Modified bamboo fiber full-biodegradable material, preparation method thereof and application of modified bamboo fiber full-biodegradable material in food preservation

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a modified bamboo fiber full-biodegradable material, with PBAT, PLA, modified bamboo powder, a plasticizer and a composite antibacterial agent as raw materials, the preparation method comprises the following steps: S1, carrying out alkali treatment modification and silane coupling agent modification on bamboo powder; s2, preparing a composite antibacterial agent by adopting a solid-phase reaction method; s3, all the components with the set amount are fully stirred; s4, carrying out high-temperature melt extrusion on the mixed component raw materials, cooling and pelletizing; s5, the particles are subjected to high-temperature tape casting, and sheets are obtained; and S6, the sheet is formed through plastic uptake. According to the modified bamboo fiber full-biodegradable material disclosed by the invention, due to the addition of the modified bamboo powder, not only can the mechanical properties of food packages be effectively improved, but also the production cost of degradable food packages can be reduced, and the degradation rate of the food packages can be increased; the compound antibacterial agent is added, so that the food package is endowed with excellent antibacterial performance, and the metabolic process of the litchis is delayed, so that the weight loss rate and the rotting rate of the litchis during storage are remarkably reduced, the shelf life of the litchis can be effectively prolonged, and meanwhile, the preservative can be applied to fresh-keeping storage of other fruits and has wide applicability.

Description

Technical Field

[0001] The invention relates to a modified bamboo fiber fully biodegradable material and a preparation method thereof and application of the material in food preservation, belonging to the technical field of polymer materials. Background Art

[0002] In recent years, in order to adapt to the fast-paced lifestyle, the emergence of disposable foam plastic lunch boxes, fresh-keeping bags, fresh-keeping boxes and other daily necessities has brought many conveniences. The most common disposal methods for these packaging materials are incineration and landfill, which will cause irreversible pollution to the environment in the long run. Therefore, developing new packaging materials that are safer, easy to degrade and easy to keep fresh is an important way to reduce plastic product pollution. Using degradable materials instead of traditional plastics is a major way to solve the problem of plastic pollution.

[0003] In order to further promote the whole-chain governance of plastic pollution, China and the International Bamboo and Rattan Organization have joined hands to implement global development initiatives and jointly launched the "Bamboo instead of plastic" initiative, which provides an effective solution to reduce plastic pollution. In order to respond to the call of "Bamboo instead of plastic" and make full use of biomass energy, natural bamboo powder has entered the field of vision of scientific researchers. Its main components are cellulose, lignin, hemicellulose, etc., among which cellulose accounts for the largest proportion. Natural fiber / polymer composite materials prepared with natural plant fibers as fillers or reinforcements and polymers as matrices have many characteristics such as good mechanical properties and strong processability. However, bamboo fibers contain a large number of hydroxyl, carboxylhydroxyl and other groups, which make them highly polar, resulting in poor interface bonding between natural plant fibers and plastic matrices. Therefore, bamboo powder needs to be modified, and its high-value resource utilization after modification is of great significance to biomass refining and environmental protection.

[0004] Polylactic acid is a non-toxic, non-irritating synthetic polymer material. Its raw materials mainly come from fermented products such as starch. It can be directly composted or incinerated after use, 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, it has biodegradability and thermoplastic properties, making it a hot topic in the packaging materials industry. Despite having so many advantages, polylactic acid is brittle, has poor impact resistance, has a low heat deformation temperature, and has poor heat resistance, which seriously limits its large-scale application in plastic packaging bags.

[0005] Food antimicrobial packaging combines packaging materials and antimicrobial preservative materials to improve the shelf life and safety of food. The limitations of ordinary antimicrobial materials are becoming more and more obvious, and the development of new antimicrobial materials is urgent. Pyridine quaternary ammonium salts have excellent antimicrobial properties. As a good hydrogen bond receptor, they can be coordinated with metal halides to form organic-inorganic hybrid materials with excellent catalytic, antimicrobial, magnetic and optical properties. Summary of the invention

[0006] In view of the above problems, the present invention provides a modified bamboo fiber fully biodegradable material, which improves the toughness of the PLA material by modifying the bamboo fiber, improves the antibacterial and fresh-keeping properties of the material by using a composite antibacterial agent, and prepares a fully biodegradable food packaging material with antibacterial properties.

[0007] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme: A modified bamboo fiber fully biodegradable material, whose raw materials 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.

[0008] Preferably, the modified bamboo powder is prepared by the following steps: placing the bamboo powder in an alkaline solution, stirring and reacting at 300-600 rpm in a water bath at 50-60°C for 4-6 hours, cooling to room temperature after the reaction, repeatedly washing with water until neutral after solid-liquid separation, and drying at 40-60°C for 24-36 hours; then placing the alkali-treated bamboo powder in an ethanol solution of a silane coupling agent, stirring and reacting at 300-800 rpm in a water bath at 30-50°C for 2-4 hours, drying at 40-60°C for 12-24 hours, crushing, and sieving to obtain the modified bamboo powder.

[0009] Preferably, the mass ratio of the bamboo powder to the alkaline solution is 1:12-18; the mass ratio of the alkali-treated bamboo powder to the ethanol solution of the silane coupling agent is 1:5-8.

[0010] More preferably, the particle size of the modified bamboo powder is 300-800 mesh. The alkaline solution is a sodium hydroxide aqueous solution with a sodium hydroxide concentration of 3-8wt%; the silane coupling agent is KH550 with a molecular weight of 200-300g / mol. The concentration of the silane coupling agent in the silane coupling agent solution is 5-15wt%.

[0011] Preferably, 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 °C for 24-36 hours; after the reaction, pour into the container while hot, remove the upper layer of liquid with a dropper, add an appropriate amount of acetone to wash, let stand and separate, remove the upper layer of liquid, and repeat the operation several times; then add an appropriate amount of ether to wash, let stand and separate, remove the upper layer of liquid, and repeat the operation several times; after natural evaporation in a dark place, put into a vacuum drying oven at 65-75 °C and dry for 12-24 hours to obtain a 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 hot, let it stand and cool, and evaporate naturally to obtain light yellow flaky crystals of tetrachloromanganese bipyridinium ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which is the composite antibacterial agent.

[0012] More preferably, the molar ratio between 1,3-dibromopropane and 4-methylpyridine in step (1) is 1:(2-4); 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).

[0013] The method for preparing the modified bamboo fiber fully biodegradable material comprises the following steps: (1) Put the polylactic acid, polybutylene terephthalate-adipate, modified bamboo powder, plasticizer, and composite antibacterial agent into a mixer, stir at 40-80 rpm for 10-20 minutes, put the uniformly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 158-163° C. in zone 1, 163-167° C. in zone 2, 167-170° C. in zone 3, 170-175° C. in zone 4, and 168-173° C. in zone 5 in sequence; after extrusion, quickly cool to room temperature for granulation, and dry to obtain composite granules.

[0014] Preferably, the plasticizer is epoxidized soybean oil with a molecular weight of 800-1100 g / mol.

[0015] Preferably, the polylactic acid has a melting point of 140-180°C, a melt index of 5-25 g / 10 min, and a heat deformation temperature of 50-70°C.

[0016] (2) The dried composite granules are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 160-163°C in zone 1, 163-166°C in zone 2, 166-172°C in zone 3, 172-175°C in zone 4, and 175-178°C in zone 5. After casting, a sheet is obtained. The sheet is subjected to vacuum forming to finally obtain a modified bamboo fiber fully biodegradable material for food antibacterial packaging.

[0017] Compared with the prior art, the present invention achieves the following beneficial effects: 1. The present invention uses bamboo powder as one of the raw materials, which can effectively improve the utilization rate of agricultural and forestry wastes and greatly reduce the manufacturing cost of degradable food packaging; 2. The present invention uses sodium hydroxide and silane coupling agent to modify bamboo powder. Alkali treatment can well remove impurities such as lignin, pectin and hemicellulose on the surface of bamboo powder, retain cellulose, increase the surface roughness of the fiber, increase the contact area between bamboo powder and polylactic acid matrix, and improve the interfacial compatibility between bamboo powder and polylactic acid matrix, but no chemical bond is formed between bamboo powder and polylactic acid. The silanol generated by the coupling agent after hydrolysis can react with the hydroxyl group on the surface of bamboo powder, and its epoxy functional group can react with the terminal hydroxyl group and carboxyl group of the polylactic acid chain, playing a role of bridging between bamboo powder and polylactic acid matrix, so the interfacial compatibility between bamboo powder and polylactic acid is highly improved.

[0018] 3. The present invention provides a composite antibacterial agent - tetrachloromanganese bipyridinium quaternary ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which has high yield, cost saving, easy operation and is conducive to industrial development. Compared with Cu-based metal complexes, the Mn-based metal complex of the present invention is more environmentally friendly and can be added to the biodegradable packaging material of the present invention to give the packaging material excellent antibacterial properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The antibacterial effect diagram of Example 1 and Comparative Example 2 on Staphylococcus aureus and Escherichia coli; Figure 2 Schematic diagram of the appearance of the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2 for the preservation test of litchi; Figure 3 The weight loss rate of the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2 in the lychee preservation test; Figure 4 The hardness of the packages prepared in Example 1, Comparative Example 1 and Comparative Example 2 in the lychee preservation test; Figure 5 Soluble solids of the lychee preservation test of the packages prepared in Example 1, Comparative Example 1 and Comparative Example 2; Figure 6 Titratable acid for the lychee preservation test of the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2; Figure 7-10 Color evaluation of the lychee preservation test for the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2; Fig.11 This is the crystal structure diagram of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4] (hydrogen atoms omitted); Fig.12 It is the cation mass spectrum of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4]; Fig.13It is the X-ray diffraction pattern of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4]; Fig.14 This is the infrared spectrum of the composite antibacterial agent [4MePy-(CH2)3-4MePy][MnCl4]. DETAILED DESCRIPTION

[0020] The following describes embodiments of the present invention. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0021] Embodiment 1: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps: Step 1: Preparation of modified bamboo powder According to the mass ratio of bamboo powder to alkaline solution of 1:15, bamboo powder was put into alkaline solution, stirred at a rate of 300r / min under the condition of constant temperature 60℃ water bath, stirred for 4h, cooled to room temperature after reaction, washed repeatedly with deionized water until neutral after solid-liquid separation, dried at 60℃ for 36h to obtain alkaline-treated bamboo powder, and then the alkaline-treated bamboo powder was put into silane coupling agent ethanol solution at a mass ratio of 1:6, stirred at a rate of 300r / min under the condition of constant temperature 50℃ water bath, stirred for 2h, dried at 60℃ for 24h, put into a grinder for crushing, and then sieved to obtain the final modified bamboo powder; The particle size of the modified bamboo powder is 500 mesh; The alkaline solution is a sodium hydroxide aqueous solution, and the concentration of sodium hydroxide is 3wt%; The silane coupling agent is KH550, with a molecular weight of 221.7 g / mol; The silane coupling agent ethanol solution has a silane coupling agent concentration of 15wt%; Step 2: Preparation of composite antimicrobial agent (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-mouth conical flask, add 30 mL of acetone to dissolve, and stir and reflux at 65-70 °C for 24 h. After the reaction, pour into a beaker while hot, remove the upper layer of liquid with a dropper, add a small amount of acetone to wash, let stand to separate, remove the upper layer of liquid, and repeat the operation three times. Repeat the above steps to wash with ether three times, evaporate naturally in the dark, and dry in a vacuum oven at 70 °C for 12 h to obtain a white powder [4MePy-(CH2)3-4MePy]Br2.

[0022] (2) Take 10 mmol [4MePy-(CH2)3-4MePy]Br2 and 10 mmol manganese chloride tetrahydrate in a conical flask, dissolve them in 20 mL methanol, add 1 mL concentrated hydrochloric acid (12 mol / L), stir and reflux at 80-90 °C for 2 h; after the reaction, pour into a beaker while hot, heat and concentrate, and let stand to cool; seal with plastic wrap, poke a hole with a syringe, and put it under a fume hood. Crystals will be obtained in about five days, and finally pale yellow flaky crystals of tetrachloromanganese bipyridinium ammonium salt [4MePy-(CH2)3-4MePy][MnCl4] will be obtained.

[0023] The molar ratio between bromopropane and pyridine is 1:2; The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0024] Step 3: Melt blending Polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer and composite antibacterial agent are put into a mixer in a mass ratio of 43:35:15:4:3, the stirring speed is 60r / min, and the stirring is carried out for 15 minutes. The uniformly mixed mixture is put into a twin-screw extruder. The heating temperature of the twin-screw extruder is controlled to 160°C in zone 1, 163°C in zone 2, 170°C in zone 3, 172°C in zone 4 and 168°C in zone 5 in sequence. After extrusion, the mixture is quickly cooled to room temperature for granulation. The obtained particles are composite granules, which are placed at 60°C for drying to obtain composite granules.

[0025] The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 4: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 163°C in zone one, 165°C in zone two, 170°C in zone three, 175°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0026] Embodiment 2: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps: Step 1: Preparation of modified bamboo powder According to the mass ratio of bamboo powder to alkaline solution of 1:15, bamboo powder is put into alkaline solution, and stirred at a rate of 500r / min under the condition of constant temperature 50℃ water bath, and stirred for 4h. After the reaction, it is cooled to room temperature, and repeatedly washed with deionized water until neutral, and dried at 50℃ for 24h to obtain alkali-treated bamboo powder. Then, the alkali-treated bamboo powder is put into silane coupling agent ethanol solution at a mass ratio of 1:6, and stirred at a rate of 500r / min under the condition of constant temperature 50℃ water bath, and stirred for 3h. It is dried at 60℃ for 18h, put into a grinder for crushing, and then sieved to obtain the final modified bamboo powder; The particle size of the modified bamboo powder is 300 mesh; The alkaline solution is a sodium hydroxide aqueous solution, and the concentration of sodium hydroxide is 4wt%; The silane coupling agent is KH550, with a molecular weight of 221.7 g / mol; The silane coupling agent ethanol solution has a silane coupling agent concentration of 10wt%; Step 2: Preparation of composite antimicrobial agent (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-mouth conical flask, add 30 mL of acetone to dissolve, and stir and reflux at 65-70 °C for 24 h. After the reaction, pour into a beaker while hot, remove the upper layer of liquid with a dropper, add a small amount of acetone to wash, let stand to separate, remove the upper layer of liquid, and repeat the operation three times. Repeat the above steps to wash with ether three times, 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.

[0027] (2) Preparation of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4]: Take 10 mmol [4MePy-(CH2)3-4MePy]Br2 and 10 mmol manganese chloride tetrahydrate in a conical flask, dissolve them in 20 mL methanol, add 1 mL concentrated hydrochloric acid (12 mol / L), stir and reflux at 80-90 °C for 2 h; after the reaction, pour into a beaker while hot, heat and concentrate, and let stand to cool; seal with plastic wrap, poke a hole with a syringe, and put it under a fume hood. Crystals will be obtained in about five days, and finally pale yellow flaky crystals of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4] will be obtained.

[0028] The molar ratio between bromopropane and pyridine is 1:2; The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0029] Step 3: Melt blending Put polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer and composite antibacterial agent into a mixer at a mass ratio of 41:40:10:4:5, stir at a speed of 60r / min, stir for 15min, put the evenly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 158°C in zone 1, 160°C in zone 2, 170°C in zone 3, 172°C in zone 4 and 168°C in zone 5 in sequence, cool rapidly to room temperature for granulation after extrusion, and obtain composite granules, which are placed at 50°C for drying to obtain composite granules; The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 4: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 160°C in zone one, 165°C in zone two, 168°C in zone three, 173°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0030] Embodiment 3: A method for preparing a modified bamboo fiber fully biodegradable material, comprising the following steps: Step 1: Preparation of modified bamboo powder According to the mass ratio of bamboo powder to alkaline solution of 1:15, bamboo powder was put into alkaline solution, stirred at a rate of 700r / min under constant temperature 40℃ water bath condition, stirred for 5h, cooled to room temperature after reaction, repeatedly washed with deionized water until neutral, dried at 55℃ for 24h to obtain alkali-treated bamboo powder, and then the alkali-treated bamboo powder was put into silane coupling agent ethanol solution at a mass ratio of 1:6, stirred at a rate of 600r / min under constant temperature 40℃ water bath condition, stirred for 4h, dried at 50℃ for 24h, put into a grinder for crushing, and then sieved to obtain the final modified bamboo powder; The particle size of the modified bamboo powder is 600 mesh; The alkaline solution is a sodium hydroxide aqueous solution, and the concentration of sodium hydroxide is 5wt%; The silane coupling agent is KH550, with a molecular weight of 221.7 g / mol; The silane coupling agent ethanol solution has a silane coupling agent concentration of 8wt%; Step 2: Preparation of composite antimicrobial agent (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-mouth conical flask, add 30 mL of acetone to dissolve, and stir and reflux at 65-70 °C for 24 h. After the reaction, pour into a beaker while hot, remove the upper layer of liquid with a dropper, add a small amount of acetone to wash, let stand to separate, remove the upper layer of liquid, and repeat the operation three times. Repeat the above steps to wash with ether three times, 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.

[0031] (2) Preparation of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4]: Take 10 mmol [4MePy-(CH2)3-4MePy]Br2 and 10 mmol manganese chloride tetrahydrate in a conical flask, dissolve them in 20 mL methanol, add 1 mL concentrated hydrochloric acid (12 mol / L), stir and reflux at 80-90 °C for 2 h; after the reaction, pour into a beaker while hot, heat and concentrate, and let stand to cool; seal with plastic wrap, poke a hole with a syringe, and put it under a fume hood. Crystals will be obtained in about five days, and finally pale yellow flaky crystals of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4] will be obtained.

[0032] The molar ratio between bromopropane and pyridine is 1:2; The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0033] Step 3: Melt blending Put polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder, plasticizer and composite antibacterial agent into a mixer at a mass ratio of 49:40:5:5:1, stir at a speed of 60r / min, stir for 15min, put the evenly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 160°C in zone 1, 162°C in zone 2, 170°C in zone 3, 175°C in zone 4 and 172°C in zone 5 in sequence, cool rapidly to room temperature for granulation after extrusion, and obtain composite granules, which are placed at 50°C for drying to obtain composite granules; The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 4: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 165°C in zone one, 168°C in zone two, 170°C in zone three, 174°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0034] Comparative Example 1: Based on Example 1, the preparation and use of the modified bamboo powder and the composite antibacterial agent in the example are removed, that is, the added amount of the modified bamboo powder and the composite antibacterial agent is zero, and they are replaced with an equal amount of polylactic acid, and the rest is the same as Example 1.

[0035] Step 1: Melt blending Put polylactic acid, polybutylene terephthalate-adipate resin and plasticizer into a mixer at a mass ratio of 61:35:4, stir at a speed of 60r / min, stir for 15min, put the evenly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 160°C in zone 1, 163°C in zone 2, 170°C in zone 3, 172°C in zone 4 and 168°C in zone 5 in sequence, cool rapidly to room temperature for granulation after extrusion, and obtain composite granules, which are placed at 60°C for drying to obtain composite granules; The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 2: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 163°C in zone one, 165°C in zone two, 170°C in zone three, 175°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0036] Comparative Example 2: On the basis of Example 1, the preparation and use of the composite antibacterial agent in the example are removed, that is, the addition amount of the composite antibacterial agent is zero, and it is replaced by an equal amount of polylactic acid, and the rest is the same as Example 1.

[0037] Step 1: Preparation of modified bamboo powder The bamboo powder was placed in an alkaline solution, stirred at a rate of 300 r / min in a water bath at a constant temperature of 60°C, and stirred for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, washed repeatedly with deionized water until neutral, and dried at 60°C for 36 hours to obtain alkali-treated bamboo powder. The alkali-treated bamboo powder was then placed in an ethanol solution of a silane coupling agent, stirred at a rate of 300 r / min in a water bath at a constant temperature of 50°C, and stirred for 2 hours. The mixture was dried at 60°C for 24 hours, and then placed in a grinder for crushing, and then sieved to obtain the final modified bamboo powder. The particle size of the modified bamboo powder is 500 mesh; The alkaline solution is a sodium hydroxide aqueous solution, and the concentration of sodium hydroxide is 3wt%; The silane coupling agent is KH550, with a molecular weight of 221.7 g / mol; The silane coupling agent ethanol solution has a silane coupling agent concentration of 15wt%; Step 2: Melt blending Put polylactic acid, polybutylene terephthalate-adipate resin, modified bamboo powder and plasticizer into a mixer at a mass ratio of 46:35:15:4, stir at a speed of 60r / min, stir for 15min, put the uniformly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 160°C in zone 1, 163°C in zone 2, 170°C in zone 3, 172°C in zone 4 and 168°C in zone 5 in sequence, cool rapidly to room temperature for granulation after extrusion, and obtain composite granules, which are placed at 60°C for drying to obtain composite granules; The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 3: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 163°C in zone one, 165°C in zone two, 170°C in zone three, 175°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0038] Comparative Example 3: On the basis of Example 1, the bamboo powder was not modified, 15 parts of modified bamboo powder were replaced by 15 parts of bamboo powder in an equal amount, and the rest was the same as Example 1.

[0039] Step 1: Preparation of bamboo powder Put the bamboo powder into a grinder for grinding, and then sieve to obtain the ground bamboo powder; The particle size of the bamboo powder is 500 mesh; Step 2: Preparation of composite antimicrobial agent (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-mouth conical flask, add 30 mL of acetone to dissolve, and stir and reflux at 65-70 °C for 24 h. After the reaction, pour into a beaker while hot, remove the upper layer of liquid with a dropper, add a small amount of acetone to wash, let stand to separate, remove the upper layer of liquid, and repeat the operation three times. Repeat the above steps to wash with ether three times, 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.

[0040] (2) Preparation of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4]: Take 10 mmol [4MePy-(CH2)3-4MePy]Br2 and 10 mmol manganese chloride tetrahydrate in a conical flask, dissolve them in 20 mL methanol, add 1 mL concentrated hydrochloric acid (12 mol / L), stir and reflux at 80-90 °C for 2 h; after the reaction, pour into a beaker while hot, heat and concentrate, and let stand to cool; seal with plastic wrap, poke a hole with a syringe, and put it under a fume hood. Crystals will be obtained in about five days, and finally pale yellow flaky crystals of tetrachloromanganese bipyridinium salt [4MePy-(CH2)3-4MePy][MnCl4] will be obtained.

[0041] The molar ratio between bromopropane and pyridine is 1:2; The molar ratio of the quaternary ammonium salt to manganese chloride tetrahydrate is 1:1.

[0042] Step 3: Melt blending Put polylactic acid, polybutylene terephthalate-adipate resin, bamboo powder, plasticizer and composite antibacterial agent into a mixer at a mass ratio of 43:35:15:4:3, stir at a speed of 60r / min, stir for 15min, put the evenly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 160°C in zone 1, 163°C in zone 2, 170°C in zone 3, 172°C in zone 4 and 168°C in zone 5 in sequence, cool rapidly to room temperature for granulation after extrusion, and obtain composite granules, which are placed at 60°C for drying to obtain composite granules; The plasticizer is epoxidized soybean oil; The molecular weight of the epoxidized soybean oil is 975.399 g / mol; The polylactic acid has a melting point of 176°C, a melt index of 21g / 10min, and a heat deformation temperature of 65°C; Step 4: Casting Blister The dried composite particles are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 163°C in zone one, 165°C in zone two, 170°C in zone three, 175°C in zone four, and 178°C in zone five. Sheets are obtained after casting, and the sheets are blister-formed to finally obtain biodegradable antibacterial food packaging.

[0043] Comparative Example 4: Based on Example 1, 3 parts of the composite antibacterial agent are replaced by 3 parts of the antibacterial agent ZnO in equal amount, and the rest is the same as Example 1.

[0044] Performance test: 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.

[0045] Table 1 Test data of various embodiments and comparative examples

[0046] From the results in Table 1, it can be seen that in Comparative Example 1, bamboo powder and antibacterial agent are not added, and its tensile strength is the lowest and the antibacterial effect is the worst. It can be seen that if polylactic acid and polybutylene terephthalate-adipate resin are simply used to mix into a composite material, the various properties of the final composite product will be seriously affected; in Comparative Example 2, no antibacterial agent is added, and its tensile strength and antibacterial performance are better than those of Comparative Example 1, which shows that the addition of modified bamboo powder can improve the tensile strength and weak antibacterial property, but there is still a big gap compared with the three embodiments; in Comparative Example 3, modified bamboo powder is not prepared, and bamboo powder is directly added, and the elongation at break is directly reduced to the minimum, and the tensile strength is also lower than the three embodiments and Comparative Example 2, which shows that the unmodified bamboo powder has particularly poor compatibility with polylactic acid, which will seriously affect the comprehensive performance of polylactic acid; the tensile strengths of Examples 1-3 are all higher than those of Comparative Examples 1-3, and Examples 1 and 2 The antibacterial performance is far superior to that of Comparative Example 1 and Comparative Example 2, indicating that the present invention can prepare excellent antibacterial packaging, which is beneficial to prevent food from being infected by microorganisms and causing spoilage in practical applications.

[0047] Fresh-keeping test: The present invention uses litchi as a representative to determine the fresh-keeping effect of the biodegradable food packaging with antibacterial function on fruits. Three litchis with similar maturity were selected and packaged with the packaging prepared in Example 1, Comparative Example 1 and Comparative Example 2, respectively. The three litchis were then placed at room temperature for 8 days to observe the freshness and physical and chemical quality changes of the litchis during the storage period.

[0048] 1. Appearance changes: Record the appearance of litchi on days 0, 2, 4, 6, and 8 during storage. Figure 2As shown in the figure, the appearance color of litchi changed significantly within 8 days. On the 4th day, litchi packaged in Comparative Example 1 began to mold, while litchi packaged in Example 1 still maintained good quality and flavor. On the 6th day, litchi packaged in Comparative Example 2 also became moldy and deteriorated. This is because the packaging of Comparative Examples 1 and 2 has poor air permeability and poor antibacterial effect. During the storage period, the water vapor generated by the respiration and transpiration of litchi cannot be transmitted, which increases the humidity in the packaging and promotes the growth of microorganisms. Example 1 only began to mold and deteriorate on the 8th day, and the mold time was delayed by 4 days compared with Comparative Example 1. Therefore, the antibacterial and degradable packaging prepared by the present invention can successfully extend the shelf life of litchi.

[0049] 2. Weight loss rate: (initial weight - final weight) / initial weight × 100%. Since litchi still undergoes transpiration and respiration after being picked, water in the cells is lost and nutrients are consumed, thus increasing the mass loss rate of litchi. Figure 3 As shown, during the storage of litchi, the mass loss rate of Example 1 was the lowest, with a weight loss rate of only 6.79% on the 8th day, indicating that the packaging prepared by the present invention reduces the respiration rate of fruits and vegetables, slows down water transpiration, and thus prolongs the storage period of litchi.

[0050] 3. Use a texture analyzer (PAUL Technology, TA.XTC-20) to measure the hardness. Figure 4 As shown, under room temperature conditions, with the extension of storage time, the hardness of each group of litchi gradually decreased, but the packaging of Example 1 effectively delayed the rate of decrease in litchi hardness.

[0051] 4. Use a handheld refractometer (0-28% Brix) to measure soluble solids. Soluble solids include soluble sugars and some soluble organic matter. As the storage time of litchi increases, it continues to respire. However, since litchi has no external nutrient source after picking, it mainly consumes soluble sugars in the fruit, which will cause the soluble solids content of litchi to gradually decrease. Figure 5 As shown, in the later stage of storage, the soluble solid content of Example 1 decreased more slowly than that of the other two groups of comparative examples, which indicates that the packaging prepared by the present invention has a better preservation effect on litchi.

[0052] 5. Use acid-base titration to determine titratable acid. The respiration of the fruit can decompose and consume part of the titratable acid. The organic acid content of overripe lychees is reduced, resulting in the loss of the characteristic flavor of the fruit. Figure 6 As shown, the titratable acid mass fraction of litchi during storage showed a gradual downward trend. The titratable acid mass fraction of litchi fruit packaged in Example 1 was significantly suppressed on the 6th day, reducing the loss of titratable acid, delaying tissue aging, and having a significant preservation effect.

[0053] 6. Use a colorimeter (NH310) to evaluate the color. The changes in parameters such as L* (brightness), a* (green-red), and b* (blue-yellow) can reflect the changing pattern of the peel color. Figure 7 As shown in FIG. 1 , the L* values ​​of Example 1 on the 2nd and 6th days are higher than those of Comparative Example 1 and Comparative Example 2, indicating that the brightness of Example 1 is better maintained; Figure 8 As shown, in the later stage of storage, the a* value of Example 1 is always higher than that of Comparative Example 1 and Comparative Example 2; Fig. 9 As shown in the figure, the b* value of litchi first increased and then decreased during storage. The decrease in b* value indicates that the yellow color of litchi peel deepens with time and eventually turns brown. Among the three litchis, Example 1 has the highest brightness L*, lower ΔE, and smaller overall color change, which indicates that the composite material prepared by the present invention gives the packaging antibacterial properties, effectively inhibits the invasion of litchi by microorganisms during storage, reduces respiration, and thus delays the ripening period of litchi.

[0054] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of implementation of the present invention. That is, equivalent changes and modifications made according to the scope of the patent application of the present invention and the contents of the specification should still fall within the scope covered by 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 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.

2. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The modified bamboo powder is prepared by the following steps: putting the bamboo powder into an alkaline solution, stirring and reacting at 300-600 rpm for 4-6 hours under a water bath condition of 50-60°C, cooling to room temperature after the reaction is completed, repeatedly washing with water until neutral after solid-liquid separation, and drying at 40-60°C for 24-36 hours; then putting the alkali-treated bamboo powder into an ethanol solution of a silane coupling agent, stirring and reacting at 300-800 rpm for 2-4 hours under a water bath condition of 30-50°C, drying at 40-60°C for 12-24 hours, crushing, and sieving to obtain the modified bamboo powder.

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

4. The modified bamboo fiber fully biodegradable material according to claim 2, characterized in that: The particle size of the modified bamboo powder is 300-800 mesh; the alkaline solution is a sodium hydroxide aqueous solution with a sodium hydroxide concentration of 3-8wt%; the silane coupling agent is KH550 with a molecular weight of 200-300g / mol; and the concentration of the silane coupling agent in the silane coupling agent solution is 5-15wt%.

5. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: 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 into the container while hot, remove the upper layer of liquid with a dropper, add an appropriate amount of acetone to wash, let stand and separate, remove the upper layer of liquid, and repeat the operation several times; then add an appropriate amount of ether to wash, let stand and separate, remove the upper layer of liquid, and repeat the operation several times; after natural evaporation in a dark place, put into a vacuum drying oven at 65-75℃ and dry 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 hot, let it stand and cool, and evaporate naturally to obtain light yellow flaky crystals of tetrachloromanganese bipyridinium ammonium salt [4MePy-(CH2)3-4MePy][MnCl4], which is the composite antibacterial agent.

6. The modified bamboo fiber fully biodegradable material according to claim 5, characterized in that: The molar ratio between 1,3-dibromopropane and 4-methylpyridine in step (1) is 1:(2-4).

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

8. The modified bamboo fiber fully biodegradable material according to claim 1, characterized in that: The plasticizer is epoxidized soybean oil with a molecular weight of 800-1100 g / mol.

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

10. The method for preparing the modified bamboo fiber fully biodegradable material according to claims 1-9, characterized in that: The following steps are involved: (1) Put the polylactic acid, polybutylene terephthalate-adipate, modified bamboo powder, plasticizer, and composite antibacterial agent into a mixer, stir at 40-80 rpm for 10-20 minutes, put the uniformly mixed mixture into a twin-screw extruder, and control the heating temperature of the twin-screw extruder to 158-163° C. in zone 1, 163-167° C. in zone 2, 167-170° C. in zone 3, 170-175° C. in zone 4, and 168-173° C. in zone 5 in sequence; after extrusion, quickly cool to room temperature for granulation, and dry to obtain composite granules; (2) The dried composite granules are put into a casting machine, and the heating temperatures of the casting machine are controlled in sequence to 160-163°C in zone 1, 163-166°C in zone 2, 166-172°C in zone 3, 172-175°C in zone 4, and 175-178°C in zone 5. After casting, a sheet is obtained, and the sheet is subjected to vacuum forming to finally obtain a modified bamboo fiber fully biodegradable material.

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