunctional requirements of food packaging.

Description

Technical Field

[0001] This invention relates to the field of food packaging technology, specifically to a biodegradable antibacterial food packaging bag and its preparation method. Background Technology

[0002] Food packaging, as a crucial means of ensuring food safety and extending shelf life, directly impacts the preservation effect and environmental friendliness of the packaging through its material selection and structural design. In recent years, with increasing global attention to plastic pollution, biodegradable materials have received widespread attention in the food packaging sector. Biodegradable polyester materials, such as polylactic acid (PLA), polybutylene terephthalate (PBAT), and polybutylene succinate (PBS), have become important candidate materials to replace traditional petroleum-based plastics due to their excellent degradability and biocompatibility. Simultaneously, adding antibacterial agents to packaging materials to inhibit the growth of food spoilage microorganisms has become an important means of enhancing packaging functionality.

[0003] However, existing biodegradable antimicrobial packaging materials still have many shortcomings. First, single biodegradable polyester materials generally have deficiencies in mechanical strength, flexibility, and gas barrier properties, making it difficult to meet the practical needs of diverse food packaging. Second, the distribution of antimicrobial agents in packaging materials is relatively simple, often involving direct blending of antimicrobial agents with the matrix resin. This simple dispersion method makes it difficult to achieve gradient distribution and differentiated control of antimicrobial components, resulting in low utilization rates and unstable preservation effects. Third, the release behavior of antimicrobial components is difficult to precisely control. Too rapid a release rate leads to a shortened shelf life, while too slow a rate affects the initial antimicrobial effect; there is a lack of effective mechanisms for regulating release behavior. Furthermore, existing technologies do not adequately consider the multifunctional integration of packaging materials, often focusing only on improving antimicrobial performance while neglecting the balance between the overall mechanical stability, barrier properties, and processing adaptability of the material, making it difficult to achieve synergistic optimization of comprehensive performance. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a biodegradable antibacterial food packaging bag and a method for preparing the same.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a biodegradable antibacterial food packaging bag, comprising the following preparation steps:

[0007] S1: Add chitosan to isopropanol, stir to swell, add sodium hydroxide solution and continue stirring, add isopropanol chloroacetate dropwise, heat and stir, after the reaction is complete, filter, wash and dry to obtain carboxymethylated chitosan.

[0008] S2: Add carboxymethyl chitosan to deionized water and stir until completely dissolved. Add N-isopropylacrylamide and stir evenly. Add ammonium persulfate and tetramethylethylenediamine. Heat the mixture under inert gas protection and react. After the reaction is complete, pour the reaction solution into acetone to precipitate. Filter, wash and dry to obtain carboxymethyl chitosan graft copolymer.

[0009] S3: Add carboxymethyl chitosan graft copolymer to deionized water, heat and stir, add ε-polylysine and emulsifier, stir to emulsify, then add sodium tripolyphosphate aqueous solution dropwise, continue stirring, centrifuge, wash and dry to obtain modified chitosan microcapsules;

[0010] S4: Mix modified chitosan microcapsules with citric acid-modified nanocellulose, stir evenly, add polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA, continue stirring evenly to obtain a mixture, add the mixture to a twin-screw extruder for melt blending, extrusion granulation, cooling, air drying and pelletizing to obtain antibacterial masterbatch; blow mold the antibacterial masterbatch, draw and wind it to obtain a biodegradable antibacterial food packaging bag.

[0011] Furthermore, the preparation method of the citric acid-modified nanocellulose is as follows:

[0012] Nanocellulose was added to deionized water and ultrasonically dispersed to obtain a nanocellulose suspension. Citric acid and sodium hypophosphite were added, and the pH of the system was adjusted to 3.5-4.5 with glacial acetic acid. The mixture was stirred and reacted in a water bath at 65℃-75℃ for 2-4 hours. After the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain citric acid-modified nanocellulose.

[0013] Furthermore, the raw materials for the citric acid-modified nanocellulose are as follows by weight: 2-5 parts nanocellulose, 120-150 parts deionized water, 1.2-2 parts citric acid, and 0.1-0.2 parts sodium hypophosphite.

[0014] Furthermore, the specific steps of S1 are as follows:

[0015] Chitosan was added to isopropanol and stirred until it swelled for 30-60 minutes. Sodium hydroxide solution was added and stirring continued for 20-40 minutes. Isopropanol chloroacetic acid was added dropwise over 30-60 minutes. After the addition was complete, the temperature was raised to 50-70°C and the reaction was stirred for 3-6 hours. After the reaction was completed, the mixture was filtered, washed successively with ethanol and deionized water, and dried under vacuum at 50-60°C to obtain carboxymethylated chitosan.

[0016] Furthermore, the specific steps of S2 are as follows:

[0017] Carboxymethyl chitosan was added to deionized water and stirred until completely dissolved. N-isopropylacrylamide was added and stirred until homogeneous. Ammonium persulfate and tetramethylethylenediamine were added, and nitrogen gas was introduced for protection. The temperature was raised to 60-80℃ and the reaction was maintained at 300-500 r / min for 6-12 h with stirring. After the reaction was completed, the reaction solution was poured into acetone to precipitate, filtered, washed with acetone, and dried under vacuum at 40-60℃ to obtain carboxymethyl chitosan graft copolymer.

[0018] Furthermore, the specific steps of S3 are as follows:

[0019] Carboxymethyl chitosan graft copolymer was added to deionized water, heated to 40-60℃, and stirred until homogeneous to obtain a graft copolymer solution. ε-polylysine and an emulsifier were added, and the mixture was stirred and emulsified at 8000-12000 r / min for 10-30 min to form an emulsion. Sodium tripolyphosphate aqueous solution was then added dropwise over 15-30 min, and stirring was continued for 30-60 min after the addition was complete. The mixture was centrifuged, washed with deionized water, and vacuum dried at 40-60℃ to obtain modified chitosan microcapsules.

[0020] Furthermore, the specific preparation steps of the mixture in S4 are as follows:

[0021] Modified chitosan microcapsules were mixed with citric acid-modified nanocellulose at room temperature and stirred until homogeneous. Polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA were then added, and stirring was continued for 15-30 minutes to obtain the mixture.

[0022] Further, the raw materials in S1 are as follows by weight: 10-20 parts chitosan, 120-200 parts isopropanol, 15-35 parts sodium hydroxide solution, and 12-30 parts isopropanol chloroacetic acid solution.

[0023] Furthermore, the sodium hydroxide solution has a mass fraction of 30%-50%; the chloroacetic acid isopropanol solution has a mass fraction of 20%-33.3%.

[0024] Further, the raw materials in S2 are as follows by weight: 5-15 parts carboxymethylated chitosan, 200-300 parts deionized water, 3-10 parts N-isopropylacrylamide, 0.5-1.2 parts ammonium persulfate, and 0.2-0.6 parts tetramethylethylenediamine.

[0025] Further, the raw materials in S3 are as follows by weight: 3-10 parts of carboxymethyl chitosan graft copolymer, 120-300 parts of deionized water, 60-150 parts of sodium tripolyphosphate aqueous solution, 2-5 parts of ε-polylysine, and 0.5-3 parts of emulsifier.

[0026] Furthermore, the mass fraction of the sodium tripolyphosphate aqueous solution is 0.5%-2.0%.

[0027] Furthermore, the emulsifier is at least one of polyoxyethylene sorbitan fatty acid ester and sorbitan fatty acid ester.

[0028] Further, the raw materials in S4 are as follows by weight: 2-8 parts modified chitosan microcapsules, 2-5 parts citric acid modified nanocellulose, 50-80 parts polylactic acid, 20-50 parts polybutylene terephthalate-adipate, and 4-8 parts POE-g-GMA.

[0029] Furthermore, the melt blending conditions in S4 are as follows: the temperature of the first zone of the twin-screw extruder is 150-160℃, the temperature of the second zone is 160-170℃, the temperature of the third zone is 170-180℃, the temperature of the fourth zone is 165-175℃, the die head temperature is 160-170℃, and the screw speed is 100-200 r / min.

[0030] Furthermore, the blow molding conditions in S4 are: blown film temperature of 150-170℃, blow-up ratio of 2.0-3.5, and traction speed of 5-15m / min.

[0031] Secondly, the present invention provides a biodegradable antibacterial food packaging bag prepared by the above-mentioned method for preparing biodegradable antibacterial food packaging bags.

[0032] The beneficial effects of this invention are:

[0033] This invention successfully constructed modified chitosan microcapsules with carboxymethyl chitosan graft copolymer as the wall material and ε-polylysine as the core material by sequentially modifying chitosan with carboxymethylation, graft copolymerizing with N-isopropylacrylamide, and then microencapsulating it with ionic crosslinking. These modified chitosan microcapsules have a dense structure, effectively inhibiting the thermal degradation and premature leakage of ε-polylysine during melt blending and blow molding, significantly improving the encapsulation stability and processing adaptability of ε-polylysine, and avoiding the uneven distribution and antibacterial failure problems caused by direct blending of ε-polylysine with the matrix resin.

[0034] This invention involves compounding modified chitosan microcapsules with citric acid-modified nanocellulose, followed by melt blending with polylactic acid, polybutylene terephthalate-adipate, and POE-g-GMA. Citric acid modification introduces carboxyl groups onto the surface of the nanocellulose, improving the interfacial compatibility between the nanocellulose and the hydrophobic polyester matrix, ensuring uniform dispersion and the formation of a reinforcing network. Simultaneously, the modified chitosan microcapsules, acting as a flexible dispersed phase within the matrix, play a role in stress transfer and energy dissipation. The synergistic effect of these two components significantly enhances the tensile strength, elongation at break, and impact toughness of the packaging bag, overcoming the shortcomings of insufficient mechanical properties in single biodegradable polyester materials.

[0035] The polylactic acid and polybutylene terephthalate (PET) used in this invention are both fully biodegradable polyester materials, while chitosan, nanocellulose, and ε-polylysine are all naturally derived biodegradable components. The resulting packaging bags can be completely decomposed by microorganisms under soil burial conditions without producing environmental pollutants. Simultaneously, the modified chitosan microcapsule structure avoids direct contact and thermal damage between ε-polylysine and the matrix, ensuring processing stability during melt blending and blow molding. This allows the packaging bags to maintain highly efficient biodegradability while possessing excellent antibacterial properties and good mechanical properties, achieving synergistic optimization of the multifunctional characteristics of food packaging materials. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The ε-polylysine used in this invention has the CAS number 28211-04-3 and was purchased from Shandong Fangchang Biotechnology Co., Ltd.

[0038] The nanocellulose used in this invention was purchased from Wuhan Kangqiong Biomedical Technology Co., Ltd.

[0039] The chitosan used in this invention was purchased from Chengdu Wanxiang Hongrun Biotechnology Co., Ltd.

[0040] The sodium tripolyphosphate used in this invention was purchased from Shandong Bairong New Material Technology Co., Ltd.

[0041] The polylactic acid used in this invention has CAS number 26023-30-3 and was purchased from Ba Shifu (Shanghai) Biomedical Technology Co., Ltd.

[0042] The polybutylene terephthalate used in this invention has the CAS number 55231-08-8 and was purchased from Wuhan Kemic Biomedical Technology Co., Ltd.

[0043] The POE-g-GMA used in this invention was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.

[0044] Example 1

[0045] A method for preparing a biodegradable antibacterial food packaging bag includes the following preparation steps:

[0046] S1: By weight, take 10 parts chitosan, 120 parts isopropanol, 15 parts 30% sodium hydroxide solution, and 12 parts 20% chloroacetic acid isopropanol solution; add chitosan to isopropanol and stir at 200 r / min at room temperature for 30 min to swell; add sodium hydroxide solution and continue stirring at 200 r / min for 20 min; add chloroacetic acid isopropanol solution dropwise over 30 min, and after the addition is complete, raise the temperature to 50℃ and stir at 300 r / min for 3 h; after the reaction is complete, filter and wash twice each with 70% ethanol aqueous solution and deionized water; vacuum dry at -0.08 MPa and 50℃ for 12 h to obtain carboxymethylated chitosan;

[0047] S2: By weight, take 5 parts of carboxymethylated chitosan, 200 parts of deionized water, 3 parts of N-isopropylacrylamide, 0.5 parts of ammonium persulfate, and 0.2 parts of tetramethylethylenediamine; add carboxymethylated chitosan to deionized water and stir at room temperature until completely dissolved. Add N-isopropylacrylamide and stir at 300 r / min for 15 min at room temperature. Add ammonium persulfate and tetramethylethylenediamine, purge with nitrogen for protection, heat to 80℃, and keep at this temperature for 6 h with stirring at 300 r / min. After the reaction is complete, pour the reaction solution into 4 times its volume of acetone to precipitate and let it stand for 1 h. Filter and wash the precipitate twice with acetone. Vacuum dry at -0.08 MPa and 40℃ for 12 h to obtain carboxymethyl chitosan graft copolymer.

[0048] S3: By weight, take 3 parts of carboxymethyl chitosan graft copolymer, 120 parts of deionized water, 60 parts of sodium tripolyphosphate aqueous solution (sodium tripolyphosphate aqueous solution mass fraction is 0.5%), 2 parts of ε-polylysine, and 0.5 parts of polyoxyethylene sorbitan fatty acid ester; add carboxymethyl chitosan graft copolymer to deionized water, heat to 40℃, and stir at 200 r / min for 20 min to obtain graft copolymer solution; add ε-polylysine and polyoxyethylene sorbitan fatty acid ester, and emulsify at high speed at 8000 r / min for 10 min to form emulsion; add sodium tripolyphosphate aqueous solution dropwise to emulsion within 15 min, and continue stirring at 300 r / min for 30 min after the addition is complete; centrifuge the reaction solution at 8000 r / min for 10 min, wash the precipitate twice with deionized water; vacuum dry at -0.08 MPa and 40℃ for 12 h to obtain modified chitosan microcapsules;

[0049] S4: By weight, take 2 parts of modified chitosan microcapsules, 2 parts of citric acid-modified nanocellulose, 50 parts of polylactic acid, 20 parts of polybutylene terephthalate-adipate, and POE-g-GMA. Four parts; modified chitosan microcapsules and citric acid-modified nanocellulose were mixed at room temperature and stirred at 300 r / min for 15 min at room temperature; polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA were added, and the mixture was stirred at 200 r / min for 15 min to obtain a mixture; the mixture was added to a twin-screw extruder for melt blending. The temperature of the first zone of the twin-screw extruder was 150℃, the second zone was 160℃, the third zone was 170℃, the fourth zone was 165℃, the die head temperature was 160℃, and the screw speed was 100 r / min; the mixture was extruded and granulated, cooled, air-dried, and granulated to obtain antibacterial masterbatch with a diameter of 2 mm; the antibacterial masterbatch was added to a blown film machine and blown into shape under the conditions of blown film temperature of 150℃, blow ratio of 2.0 and traction speed of 5 m / min, and then drawn and wound to obtain a biodegradable antibacterial food packaging bag.

[0050] The preparation method of citric acid modified cellulose nanoparticles is as follows:

[0051] By weight, 2 parts of nanocellulose, 120 parts of deionized water, 1.2 parts of citric acid, and 0.1 parts of sodium hypophosphite were taken. The nanocellulose was added to the deionized water and ultrasonically dispersed for 10 min at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz to obtain a nanocellulose suspension. Citric acid and sodium hypophosphite were added, and the pH of the system was adjusted to 3.5 with glacial acetic acid. The reaction was carried out in a 65℃ water bath at a speed of 300 r / min for 2 h. After the reaction was completed, the precipitate was centrifuged at 8000 r / min for 10 min and washed twice with deionized water. The precipitate was vacuum dried at a vacuum degree of -0.08 MPa and a temperature of 50℃ for 12 h to obtain citric acid modified nanocellulose.

[0052] Example 2

[0053] A method for preparing a biodegradable antibacterial food packaging bag includes the following preparation steps:

[0054] S1: By weight, take 15 parts chitosan, 160 parts isopropanol, 25 parts of 40% sodium hydroxide solution, and 21 parts of 27% chloroacetic acid isopropanol solution; add chitosan to isopropanol and stir at 300 r / min at room temperature for 45 min to swell; add sodium hydroxide solution and continue stirring at 300 r / min for 30 min; add chloroacetic acid isopropanol solution dropwise over 45 min, and after the addition is complete, raise the temperature to 60℃ and stir at 400 r / min for 4.5 h; after the reaction is complete, filter and wash twice each with 75% ethanol aqueous solution and deionized water; vacuum dry at -0.09 MPa and 55℃ for 16 h to obtain carboxymethylated chitosan;

[0055] S2: By weight, take 10 parts of carboxymethylated chitosan, 250 parts of deionized water, 7 parts of N-isopropylacrylamide, 0.7 parts of ammonium persulfate, and 0.4 parts of tetramethylethylenediamine; add carboxymethylated chitosan to deionized water and stir at room temperature until completely dissolved. Add N-isopropylacrylamide and stir at 300 r / min for 35 min at room temperature. Add ammonium persulfate and tetramethylethylenediamine, purge with nitrogen for protection, heat to 70℃, and keep at this temperature for 9 h with stirring at 400 r / min. After the reaction is complete, pour the reaction solution into 4 times its volume of acetone to precipitate and let it stand for 1.5 h. Filter and wash the precipitate twice with acetone. Vacuum dry at -0.09 MPa and 50℃ for 18 h to obtain carboxymethyl chitosan graft copolymer.

[0056] S3: By weight, take 7 parts of carboxymethyl chitosan graft copolymer, 220 parts of deionized water, 100 parts of sodium tripolyphosphate aqueous solution (sodium tripolyphosphate aqueous solution mass fraction is 1.2%), 3 parts of ε-polylysine, and 1.5 parts of dehydrated sorbitan fatty acid ester; add carboxymethyl chitosan graft copolymer to deionized water, heat to 50℃, and stir at 300 r / min for 30 min to obtain graft copolymer solution; add ε-polylysine and dehydrated sorbitan fatty acid ester, and emulsify at high speed of 10000 r / min for 20 min to form emulsion; add sodium tripolyphosphate aqueous solution dropwise to emulsion within 22 min, and continue stirring at 400 r / min for 45 min after the addition is complete; centrifuge the reaction solution at 10000 r / min for 15 min, wash the precipitate twice with deionized water; vacuum dry at -0.09 MPa and 50℃ for 18 h to obtain modified chitosan microcapsules;

[0057] S4: By weight, take 5 parts of modified chitosan microcapsules, 3 parts of citric acid-modified nanocellulose, 65 parts of polylactic acid, 35 parts of polybutylene terephthalate-adipate, and POE-g-GMA. Six parts were prepared. Modified chitosan microcapsules were mixed with citric acid-modified nanocellulose at room temperature and stirred at 300 rpm for 20 min at room temperature. Polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA were added, and the mixture was stirred at 300 rpm for 22 min to obtain a mixture. The mixture was added to a twin-screw extruder for melt blending. The temperature of the first zone of the twin-screw extruder was 155℃, the second zone was 165℃, the third zone was 175℃, the fourth zone was 170℃, the die head temperature was 165℃, and the screw speed was 150 rpm. The mixture was extruded and granulated, cooled, air-dried, and granulated to obtain antibacterial masterbatch with a diameter of 3 mm. The antibacterial masterbatch was added to a blown film machine and blown into shape under the conditions of blown film temperature of 160℃, blow ratio of 2.8, and traction speed of 10 m / min. The mixture was then drawn and wound to obtain a biodegradable antibacterial food packaging bag.

[0058] Preparation of citric acid-modified nanocellulose:

[0059] By weight, 3 parts of nanocellulose, 135 parts of deionized water, 1.6 parts of citric acid, and 0.15 parts of sodium hypophosphite were taken. The nanocellulose was added to the deionized water and ultrasonically dispersed for 20 min at an ultrasonic power of 350 W and an ultrasonic frequency of 50 kHz to obtain a nanocellulose suspension. Citric acid and sodium hypophosphite were added, and the pH of the system was adjusted to 4.0 with glacial acetic acid. The reaction was carried out in a 70℃ water bath at a speed of 400 r / min for 3 h. After the reaction was completed, the precipitate was centrifuged at 10000 r / min for 15 min and washed twice with deionized water. The precipitate was vacuum dried at a vacuum degree of -0.09 MPa and a temperature of 55℃ for 18 h to obtain citric acid modified nanocellulose.

[0060] Example 3

[0061] A method for preparing a biodegradable antibacterial food packaging bag includes the following preparation steps:

[0062] S1: By weight, take 20 parts chitosan, 200 parts isopropanol, 35 parts of 50% sodium hydroxide solution, and 30 parts of 33.3% chloroacetic acid isopropanol solution; add chitosan to isopropanol and stir at 400 r / min at room temperature for 60 min to swell; add sodium hydroxide solution and continue stirring at 400 r / min for 40 min; add chloroacetic acid isopropanol solution dropwise over 60 min, and after the addition is complete, raise the temperature to 70℃ and stir at 500 r / min for 6 h; after the reaction is complete, filter and wash twice each with 80% ethanol aqueous solution and deionized water; vacuum dry at -0.1 MPa and 60℃ for 24 h to obtain carboxymethylated chitosan;

[0063] S2: By weight, take 15 parts of carboxymethylated chitosan, 300 parts of deionized water, 10 parts of N-isopropylacrylamide, 1.2 parts of ammonium persulfate, and 0.6 parts of tetramethylethylenediamine; add carboxymethylated chitosan to deionized water and stir at room temperature until completely dissolved; add N-isopropylacrylamide and stir at 300 r / min for 40 min at room temperature; add ammonium persulfate and tetramethylethylenediamine; purge with nitrogen for protection; heat to 60℃ and keep at 500 r / min for 12 h with stirring; after the reaction is complete, pour the reaction solution into 5 times its volume of acetone to precipitate and let stand for 2 h; filter and wash the precipitate 3 times with acetone; vacuum dry at -0.1 MPa and 60℃ for 24 h to obtain carboxymethyl chitosan graft copolymer;

[0064] S3: By weight, take 10 parts of carboxymethyl chitosan graft copolymer, 300 parts of deionized water, 150 parts of sodium tripolyphosphate aqueous solution (sodium tripolyphosphate aqueous solution mass fraction is 2.0%), 5 parts of ε-polylysine, and 3 parts of polyoxyethylene sorbitan fatty acid ester; add carboxymethyl chitosan graft copolymer to deionized water, heat to 60℃, and stir at 400 r / min for 40 min to obtain graft copolymer solution; add ε-polylysine and polyoxyethylene sorbitan fatty acid ester, and emulsify at high speed at 12000 r / min for 30 min to form emulsion; within 30 min, add sodium tripolyphosphate aqueous solution dropwise to emulsion, and continue stirring at 500 r / min for 60 min after the addition is complete; centrifuge the reaction solution at 12000 r / min for 20 min, wash the precipitate 3 times with deionized water; vacuum dry at -0.1 MPa and 60℃ for 24 h to obtain modified chitosan microcapsules;

[0065] S4: By weight, take 8 parts of modified chitosan microcapsules, 5 parts of citric acid-modified nanocellulose, 80 parts of polylactic acid, 50 parts of polybutylene terephthalate-adipate, and POE-g-GMA. Eight parts were prepared. Modified chitosan microcapsules and citric acid-modified nanocellulose were mixed at room temperature and stirred at 300 rpm for 25 min at room temperature. Polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA were added, and the mixture was stirred at 400 rpm for 30 min to obtain a mixture. The mixture was added to a twin-screw extruder for melt blending. The temperature of the first zone of the twin-screw extruder was 160℃, the second zone was 170℃, the third zone was 180℃, the fourth zone was 175℃, the die head temperature was 170℃, and the screw speed was 200 rpm. The mixture was extruded and granulated, cooled, air-dried, and pelletized to obtain antibacterial masterbatch with a diameter of 2 mm. The antibacterial masterbatch was added to a blown film machine and blown into shape under the conditions of blown film temperature of 170℃, blow ratio of 3.5, and traction speed of 15 m / min. The mixture was then drawn and wound to obtain a biodegradable antibacterial food packaging bag.

[0066] Preparation of citric acid-modified nanocellulose:

[0067] By weight, 5 parts of nanocellulose, 150 parts of deionized water, 2 parts of citric acid, and 0.2 parts of sodium hypophosphite were taken. The nanocellulose was added to the deionized water and ultrasonically dispersed for 30 min at an ultrasonic power of 500 W and an ultrasonic frequency of 60 kHz to obtain a nanocellulose suspension. Citric acid and sodium hypophosphite were added, and the pH of the system was adjusted to 4.5 with glacial acetic acid. The reaction was carried out in a 75℃ water bath at a speed of 500 r / min for 4 h. After the reaction was completed, the mixture was centrifuged at 12000 r / min for 20 min and the precipitate was washed 3 times with deionized water. The mixture was vacuum dried at a vacuum degree of -0.1 MPa and a temperature of 60℃ for 24 h to obtain citric acid modified nanocellulose.

[0068] Comparative Example 1

[0069] Compared with Example 1, this comparative example omits step S1 and replaces "carboxymethylated chitosan" in S2 with an equal mass of "chitosan"; the remaining steps and parameters are the same, and will not be repeated in this comparative example. The final result is a biodegradable antibacterial food packaging bag.

[0070] Comparative Example 2

[0071] Compared with Example 1, this comparative example omits step S2 and replaces "carboxymethyl chitosan graft copolymer" in S3 with an equal mass of "carboxymethylated chitosan". The remaining steps and parameters are the same, and will not be repeated in this comparative example. The final result is a biodegradable antibacterial food packaging bag.

[0072] Comparative Example 3

[0073] Compared with Example 1, this comparative example omits step S3 and replaces the "modified chitosan microcapsules" in S4 with an equal mass of "carboxymethyl chitosan graft copolymer"; the remaining steps and parameters are the same, and will not be repeated in this comparative example. Finally, a biodegradable antibacterial food packaging bag is obtained.

[0074] Comparative Example 4

[0075] Compared with Example 1, the "citric acid modified nanocellulose" in S4 was replaced with an equal mass of "nanocellulose"; the remaining steps and parameters were the same, and will not be repeated in this comparative example. Finally, a biodegradable antibacterial food packaging bag was obtained.

[0076] Comparative Example 5

[0077] Compared with Example 1, the "citric acid modified nanocellulose" in S4 was replaced with an equal mass of "modified chitosan microcapsules"; the remaining steps and parameters were the same, and will not be repeated in this comparative example. Finally, a biodegradable antibacterial food packaging bag was obtained.

[0078] Comparative Example 6

[0079] Compared with Example 1, the "modified chitosan microcapsules" in S4 were replaced with an equal mass of "citric acid modified nanocellulose"; the remaining steps and parameters were the same, and will not be repeated in this comparative example. Finally, a biodegradable antibacterial food packaging bag was obtained.

[0080] The performance of the biodegradable antibacterial food packaging bags prepared in Examples 1-3 and the biodegradable antibacterial food packaging bags prepared in Comparative Examples 1-6 was tested, and the results are recorded in Table 1.

[0081] Mechanical property testing: Referring to GB / T 1040.1-2018, the tensile properties of biodegradable antibacterial food packaging bag samples were tested using a universal tensile testing machine. Before the test, the packaging bag samples were cut into dumbbell-shaped specimens and placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours for conditioning. The tensile speed was set to 50 mm / min, and the tensile strength and elongation at break of the specimens were measured. Referring to GB / T 1843-2008, the impact strength was tested using an electronic impact testing machine. Before the test, the specimens were conditioned under the same environmental conditions, and the impact strength of the specimens was measured to evaluate the mechanical properties of the packaging bags.

[0082] Biodegradability testing: Biodegradable antibacterial food packaging bag samples were buried in the experimental field at a depth of about 15 cm and naturally buried for 3 months under shaded conditions. During the burial period, the soil moisture was maintained at 60%-70% of field capacity. After the burial period, the packaging bag samples were taken out, the surface soil was gently rinsed with deionized water, and the samples were allowed to dry naturally at room temperature. The degree of degradation of the packaging bag samples was evaluated by weighing, and the mass loss rate of the packaging bag samples was recorded to determine the biodegradability of the samples.

[0083] Antibacterial performance testing: Referring to QB / T 2591-2003 standard, *Escherichia coli* (ATCC 8739) and *Staphylococcus aureus* (ATCC 6538) were used as test bacteria. The packaging bag samples were cut into 50mm × 50mm specimens, and 0.2 mL of a 1×10⁻⁶ solution was added to the surface. 6 A bacterial suspension of CFU / mL was covered with a polyethylene film and incubated at 35°C and 90% relative humidity for 24 hours. The suspension was then washed with phosphate buffer, viable bacteria were counted, and the inhibition rate was calculated.

[0084] Antibacterial durability test: At room temperature, the packaging bag sample was soaked in sterile deionized water for 30 days (the water was changed every 3 days). After being taken out and dried, its antibacterial rate was determined again according to the above antibacterial performance test method.

[0085] Table 1: Detection data of biodegradable antibacterial food packaging bags

[0086]

[0087] According to the data shown in Table 1, the biodegradable antibacterial food packaging bags prepared in Examples 1-3 of the present invention exhibit excellent comprehensive performance in terms of tensile strength, elongation at break, impact strength, mass loss rate, and antibacterial properties, which are significantly better than those in Comparative Examples 1-6.

[0088] Data from Example 1 and Comparative Example 1 show that in Comparative Example 1, "carboxymethylated chitosan" was replaced with "chitosan" in step S2. Because chitosan has poor solubility in isopropanol and water, it cannot effectively undergo carboxymethylation, leading to difficulties in subsequent graft copolymerization and the formation of stable carboxymethyl chitosan graft copolymers. This, in turn, affects the formation of modified chitosan microcapsules and the encapsulation efficiency of ε-polylysine. Furthermore, the compatibility of chitosan with polylactic acid and polybutylene terephthalate (PET) matrices is much lower than that of carboxymethylated chitosan, resulting in uneven dispersion of the filler in the matrix and weak interfacial bonding. Therefore, the mechanical properties, degradation properties, and antibacterial durability of Comparative Example 1 are significantly lower than those of Example 1.

[0089] Data from Example 1 and Comparative Example 2 show that in Comparative Example 2, "carboxymethyl chitosan graft copolymer" was replaced with "carboxymethylated chitosan" in step S3, meaning that N-isopropylacrylamide graft copolymerization was not performed. Without the grafted segments, although the carboxymethylated chitosan could still form microcapsules through ionic crosslinking, the wall structure lacked density and the encapsulation stability was poor, resulting in a low ε-polylysine encapsulation rate and a greater likelihood of premature leakage during processing and storage. Therefore, the initial antibacterial performance of Comparative Example 2 decreased, and its antibacterial durability was significantly inferior to that of Example 1. Simultaneously, the mechanical properties were also reduced due to insufficient microcapsule integrity.

[0090] As shown by the data from Example 1 and Comparative Example 3, in step S4 of Comparative Example 3, the "modified chitosan microcapsules" were replaced with "carboxymethyl chitosan graft copolymer," thus completely omitting the microencapsulation step. The carboxymethyl chitosan graft copolymer was directly blended with ε-polylysine and the matrix. The ε-polylysine was not effectively encapsulated and was largely lost through volatilization during melt blending and blow molding. Simultaneously, it was unevenly dispersed in the polylactic acid and polybutylene terephthalate (PET) matrices, easily leading to phase separation and the formation of internal defects and stress concentration points. Therefore, Comparative Example 3 exhibited the worst mechanical properties among all samples, and its antibacterial durability decreased sharply due to the rapid loss of ε-polylysine. Only its initial antibacterial performance was slightly higher than that of Comparative Example 1 and Comparative Example 2 due to the residual ε-polylysine.

[0091] As shown by the data from Example 1 and Comparative Example 4, in step S4 of Comparative Example 4, "citric acid-modified nanocellulose" was replaced with unmodified "nanocellulose". Unmodified nanocellulose has a surface rich in hydroxyl groups, exhibiting strong hydrophilicity. However, it has poor compatibility with the hydrophobic polylactic acid and polybutylene terephthalate (PET) matrices, making it prone to agglomeration during melt blending and hindering uniform dispersion, thus weakening the reinforcing effect. Therefore, the mechanical properties of Comparative Example 4 are slightly lower than those of Example 1. However, due to the intact preservation of the microcapsule structure, the antibacterial properties and antibacterial durability are only slightly affected.

[0092] As shown in the data from Example 1 and Comparative Example 5, this comparative example only added modified chitosan microcapsules and did not add citric acid-modified nanocellulose. Compared with Example 1, its mechanical properties decreased significantly, with tensile strength, elongation at break, and impact strength all significantly lower than those of Example 1. This is because the rigid reinforcing network formed by citric acid-modified nanocellulose was lacking, and the microcapsules alone, as a flexible dispersed phase, could not provide sufficient stress transfer and structural support. However, due to the intact microcapsule structure, the encapsulation and sustained-release effect of the antibacterial agent ε-polylysine remained good, so its initial and sustained antibacterial properties were basically equivalent to those of Example 1. In terms of degradation performance, due to the lack of the hydrophilic interface of nanocellulose, the mass loss rate was slightly lower than that of Example 1, but it still exhibited good biodegradability.

[0093] Data from Example 1 and Comparative Example 6 show that the comparative example only added citric acid-modified nanocellulose, completely omitting modified chitosan microcapsules. Its mechanical properties were also significantly lower than those of Example 1. Although citric acid modification improved the compatibility of nanocellulose with the matrix and formed a reinforcing network, the lack of microcapsules as a flexible dispersed phase for stress transfer and energy dissipation resulted in limited improvement in toughness. Because the microcapsules were completely replaced, ε-polylysine was not introduced into the system, thus reducing the antibacterial ability of the packaging bag, with both initial and sustained antibacterial rates significantly lower. Degradation performance was similar to Comparative Example 5, slightly lower than Example 1. These results conversely demonstrate that modified chitosan microcapsules are the only effective carrier for the antibacterial agent, and also highlight the synergistic effect of the two in terms of mechanical properties.

[0094] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable antibacterial food packaging bag, characterized in that, The preparation steps include the following: S1: Add chitosan to isopropanol, stir to swell, add sodium hydroxide solution and continue stirring, add isopropanol chloroacetate dropwise, heat and stir, after the reaction is complete, filter, wash and dry to obtain carboxymethyl chitosan; S2: Add carboxymethyl chitosan to deionized water and stir until completely dissolved. Add N-isopropylacrylamide and stir evenly. Add ammonium persulfate and tetramethylethylenediamine. Heat the mixture under inert gas protection and react. After the reaction is complete, pour the reaction solution into acetone to precipitate. Filter, wash and dry to obtain carboxymethyl chitosan graft copolymer. S3: Add carboxymethyl chitosan graft copolymer to deionized water, heat and stir, add ε-polylysine and emulsifier, stir to emulsify, then add sodium tripolyphosphate aqueous solution dropwise, continue stirring, centrifuge, wash and dry to obtain modified chitosan microcapsules; S4: Mix modified chitosan microcapsules with citric acid-modified nanocellulose, stir evenly, add polylactic acid, polybutylene terephthalate-adipate and POE-g-GMA, and continue stirring evenly to obtain a mixture; add the mixture to a twin-screw extruder for melt blending, extrusion granulation, cooling, air drying and pelletizing to obtain antibacterial masterbatch; blow mold the antibacterial masterbatch, draw and wind it to obtain a biodegradable antibacterial food packaging bag.

2. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The method for preparing the citric acid-modified nanocellulose is as follows: Nanocellulose was added to deionized water and ultrasonically dispersed to obtain a nanocellulose suspension. Citric acid and sodium hypophosphite were added, and the pH of the system was adjusted to 3.5-4.5 with glacial acetic acid. The mixture was stirred and reacted in a water bath at 65℃-75℃ for 2-4 hours. After the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain citric acid-modified nanocellulose.

3. The method for preparing a biodegradable antibacterial food packaging bag according to claim 2, characterized in that, The raw materials for the citric acid-modified nanocellulose are as follows by weight: 2-5 parts nanocellulose, 120-150 parts deionized water, 1.2-2 parts citric acid, and 0.1-0.2 parts sodium hypophosphite.

4. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The raw materials in S1 are as follows by weight: 10-20 parts chitosan, 120-200 parts isopropanol, 15-35 parts sodium hydroxide solution, and 12-30 parts isopropanol chloroacetic acid solution.

5. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The raw materials in S2 are as follows by weight: 5-15 parts carboxymethylated chitosan, 200-300 parts deionized water, 3-10 parts N-isopropylacrylamide, 0.5-1.2 parts ammonium persulfate, and 0.2-0.6 parts tetramethylethylenediamine.

6. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The raw materials in S3 are as follows by weight: 3-10 parts of carboxymethyl chitosan graft copolymer, 120-300 parts of deionized water, 60-150 parts of sodium tripolyphosphate aqueous solution, 2-5 parts of ε-polylysine, and 0.5-3 parts of emulsifier.

7. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The raw materials in S4 are as follows by weight: 2-8 parts modified chitosan microcapsules, 2-5 parts citric acid modified nanocellulose, 50-80 parts polylactic acid, 20-50 parts polybutylene terephthalate-adipate, and 4-8 parts POE-g-GMA.

8. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The melt blending conditions in S4 are as follows: the temperature of the first zone of the twin-screw extruder is 150-160℃, the temperature of the second zone is 160-170℃, the temperature of the third zone is 170-180℃, the temperature of the fourth zone is 165-175℃, the die head temperature is 160-170℃, and the screw speed is 100-200 r / min.

9. The method for preparing a biodegradable antibacterial food packaging bag according to claim 1, characterized in that, The conditions for blow molding in S4 are: blown film temperature of 150-170℃, blow-up ratio of 2.0-3.5, and traction speed of 5-15m / min.

10. A biodegradable antibacterial food packaging bag prepared by the method of any one of claims 1-9.

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