A modified bamboo fiber fully biodegradable material, its preparation method, and its application in food preservation.

Abstract

This invention belongs to the field of polymer materials technology and discloses a modified bamboo fiber fully biodegradable material. Using PBAT, PLA, modified bamboo powder, plasticizer, and composite antibacterial agent as raw materials, the preparation steps include: S1: Alkali treatment modification and silane coupling agent modification of bamboo powder; S2: Preparation of composite antibacterial agent using a solid-phase reaction method; S3: Thorough stirring of the predetermined amounts of each component; S4: High-temperature melt extrusion of the mixed raw materials, followed by cooling and pelletizing; S5: High-temperature casting of the pellets to obtain sheets; S6: Sheets formed by vacuum forming. In this modified bamboo fiber fully biodegradable material, the addition of modified bamboo powder not only effectively improves the mechanical properties of food packaging but also reduces the production cost of biodegradable food packaging and accelerates the degradation rate. The addition of the composite antibacterial agent endows the food packaging with excellent antibacterial properties, which helps to slow down the metabolic process of lychee, thereby significantly reducing the weight loss and decay rate of lychee during storage and effectively extending the shelf life of lychee. It can also be applied to the preservation and storage of other fruits, demonstrating wide applicability.

Description

Technical Field

[0001] This invention relates to a modified bamboo fiber fully biodegradable material, its preparation method, and its application in food preservation, belonging to the field of polymer materials technology. Background Technology

[0002] In recent years, to adapt to a fast-paced lifestyle, disposable foam plastic lunch boxes, food storage bags, and food containers have brought numerous conveniences. Currently, the most common methods for disposing of these packaging materials are incineration and landfill, which will cause irreversible environmental pollution in the long run. Therefore, developing safer, more biodegradable, and easier-to-preserve new packaging materials is an important way to reduce plastic pollution, and using biodegradable materials to replace traditional plastics is a major approach to solving the plastic pollution problem.

[0003] To further promote the comprehensive management of plastic pollution, China, together with the International Bamboo and Rattan Organisation (INBAR), has launched the "Bamboo for Plastic" initiative to implement global development initiatives, providing an effective solution for reducing plastic pollution. In response to the call for "Bamboo for Plastic" and to fully utilize biomass energy, natural bamboo powder has come into the research field. Its main components are cellulose, lignin, and hemicellulose, with cellulose accounting for the largest proportion. Natural fiber / polymer composites prepared using natural plant fibers as fillers or reinforcements and polymers as the matrix have many advantages, such as good mechanical properties and strong processability. However, bamboo fibers contain a large number of hydroxyl and carboxyl groups, giving them strong polarity, which leads to poor interfacial bonding between natural plant fibers and the plastic matrix. Therefore, bamboo powder needs to be modified. High-value resource utilization through modification is of great significance for biomass refining and environmental protection.

[0004] Polylactic acid (PLA) is a non-toxic and non-irritating synthetic polymer material. Its raw materials mainly come from fermented products such as starch. After use, it can be directly composted or incinerated, and can eventually be completely decomposed into CO2 and H2O, with minimal impact on the environment, meeting the requirements of sustainable development. At the same time, its biodegradability and thermoplasticity have made it a focus of attention in the packaging materials industry. Despite these advantages, PLA's brittleness, poor impact resistance, low heat distortion temperature, and poor heat resistance severely limit its large-scale application in plastic packaging bags.

[0005] Antimicrobial packaging for food combines packaging materials with antimicrobial and preservative materials to improve food shelf life and safety. However, the limitations of ordinary antimicrobial materials are becoming increasingly apparent, making the development of novel antimicrobial materials urgent. Pyridine quaternary ammonium salts possess excellent antimicrobial properties and, as a good hydrogen bond acceptor, can coordinate with metal halides to form organic-inorganic hybrid materials with excellent catalytic, antimicrobial, magnetic, and optical properties. Summary of the Invention

[0006] To address the above problems, this invention provides a modified bamboo fiber fully biodegradable material. By modifying bamboo fiber, the toughness of PLA material is improved, and by using a composite antibacterial agent, the antibacterial and preservation properties of the material are enhanced, thus preparing a food packaging material that is fully biodegradable and has antibacterial properties.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A modified bamboo fiber fully biodegradable material, the raw materials of which mainly include the following components in parts by weight: 30-65 parts of polylactic acid, 30-50 parts of polybutylene terephthalate-adipate, 5-15 parts of modified bamboo powder, 2-6 parts of plasticizer and 1-5 parts of composite antibacterial agent.

[0009] Preferably, the modified bamboo powder is prepared by the following steps: bamboo powder is placed in an alkaline solution and stirred at 300-600 rpm for 4-6 hours under a water bath at 50-60℃. After the reaction is completed, the mixture is cooled to room temperature, and after solid-liquid separation, it is repeatedly washed with water until neutral. It is then dried at 40-60℃ for 24-36 hours. The alkali-treated bamboo powder is then placed in an ethanol solution of silane coupling agent and stirred at 300-800 rpm for 2-4 hours under a water bath at 30-50℃. It is then dried at 40-60℃ for 12-24 hours, pulverized, and sieved to obtain the modified bamboo powder.

[0010] Preferably, the mass ratio of bamboo powder to alkaline solution is 1:12-18; the mass ratio of alkali-treated bamboo powder to ethanol solution of silane coupling agent is 1:5-8.

[0011] More preferably, the modified bamboo powder has a particle size of 300-800 mesh. The alkaline solution is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 3-8 wt%; the silane coupling agent is KH550 with a molecular weight of 200-300 g / mol. The concentration of the silane coupling agent in the silane coupling agent solution is 5-15 wt%.

[0012] Preferably, the composite antibacterial agent is prepared by the following steps:

[0013] (1) Weigh a certain amount of 4-methylpyridine and 1,3-dibromopropane into a container, add an appropriate amount of acetone to dissolve, stir and reflux at 65-70 °C for 24-36 h; after the reaction, pour it into a container while hot, remove the upper liquid with a dropper, add an appropriate amount of acetone to wash, let stand to separate the layers, remove the upper liquid, repeat the operation several times; then add an appropriate amount of ether to wash, let stand to separate the layers, remove the upper liquid, repeat the operation several times; after evaporating naturally in the dark, put it into a vacuum drying oven at 65-75 °C for 12-24 h to obtain white powder [4MePy-(CH2)3-4MePy]Br2;

[0014] (2) Take a certain amount of [4MePy-(CH2)3-4MePy]Br2 and manganese chloride tetrahydrate in a container, add an appropriate amount of methanol to dissolve, and add an appropriate amount of concentrated hydrochloric acid. Stir and reflux at 80-90 ℃ for 2-4 h. After the reaction, pour it into a container while it is hot, let it stand and cool, and let it evaporate naturally to obtain light yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which is the composite antibacterial agent.

[0015] More preferably, the molar ratio between 1,3-dibromopropane and 4-methylpyridine in step (1) is 1:(2-4).

[0016] More preferably, the molar ratio of the [4MePy-(CH2)3-4MePy]Br2 quaternary ammonium salt and manganese chloride tetrahydrate in step (2) is 1:(0.8-1.2).

[0017] The preparation method of the above-mentioned modified bamboo fiber fully biodegradable material includes the following steps:

[0018] (1) The polylactic acid, polybutylene terephthalate, modified bamboo powder, plasticizer, and composite antibacterial agent are put into a mixer and stirred at 40-80 rpm for 10-20 minutes. The uniformly mixed material is then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder is controlled sequentially as follows: Zone 1 158-163℃, Zone 2 163-167℃, Zone 3 167-170℃, Zone 4 170-175℃, and Zone 5 168-173℃. After extrusion, the material is rapidly cooled to room temperature for granulation and then dried to obtain composite granules.

[0019] Preferably, the plasticizer is epoxidized soybean oil with a molecular weight of 800-1100 g / mol.

[0020] Preferably, the polylactic acid has a melting point of 140-180℃, a melt index of 5-25g / 10min, and a heat distortion temperature of 50-70℃.

[0021] (2) The dried composite granules are fed into the casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1 160-163℃, Zone 2 163-166℃, Zone 3 166-172℃, Zone 4 172-175℃, Zone 5 175-178℃. After casting, a sheet is obtained. The sheet is then thermoformed to obtain a modified bamboo fiber fully biodegradable material for use in food antibacterial packaging.

[0022] Compared with the prior art, the present invention achieves the following beneficial effects:

[0023] 1. This invention uses bamboo powder as one of the raw materials, which can effectively improve the utilization rate of agricultural and forestry waste and greatly reduce the manufacturing cost of biodegradable food packaging;

[0024] 2. This invention modifies bamboo powder using sodium hydroxide and a silane coupling agent. Alkali treatment effectively removes impurities such as lignin, pectin, and hemicellulose from the bamboo powder surface while retaining cellulose, increasing the surface roughness of the fibers. This increases the contact area between the bamboo powder and the polylactic acid (PLA) matrix, improving the interfacial compatibility. However, it does not form chemical bonds between the bamboo powder and PLA. The silanol generated from the hydrolysis of the coupling agent reacts with the hydroxyl groups on the bamboo powder surface, and its epoxy functional groups react with the terminal hydroxyl and carboxyl groups of the PLA chains, acting as a bridge between the bamboo powder and the PLA matrix. Therefore, the interfacial compatibility between bamboo powder and PLA is significantly improved.

[0025] 3. This invention provides a composite antibacterial agent—manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which has high yield, saves costs, is easy to operate, and is conducive to industrial development. Compared with Cu-based metal complexes, the Mn-based metal complex of this invention is more environmentally friendly. When added to the biodegradable packaging material of this invention, it can endow the packaging material with excellent antibacterial properties. Attached Figure Description

[0026] Figure 1 The diagram shows the antibacterial effects of Example 1 and Comparative Example 2 against Staphylococcus aureus and Escherichia coli.

[0027] Figure 2 This is a schematic diagram of the appearance of the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2 for the preservation of lychees.

[0028] Figure 3 The weight loss rate of the packaging prepared in Example 1, Comparative Example 1, and Comparative Example 2 for lychee preservation test;

[0029] Figure 4 The hardness of the packaging prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested in the preservation of lychees.

[0030] Figure 5 The soluble solids from the packaging prepared in Example 1, Comparative Example 1, and Comparative Example 2 for the preservation of lychees;

[0031] Figure 6 Titratable acidity of the packaging prepared for Example 1, Comparative Example 1 and Comparative Example 2 for lychee preservation test;

[0032] Figure 7-10 The color evaluation of the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2 for lychee preservation test;

[0033] Figure 11Crystal structure diagram of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4] (hydrogen atoms omitted);

[0034] Figure 12 The mass spectrum of the compound antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4] is shown.

[0035] Figure 13 X-ray diffraction pattern of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4];

[0036] Figure 14 The infrared spectrum of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4]. Detailed Implementation

[0037] The following describes embodiments of the present invention. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0038] Example 1: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps:

[0039] Step 1: Preparation of modified bamboo powder

[0040] Bamboo powder was added to an alkaline solution at a mass ratio of 1:15. The mixture was stirred at 300 r / min for 4 hours in a constant temperature 60℃ water bath. After the reaction was completed, the mixture was cooled to room temperature. After solid-liquid separation, the mixture was repeatedly washed with deionized water until neutral. The mixture was then dried at 60℃ for 36 hours to obtain alkali-treated bamboo powder. The alkali-treated bamboo powder was then added to a silane coupling agent ethanol solution at a mass ratio of 1:6. The mixture was stirred at 300 r / min for 2 hours in a constant temperature 50℃ water bath. The mixture was then dried at 60℃ for 24 hours. The mixture was then pulverized in a pulverizer and sieved to obtain the final modified bamboo powder.

[0041] The modified bamboo powder has a particle size of 500 mesh;

[0042] The alkaline solution is an aqueous solution of sodium hydroxide with a concentration of 3 wt%.

[0043] The silane coupling agent is KH550 with a molecular weight of 221.7 g / mol;

[0044] The silane coupling agent ethanol solution has a silane coupling agent concentration of 15 wt%.

[0045] Step 2: Preparation of the compound antibacterial agent

[0046] (1) Weigh 2.79 g (0.03 mol) of 4-methylpyridine and 3.03 g (0.015 mol) of 1,3-dibromopropane into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65-70 °C for 24 h; after the reaction, pour the mixture into a beaker while hot, remove the upper liquid with a dropper, add a small amount of acetone to wash, let stand to separate the layers, remove the upper liquid, and repeat the operation 3 times; wash with ether 3 times in the same manner as above, let it evaporate naturally in the dark, and then put it into a vacuum drying oven at 70 °C for 12 h to obtain a white powder [4MePy-(CH2)3-4MePy]Br2.

[0047] (2) Take 10 mmol of [4MePy-(CH2)3-4MePy]Br2 and 10 mmol of manganese chloride tetrahydrate into an Erlenmeyer flask, add 20 mL of methanol to dissolve, add 1 mL of concentrated hydrochloric acid (12 mol / L), stir and reflux at 80-90 °C for 2 h; after the reaction, pour it into a beaker while hot, heat to concentrate, and let it stand to cool; seal with plastic wrap, poke a hole with a syringe, put it under a fume hood, and obtain crystals in about five days, finally obtaining light yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4].

[0048] The molar ratio between bromopropane and pyridine is 1:2;

[0049] The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0050] Step 3: Melt blending

[0051] Polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer, and composite antibacterial agent were added to a mixer in a mass ratio of 43:35:15:4:3. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: zone 1 160℃, zone 2 163℃, zone 3 170℃, zone 4 172℃, and zone 5 168℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 60℃.

[0052] The plasticizer is epoxidized soybean oil;

[0053] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0054] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0055] Step 4: Casting and vacuum forming

[0056] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1: 163℃, Zone 2: 165℃, Zone 3: 170℃, Zone 4: 175℃, and Zone 5: 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0057] Example 2: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps:

[0058] Step 1: Preparation of modified bamboo powder

[0059] Bamboo powder was added to an alkaline solution at a mass ratio of 1:15. The mixture was stirred at 500 r / min for 4 hours under a constant temperature of 50℃ water bath. After the reaction was completed, the mixture was cooled to room temperature and washed repeatedly with deionized water until neutral. The mixture was then dried at 50℃ for 24 hours to obtain alkali-treated bamboo powder. The alkali-treated bamboo powder was then added to a silane coupling agent ethanol solution at a mass ratio of 1:6. The mixture was stirred at 500 r / min for 3 hours under a constant temperature of 50℃ water bath. The mixture was then dried at 60℃ for 18 hours and pulverized in a pulverizer. Finally, it was sieved to obtain the final modified bamboo powder.

[0060] The modified bamboo powder has a particle size of 300 mesh;

[0061] The alkaline solution is an aqueous solution of sodium hydroxide with a sodium hydroxide concentration of 4 wt%.

[0062] The silane coupling agent is KH550 with a molecular weight of 221.7 g / mol;

[0063] The silane coupling agent ethanol solution has a silane coupling agent concentration of 10 wt%.

[0064] Step 2: Preparation of the compound antibacterial agent

[0065] (1) Preparation of quaternary ammonium salt [4MePy-(CH2)3-4MePy]Br2: Weigh 2.79 g (0.03 mol) of 4-methylpyridine and 3.03 g (0.015 mol) of 1,3-dibromopropane into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70 °C for 24 h; after the reaction, pour the solution into a beaker while hot, remove the upper liquid with a dropper, add a small amount of acetone to wash, let stand to separate the layers, remove the upper liquid, repeat the operation 3 times; wash with ether 3 times in the same way as above, evaporate naturally in the dark, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain white powder [4MePy-(CH2)3-4MePy]Br2.

[0066] (2) Preparation of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4]: 10 mmol of [4MePy-(CH2)3-4MePy]Br2 and 10 mmol of manganese chloride tetrahydrate were placed in an Erlenmeyer flask, dissolved in 20 mL of methanol, and 1 mL of concentrated hydrochloric acid (12 mol / L) was added. The mixture was stirred and refluxed at 80~90 °C for 2 h. After the reaction, the mixture was poured into a beaker while hot, heated to concentrate, and allowed to cool. The beaker was sealed with plastic wrap, punctured with a syringe, and placed under a fume hood. Crystals were obtained after about five days. Finally, pale yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4] were obtained.

[0067] The molar ratio between bromopropane and pyridine is 1:2;

[0068] The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0069] Step 3: Melt blending

[0070] Polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer, and composite antibacterial agent were added to a mixer in a mass ratio of 41:40:10:4:5. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: zone 1 158℃, zone 2 160℃, zone 3 170℃, zone 4 172℃, and zone 5 168℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 50℃.

[0071] The plasticizer is epoxidized soybean oil;

[0072] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0073] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0074] Step 4: Casting and vacuum forming

[0075] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1 160℃, Zone 2 165℃, Zone 3 168℃, Zone 4 173℃, and Zone 5 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0076] Example 3: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps:

[0077] Step 1: Preparation of modified bamboo powder

[0078] Bamboo powder was added to an alkaline solution at a mass ratio of 1:15. The mixture was stirred at 700 r / min in a water bath at a constant temperature of 40℃ for 5 hours. After the reaction was completed, the mixture was cooled to room temperature and washed repeatedly with deionized water until neutral. The mixture was then dried at 55℃ for 24 hours to obtain alkali-treated bamboo powder. The alkali-treated bamboo powder was then added to a silane coupling agent ethanol solution at a mass ratio of 1:6. The mixture was stirred at 600 r / min in a water bath at a constant temperature of 40℃ for 4 hours. The mixture was then dried at 50℃ for 24 hours and pulverized in a pulverizer. Finally, it was sieved to obtain the final modified bamboo powder.

[0079] The modified bamboo powder has a particle size of 600 mesh;

[0080] The alkaline solution is an aqueous solution of sodium hydroxide with a sodium hydroxide concentration of 5 wt%.

[0081] The silane coupling agent is KH550 with a molecular weight of 221.7 g / mol;

[0082] The silane coupling agent ethanol solution has a silane coupling agent concentration of 8 wt%.

[0083] Step 2: Preparation of the compound antibacterial agent

[0084] (1) Preparation of quaternary ammonium salt [4MePy-(CH2)3-4MePy]Br2: Weigh 2.79 g (0.03 mol) of 4-methylpyridine and 3.03 g (0.015 mol) of 1,3-dibromopropane into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70 °C for 24 h; after the reaction, pour the solution into a beaker while hot, remove the upper liquid with a dropper, add a small amount of acetone to wash, let stand to separate the layers, remove the upper liquid, repeat the operation 3 times; wash with ether 3 times in the same way as above, evaporate naturally in the dark, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain white powder [4MePy-(CH2)3-4MePy]Br2.

[0085] (2) Preparation of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4]: 10 mmol of [4MePy-(CH2)3-4MePy]Br2 and 10 mmol of manganese chloride tetrahydrate were placed in an Erlenmeyer flask, dissolved in 20 mL of methanol, and 1 mL of concentrated hydrochloric acid (12 mol / L) was added. The mixture was stirred and refluxed at 80~90 °C for 2 h. After the reaction, the mixture was poured into a beaker while hot, heated to concentrate, and allowed to cool. The beaker was sealed with plastic wrap, punctured with a syringe, and placed under a fume hood. Crystals were obtained after about five days. Finally, pale yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4] were obtained.

[0086] The molar ratio between bromopropane and pyridine is 1:2;

[0087] The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0088] Step 3: Melt blending

[0089] Polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer, and composite antibacterial agent were added to a mixer in a mass ratio of 49:40:5:5:1. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: Zone 1 160℃, Zone 2 162℃, Zone 3 170℃, Zone 4 175℃, and Zone 5 172℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 50℃.

[0090] The plasticizer is epoxidized soybean oil;

[0091] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0092] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0093] Step 4: Casting and vacuum forming

[0094] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1 165℃, Zone 2 168℃, Zone 3 170℃, Zone 4 174℃, and Zone 5 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0095] Comparative Example 1: Based on Example 1, the preparation and use of modified bamboo powder and composite antibacterial agent in the example were removed, that is, the amount of modified bamboo powder and composite antibacterial agent added was zero, and they were replaced with an equal amount of polylactic acid, and the rest was the same as in Example 1.

[0096] Step 1: Melt blending

[0097] Polylactic acid, polybutylene terephthalate-adipate resin, and plasticizer were added to a mixer at a mass ratio of 61:35:4. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: zone 1 160℃, zone 2 163℃, zone 3 170℃, zone 4 172℃, and zone 5 168℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 60℃.

[0098] The plasticizer is epoxidized soybean oil;

[0099] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0100] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0101] Step 2, Casting and Vacuum Forming

[0102] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1: 163℃, Zone 2: 165℃, Zone 3: 170℃, Zone 4: 175℃, and Zone 5: 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0103] Comparative Example 2:

[0104] Based on Example 1, the preparation and use of the composite antibacterial agent in the example are removed, that is, the amount of composite antibacterial agent added is zero, and it is replaced with an equal amount of polylactic acid, and the rest is the same as in Example 1.

[0105] Step 1: Preparation of modified bamboo powder

[0106] Bamboo powder was placed in an alkaline solution and stirred at 300 r / min for 4 hours under a constant temperature 60℃ water bath. After the reaction was completed, the mixture was cooled to room temperature and washed repeatedly with deionized water until neutral. It was then dried at 60℃ for 36 hours to obtain alkali-treated bamboo powder. The alkali-treated bamboo powder was then placed in a silane coupling agent ethanol solution and stirred at 300 r / min for 2 hours under a constant temperature 50℃ water bath. It was then dried at 60℃ for 24 hours, pulverized in a pulverizer, and then sieved to obtain the final modified bamboo powder.

[0107] The modified bamboo powder has a particle size of 500 mesh;

[0108] The alkaline solution is an aqueous solution of sodium hydroxide with a concentration of 3 wt%.

[0109] The silane coupling agent is KH550 with a molecular weight of 221.7 g / mol;

[0110] The silane coupling agent ethanol solution has a silane coupling agent concentration of 15 wt%.

[0111] Step 2, melt blending

[0112] Polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, and plasticizer were added to a mixer in a mass ratio of 46:35:15:4. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: Zone 1 160℃, Zone 2 163℃, Zone 3 170℃, Zone 4 172℃, and Zone 5 168℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 60℃.

[0113] The plasticizer is epoxidized soybean oil;

[0114] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0115] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0116] Step 3, Casting and Vacuum Forming

[0117] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1: 163℃, Zone 2: 165℃, Zone 3: 170℃, Zone 4: 175℃, and Zone 5: 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0118] Comparative Example 3:

[0119] Based on Example 1, the bamboo powder was not modified, but 15 parts of modified bamboo powder were replaced with an equal amount of bamboo powder, and the rest was the same as in Example 1.

[0120] Step 1: Preparation of bamboo powder

[0121] Bamboo powder is put into a grinder and ground, and then sieved to obtain the ground bamboo powder.

[0122] The bamboo powder has a particle size of 500 mesh;

[0123] Step 2: Preparation of the compound antibacterial agent

[0124] (1) Preparation of quaternary ammonium salt [4MePy-(CH2)3-4MePy]Br2: Weigh 2.79 g (0.03 mol) of 4-methylpyridine and 3.03 g (0.015 mol) of 1,3-dibromopropane into a 100 mL ground glass conical flask, add 30 mL of acetone to dissolve, stir and reflux at 65~70 °C for 24 h; after the reaction, pour the solution into a beaker while hot, remove the upper liquid with a dropper, add a small amount of acetone to wash, let stand to separate the layers, remove the upper liquid, repeat the operation 3 times; wash with ether 3 times in the same way as above, evaporate naturally in the dark, and then dry in a vacuum drying oven at 70 °C for 12 h to obtain white powder [4MePy-(CH2)3-4MePy]Br2.

[0125] (2) Preparation of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4]: 10 mmol of [4MePy-(CH2)3-4MePy]Br2 and 10 mmol of manganese chloride tetrahydrate were placed in an Erlenmeyer flask, dissolved in 20 mL of methanol, and 1 mL of concentrated hydrochloric acid (12 mol / L) was added. The mixture was stirred and refluxed at 80~90 °C for 2 h. After the reaction, the mixture was poured into a beaker while hot, heated to concentrate, and allowed to cool. The beaker was sealed with plastic wrap, punctured with a syringe, and placed under a fume hood. Crystals were obtained after about five days. Finally, pale yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4] were obtained.

[0126] The molar ratio between bromopropane and pyridine is 1:2;

[0127] The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0128] Step 3: Melt blending

[0129] Polylactic acid, polybutylene terephthalate-adipate resin, bamboo powder, plasticizer, and composite antibacterial agent were added to a mixer in a mass ratio of 43:35:15:4:3. The mixing speed was 60 r / min, and the mixture was stirred for 15 min. The uniformly mixed material was then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder was controlled sequentially as follows: Zone 1 160℃, Zone 2 163℃, Zone 3 170℃, Zone 4 172℃, and Zone 5 168℃. After extrusion, the material was rapidly cooled to room temperature and granulated. The resulting granules were composite granules, which were then dried at 60℃.

[0130] The plasticizer is epoxidized soybean oil;

[0131] The epoxidized soybean oil has a molecular weight of 975.399 g / mol;

[0132] The polylactic acid has a melting point of 176°C, a melt index of 21 g / 10 min, and a heat distortion temperature of 65°C.

[0133] Step 4: Casting and vacuum forming

[0134] The dried composite granules are fed into a casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1: 163℃, Zone 2: 165℃, Zone 3: 170℃, Zone 4: 175℃, and Zone 5: 178℃. After casting, a sheet is obtained. The sheet is then thermoformed to finally obtain biodegradable antibacterial food packaging.

[0135] Comparative Example 4:

[0136] Based on Example 1, 3 parts of the compound antibacterial agent were replaced with an equal amount of 3 parts of antibacterial agent ZnO, and the rest were the same as in Example 1.

[0137] Performance testing: The biodegradable materials prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 were tested for tensile strength, elongation at break and antibacterial rate. The specific results are shown in the table below.

[0138] Table 1 Test data for each embodiment and comparative example

[0139]

[0140] As shown in Table 1, Comparative Example 1, without the addition of bamboo powder and antibacterial agent, exhibited the lowest tensile strength and the worst antibacterial effect. This indicates that simply using polylactic acid and polybutylene terephthalate (PET) resin to form a composite material severely impacts the various properties of the final product. Comparative Example 2, without the addition of antibacterial agent, showed better tensile strength and antibacterial properties than Comparative Example 1. This suggests that adding modified bamboo powder can improve tensile strength and slightly enhance antibacterial properties, but the difference compared to the three examples is still significant. In Comparative Example 3, without preparing modified bamboo powder, bamboo powder was directly added, resulting in the lowest elongation at break and lower tensile strength compared to the three examples and Comparative Example 2. This indicates that unmodified bamboo powder has particularly poor compatibility with polylactic acid, severely affecting the overall performance of polylactic acid. The tensile strength of Examples 1-3 was higher than that of Comparative Examples 1-3, and Examples 1 and 2 showed even higher tensile strengths. The antibacterial properties exhibited are far superior to those of Comparative Examples 1 and 2, indicating that the antibacterial packaging prepared by the present invention is of excellent quality and is beneficial in preventing food from being contaminated by microorganisms and thus spoiling in practical applications.

[0141] Preservation Test: This invention uses lychee as a representative example to determine the preservation effect of biodegradable food packaging with antibacterial function on fruit. Three samples of lychee with similar maturity were selected and packaged using the packaging prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively. The three samples of lychee were then placed at room temperature for 8 days, and the changes in freshness and physicochemical quality of the lychee during the storage period were observed.

[0142] 1. Appearance Changes: Record the appearance of the lychees at 0, 2, 4, 6, and 8 days during storage, such as... Figure 2 As shown, the appearance and color of the lychees changed significantly within 8 days. On the 4th day, the lychees packaged in Comparative Example 1 began to show signs of mold, while the lychees packaged in Example 1 maintained good quality and flavor. By the 6th day, the lychees packaged in Comparative Example 2 also showed signs of mold and spoilage. This was because the packaging of Comparative Example 1 and Comparative Example 2 had poor air permeability and antibacterial effect. The moisture generated by respiration and transpiration during storage could not escape, leading to increased humidity inside the packaging and promoting microbial growth. Example 1 only showed signs of mold and spoilage on the 8th day, a delay of 4 days compared to Comparative Example 1. Therefore, the antibacterial and biodegradable packaging prepared in this invention can successfully extend the shelf life of lychees.

[0143] 2. Weight loss rate: (Initial weight - Final weight) / Initial weight × 100%. Because lychees continue to transpire and respire after harvesting, they lose water and nutrients from their cells, thus increasing the weight loss rate. Figure 3 As shown, Example 1 had the lowest weight loss rate during lychee storage, with a weight loss rate of only 6.79% on the 8th day. This indicates that the packaging prepared in this invention reduces the respiration rate of fruits and vegetables, slows down water evaporation, and thus extends the storage period of lychees.

[0144] 3. Hardness was measured using a texture analyzer (Paul Tech, TA.XTC-20). For example... Figure 4 As shown, under room temperature conditions, the hardness of lychees in each group gradually decreased with the extension of storage time, but the packaging in Example 1 effectively slowed down the rate of decrease in lychee hardness.

[0145] 4. Use a handheld refractometer (0-28% Brix) to determine the soluble solids content. Soluble solids include soluble sugars and some soluble organic matter. As the storage time of lychees increases, they continuously undergo respiration. However, since lychees have no external nutrient source after harvesting, they mainly consume the soluble sugars within the fruit, which leads to a gradual decrease in the soluble solids content. Figure 5 As shown, in the later stages of storage, the soluble solids content of Example 1 decreased more slowly than that of the other two comparative groups, indicating that the packaging prepared by the present invention has a better preservation effect on lychees.

[0146] 5. Use acid-base titration to determine titratable acids. Fruit respiration can decompose and consume some titratable acids; overripe lychees have lower organic acid content, leading to a loss of characteristic flavor. For example... Figure 6As shown, the titratable acid content of litchi gradually decreased during storage. In Example 1, the titratable acid content of the packaged litchi fruit was significantly inhibited on day 6, reducing the loss of titratable acid, delaying tissue senescence, and demonstrating a significant preservation effect.

[0147] 6. Use a colorimeter (NH310) for color evaluation. Changes in parameters such as L* (brightness), a* (green-red), and b* (blue-yellow) can reflect the color variation of the fruit peel. Figure 7 As shown, on days 2 and 6, the L* value of Example 1 was higher than that of Comparative Example 1 and Comparative Example 2, indicating that the brightness of Example 1 was maintained better; Figure 8 As shown, during the later stages of storage, the a* value of Example 1 was consistently higher than that of Comparative Example 1 and Comparative Example 2; Figure 9 As shown, the b* value of lychee first increases and then decreases during storage. The decrease in b* value indicates that the yellow color of the lychee peel deepens over time and eventually turns brown. Among the three lychee samples, Example 1 has the highest brightness L* and the lowest ΔE, with a smaller overall color change. This indicates that the composite material prepared in this invention imparts antibacterial properties to the packaging, effectively inhibits microbial invasion of lychee during storage, reduces respiration, and thus delays the ripening period of lychee.

[0148] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the specification of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A modified bamboo fiber fully biodegradable material, characterized in that, The raw materials mainly include the following components by weight: 30-65 parts polylactic acid, 30-50 parts polybutylene terephthalate-adipate, 5-15 parts modified bamboo powder, 2-6 parts plasticizer, and 1-5 parts composite antibacterial agent; the plasticizer is epoxidized soybean oil with a molecular weight of 800-1100 g / mol. The modified bamboo powder is prepared by the following steps: bamboo powder is placed in an alkaline solution and stirred at 300-600 rpm for 4-6 hours under a water bath at 50-60℃. After the reaction is completed, the mixture is cooled to room temperature, and after solid-liquid separation, it is repeatedly washed with water until neutral. It is then dried at 40-60℃ for 24-36 hours. The alkali-treated bamboo powder is then placed in an ethanol solution of silane coupling agent and stirred at 300-800 rpm for 2-4 hours under a water bath at 30-50℃. It is then dried at 40-60℃ for 12-24 hours, pulverized, and sieved to obtain the modified bamboo powder. The composite antibacterial agent is prepared by the following steps: (1) Weigh a certain amount of 4-methylpyridine and 1,3-dibromopropane into a container, add an appropriate amount of acetone to dissolve, stir and reflux at 65-70℃ for 24-36h; after the reaction, pour it into a container while hot, remove the upper liquid with a dropper, add an appropriate amount of acetone to wash, let stand to separate the layers, remove the upper liquid, repeat the operation several times; then add an appropriate amount of ether to wash, let stand to separate the layers, remove the upper liquid, repeat the operation several times; after evaporating naturally in the dark, put it into a vacuum drying oven at 65-75℃ for 12-24h to obtain white powder [4MePy-(CH2)3-4MePy]Br2; (2) Take a certain amount of [4MePy-(CH2)3-4MePy]Br2 and manganese chloride tetrahydrate in a container, add an appropriate amount of methanol to dissolve, and add an appropriate amount of concentrated hydrochloric acid. Stir and reflux at 80-90 ℃ for 2-4 h. After the reaction, pour it into a container while it is hot, let it stand and cool, and let it evaporate naturally to obtain light yellow flaky crystals of manganese tetrachlorobispyridine quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which is the composite antibacterial agent.

2. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The mass ratio of bamboo powder to alkaline solution used is 1:12-18; the mass ratio of alkali-treated bamboo powder to ethanol solution of silane coupling agent used is 1:5-8.

3. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The modified bamboo powder has a particle size of 300-800 mesh; the alkaline solution is an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 3-8 wt%; the silane coupling agent is KH550 with a molecular weight of 200-300 g / mol; and the concentration of the silane coupling agent in the silane coupling agent solution is 5-15 wt%.

4. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The molar ratio between 1,3-dibromopropane and 4-methylpyridine in step (1) is 1:(2-4).

5. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The molar ratio of the [4MePy-(CH2)3-4MePy]Br2 quaternary ammonium salt and manganese chloride tetrahydrate in step (2) is 1:(0.8-1.2).

6. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The polylactic acid has a melting point of 140-180℃, a melt index of 5-25g / 10min, and a heat distortion temperature of 50-70℃.

7. A method for preparing the modified bamboo fiber fully biodegradable material according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The polylactic acid, polybutylene terephthalate, modified bamboo powder, plasticizer, and composite antibacterial agent are put into a mixer and stirred at 40-80 rpm for 10-20 minutes. The uniformly mixed material is then fed into a twin-screw extruder. The heating temperature of the twin-screw extruder is controlled sequentially as follows: Zone 1 158-163℃, Zone 2 163-167℃, Zone 3 167-170℃, Zone 4 170-175℃, and Zone 5 168-173℃. After extrusion, the material is rapidly cooled to room temperature for granulation and then dried to obtain composite granules. (2) The dried composite granules are fed into the casting machine. The heating temperature of the casting machine is controlled sequentially as follows: Zone 1 160-163℃, Zone 2 163-166℃, Zone 3 166-172℃, Zone 4 172-175℃, Zone 5 175-178℃. After casting, a sheet is obtained. The sheet is then vacuum-formed to finally obtain the modified bamboo fiber fully biodegradable material.

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