Preparation method and application of hydrophobic antibacterial fresh-keeping composite paper

Abstract

The invention discloses a preparation method and application of hydrophobic antibacterial fresh-keeping composite paper, and belongs to the technical field of functional materials. According to the invention, carboxymethyl cellulose is used as a stabilizer, a fixing agent and a growth template, and in-situ synthesis and stabilization of nano-zinc oxide are realized through a molecular self-assembly strategy; zinc chloride is used as a zinc source, ammonia water is used as a precipitator, and the lattice growth kinetics of zinc oxide is regulated and controlled by using a reducing group of carboxymethyl cellulose under a microwave-assisted hydrothermal condition, so that nano zinc oxide particles with uniform particle size distribution are prepared; nano cellulose and polyvinyl alcohol are crosslinked through boric acid ester bonds to form a three-dimensional interpenetrating network structure, so that the composite paper is endowed with excellent hydrophobicity and mechanical strength, and moisture evaporation and microbial permeation are inhibited through a physical barrier effect; the multi-stage protection reduces the rotting deterioration or quality reduction of food caused by factors such as mechanical damage, water evaporation and microbial pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a preparation method and application of a hydrophobic antibacterial fresh-keeping composite paper. Background Art

[0002] Due to their special physical and chemical properties, fruits and vegetables are prone to rot, deterioration or quality decline due to mechanical damage, water evaporation, microbial contamination, etc. during the processes of picking, transportation, storage and sale, resulting in economic losses and food safety problems. At present, most of the commonly used fresh-keeping packaging materials for fruits and vegetables are petroleum-based products, which have problems such as being difficult to degrade and easily causing environmental pollution. Therefore, developing new fresh-keeping packaging materials from green and degradable raw materials is an important measure in line with the trend of the times.

[0003] Nano-zinc oxide is a multifunctional new inorganic material, and its particle size is generally between 1 - 100 nm. Due to the small molecule effect caused by its small size, it has very excellent application value in the antibacterial field and has properties that cannot be compared with ordinary chemical antibacterial agents. Polyvinyl alcohol has the characteristics of low cost, good film-forming property, safety and non-toxicity, and can be used as an ideal raw material for preparing food fresh-keeping packaging materials. Therefore, how to combine the antibacterial properties of nano-zinc oxide with the non-toxic and degradable advantages of polyvinyl alcohol to prepare a fresh-keeping packaging material that can reduce the deterioration rate of fruits and vegetables has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a preparation method and application of a hydrophobic antibacterial fresh-keeping composite paper.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a hydrophobic antibacterial fresh-keeping composite paper, comprising the following steps:

[0007] (1) Dissolve carboxymethyl cellulose in an alkali-urea solution, then add zinc chloride and ammonia water for microwave heating reaction, and then obtain a carboxymethyl cellulose solution of nano-zinc oxide through dialysis;

[0008] (2) Dissolve polyvinyl alcohol in water, then add nano-cellulose, the carboxymethyl cellulose solution of nano-zinc oxide described in step (1) and a cross-linking agent, and after mixing, carry out papermaking to obtain the hydrophobic antibacterial fresh-keeping composite paper.

[0009] Technical Principle:

[0010] The present invention uses carboxymethyl cellulose as a stabilizer, fixative, and growth template, and realizes the in-situ synthesis and stabilization of nano-zinc oxide through a molecular self-assembly strategy. Using zinc chloride as the zinc source and ammonia water as the precipitant, under microwave-assisted hydrothermal conditions, the carboxymethyl, carboxyl, hydroxyl, and aldehyde groups of carboxymethyl cellulose are used to regulate the lattice growth kinetics of zinc oxide, and nano-zinc oxide particles with a uniform particle size distribution are prepared. Crosslinking nano-cellulose and polyvinyl alcohol through borate bonds to form a three-dimensional interpenetrating network structure, and the carboxymethyl cellulose that stabilizes nano-zinc oxide is uniformly dispersed in the matrix to form a multi-scale reinforcement system. Nano-zinc oxide, as an antibacterial agent, has the advantages of good antibacterial effect and no drug resistance. Combined with the stabilizing effect of carboxymethyl cellulose, slow and precise antibacterial is achieved, avoiding the problem of bacterial drug resistance caused by traditional chemical antibacterial agents. The nano-cellulose-polyvinyl alcohol crosslinked network endows the composite paper with excellent hydrophobicity and mechanical strength, inhibits water evaporation and microbial penetration through physical barrier effects, and multi-level protection reduces the spoilage or quality decline of food caused by factors such as mechanical damage, water evaporation, and microbial contamination.

[0011] Further, in step (1), the dosage ratio of the carboxymethyl cellulose, alkali-urea solution, zinc chloride, and ammonia water is (1-10) g: 100 mL: (1-5) g: (10-20) mL; the alkali-urea solution is a mixed aqueous solution of potassium hydroxide and urea, and the mass concentration of potassium hydroxide in the alkali-urea solution is 5-12%, and the mass concentration of urea is 7-12%.

[0012] Further, in step (1), the microwave power of the microwave heating reaction is 400-900 W, the temperature is 30-80 °C, and the time is 30-90 min.

[0013] Further, in step (1), the dialysis time is 72-120 h, and the dialysis bag specification for dialysis is 1000-10000 Da.

[0014] Further, in step (2), the dosage ratio of the polyvinyl alcohol, nano-cellulose, and carboxymethyl cellulose solution of nano-zinc oxide is (1-10) g: (2-5) g: (20-50) mL.

[0015] Further, in step (2), the diameter of the nano-cellulose is 5-10 nm, and the length is 100-300 nm.

[0016] Further, in step (2), the temperature of the mixing is 80 °C, and the time is 2-4 h; and / or,

[0017] After the mixing, a defoaming step is further included; the temperature of the defoaming is 25 °C, and the time is 1-2 h.

[0018] Further, in step (2), the specific steps of papermaking are as follows: placing the obtained mixed solution in a vacuum heating coating machine for papermaking; the heating temperature for papermaking is 40 - 60°C, and the vacuum degree is 0.02 - 0.08 MPa.

[0019] Further, the preparation method of the hydrophobic antibacterial fresh - keeping composite paper includes the following steps:

[0020] (1) Dissolve 1 - 10 g of carboxymethyl cellulose in 100 mL of an alkali - urea solution (the alkali - urea solution is a mixed aqueous solution of potassium hydroxide and urea, the mass concentration of potassium hydroxide in the alkali - urea solution is 5 - 12%, and the mass concentration of urea is 7 - 12%). Add 1 - 5 g of zinc chloride, stir evenly, then add 10 - 20 mL of ammonia water, continue stirring, and then place the mixed solution in a microwave reaction kettle. React at 400 - 900 W and 30 - 80°C for 30 - 90 min. After the reaction, place the reaction solution in a dialysis bag for dialysis for 72 - 120 h. The specification of the dialysis bag is 1000 - 10000 Da to obtain a carboxymethyl cellulose solution with stable nano - zinc oxide.

[0021] (2) Dissolve 1 - 10 g of polyvinyl alcohol in 100 mL of deionized water, add 2 - 5 g of nanocellulose, then add 20 - 50 mL of the carboxymethyl cellulose solution with stable nano - zinc oxide obtained in step (1), add 5 - 10 g of genipin, stir in a water bath at 80°C for 2 - 4 h, then place it in a vacuum drying oven at 25°C for defoaming for 1 - 2 h. After that, use a vacuum heating coating machine to make paper from the defoamed liquid obtained by defoaming to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper with stable nano - zinc oxide, which is the hydrophobic antibacterial fresh - keeping composite paper.

[0022] The present invention provides a hydrophobic antibacterial fresh - keeping composite paper prepared by the preparation method described in the above technical solution.

[0023] The present invention also provides the application of the hydrophobic antibacterial fresh - keeping composite paper described in the above technical solution in the field of food preservation.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The preparation method provided by the present invention is simple, green, and efficient. During the process of preparing the carboxymethyl cellulose solution with nano - zinc oxide, no surfactant and chemical stabilizer need to be added. Moreover, nano - zinc oxide, as a physical antibacterial agent, can effectively avoid the harm of chemical fungicides to the environment and human body. At the same time, after nanocellulose is cross - linked with polyvinyl alcohol, the composite paper has the advantages of hydrophobicity, biodegradability, and strong physical properties, and is suitable for the packaging and transportation of food, especially fruits and vegetables.

[0026] The preparation method of the present invention has low cost, simple operation, and low requirements for the operation environment and equipment. The prepared composite paper is green and degradable, hydrophobic and non-toxic, antibacterial and non-resistant to drugs, and has good mechanical properties and flexibility, showing great potential in the field of food packaging such as fruits and vegetables. Description of the Drawings

[0027] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0028] Figure 1 The antibacterial effect diagrams of the composite paper CMC / PVA prepared in Comparative Example 1, the composite paper CMC / PVA / NC prepared in Comparative Example 2, and the composite paper CMC@ZnO NPs / PVA / NC prepared in Example 1 against Escherichia coli and Staphylococcus aureus. Detailed Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0031] The embodiments of the present invention provide a preparation method of a hydrophobic antibacterial fresh-keeping composite paper, including the following steps:

[0032] (1) Dissolve carboxymethyl cellulose in an alkali-urea solution, then add zinc chloride and ammonia water for microwave heating reaction, and then obtain a carboxymethyl cellulose solution of nano-zinc oxide through dialysis;

[0033] (2) Dissolve polyvinyl alcohol in water, then add nanocellulose, the carboxymethyl cellulose solution of nano-zinc oxide in step (1), and a cross-linking agent, and mix them for papermaking to obtain the hydrophobic antibacterial fresh-keeping composite paper.

[0034] In a preferred embodiment, in step (1), the dosage ratio of the carboxymethyl cellulose, alkali-urea solution, zinc chloride, and ammonia water is (1-10) g∶100 mL∶(1-5) g∶(10-20) mL, and more preferably (3-10) g∶100 mL∶(2-5) g∶(10-20) mL; the alkali-urea solution is a mixed aqueous solution of potassium hydroxide and urea, and the mass concentration of potassium hydroxide in the alkali-urea solution is 5-12%, more preferably 7-12%; the mass concentration of urea in the alkali-urea solution is 7-12%. Nano-zinc oxide is a multifunctional new inorganic material, and its particle size is generally between 1-100 nm. Due to the small molecule effect, it has very excellent application value in the antibacterial field and has properties that cannot be compared with ordinary chemical antibacterial agents. Carboxymethyl cellulose is a cellulose-based modified product prepared by grafting carboxymethyl groups onto the cellulose molecular chain. Since the grafted carboxymethyl groups have certain redox capabilities, and the carboxyl, hydroxyl, and aldehyde groups inherent in cellulose itself, carboxymethyl cellulose can prepare and stabilize nano-zinc oxide particles without adding chemical reducing agents and stabilizers. The present invention uses carboxymethyl cellulose as a stabilizer, fixative, and growth template, and realizes the in-situ synthesis and stabilization of nano-zinc oxide through a molecular self-assembly strategy; uses zinc chloride as a zinc source and ammonia water as a precipitant, and under microwave-assisted hydrothermal conditions, regulates the lattice growth kinetics of zinc oxide by using the reducing groups such as carboxymethyl, carboxyl, hydroxyl, and aldehyde groups of carboxymethyl cellulose to prepare nano-zinc oxide particles with uniform particle size distribution; selects nano-zinc oxide with strong bactericidal effect and no drug resistance as an antibacterial agent, and when contacting bacteria or microorganisms, rapidly releases nanoparticles by relying on the small molecule effect to destroy the cell integrity of bacteria or microorganisms, achieving the purpose of sterilization, and realizes slow and precise antibacterial through the stabilizing effect of carboxymethyl cellulose, avoiding the problem of bacterial drug resistance caused by traditional chemical antibacterial agents.

[0035] In a preferred embodiment, in step (1), the specific addition method of zinc chloride and ammonia water is as follows: first add zinc chloride and stir for 1-2 h, then add ammonia water and stir for 1-2 h, and then carry out microwave heating reaction; the addition method of ammonia water is dropwise addition. The present invention helps the carboxymethyl cellulose to stabilize zinc oxide by adding zinc chloride and ammonia water separately. Adding them simultaneously is likely to form flocs or precipitates, resulting in poor stabilization effect; the dropwise addition of ammonia water helps the carboxymethyl cellulose to uniformly fix nano-zinc oxide. Adding it all at once is likely to cause the aggregation of nano-zinc oxide and then form precipitates, with poor effect.

[0036] In a preferred embodiment, in step (1), the microwave power of the microwave heating reaction is 400 - 900 W, more preferably 600 - 900 W; the temperature of the microwave heating reaction is 30 - 80 °C, more preferably 50 - 80 °C; the time of the microwave heating reaction is 30 - 90 min, more preferably 45 - 90 min; the equipment for the microwave heating reaction is a microwave reaction kettle.

[0037] In a preferred embodiment, in step (1), the dialysis time is 72 - 120 h, and the dialysis bag specification for dialysis is 1000 - 10000 Da. When dialyzing, it should be ensured that unreacted ions are completely precipitated.

[0038] In a preferred embodiment, in step (2), the dosage ratio of polyvinyl alcohol, nanocellulose, and carboxymethyl cellulose solution of nanometer zinc oxide is (1 - 10) g : (2 - 5) g : (20 - 50) mL, more preferably (5 - 10) g : (2 - 5) g : (30 - 50) mL. Polyvinyl alcohol has the characteristics of low cost, good film-forming property, safety and non-toxicity, and can be an ideal raw material for preparing food fresh-keeping packaging materials. In the present invention, polyvinyl alcohol is compounded with carboxymethyl cellulose for stabilizing nanometer zinc oxide into paper for the fresh-keeping packaging of fruits and vegetables and other foods. It can not only solve the problem of food spoilage caused by bacterial and microbial contamination, but also protect the loss of food caused by external mechanical damage depending on the good flexibility and other mechanical properties of the composite paper. In the present invention, chemical cross-linking is carried out between nanocellulose molecules and polyvinyl alcohol molecules to form a stable network structure, which not only effectively improves the hydrophobic property of the composite paper, but also further improves the mechanical and physical properties of the composite paper, such as tensile strength, tear index, etc.

[0039] In a preferred embodiment, in step (2), the diameter of the nanocellulose is 5 - 10 nm, and the length is 100 - 300 nm.

[0040] In a preferred embodiment, in step (2), the cross-linking agent is selected from genipin; the mass ratio of the cross-linking agent to polyvinyl alcohol is (5 - 10) : (1 - 10).

[0041] In a preferred embodiment, in step (2), the temperature of the mixing is 80 °C, the time is 2 - 4 h; the mixing method is stirring.

[0042] In a preferred embodiment, in step (2), after mixing, it further includes a defoaming step; the temperature of the defoaming is 25 °C, the time is 1 - 2 h; the equipment for defoaming is a vacuum drying oven.

[0043] In a preferred embodiment, in step (2), the specific steps of papermaking are as follows: placing the obtained mixed solution in a vacuum heating coating machine for papermaking; the heating temperature for papermaking is 40 - 60 °C, more preferably 50 - 60 °C; the vacuum degree for papermaking is 0.02 - 0.08 MPa, more preferably 0.04 - 0.08 MPa.

[0044] In a preferred embodiment, in step (2), after papermaking, a drying step is further included; the drying temperature is 60 - 90 °C, more preferably 80 - 90 °C; the drying time is 2 - 10 h, more preferably 5 - 10 h.

[0045] The present invention provides a hydrophobic antibacterial fresh - keeping composite paper prepared by the preparation method described in the above technical solution.

[0046] The present invention also provides the application of the hydrophobic antibacterial fresh - keeping composite paper described in the above technical solution in the field of food preservation. The composite paper prepared by the present invention can be applied to the packaging and transportation of foods such as fruits and vegetables due to its hydrophobic, degradable and antibacterial properties.

[0047] In a preferred embodiment, the food includes fruits, vegetables, snacks or pastries; further, the food includes cherry tomatoes, grapes, cucumbers, baby cabbages, Chinese cabbages, strawberries, nuts or bread.

[0048] In the embodiments of the present invention, room temperature refers to "25 ± 2 °C".

[0049] Unless otherwise specified, the raw materials in the embodiments of the present invention are all obtained through commercial channels.

[0050] In the following examples and comparative examples, polyvinyl alcohol was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., 99% hydrolyzed; carboxymethyl cellulose was purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; nano - cellulose was purchased from Tianjin Wood Elf Biotechnology Co., Ltd.

[0051] Example 1

[0052] A preparation method of a hydrophobic antibacterial fresh - keeping composite paper, the specific steps are as follows:

[0053] (1) Dissolve 1 g of carboxymethyl cellulose (CMC) in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 5%, and the mass concentration of urea is 7%), add 1 g of zinc chloride, stir for 1 h, then dropwise add 10 mL of ammonia water, continue to stir for 1 h, and then place the mixed solution in a microwave reaction kettle, react at 400 W and 30 °C for 30 min. After the reaction is completed, place the reaction solution in a 1000 Da dialysis bag and dialyze for 72 h to obtain a carboxymethyl cellulose solution (CMC@ZnO NPs) with stable nano - zinc oxide.

[0054] (2) Dissolve 10 g of polyvinyl alcohol in 100 mL of deionized water, add 5 g of nanocellulose with a diameter of 5 - 10 nm and a length of 100 - 300 nm, then add 20 mL of the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide obtained in step (1), add 5 g of genipin, stir for 2 h in a water bath at 80 °C, then place it in a vacuum drying oven at 25 °C for defoaming for 1 h. After that, place the defoamed liquid in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 40 °C and a vacuum degree of 0.02 MPa. After the papermaking is completed, dry it at 60 °C for 5 h to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper for stabilizing nanometer zinc oxide (CMC@ZnONPs / PVA / NC), which is the hydrophobic antibacterial fresh-keeping composite paper.

[0055] Example 2

[0056] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper is as follows:

[0057] (1) Dissolve 3 g of carboxymethyl cellulose (CMC) in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 7% and the mass concentration of urea is 12%), add 2 g of zinc chloride, stir for 2 h and then dropwise add 15 mL of ammonia water, continue to stir for 2 h. Then place the mixed solution in a microwave reaction kettle and react at 600 W and 50 °C for 45 min. After the reaction is completed, place the reaction solution in a dialysis bag with a molecular weight cut-off of 1000 Da for dialysis for 96 h to obtain a carboxymethyl cellulose solution for stabilizing nanometer zinc oxide (CMC@ZnO NPs).

[0058] (2) Dissolve 5 g of polyvinyl alcohol in 100 mL of deionized water, add 5 g of nanocellulose with a diameter of 5 - 10 nm and a length of 100 - 300 nm, then add 30 mL of the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide obtained in step (1), add 6 g of genipin, stir for 3 h in a water bath at 80 °C, then place it in a vacuum drying oven at 25 °C for defoaming for 2 h. After that, place the defoamed liquid in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 50 °C and a vacuum degree of 0.04 MPa. After the papermaking is completed, dry it at 80 °C for 8 h to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper for stabilizing nanometer zinc oxide (CMC@ZnONPs / PVA / NC), which is the hydrophobic antibacterial fresh-keeping composite paper.

[0059] Example 3

[0060] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper is as follows:

[0061] (1) Dissolve 6 g of carboxymethyl cellulose (CMC) in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 12%, and the mass concentration of urea is 7%). Add 4 g of zinc chloride, stir for 2 h, then gradually add 20 mL of ammonia water dropwise, and continue to stir for 2 h. Then place the mixed solution in a microwave reactor and react at 800 W and 60 °C for 90 min. After the reaction is completed, place the reaction solution in a 1000 Da dialysis bag for 96 h to obtain a carboxymethyl cellulose solution (CMC@ZnO NPs) that stabilizes nano-zinc oxide.

[0062] (2) Dissolve 5 g of polyvinyl alcohol in 100 mL of deionized water, add 5 g of nanocellulose with a diameter of 5 - 10 nm and a length of 100 - 300 nm, then add 50 mL of the carboxymethyl cellulose solution (CMC@ZnO NPs) that stabilizes nano-zinc oxide obtained in step (1). Add 8 g of genipin, stir in a water bath at 80 °C for 4 h, then place it in a vacuum drying oven at 25 °C to defoam for 2 h. After that, place the defoamed solution in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 60 °C and a vacuum degree of 0.06 MPa. After the papermaking is completed, dry it at 90 °C for 10 h to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper (CMC@ZnO NPs / PVA / NC) that stabilizes nano-zinc oxide, which is the hydrophobic antibacterial fresh-keeping composite paper.

[0063] Example 4

[0064] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper, the specific steps are as follows:

[0065] (1) Dissolve 10 g of carboxymethyl cellulose (CMC) in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 12%, and the mass concentration of urea is 12%). Add 5 g of zinc chloride, stir for 2 h, then gradually add 20 mL of ammonia water dropwise, and continue to stir for 2 h. Then place the mixed solution in a microwave reactor and react at 900 W and 80 °C for 90 min. After the reaction is completed, place the reaction solution in a 1000 Da dialysis bag for dialysis for 120 h to obtain a carboxymethyl cellulose solution (CMC@ZnO NPs) that stabilizes nano-zinc oxide.

[0066] (2) Dissolve 10 g of polyvinyl alcohol in 100 mL of deionized water, add 5 g of nanocellulose with a diameter of 5 - 10 nm and a length of 100 - 300 nm, then add 50 mL of the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide obtained in step (1), add 10 g of genipin, stir at 80 °C in a water bath for 4 h, then place it in a vacuum drying oven at 25 °C for defoaming for 2 h. After that, place the defoamed liquid in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 60 °C and a vacuum degree of 0.08 MPa. After the papermaking is completed, dry it at 90 °C for 10 h to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper (CMC@ZnO NPs / PVA / NC) for stabilizing nanometer zinc oxide, which is the hydrophobic antibacterial fresh-keeping composite paper.

[0067] Comparative Example 1

[0068] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper, which is different from Example 1 in that nanocellulose and the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide are not introduced. The specific steps are as follows:

[0069] Dissolve 1 g of carboxymethyl cellulose in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 5%, and the mass concentration of urea is 7%) to obtain a carboxymethyl cellulose solution. Dissolve 10 g of polyvinyl alcohol in 100 mL of deionized water, then add 20 mL of the above carboxymethyl cellulose solution, add 5 g of genipin, stir at 80 °C in a water bath for 2 h, then place it in a vacuum drying oven at 25 °C for defoaming for 1 h. After that, place the defoamed liquid in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 40 °C and a vacuum degree of 0.02 MPa. After the papermaking is completed, dry it at 60 °C for 5 h to obtain a carboxymethyl cellulose / polyvinyl alcohol composite paper (CMC / PVA).

[0070] Comparative Example 2

[0071] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper, which is different from Example 1 in that the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide is not introduced. The specific steps are as follows:

[0072] Dissolve 1 g of carboxymethyl cellulose (CMC) in 100 mL of an aqueous mixed solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 5%, and the mass concentration of urea is 7%) to obtain a carboxymethyl cellulose solution. Dissolve 10 g of polyvinyl alcohol in 100 mL of deionized water, add 5 g of nanocellulose with a diameter of 5 - 10 nm and a length of 100 - 300 nm, then add 20 mL of the above carboxymethyl cellulose solution, add 5 g of genipin, stir for 2 h in a water bath at 80 °C, then place it in a vacuum drying oven at 25 °C for defoaming for 1 h. After that, place the defoamed solution in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 40 °C and a vacuum degree of 0.02 MPa. After the papermaking is completed, dry it at 60 °C for 5 h to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper (CMC / PVA / NC).

[0073] Comparative Example 3

[0074] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper, which is different from Example 1 in that nanocellulose is not introduced. The specific steps are as follows:

[0075] Step (1) is the same as that in Example 1;

[0076] (2) Dissolve 10 g of polyvinyl alcohol in 100 mL of deionized water, add 20 mL of the carboxymethyl cellulose solution for stabilizing nanometer zinc oxide obtained in step (1), add 5 g of genipin, stir for 2 h in a water bath at 80 °C, then place it in a vacuum drying oven at 25 °C for defoaming for 1 h. After that, place the defoamed solution in a vacuum heating coating machine to make paper under the conditions of a heating temperature of 40 °C and a vacuum degree of 0.02 MPa. After the papermaking is completed, dry it at 60 °C for 5 h to obtain a carboxymethyl cellulose / polyvinyl alcohol composite paper for stabilizing nanometer zinc oxide (CMC@ZnO NPs / PVA).

[0077] Comparative Example 4

[0078] A preparation method of a hydrophobic antibacterial fresh-keeping composite paper, the specific steps are as follows:

[0079] (1) Dissolve 1 g of carboxymethyl cellulose (CMC) in 100 mL of an aqueous mixed solution of potassium hydroxide and urea (the mass concentration of potassium hydroxide is 5%, and the mass concentration of urea is 7%), add 1 g of zinc chloride and 10 mL of ammonia water at the same time, stir for 1 h, then place the mixed solution in a microwave reaction kettle, react at 400 W and 30 °C for 30 min. After the reaction is completed, place the reaction solution in a dialysis bag and dialyze for 72 h to obtain a carboxymethyl cellulose solution for stabilizing nanometer zinc oxide (CMC@ZnO NPs).

[0080] Step (2) is the same as that in Example 1.

[0081] The hydrophobic properties of the composite papers prepared in Examples 1-4 and Comparative Examples 1-4 were measured using a fully automatic video optical contact angle measuring instrument (model: OCA50, made in Germany). Three parallel samples of each composite paper were tested and the average value was taken. The results are shown in Table 1.

[0082] The antibacterial rates of the composite papers prepared in Examples 1-4 and Comparative Examples 1-4 were determined by the plate counting method. The measurement results are shown in Table 1. The specific test process was as follows: First, the bacterial solutions of Escherichia coli and Staphylococcus aureus were cultured. Then, the bacterial solution concentration was diluted in a gradient manner until the ultraviolet OD600 value was in the range of 0.6-0.8. The composite paper was cut into a circle with a diameter of 1 cm and contacted with 0.1 mL of the bacterial solution for 0.5 h. After taking out the composite paper, it was placed in 30 mL of phosphate buffer solution (0.05 moL / L, pH = 7.2) and ultrasonicated for 5 min to obtain a mixed solution. 200 μL of the above mixed solution was extracted, and the mixed solution was evenly coated on the agar medium by the coating method. After incubating at 37 °C for 24 h, the growth of bacteria on the plate was observed and counted. The blank control group was a co-mixed solution of 0.1 mL of the bacterial solution and 30 mL of phosphate buffer solution (0.05 moL / L, pH = 7.2). The antibacterial rate was the ratio of the reduction in the number of bacteria in the experimental group to the number of bacteria in the blank control group.

[0083] Table 1 Hydrophobic properties and antibacterial rates of the composite papers prepared in Examples 1-4 and Comparative Examples 1-4

[0084]

[0085] Comparing Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, since the carboxymethyl cellulose solution for stabilizing nano zinc oxide was not introduced with nano cellulose, the abundant hydrophilic hydroxyl groups on the surface of polyvinyl alcohol were not reduced, resulting in a significant decrease in the contact angle of the obtained composite paper. At the same time, since polyvinyl alcohol and carboxymethyl cellulose do not have antibacterial properties, the composite paper of Comparative Example 1 has no antibacterial property.

[0086] Comparing Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, since nano zinc oxide was not introduced and polyvinyl alcohol and nano cellulose do not have antibacterial ability, the obtained composite paper has no inhibitory effect on Escherichia coli and Staphylococcus aureus. At the same time, since nano cellulose can form a stable network structure with polyvinyl alcohol through chemical crosslinking and fill the holes and gaps of the composite paper, the contact angle of the composite paper prepared in Comparative Example 2 with water is significantly improved compared with that of Comparative Example 1.

[0087] Comparison of Example 1 and Comparative Example 3 shows that the contact angle of the composite paper obtained in Comparative Example 3 is greatly reduced due to the lack of nanocellulose. The main reason is that the abundant hydrophilic hydroxyl groups on the surface of the polyvinyl alcohol molecules are not cross-linked with the nanocellulose, and there are a large number of holes and gaps between the fibers. In addition, the composite paper successfully and stably loads a large number of nano zinc oxide particles, so the composite paper still has excellent antibacterial effect.

[0088] Comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, since zinc chloride and ammonia solution are added to the carboxymethyl cellulose solution at the same time, the zinc oxide prepared is of different sizes and uneven in size, resulting in unstable chemical properties of zinc oxide. The prepared carboxymethyl cellulose solution of stable nano zinc oxide is prone to sedimentation, so the antibacterial rate of the prepared composite paper against Escherichia coli and Staphylococcus aureus is greatly reduced, but it still has a certain antibacterial ability, which is derived from the excellent antibacterial activity of nano zinc oxide itself. In addition, although the carboxymethyl cellulose solution of stable nano zinc oxide is unstable, it does not affect the chemical cross-linking effect of polyvinyl alcohol and nano cellulose. Therefore, compared with Example 1, the contact angle of the composite paper prepared in Comparative Example 4 does not change much.

[0089] Figure 1 The antibacterial effect diagram of the composite paper CMC / PVA prepared in comparative example 1, the composite paper CMC / PVA / NC prepared in comparative example 2 and the composite paper CMC@ZnO NPs / PVA / NC prepared in example 1 on Escherichia coli and Staphylococcus aureus. Figure 1 It can be seen that the composite paper CMC / PVA and CMC / PVA / NC showed no antibacterial effect on Escherichia coli and Staphylococcus aureus, the surface of the agar culture medium was covered with colonies, and the growth and reproduction of the colonies were not significantly inhibited; while the composite paper CMC@ZnO NPs / PVA / NC showed a significant inhibitory effect on Escherichia coli and Staphylococcus aureus, the reproduction and expansion of the colonies in the agar culture medium was inhibited, and a large number of blank spaces without bacterial contamination were shown, thanks to the antibacterial effect of nano-zinc oxide fixed in the composite paper.

[0090] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a hydrophobic, antibacterial and fresh-keeping composite paper, characterized in that: The following steps are involved: (1) dissolving carboxymethyl cellulose in an alkaline urea solution, then adding zinc chloride and ammonia water to carry out microwave heating reaction, and then dialyzing to obtain a carboxymethyl cellulose solution of nano zinc oxide; (2) dissolving polyvinyl alcohol in water, then adding nanocellulose, the carboxymethyl cellulose solution of nano zinc oxide in step (1) and a crosslinking agent, mixing and then making paper to obtain the hydrophobic antibacterial fresh-keeping composite paper.

2. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (1), the amount ratio of the carboxymethyl cellulose, alkaline urea solution, zinc chloride and ammonia water is (1-10) g: 100 mL: (1-5) g: (10-20) mL; the alkaline urea solution is a mixed aqueous solution of potassium hydroxide and urea, the mass concentration of potassium hydroxide in the alkaline urea solution is 5-12%, and the mass concentration of urea is 7-12%.

3. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (1), the microwave power of the microwave heating reaction is 400-900 W, the temperature is 30-80° C., and the time is 30-90 min.

4. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (1), the dialysis time is 72 to 120 hours, and the dialysis bag specification is 1000-10000Da.

5. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (2), the usage ratio of the polyvinyl alcohol, nanocellulose and carboxymethyl cellulose solution of nano zinc oxide is (1-10) g: (2-5) g: (20-50) mL.

6. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1 or 5, characterized in that: In step (2), the diameter of the nanocellulose is 5 to 10 nm and the length is 100 to 300 nm.

7. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (2), the mixing temperature is 80° C. and the mixing time is 2 to 4 hours; and / or, The mixing step further includes a degassing step; the degassing temperature is 25° C. and the time is 1 to 2 hours.

8. The method for preparing the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 1, characterized in that: In step (2), the specific steps of papermaking are: placing the mixed solution obtained by mixing in a vacuum heating coating machine for papermaking; the heating temperature of the papermaking is 40-60° C., and the vacuum degree is 0.02-0.08 MPa.

9. A hydrophobic, antibacterial, fresh-keeping composite paper prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hydrophobic, antibacterial and fresh-keeping composite paper according to claim 9 in the field of food preservation.

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