Preparation method and application of hydrophobic antibacterial fresh-keeping composite paper
The hydrophobic antibacterial preservation composite paper, which utilizes a cross-linked network of nano-zinc oxide and polyvinyl alcohol, solves the problems of difficult degradation and drug resistance in fruit and vegetable preservation materials, and achieves a highly efficient preservation and environmentally friendly packaging solution for fruits and vegetables.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QILU UNIVERSITY OF TECHNOLOGY (SHANDONG ACADEMY OF SCIENCES)
- Filing Date
- 2025-04-16
- Publication Date
- 2026-07-14
AI Technical Summary
Existing fruit and vegetable preservation packaging materials are mostly petroleum-based products, which are difficult to degrade and cause environmental pollution. At the same time, traditional chemical antibacterial agents have drug resistance problems and are difficult to effectively prevent fruits and vegetables from rotting and deteriorating during harvesting, transportation and storage.
A method for preparing hydrophobic antibacterial and food-preserving composite paper combining nano-zinc oxide and polyvinyl alcohol is proposed. Nano-zinc oxide is synthesized in situ under microwave-assisted hydrothermal conditions using carboxymethyl cellulose stabilizer. The nano-zinc oxide is then cross-linked with polyvinyl alcohol to form a three-dimensional network structure, achieving uniform dispersion and stability of the nano-zinc oxide. This results in antibacterial properties while avoiding drug resistance, and enhances hydrophobicity and mechanical strength.
The prepared composite paper is green and biodegradable, hydrophobic, antibacterial and non-drug resistant, and can effectively prevent fruits and vegetables from rotting due to mechanical damage, moisture evaporation and microbial contamination. It is suitable for packaging and transporting fruits, vegetables and other foods.
Smart Images
Figure CN120061173B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of functional materials technology, and in particular relates to a method for preparing and applying a hydrophobic antibacterial and food-preserving composite paper. Background Technology
[0002] Due to their unique physical and chemical properties, fruits and vegetables are prone to spoilage or quality deterioration during harvesting, transportation, storage, and sales due to factors such as mechanical damage, moisture evaporation, and microbial contamination, leading to economic losses and food safety issues. Currently, most commonly used fruit and vegetable preservation packaging materials are petroleum-based, which are difficult to degrade and easily cause environmental pollution. Therefore, developing new fruit and vegetable preservation packaging materials using green and biodegradable raw materials is a crucial step in keeping with the trends of the times.
[0003] Nano-zinc oxide is a novel, multifunctional inorganic material with particle sizes typically ranging from 1 to 100 nm. Its small size and the resulting small-molecule effect give it exceptional value in the antibacterial field, exhibiting properties unmatched by ordinary chemical antibacterial agents. Polyvinyl alcohol (PVA) is low-cost, has good film-forming properties, and is safe and non-toxic, making it an ideal raw material for preparing food preservation packaging materials. Therefore, combining the antibacterial properties of nano-zinc oxide with the non-toxic and biodegradable advantages of PVA to prepare a preservation packaging material that can reduce the spoilage rate of fruits and vegetables has become a pressing technical problem to be solved in this field. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a method for preparing and applying a hydrophobic antibacterial and food-preserving composite paper.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] This invention provides a method for preparing a hydrophobic antibacterial and food-preserving composite paper, comprising the following steps:
[0007] (1) Dissolve carboxymethyl cellulose in alkaline urea solution, then add zinc chloride and ammonia water for microwave heating reaction, and then obtain carboxymethyl cellulose solution with nano zinc oxide by dialysis;
[0008] (2) Dissolve polyvinyl alcohol in water, then add nanocellulose, carboxymethyl cellulose solution of nano zinc oxide from step (1) and crosslinking agent, mix and then make paper to obtain the hydrophobic antibacterial and fresh-keeping composite paper.
[0009] Technical principle:
[0010] This invention utilizes carboxymethyl cellulose (CMC) as a stabilizer, fixative, and growth template to achieve in-situ synthesis and stabilization of nano-zinc oxide through a molecular self-assembly strategy. Using zinc chloride as the zinc source and ammonia as a precipitant, under microwave-assisted hydrothermal conditions, the reducing groups (carboxymethyl, carboxyl, hydroxyl, and aldehyde groups) of CMC regulate the lattice growth kinetics of zinc oxide, resulting in uniformly distributed nano-zinc oxide particles. By crosslinking nano-cellulose with polyvinyl alcohol via borate ester bonds to form a three-dimensional interpenetrating network structure, the CMC stabilized in the nano-zinc oxide is uniformly dispersed in the matrix, forming a multi-scale reinforced system. Nano-zinc oxide, as an antibacterial agent, possesses the advantages of good antibacterial effect without inducing drug resistance. Combined with the stabilizing effect of CMC, it achieves slow and precise antibacterial action, avoiding the bacterial resistance problems caused by traditional chemical antibacterial agents. The CMC-polyvinyl alcohol crosslinked network endows the composite paper with excellent hydrophobicity and mechanical strength, inhibiting moisture evaporation and microbial penetration through physical barrier effects. This multi-level protection reduces spoilage or quality decline in food caused by mechanical damage, moisture evaporation, and microbial contamination.
[0011] Further, in step (1), the ratio of carboxymethyl cellulose, alkaline urea solution, zinc chloride and ammonia 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, wherein the mass concentration of potassium hydroxide in the alkaline urea solution is 5-12% and the mass concentration of urea is 7-12%.
[0012] Furthermore, in step (1), the microwave power of the microwave heating reaction is 400-900W, the temperature is 30-80℃, and the time is 30-90min.
[0013] Further, in step (1), the dialysis time is 72 to 120 hours, and the dialysis bag specifications are 1000-10000 Da.
[0014] Further, in step (2), the ratio of the amount of polyvinyl alcohol, nanocellulose and nanozinc oxide carboxymethyl cellulose solution is (1-10)g:(2-5)g:(20-50)mL.
[0015] Furthermore, in step (2), the diameter of the nanocellulose is 5-10 nm and the length is 100-300 nm.
[0016] Further, in step (2), the mixing temperature is 80°C, and the time is 2–4 hours; and / or,
[0017] The mixture also includes a degassing step; the degassing temperature is 25°C and the time is 1 to 2 hours.
[0018] Further, in step (2), the specific steps of papermaking are as follows: the mixed solution obtained by mixing is placed in a vacuum heating coating machine for papermaking; the heating temperature of papermaking is 40-60℃ and the vacuum degree is 0.02-0.08MPa.
[0019] Furthermore, the preparation method of the hydrophobic antibacterial preservation composite paper includes the following steps:
[0020] (1) Dissolve 1-10g of carboxymethyl cellulose in 100mL of alkaline urea solution (alkaline urea solution is a mixed aqueous solution of potassium hydroxide and urea, with a mass concentration of 5-12% for potassium hydroxide and 7-12% for urea), add 1-5g of zinc chloride, stir evenly, then add 10-20mL of ammonia water, continue stirring, then place the mixed solution in a microwave reactor and react at 400-900W and 30-80℃ for 30-90min. After the reaction, place the reaction solution in a dialysis bag and dialyze for 72-120h. The dialysis bag has a specification of 1000-10000Da to obtain a carboxymethyl cellulose solution with stable nano zinc oxide.
[0021] (2) Dissolve 1-10g of polyvinyl alcohol in 100mL of deionized water, add 2-5g of nanocellulose, then add 20-50mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 5-10g of genipin, stir in a water bath at 80℃ for 2-4h, then place in a vacuum drying oven at 25℃ for 1-2h to degas, and then use a vacuum heating coating machine to make paper from the degassing liquid to obtain carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper of stable nano zinc oxide, which is hydrophobic antibacterial preservation composite paper.
[0022] The present invention provides a hydrophobic antibacterial and food-preserving composite paper prepared by the preparation method described in the above technical solution.
[0023] This invention also provides the application of the hydrophobic antibacterial preservation 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 this invention is simple, green, and efficient. No surfactants or chemical stabilizers are needed during the preparation of the carboxymethyl cellulose solution containing nano-zinc oxide. Furthermore, nano-zinc oxide, as a physical antibacterial agent, effectively avoids the environmental and human health hazards associated with chemical disinfectants. Simultaneously, after crosslinking nano-cellulose with polyvinyl alcohol, the resulting composite paper possesses advantages such as hydrophobicity, biodegradability, and strong physical properties, making it suitable for packaging and transporting food, especially fruits and vegetables.
[0026] The preparation method of this invention is low in cost, simple to operate, and has low requirements for operating environment and equipment. The prepared composite paper is green and biodegradable, hydrophobic and non-toxic, antibacterial and non-drug resistant, and has good mechanical properties and flexibility. It has great potential for application in the field of food packaging such as fruits and vegetables. Attached Figure Description
[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:
[0028] Figure 1 The graph shows the antibacterial effects 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 Implementation
[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0031] This invention provides a method for preparing a hydrophobic antibacterial and food-preserving composite paper, comprising the following steps:
[0032] (1) Dissolve carboxymethyl cellulose in alkaline urea solution, then add zinc chloride and ammonia water for microwave heating reaction, and then obtain carboxymethyl cellulose solution with nano zinc oxide by dialysis;
[0033] (2) Dissolve polyvinyl alcohol in water, then add nanocellulose, carboxymethyl cellulose solution of nano zinc oxide from step (1) and crosslinking agent, mix and then make paper to obtain the hydrophobic antibacterial and fresh-keeping composite paper.
[0034] In a preferred embodiment, in step (1), the ratio of carboxymethyl cellulose, alkali urea solution, zinc chloride, and ammonia is (1-10) g: 100 mL: (1-5) g: (10-20) mL, 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, wherein the mass concentration of potassium hydroxide in the alkali urea solution is 5-12%, more preferably 7-12%; and the mass concentration of urea in the alkali urea solution is 7-12%. Nano zinc oxide is a novel, multifunctional inorganic material with particle sizes generally between 1-100 nm. Due to its small molecule effect, it has excellent application value in the antibacterial field and possesses properties unmatched by ordinary chemical antibacterial agents. Carboxymethyl cellulose is a cellulose-based modified product, prepared by grafting carboxymethyl groups onto the cellulose molecular chain. Because the grafted carboxymethyl groups have certain redox capabilities, and combined with the reducing groups such as carboxyl, hydroxyl, and aldehyde groups inherent in cellulose itself, carboxymethyl cellulose can be used to prepare and stabilize nano-zinc oxide particles without adding chemical reducing agents and stabilizers. This invention utilizes carboxymethyl cellulose as a stabilizer, fixative, and growth template to achieve in-situ synthesis and stabilization of nano-zinc oxide through a molecular self-assembly strategy. Using zinc chloride as the zinc source and ammonia as the precipitant, under microwave-assisted hydrothermal conditions, the reducing groups of carboxymethyl cellulose (carboxymethyl, carboxyl, hydroxyl, and aldehyde groups) regulate the lattice growth kinetics of zinc oxide, resulting in uniformly distributed nano-zinc oxide particles. Nano-zinc oxide, possessing strong bactericidal activity and without inducing drug resistance, is selected as an antibacterial agent. Upon contact with bacteria or microorganisms, it rapidly releases nanoparticles through a small molecule effect, disrupting the integrity of bacterial or microbial cells to achieve sterilization. The stabilizing effect of carboxymethyl cellulose enables slow and precise antibacterial action, avoiding the bacterial resistance problems caused by traditional chemical antibacterial agents.
[0035] In a preferred embodiment, in step (1), the zinc chloride and ammonia are added as follows: zinc chloride is added and stirred for 1-2 hours, then ammonia is added and stirred for 1-2 hours, followed by microwave heating reaction; the ammonia is added dropwise. This invention helps stabilize zinc oxide with carboxymethyl cellulose by adding zinc chloride and ammonia separately. Adding them simultaneously easily forms flocculent matter or precipitate, resulting in poor stabilization. Adding ammonia dropwise helps the nano-zinc oxide be uniformly fixed by carboxymethyl cellulose; adding it all at once easily causes the nano-zinc oxide to agglomerate and precipitate, resulting in poor stabilization.
[0036] In a preferred embodiment, in step (1), the microwave power of the microwave heating reaction is 400-900W, more preferably 600-900W; the temperature of the microwave heating reaction is 30-80℃, more preferably 50-80℃; the time of the microwave heating reaction is 30-90min, more preferably 45-90min; and the equipment for the microwave heating reaction is a microwave reactor.
[0037] In a preferred embodiment, in step (1), the dialysis time is 72–120 hours, and the dialysis bag has a capacity of 1000–10000 Da. During dialysis, it should be ensured that all unreacted ions are completely precipitated.
[0038] In a preferred embodiment, in step (2), the ratio of the amount of polyvinyl alcohol, nanocellulose, and carboxymethyl cellulose solution containing nano-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 properties, and safety and non-toxicity, and can be used as an ideal raw material for preparing food preservation packaging materials. This invention combines polyvinyl alcohol with carboxymethyl cellulose containing stable nano-zinc oxide to form paper, which is used for the preservation packaging of fruits, vegetables, and other foods. This not only solves the problem of food spoilage caused by bacterial and microbial contamination, but also protects food from damage caused by external mechanical forces by relying on the good flexibility and other mechanical properties of the composite paper. This invention utilizes the chemical cross-linking of nanocellulose molecules and polyvinyl alcohol molecules to form a stable network structure, which not only effectively improves the hydrophobic properties of the composite paper, but also further improves the mechanical and physical properties of the composite paper, such as tensile strength and tear index.
[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 crosslinking agent is selected from genipin; the mass ratio of the crosslinking agent to polyvinyl alcohol is (5-10):(1-10).
[0041] In a preferred embodiment, in step (2), the mixing temperature is 80°C and the time is 2 to 4 hours; the mixing method is stirring.
[0042] In a preferred embodiment, step (2) further includes a degassing step after mixing; the degassing temperature is 25°C and the time is 1-2 hours; the degassing equipment is a vacuum drying oven.
[0043] In a preferred embodiment, in step (2), the specific steps of papermaking are as follows: the mixed solution obtained by mixing is placed in a vacuum heating coating machine for papermaking; the heating temperature of papermaking is 40-60℃, more preferably 50-60℃; the vacuum degree of papermaking is 0.02-0.08MPa, more preferably 0.04-0.08MPa.
[0044] In a preferred embodiment, step (2) further includes a drying step after papermaking; the drying temperature is 60-90°C, more preferably 80-90°C; the drying time is 2-10 hours, more preferably 5-10 hours.
[0045] The present invention provides a hydrophobic antibacterial and food-preserving composite paper prepared by the preparation method described in the above technical solution.
[0046] This invention also provides the application of the hydrophobic and antibacterial preservative composite paper described above in the field of food preservation. The composite paper prepared by this invention, possessing hydrophobic, biodegradable, and antibacterial properties, can be used in the packaging and transportation of fruits, vegetables, and other foods.
[0047] In a preferred embodiment, the food includes fruits, vegetables, snacks, or pastries; further, the food includes cherry tomatoes, grapes, cucumbers, bok choy, cabbage, strawberries, nuts, or bread.
[0048] In this embodiment of the invention, room temperature refers to "25±2℃".
[0049] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.
[0050] In the following examples and comparative examples, polyvinyl alcohol was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and was 99% hydrolyzed; carboxymethyl cellulose was purchased from Shanghai McLean Biochemical Technology Co., Ltd.; and nanocellulose was purchased from Tianjin Wood Elf Biotechnology Co., Ltd.
[0051] Example 1
[0052] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, the specific steps of which are as follows:
[0053] (1) Dissolve 1g of carboxymethyl cellulose (CMC) in 100mL 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 1g of zinc chloride, stir for 1h, then add 10mL of ammonia dropwise, continue stirring for 1h, then place the mixed solution in a microwave reactor and react at 400W and 30℃ for 30min. After the reaction is completed, place the reaction solution in a 1000Da dialysis bag for dialysis for 72h to obtain a carboxymethyl cellulose solution of stable nano zinc oxide (CMC@ZnO NPs).
[0054] (2) Dissolve 10g of polyvinyl alcohol in 100mL of deionized water, add 5g of nanocellulose with a diameter of 5-10nm and a length of 100-300nm, add 20mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 5g of genipin, stir in a water bath at 80℃ for 2h, then place in a vacuum drying oven at 25℃ for 1h to degas, then place the degassing liquid in a vacuum heating coating machine to make paper under the conditions of heating temperature of 40℃ and vacuum degree of 0.02MPa, and after the paper is made, dry at 60℃ for 5h to obtain carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper of stable nano zinc oxide (CMC@ZnONPs / PVA / NC), which is a hydrophobic antibacterial and fresh-keeping composite paper.
[0055] Example 2
[0056] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, the specific steps of which are as follows:
[0057] (1) Dissolve 3g of carboxymethyl cellulose (CMC) in 100mL 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 2g of zinc chloride, stir for 2h, then add 15mL of ammonia dropwise, continue stirring for 2h, then place the mixed solution in a microwave reactor and react at 600W and 50℃ for 45min. After the reaction is completed, place the reaction solution in a 1000Da dialysis bag and dialyze for 96h to obtain a carboxymethyl cellulose solution of stable nano zinc oxide (CMC@ZnO NPs).
[0058] (2) Dissolve 5g of polyvinyl alcohol in 100mL of deionized water, add 5g of nanocellulose with a diameter of 5-10nm and a length of 100-300nm, add 30mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 6g of genipin, stir in a water bath at 80℃ for 3h, then place in a vacuum drying oven at 25℃ for 2h to degas, then place the degassing liquid in a vacuum heating coating machine to make paper under the conditions of heating temperature of 50℃ and vacuum degree of 0.04MPa, and after the paper is made, dry at 80℃ for 8h to obtain carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper of stable nano zinc oxide (CMC@ZnONPs / PVA / NC), which is hydrophobic antibacterial and fresh-keeping composite paper.
[0059] Example 3
[0060] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, the specific steps of which are as follows:
[0061] (1) Dissolve 6g of carboxymethyl cellulose (CMC) in 100mL 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 4g of zinc chloride, stir for 2h, then add 20mL of ammonia dropwise, continue stirring for 2h, then place the mixed solution in a microwave reactor and react at 800W and 60℃ for 90min. After the reaction is completed, place the reaction solution in a 1000Da dialysis bag for 96h to obtain a carboxymethyl cellulose solution of stable nano zinc oxide (CMC@ZnO NPs).
[0062] (2) Dissolve 5g of polyvinyl alcohol in 100mL of deionized water, add 5g of nanocellulose with a diameter of 5-10nm and a length of 100-300nm, add 50mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 8g of genipin, stir in a water bath at 80℃ for 4h, then place in a vacuum drying oven at 25℃ for 2h to degas, then place the degassing liquid in a vacuum heating coating machine to make paper under the conditions of heating temperature of 60℃ and vacuum degree of 0.06MPa, and after the paper is made, dry at 90℃ for 10h to obtain carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper of stable nano zinc oxide (CMC@ZnONPs / PVA / NC), which is a hydrophobic antibacterial and fresh-keeping composite paper.
[0063] Example 4
[0064] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, the specific steps of which are as follows:
[0065] (1) Dissolve 10g of carboxymethyl cellulose (CMC) in 100mL 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 5g of zinc chloride, stir for 2h, then add 20mL of ammonia dropwise, continue stirring for 2h, then place the mixed solution in a microwave reactor and react at 900W and 80℃ for 90min. After the reaction is completed, place the reaction solution in a 1000Da dialysis bag and dialyze for 120h to obtain a carboxymethyl cellulose solution of stable nano zinc oxide (CMC@ZnO NPs).
[0066] (2) Dissolve 10g of polyvinyl alcohol in 100mL of deionized water, add 5g of nanocellulose with a diameter of 5-10nm and a length of 100-300nm, add 50mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 10g of genipin, stir in an 80℃ water bath for 4h, then place in a 25℃ vacuum drying oven for degassing for 2h, then place the degassing liquid in a vacuum heating coating machine and make paper under the conditions of heating temperature of 60℃ and vacuum degree of 0.08MPa. After the paper is made, dry at 90℃ for 10h to obtain carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper of stable nano zinc oxide (CMC@ZnO NPs / PVA / NC), which is a hydrophobic antibacterial and fresh-keeping composite paper.
[0067] Comparative Example 1
[0068] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, differing from Example 1 in that a carboxymethyl cellulose solution containing nanocellulose and stable nano-zinc oxide is not introduced. The specific steps are as follows:
[0069] 1 g of carboxymethyl cellulose was dissolved in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (potassium hydroxide concentration was 5% by mass, and urea concentration was 7% by mass) to obtain a carboxymethyl cellulose solution. 10 g of polyvinyl alcohol was dissolved in 100 mL of deionized water, and then 20 mL of the above carboxymethyl cellulose solution was added. 5 g of genipin was added, and the mixture was stirred in an 80°C water bath for 2 h. Then, it was placed in a 25°C vacuum drying oven for degassing for 1 h. After degassing, the solution was placed in a vacuum heating coating machine and paper was made under conditions of 40°C heating and 0.02 MPa vacuum. After papermaking, it was dried at 60°C for 5 h to obtain carboxymethyl cellulose / polyvinyl alcohol composite paper (CMC / PVA).
[0070] Comparative Example 2
[0071] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, differing from Example 1 in that a carboxymethyl cellulose solution stabilizing nano-zinc oxide is not introduced. The specific steps are as follows:
[0072] 1 g of carboxymethyl cellulose (CMC) was dissolved in 100 mL of a mixed aqueous solution of potassium hydroxide and urea (potassium hydroxide concentration was 5% by mass, and urea concentration was 7% by mass) to obtain a carboxymethyl cellulose solution. 10 g of polyvinyl alcohol was dissolved in 100 mL of deionized water, and 5 g of nanocellulose with a diameter of 5–10 nm and a length of 100–300 nm was added. Then, 20 mL of the above carboxymethyl cellulose solution was added, along with 5 g of genipin. The mixture was stirred in an 80°C water bath for 2 hours, and then placed in a 25°C vacuum drying oven for degassing for 1 hour. The degassed solution was then placed in a vacuum heating coating machine at a heating temperature of 40°C and a vacuum degree of 0.02 MPa to form paper. After paper forming, the paper was dried at 60°C for 5 hours to obtain a carboxymethyl cellulose / polyvinyl alcohol / nanocellulose composite paper (CMC / PVA / NC).
[0073] Comparative Example 3
[0074] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, which differs from Example 1 in that nanocellulose is not introduced, and the specific steps are as follows:
[0075] Step (1) is the same as in Example 1;
[0076] (2) Dissolve 10g of polyvinyl alcohol in 100mL of deionized water, add 20mL of carboxymethyl cellulose solution of stable nano zinc oxide obtained in step (1), add 5g of genipin, stir in a water bath at 80℃ for 2h, then place in a vacuum drying oven at 25℃ for 1h to degas, and then place the degassing liquid in a vacuum heating coating machine to make paper under the conditions of heating temperature at 40℃ and vacuum degree at 0.02MPa. After the paper is made, dry at 60℃ for 5h to obtain carboxymethyl cellulose / polyvinyl alcohol composite paper (CMC@ZnO NPs / PVA) of stable nano zinc oxide.
[0077] Comparative Example 4
[0078] A method for preparing a hydrophobic antibacterial and food-preserving composite paper, the specific steps of which are as follows:
[0079] (1) Dissolve 1g of carboxymethyl cellulose (CMC) in 100mL 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 1g of zinc chloride and 10mL of ammonia water, stir for 1h, then place the mixed solution in a microwave reactor and react at 400W and 30℃ for 30min. After the reaction is completed, place the reaction solution in a dialysis bag and dialyze for 72h to obtain a carboxymethyl cellulose solution of stable nano zinc oxide (CMC@ZnO NPs).
[0080] Step (2) is the same as 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 were tested for each composite paper and the average value was taken. The results are shown in Table 1.
[0082] The antibacterial rate of the composite paper prepared in Examples 1-4 and Comparative Examples 1-4 was determined by plate counting method. The results are shown in Table 1. The specific testing procedure was as follows: *Escherichia coli* and *Staphylococcus aureus* were cultured first, and then the bacterial concentration was serially diluted to a UV OD600 value within the range of 0.6-0.8. The composite paper was cut into circles with a diameter of 1 cm and contacted with 0.1 mL of bacterial solution for 0.5 h. The composite paper was then removed and placed in 30 mL of phosphate buffer solution (0.05 mol / L, pH = 7.2), and sonicated for 5 min to obtain a mixture. 200 μL of the above mixture was extracted and evenly spread onto agar medium using a coating method. After incubation at 37℃ for 24 h, bacterial growth on the plates was observed and counted. The blank control group consisted of a mixture of 0.1 mL of 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 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, because no nanocellulose and carboxymethyl cellulose solution stabilizing nano-zinc oxide were introduced, 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 resulting composite paper. Furthermore, since polyvinyl alcohol and carboxymethyl cellulose do not possess antibacterial properties, the composite paper of Comparative Example 1 lacks antibacterial properties.
[0086] Comparing Example 1 and Comparative Example 2, it can be seen that, due to the absence of nano-zinc oxide and the lack of antibacterial properties of polyvinyl alcohol and nanocellulose, the composite paper obtained in Comparative Example 2 showed no inhibitory effect on Escherichia coli and Staphylococcus aureus. Meanwhile, because nanocellulose can chemically crosslink with polyvinyl alcohol to form a stable network structure, filling the pores and gaps in the composite paper, the contact angle between the composite paper prepared in Comparative Example 2 and water was significantly improved compared to Comparative Example 1.
[0087] Comparing Example 1 and Comparative Example 3, it can be seen that the contact angle of the composite paper obtained in Comparative Example 3 decreased significantly due to the absence of nanocellulose. This is mainly because the abundant hydrophilic hydroxyl groups on the surface of polyvinyl alcohol molecules did not crosslink with nanocellulose, and there were numerous pores and gaps between the fibers. Furthermore, the composite paper successfully and stably loaded a large number of nano-zinc oxide particles, thus maintaining its excellent antibacterial effect.
[0088] Comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, because zinc chloride and ammonia solution were added to the carboxymethyl cellulose solution simultaneously, the zinc oxide prepared was of inconsistent size and uneven in shape, resulting in unstable chemical properties of the zinc oxide. The resulting stable nano-zinc oxide carboxymethyl cellulose solution was prone to sedimentation, thus significantly reducing the antibacterial rate of the prepared composite paper against Escherichia coli and Staphylococcus aureus. However, it still possesses some antibacterial ability due to the excellent antibacterial activity inherent in the nano-zinc oxide itself. Furthermore, although the stable nano-zinc oxide carboxymethyl cellulose solution was unstable, it did not affect the chemical cross-linking effect between polyvinyl alcohol and nano-cellulose. Therefore, compared to Example 1, the contact angle of the composite paper prepared in Comparative Example 4 did not change significantly.
[0089] Figure 1 The graph shows the antibacterial effects 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. Figure 1 It can be seen that the composite paper CMC / PVA and CMC / PVA / NC did not show any antibacterial effect against Escherichia coli and Staphylococcus aureus. The surface of the agar medium was covered with colonies, and the growth and reproduction of the colonies were not significantly inhibited. However, the composite paper CMC@ZnO NPs / PVA / NC showed a significant inhibitory effect on Escherichia coli and Staphylococcus aureus. The reproduction and expansion of colonies in the agar medium were inhibited, and a large number of blank areas were not contaminated by bacteria. This is attributed to the antibacterial effect of the nano zinc oxide fixed in the composite paper.
[0090] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing a hydrophobic antibacterial and food-preserving composite paper, characterized in that, Includes the following steps: (1) Dissolve carboxymethyl cellulose in alkaline urea solution, then add zinc chloride and ammonia water for microwave heating reaction, and then obtain carboxymethyl cellulose solution with nano zinc oxide by dialysis; (2) Dissolve polyvinyl alcohol in water, then add nanocellulose, carboxymethyl cellulose solution of nano zinc oxide from step (1) and crosslinking agent, mix, degas, and make paper to obtain the hydrophobic antibacterial and fresh-keeping composite paper. In step (1), the ratio of carboxymethyl cellulose, alkaline urea solution, zinc chloride and ammonia 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, wherein the mass concentration of potassium hydroxide in the alkaline urea solution is 5-12% and the mass concentration of urea is 7-12%; In step (1), the zinc chloride and ammonia are added as follows: zinc chloride is added and stirred for 1-2 hours, then ammonia is added and stirred for 1-2 hours, and then microwave heating reaction is carried out; the ammonia is added drop by drop. The specific steps of the papermaking process are as follows: the mixed solution obtained after degassing is placed in a vacuum heating coating machine for papermaking; In step (2), the ratio of the amount of polyvinyl alcohol, nanocellulose and nanozinc oxide carboxymethyl cellulose solution used is (1-10) g: (2-5) g: (20-50) mL; In step (2), the diameter of the nanocellulose is 5-10 nm and the length is 100-300 nm; In step (2), the crosslinking agent is selected from genipin; the mass ratio of the crosslinking agent to polyvinyl alcohol is (5-10):(1-10).
2. The method for preparing the hydrophobic antibacterial and food-preserving composite paper according to claim 1, characterized in that, In step (1), the microwave power of the microwave heating reaction is 400-900W, the temperature is 30-80℃, and the time is 30-90min.
3. The method for preparing the hydrophobic antibacterial and food-preserving composite paper according to claim 1, characterized in that, In step (1), the dialysis time is 72 to 120 hours, and the dialysis bag has a specification of 1000 to 10000 Da.
4. The method for preparing the hydrophobic antibacterial and food-preserving composite paper according to claim 1, characterized in that, In step (2), the mixing temperature is 80°C and the time is 2-4 hours; and / or, the degassing temperature is 25°C and the time is 1-2 hours.
5. The method for preparing the hydrophobic antibacterial and food-preserving composite paper according to claim 1, characterized in that, In step (2), the heating temperature for papermaking is 40-60℃ and the vacuum degree is 0.02-0.08MPa.
6. A hydrophobic antibacterial and food-preserving composite paper prepared by the preparation method according to any one of claims 1 to 5.
7. The application of the hydrophobic antibacterial preservation composite paper as described in claim 6 in the field of food preservation.