Preparation method of natural plant essential oil modified antibacterial nanocellulose

Abstract

The invention discloses a preparation method of natural plant essential oil modified antibacterial nanocellulose, and relates to the technical field of material science, fresh lavandula angustifolia is used as a raw material, after cleaning and crushing, supercritical CO2 extraction is adopted to refine essential oil, and bamboo pulp cellulose is subjected to TEMPO oxidation and high pressure homogenization to prepare nanocellulose. The preparation method has the advantages that the lavender essential oil is extracted by adopting a supercritical CO2 extraction technology, so that the damage of a traditional organic solvent to active ingredients of the essential oil is avoided, and the integrity and the high activity of natural antibacterial ingredients are ensured; the problems that an existing material is single in antibacterial function and short in time efficiency and cannot meet the requirements of high-end medical scenes are solved, then the layered double hydroxide nanosheet load slow release technology is combined, the antibacterial time efficiency is remarkably prolonged, the limitation of the existing material is broken through, and a more reliable and more effective antibacterial solution is provided for high-end medical treatment.

Description

Technical Field

[0001] The invention relates to the field of material science and technology, and in particular to a method for preparing natural plant essential oil-modified antibacterial nanocellulose. Background Art

[0002] Research on antibacterial nanocellulose modified with natural plant essential oils is an important innovative direction in the fields of materials science and green chemistry. Nanocellulose is a nanoscale material extracted from natural biomass (such as wood and plant fibers). It has a high specific surface area, good biocompatibility, degradability, and mechanical properties. It shows broad application prospects in food packaging, biomedicine, textile industry and other fields. However, the antibacterial properties of pure nanocellulose itself are limited, which restricts its further application in scenarios requiring antibacterial protection.

[0003] Existing technologies have certain defects. First, the antibacterial components of plant essential oils are easily decomposed under high temperature, light or high humidity environments, resulting in a decrease in antibacterial effect. The antibacterial effectiveness period of traditional essential oil dressings is only 3-5 years, which makes it unable to meet the needs of high-end medical scenarios, such as surgical implants and long-lasting antibacterial dressings. Secondly, existing antibacterial materials rely on chemical modifications, such as quaternary ammonium salts, which have toxic residues and are non-degradable, with poor biocompatibility, making it difficult to pass medical-grade safety certification. To this end, we propose a method for preparing antibacterial nanocellulose modified with natural plant essential oils. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing natural plant essential oil-modified antibacterial nanocellulose.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing antibacterial nanocellulose modified with natural plant essential oil, the preparation method comprising the following specific steps:

[0006] Step 1: Select fresh narrow-leaved lavender flowers as natural plants, rinse them with clean water to remove dust, impurities and insect eggs that may be attached to the surface, dry the surface water after rinsing, and then use a chopper to crush the flowers;

[0007] Step 2: extracting refined lavender essential oil from lavender powder using supercritical CO2 extraction;

[0008] Step 3: Using natural bamboo pulp cellulose as raw material, nanocellulose is prepared by TEMPO oxidation combined with high-pressure homogenization treatment;

[0009] Step 4: preparing zinc-aluminum layered double hydroxide nanosheets by coprecipitation method;

[0010] Step 5: mixing the refined lavender essential oil obtained in step 2 with the zinc-aluminum layered double hydroxide nanosheets prepared in step 4, adding the mixture into an ultrasonic dispersion container containing deionized water for ultrasonic dispersion, so that the lavender essential oil is evenly loaded onto the zinc-aluminum layered double hydroxide nanosheets to form essential oil-loaded zinc-aluminum layered double hydroxide nanosheets;

[0011] Step 6: adding the essential oil-loaded zinc-aluminum layered double hydroxide nanosheets and the nanocellulose prepared in step 3 into a reactor and mixing them, adding deionized water and stirring to form a mixture with a pH-responsive sustained-release function;

[0012] Step 7: The mixture obtained in step 6 is washed with deionized water, stirred and centrifuged after washing, and then the product is freeze-dried and pre-treated, and then vacuum-dried to remove moisture to obtain pH-responsive sustained-release antibacterial nanocellulose.

[0013] As a further embodiment of the present invention, in step 1, the selected lavender flowers are picked 3-5 days after the flowering period and are processed within 2-4 hours after picking. The lavender flowers are crushed and sieved with a 2-3 mm filter. After the lavender flowers are rinsed, natural bamboo fiber absorbent paper is used to absorb surface moisture.

[0014] As a further solution of the present invention: in step 2, the specific extraction process is as follows:

[0015] The lavender powder is evenly loaded into a supercritical extraction kettle, with the loading amount being 60%-70% of the volume of the extraction kettle. Purified CO2 gas is introduced into the extraction kettle, so that the pressure in the extraction kettle is gradually increased to 22MPa-25MPa within 15min-20min. At the same time, the temperature of the extraction kettle is adjusted to 38°C-41°C through a circulating hot water bath, so that the CO2 extracts the powder under a supercritical state. The extraction time is 2.5h-3h. During this period, the material in the extraction kettle is stirred at a speed of 80r / min-100r / min by a stirring device to promote the mass transfer process. After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline, and the essential oil and CO2 are separated by adjusting the pressure and temperature in the separation kettle.

[0016] As a further embodiment of the present invention, in step 2, the specific operation of separating the essential oil and CO2 by adjusting the pressure and temperature in the separation kettle is as follows: first, the pressure of the separation kettle is reduced to 7MPa-8MPa within 10min-15min, and the temperature is maintained at 38°C-40°C, so that the lavender essential oil is precipitated from the supercritical CO2 fluid to obtain crude lavender essential oil, and then the crude lavender essential oil is filtered using a polyethersulfone microporous filter membrane with a pore size of 0.45μm-0.6μm at -0.08MPa to -0.1MPa to remove tiny impurity particles therein to obtain refined lavender essential oil.

[0017] As a further solution of the present invention: In step 3, the specific process of preparing nanocellulose by TEMPO oxidation combined with high-pressure homogenization is as follows:

[0018] Natural bamboo pulp cellulose is placed in deionized water to prepare a suspension with a mass fraction of 2%-3%. TEMPO reagent is added to the suspension at a mass fraction of 0.2%-0.4% of the cellulose mass. At the same time, 1.2%-1.5% of NaBr is added as an auxiliary agent. Stir evenly. Under stirring, 11%-13% of NaCl is slowly added dropwise. lO solution for oxidation reaction, the dropwise addition rate is controlled at 1mL / min-2mL / min, the reaction time is 2.5h-3h, and 1M sodium hydroxide solution is used to maintain the pH value of the reaction system at 10-10.5 during the reaction. After the oxidation reaction is completed, ethanol produced by the biological fermentation method is added at a volume ratio of ethanol to the reaction system of 1:3-4 to terminate the reaction. The reaction product is then separated by centrifugation and repeatedly washed with deionized water 3-4 times until the pH value of the washing liquid reaches 6.7-7.2. The washed product is redispersed in deionized water to prepare a suspension with a mass fraction of 1%-2%. The suspension is then treated by a high-pressure homogenizer at a pressure of 110MPa-120MPa, and the treatment is circulated 3-4 times, with each treatment time being 25S-30S, so that the cellulose is further refined into nanocellulose.

[0019] As a further embodiment of the present invention: in the step 4, the specific process for preparing zinc-aluminum layered double hydroxide nanosheets is as follows: a mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate are prepared respectively, the molar ratio of zinc nitrate to aluminum nitrate is 2.5-3:1, the total concentration of metal ions in the mixed solution is 0.5 mol / L-0.6 mol / L, the concentration of sodium hydroxide in the mixed alkaline solution of sodium hydroxide and sodium carbonate is 1.5 mol / L-2 mol / L, and the concentration of sodium carbonate is 0.5 mol / L-0.7 mol / L. l / L, and adjust the pH value of the mixed alkali solution to 10.5-10.7 with dilute hydrochloric acid or sodium hydroxide solution, and add the metal salt mixed solution dropwise to the mixed alkali solution at a rate of 5mL / min-8mL / min under the stirring condition of 300r / min-400r / min. During the dropwise addition process, the reaction system temperature is maintained at 70℃-72℃, and stirring is continued for 9h-10h. After the reaction is completed, the product is separated by centrifugation and repeatedly washed with deionized water for 4-5 times until no nitrate ions are detected in the washing liquid when tested with silver nitrate solution. The washed product is dried at 60℃-70℃ for 12h-15h, and then ground into powder to obtain zinc-aluminum layered double hydroxide nanosheets.

[0020] As a further embodiment of the present invention: in the step 5, the refined lavender essential oil and the aluminum layered double hydroxide nanosheets are mixed in a mass ratio of 1:6-7, the temperature of the ultrasonic dispersion container is controlled at 23°C-27°C by a circulating cold water bath to avoid thermal degradation of the essential oil, and an ultrasonic power of 220W is used for dispersion, and the dispersion time is 50min-60min.

[0021] As a further embodiment of the present invention: in step six, the zinc-aluminum layered double hydroxide nanosheets loaded with essential oil and the nanocellulose prepared in step three are mixed in a mass ratio of 1:7-8, deionized water is added to make the solid content of the mixed system 2wt%-4wt%, and the mixture is stirred in a reactor at a speed of 350r / min-450r / min for 1.2h-2h.

[0022] As a further embodiment of the present invention: in the step seven, the mixture obtained in the step six is washed with deionized water 3-4 times, and the mixed product is mixed with deionized water in a mass ratio of 1:5-8 during each washing, stirred for 10-15 minutes, and then centrifuged. The freeze-drying pretreatment is pre-freezing at -45°C to -40°C for 2.5h-3h, and then vacuum drying at 42°C-45°C for 20h-23h.

[0023] By adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The present invention uses supercritical CO2 extraction technology to extract lavender essential oil, avoiding the destruction of the active ingredients of the essential oil by traditional organic solvents, ensuring the integrity and high activity of the natural antibacterial components. On this basis, the lavender essential oil is loaded with layered double hydroxide nanosheets, realizing the controlled sustained release of the antibacterial components in the acidic wound environment, solving the problem that the existing materials have a single antibacterial function and a short time effect and cannot meet the needs of high-end medical scenarios (surgical implants, long-acting antibacterial dressings). By relying on supercritical CO2 extraction to ensure the quality of the essential oil and combining the loading and sustained release technology of layered double hydroxide nanosheets, the antibacterial time effect is significantly extended, breaking through the limitations of existing materials and providing a more reliable and effective antibacterial solution for high-end medical treatment.

[0025] 2. The present invention adopts green technology throughout the entire process, such as using bio-fermentation ethanol to terminate the reaction, conducting pH monitoring, and recycling CO2, thereby avoiding chemical pollution and meeting the safety standards of medical-grade materials. Natural bamboo pulp cellulose is used as a water-absorbing material, retaining its biocompatibility. At the same time, it is combined with natural ingredients such as lavender essential oil to give the material natural and green characteristics. This green and natural material is not only safe and reliable, but also reduces the cost of industrial production, promotes the innovative application of green and natural materials in the medical and health industry, and can be widely used in degradable surgical sutures, artificial skin scaffolds and other fields, meeting the demand for environmentally friendly materials in high-end medical care. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the method steps in an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of parameter comparison in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0029] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Please see the attached Figure 1 The present invention provides a method for preparing antibacterial nanocellulose modified with natural plant essential oils, the preparation method comprising the following specific steps:

[0031] Step 1: Select fresh narrow-leaved lavender flowers as natural plants, rinse them with clean water to remove dust, impurities and insect eggs that may be attached to the surface, dry the surface water after rinsing, and then use a chopper to crush the flowers;

[0032] Step 2: extracting refined lavender essential oil from lavender powder using supercritical CO2 extraction;

[0033] Step 3: Using natural bamboo pulp cellulose as raw material, nanocellulose is prepared by TEMPO oxidation combined with high-pressure homogenization treatment;

[0034] Step 4: preparing zinc-aluminum layered double hydroxide nanosheets by coprecipitation method;

[0035] Step 5: mixing the refined lavender essential oil obtained in step 2 with the zinc-aluminum layered double hydroxide nanosheets prepared in step 4, adding the mixture into an ultrasonic dispersion container containing deionized water for ultrasonic dispersion, so that the lavender essential oil is evenly loaded onto the zinc-aluminum layered double hydroxide nanosheets to form essential oil-loaded zinc-aluminum layered double hydroxide nanosheets;

[0036] Step 6: adding the essential oil-loaded zinc-aluminum layered double hydroxide nanosheets and the nanocellulose prepared in step 3 into a reactor and mixing them, adding deionized water and stirring to form a mixture with a pH-responsive sustained-release function;

[0037] Step 7: The mixture obtained in step 6 is washed with deionized water, stirred and centrifuged after washing, and then the product is freeze-dried and pre-treated, and then vacuum-dried to remove moisture to obtain pH-responsive sustained-release antibacterial nanocellulose.

[0038] In one embodiment of the present invention: in step 1, the selected narrow-leaved lavender flowers are flowers picked 3-5 days after the flowering period, and are processed within 2 hours to 4 hours after picking. The narrow-leaved lavender flowers are crushed and sieved with a 2mm to 3mm filter mesh. After the narrow-leaved lavender flowers are rinsed, natural bamboo fiber absorbent paper is used to absorb the surface moisture.

[0039] In one embodiment of the present invention: in step 2, the specific extraction process is as follows:

[0040] The lavender powder is evenly loaded into a supercritical extraction kettle, with the loading amount being 60%-70% of the volume of the extraction kettle. Purified CO2 gas is introduced into the extraction kettle, so that the pressure in the extraction kettle is gradually increased to 22MPa-25MPa within 15min-20min. At the same time, the temperature of the extraction kettle is adjusted to 38°C-41°C through a circulating hot water bath, so that the CO2 extracts the powder under a supercritical state. The extraction time is 2.5h-3h. During this period, the material in the extraction kettle is stirred at a speed of 80r / min-100r / min by a stirring device to promote the mass transfer process. After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline, and the essential oil and CO2 are separated by adjusting the pressure and temperature in the separation kettle.

[0041] In one embodiment of the present invention: in step 2, the specific operation of separating the essential oil and CO2 by adjusting the pressure and temperature in the separation kettle is as follows: first, the pressure of the separation kettle is reduced to 7MPa-8MPa within 10min-15min, and the temperature is maintained at 38°C-40°C, so that the lavender essential oil is precipitated from the supercritical CO2 fluid to obtain crude lavender essential oil, and then the crude lavender essential oil is filtered, using a polyethersulfone microporous filter membrane with a pore size of 0.45μm-0.6μm at -0.08MPa to -0.1MPa to remove tiny impurity particles therein to obtain refined lavender essential oil.

[0042] In one embodiment of the present invention: In step 3, the specific process for preparing nanocellulose by TEMPO oxidation combined with high-pressure homogenization is as follows:

[0043] Natural bamboo pulp cellulose is placed in deionized water to prepare a suspension with a mass fraction of 2%-3%. TEMPO reagent is added to the suspension at a mass fraction of 0.2%-0.4% of the cellulose mass. At the same time, 1.2%-1.5% of NaBr is added as an auxiliary agent. Stir evenly. Under stirring, 11%-13% of NaCl is slowly added dropwise. lO solution for oxidation reaction, the dropwise addition rate is controlled at 1mL / min-2mL / min, the reaction time is 2.5h-3h, and 1M sodium hydroxide solution is used to maintain the pH value of the reaction system at 10-10.5 during the reaction. After the oxidation reaction is completed, ethanol produced by the biological fermentation method is added at a volume ratio of ethanol to the reaction system of 1:3-4 to terminate the reaction. The reaction product is then separated by centrifugation and repeatedly washed with deionized water 3-4 times until the pH value of the washing liquid reaches 6.7-7.2. The washed product is redispersed in deionized water to prepare a suspension with a mass fraction of 1%-2%. The suspension is then treated by a high-pressure homogenizer at a pressure of 110MPa-120MPa, and the treatment is circulated 3-4 times, with each treatment time being 25S-30S, so that the cellulose is further refined into nanocellulose.

[0044] In one embodiment of the present invention: in step 4, the specific process for preparing zinc-aluminum layered double hydroxide nanosheets is as follows: a mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate are prepared respectively, the molar ratio of zinc nitrate to aluminum nitrate is 2.5-3:1, the total concentration of metal ions in the mixed solution is 0.5 mol / L-0.6 mol / L, the concentration of sodium hydroxide in the mixed alkaline solution of sodium hydroxide and sodium carbonate is 1.5 mol / L-2 mol / L, and the concentration of sodium carbonate is 0.5 mol / L-0.7 mol / L. l / L, and adjust the pH value of the mixed alkali solution to 10.5-10.7 with dilute hydrochloric acid or sodium hydroxide solution, and add the metal salt mixed solution dropwise to the mixed alkali solution at a rate of 5mL / min-8mL / min under the stirring condition of 300r / min-400r / min. During the dropwise addition process, the reaction system temperature is maintained at 70℃-72℃, and stirring is continued for 9h-10h. After the reaction is completed, the product is separated by centrifugation and repeatedly washed with deionized water for 4-5 times until no nitrate ions are detected in the washing liquid when tested with silver nitrate solution. The washed product is dried at 60℃-70℃ for 12h-15h, and then ground into powder to obtain zinc-aluminum layered double hydroxide nanosheets.

[0045] In one embodiment of the present invention: in step 5, the refined lavender essential oil and the aluminum-type layered double hydroxide nanosheets are mixed in a mass ratio of 1:6-7, the temperature of the ultrasonic dispersion container is controlled at 23°C-27°C by a circulating cold water bath to avoid thermal degradation of the essential oil, and an ultrasonic power of 220W is used for dispersion, and the dispersion time is 50min-60min.

[0046] In one embodiment of the present invention: in step six, the zinc-aluminum layered double hydroxide nanosheets loaded with essential oil and the nanocellulose prepared in step three are mixed in a mass ratio of 1:7-8, deionized water is added to make the solid content of the mixed system 2wt%-4wt%, and the mixture is stirred in a reactor at a speed of 350r / min-450r / min for 1.2h-2h.

[0047] In one embodiment of the present invention: in step seven, the mixture obtained in step six is washed with deionized water 3-4 times, and the mixed product is mixed with deionized water in a mass ratio of 1:5-8 during each washing, stirred for 10min-15min, and then centrifuged. The freeze-drying pretreatment is pre-freezing at -45°C to -40°C for 2.5h-3h, and then vacuum drying at 42°C-45°C for 20h-23h.

[0048] Example 1, please refer to the attached Figure 1, select fresh narrow-leaved lavender flowers picked 5 days after the flowering period, and process them within 4 hours after picking. Rinse with clean water to remove dust, impurities and insect eggs that may be attached to the surface. After rinsing, use natural bamboo fiber absorbent paper to absorb the surface moisture. Then use a chopper to crush the flowers. After crushing, sieve with a 3mm filter. Supercritical CO2 extraction method is used to extract refined lavender essential oil from lavender powder. The lavender powder is evenly loaded into the supercritical extraction kettle. The loading amount is 70% of the volume of the extraction kettle. Purified CO2 gas is introduced into the extraction kettle to gradually increase the pressure in the extraction kettle to 25MPa within 20 minutes. At the same time, the temperature of the extraction kettle is adjusted to 41°C through a circulating hot water bath, so that CO2 extracts the powder under supercritical state. The extraction time is 3 hours, during which the stirring device is used at 100r / min. The rotation speed stirs the material in the extraction kettle to promote the mass transfer process. After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline. The pressure of the separation kettle is first reduced to 8MPa within 15 minutes and the temperature is maintained at 40°C to allow the lavender essential oil to precipitate from the supercritical CO2 fluid to obtain crude lavender essential oil. The crude lavender essential oil is then filtered using a polyethersulfone microporous filter membrane with a pore size of 0.6μm at -0.08MPa to remove tiny impurity particles and obtain refined lavender essential oil. Natural bamboo pulp cellulose is used as raw material to prepare nanocellulose through TEMPO oxidation combined with high-pressure homogenization treatment. Natural bamboo pulp cellulose is placed in deionized water and prepared into a suspension with a mass fraction of 3%. TEMPO reagent is added to the suspension at a mass fraction of 0.4% of the cellulose mass. At the same time, 1.5% of NaBr is added as an auxiliary agent and stirred evenly. Under stirring, 13% NaCl is slowly added at a drop rate of 2mL / min. lO solution for oxidation reaction, the reaction time is 3h, and 1M sodium hydroxide solution is used to maintain the pH value of the reaction system at 10.5 during the reaction. After the oxidation reaction is completed, ethanol produced by the biological fermentation method is added at a volume ratio of ethanol to the reaction system of 1:4 to terminate the reaction. The reaction product is then separated by centrifugation and repeatedly washed with deionized water 4 times until the pH value of the washing liquid reaches 7.2. The washed product is redispersed in deionized water to prepare a suspension with a mass fraction of 2%. The suspension is then treated by a high-pressure homogenizer at a pressure of 120MPa. The high-pressure homogenization treatment is repeated 4 times, with each treatment time of 30s, so that the cellulose is further refined into nanocellulose.Zinc-aluminum layered double hydroxide nanosheets were prepared by a coprecipitation method. A mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate were prepared respectively. The molar ratio of zinc nitrate to aluminum nitrate was 3:1. The total concentration of metal ions in the mixed solution was 0.6 mol / L. The concentration of sodium hydroxide in the mixed alkaline solution of sodium hydroxide and sodium carbonate was 2 mol / L and the concentration of sodium carbonate was 0.7 mol / L. The pH value of the mixed alkaline solution was adjusted to 10.7 with dilute hydrochloric acid or sodium hydroxide solution. The metal salt mixed solution was added dropwise to the mixed alkaline solution at a rate of 8 mL / min under stirring at 400 r / min. The reaction system temperature was maintained at 72°C during the addition process and stirring was continued for 10 hours. After the reaction was completed, the product was separated by centrifugation and repeatedly washed with deionized water five times until no nitrate ions were detected in the washing solution using silver nitrate solution. The washed product was dried at 70°C for 15 hours and then ground into powder to obtain zinc-aluminum layered double hydroxide nanosheets. Refined lavender essential oil and zinc-aluminum layered double hydroxide nanosheets were mixed in a mass ratio of 1:7 and added to an ultrasonic dispersion container containing deionized water. The temperature of the ultrasonic dispersion container was controlled at 27°C by a circulating cold water bath. Ultrasonic dispersion was performed at 220W for 60 minutes to uniformly load the lavender essential oil onto the zinc-aluminum layered double hydroxide nanosheets, forming essential oil-loaded zinc-aluminum layered double hydroxide nanosheets. The essential oil-loaded zinc-aluminum layered double hydroxide nanosheets and nanocellulose were added to a reactor in a mass ratio of 1:8. Deionized water was added to a solid content of the mixture of 4wt%. The mixture was stirred in the reactor at 450 rpm for 2 hours to form a mixture with pH-responsive sustained-release function. The mixture was washed four times with deionized water. During each washing, the mixed product was mixed with deionized water in a mass ratio of 1:8, stirred for 15 minutes, and then centrifuged. The mixture was pre-frozen at -40°C for 3 hours for freeze-drying pretreatment, and then vacuum-dried at 45°C for 23 hours to remove moisture to obtain pH-responsive sustained-release antibacterial nanocellulose.

[0049] Example 2, please refer to the attached Figure 1, select fresh narrow-leaved lavender flowers picked 3 days after the flowering period, and process them within 2 hours after picking. Rinse with clean water to remove dust, impurities and insect eggs that may be attached to the surface. After rinsing, use natural bamboo fiber absorbent paper to absorb the surface moisture. Then use a chopper to crush the flowers. After crushing, sieve with a 2mm filter. Supercritical CO2 extraction method is used to extract refined lavender essential oil from lavender powder. The lavender powder is evenly loaded into the supercritical extraction kettle. The loading amount is 60% of the volume of the extraction kettle. Purified CO2 gas is introduced into the extraction kettle to gradually increase the pressure in the extraction kettle to 22MPa within 15 minutes. At the same time, the temperature of the extraction kettle is adjusted to 38°C through a circulating hot water bath, so that CO2 extracts the powder under supercritical state. The extraction time is 2.5 hours, during which the stirring device is used to stir the powder at 80r / min. The rotation speed stirs the material in the extraction kettle to promote the mass transfer process. After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline. The pressure of the separation kettle is first reduced to 7MPa within 10 minutes and the temperature is maintained at 38°C to allow the lavender essential oil to precipitate from the supercritical CO2 fluid to obtain crude lavender essential oil. The crude lavender essential oil is then filtered using a polyethersulfone microporous filter membrane with a pore size of 0.45μm at -0.1MPa to remove tiny impurity particles and obtain refined lavender essential oil. Natural bamboo pulp cellulose is used as raw material to prepare nanocellulose through TEMPO oxidation combined with high-pressure homogenization treatment. Natural bamboo pulp cellulose is placed in deionized water and prepared into a suspension with a mass fraction of 2%. TEMPO reagent is added to the suspension at a mass fraction of 0.2% of the cellulose mass. At the same time, 1.2% of NaBr is added as an auxiliary agent and stirred evenly. Under stirring, 11% NaCl is slowly added at a drop rate of 1mL / min. lO solution for oxidation reaction, the reaction time is 2.5h, and 1M sodium hydroxide solution is used to maintain the pH value of the reaction system at 10 during the reaction. After the oxidation reaction, ethanol produced by the biological fermentation method is added at a volume ratio of ethanol to the reaction system of 1:3 to terminate the reaction. The reaction product is then separated by centrifugation and repeatedly washed with deionized water three times until the pH value of the washing liquid reaches 6.7. The washed product is redispersed in deionized water to prepare a suspension with a mass fraction of 1%. The suspension is then treated by a high-pressure homogenizer at a pressure of 110MPa. The high-pressure homogenization treatment is repeated three times, with each treatment time of 25s, to further refine the cellulose into nanocellulose.Zinc-aluminum layered double hydroxide nanosheets were prepared by a coprecipitation method. A mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate were prepared respectively. The molar ratio of zinc nitrate to aluminum nitrate was 2.5:1. The total concentration of metal ions in the mixed solution was 0.5 mol / L. In the mixed alkaline solution of sodium hydroxide and sodium carbonate, the concentration of sodium hydroxide was 1.5 mol / L and the concentration of sodium carbonate was 0.5 mol / L. The pH value of the mixed alkaline solution was adjusted to 10.5 with dilute hydrochloric acid or sodium hydroxide solution. The metal salt mixed solution was added dropwise to the mixed alkaline solution at a rate of 5 mL / min under stirring at 300 r / min. The temperature of the reaction system was maintained at 70°C during the addition process and stirring was continued for 9 hours. After the reaction was completed, the product was separated by centrifugation and repeatedly washed with deionized water four times until no nitrate ions were detected in the washing solution using silver nitrate solution. The washed product was dried at 60°C for 12 hours and then ground into powder to obtain zinc-aluminum layered double hydroxide nanosheets. Refined lavender essential oil and zinc-aluminum layered double hydroxide nanosheets were mixed in a mass ratio of 1:6 and added to an ultrasonic dispersion container containing deionized water. The temperature of the ultrasonic dispersion container was controlled at 23°C by a circulating cold water bath. Ultrasonic dispersion was performed at 220W for 50 minutes to uniformly load the lavender essential oil onto the zinc-aluminum layered double hydroxide nanosheets, forming essential oil-loaded zinc-aluminum layered double hydroxide nanosheets. The essential oil-loaded zinc-aluminum layered double hydroxide nanosheets and nanocellulose were added to a reactor in a mass ratio of 1:7. Deionized water was added to a solid content of 2wt% of the mixture. The mixture was stirred in the reactor at 350 rpm for 1.2 hours to form a mixture with pH-responsive sustained-release function. The mixture was washed three times with deionized water. During each washing, the mixed product was mixed with deionized water in a mass ratio of 1:5, stirred for 10 minutes, and then centrifuged. The mixture was pre-frozen at -45°C for 2.5 hours for freeze-drying pretreatment, and then vacuum-dried at 42°C for 20 hours to remove moisture to obtain pH-responsive sustained-release antibacterial nanocellulose.

[0050] Example 3, please refer to the attached Figure 1 , Step 1: Lavender pretreatment

[0051] Raw Material Selection: Carefully selected lavender flowers are harvested three days after flowering. At this stage, the natural antibacterial and anti-inflammatory properties of the flowers reach a high level, laying an excellent foundation for the subsequent extraction of high-quality lavender essential oil. Furthermore, to maximize the preservation of the active ingredients in the flowers, processing begins within two hours of harvesting.

[0052] Cleaning operation: Place the selected narrow-leaved lavender flowers under running water and rinse for 5 minutes. Running water can effectively remove dust, impurities and possible insect eggs attached to the surface of the flowers to ensure the cleanliness of the flowers. After rinsing, use absorbent paper made of natural bamboo fiber to dry the moisture on the surface of the flowers. Bamboo fiber absorbent paper not only has good water absorption, but its natural and environmentally friendly characteristics also meet the green and natural requirements of the entire preparation process.

[0053] Mincing: Use a mincer to chop the processed flowers into 2mm pieces, and then pass them through a 2mm filter. This is to make the particle size of the pieces more uniform, which is conducive to the full extraction of essential oils in the subsequent supercritical CO2 extraction process.

[0054] Step 2: Supercritical CO2 extraction of essential oils

[0055] Filling material: Evenly fill the supercritical fluid extraction vessel with the lavender powder obtained in step 1, filling it at 65% of the vessel's volume. A suitable filling amount ensures sufficient contact between the CO2 and the powder, improving extraction efficiency.

[0056] Adjusting parameters: Purified CO2 gas is introduced into the extraction kettle, and the pressure in the extraction kettle is gradually increased to 22MPa within 15-20 minutes. At the same time, the temperature of the extraction kettle is adjusted to 38°C using a circulating hot water bath. In this process, it is very important to accurately control the rate of increase and the final value of the pressure and temperature, because the properties of supercritical CO2 are extremely sensitive to pressure and temperature. Only under appropriate conditions can CO2 exhibit good extraction performance.

[0057] Extraction: Maintaining the aforementioned pressure and temperature conditions, the CO2 extracts the powder under supercritical conditions for 2.5 hours. During this time, the contents of the extraction kettle are stirred at 90 rpm. This stirring promotes mass transfer between the CO2 and the powder, allowing the lavender essential oil to dissolve more fully in the supercritical CO2.

[0058] Separation of essential oil: After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline. The pressure of the separation kettle is first reduced to 7MPa within 10-15 minutes, and the temperature is maintained at 38°C, so that the lavender essential oil is precipitated from the supercritical CO2 fluid to obtain crude lavender essential oil.

[0059] Filtration and refining: The crude lavender essential oil is filtered using a 0.45 μm polyethersulfone membrane at a pressure of -0.09 MPa to remove any tiny impurity particles that may be present, thereby obtaining refined lavender essential oil;

[0060] Step 3: Nanocellulose preparation

[0061] Preparation of suspension: natural bamboo pulp cellulose is placed in deionized water to prepare a suspension with a mass fraction of 2.5%. Natural bamboo pulp cellulose is a renewable green resource and a high-quality raw material for preparing nanocellulose;

[0062] Adding reagents: Add TEMPO reagent with a purity of not less than 98% to the suspension in an amount of 0.2% of the mass of the cellulose, and add analytically pure NaBr as an auxiliary agent, and stir evenly. TEMPO reagent and NaBr auxiliary agent play an important catalytic role in the subsequent oxidation reaction.

[0063] Oxidation reaction: Under stirring, slowly add NaClO solution with an available chlorine content of 10%-12% for oxidation reaction. The addition rate is controlled at 1.5 mL / min. During the reaction, the pH value of the reaction system is maintained at 10.2±0.1 using 1 M sodium hydroxide solution. The reaction time is 2.5 hours. Precise control of the addition rate and pH value can ensure the smooth progress of the oxidation reaction and avoid over-oxidation or under-oxidation.

[0064] Termination reaction: After the oxidation reaction is completed, ethanol produced by biological fermentation is added at a volume ratio of 1:3 between ethanol and the reaction system to terminate the reaction. Ethanol produced by biological fermentation is green and environmentally friendly, which conforms to the green concept of the entire preparation process.

[0065] Centrifugal washing: The reaction product was separated by centrifugation and washed repeatedly with deionized water 3-4 times until the pH value of the washing solution was close to neutral;

[0066] High-pressure homogenization: The washed product is redispersed in deionized water to form a 1%-2% suspension by mass, which is then passed through a high-pressure homogenizer. The high-pressure homogenization process is performed at a pressure of 110 MPa, with three cycles of 25 seconds each, to further refine the cellulose into nanocellulose.

[0067] Step 4: Synthesis of LDH nanosheets

[0068] Preparation of solution: preparing a mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate respectively, wherein the molar ratio of zinc nitrate to aluminum nitrate is 2.5:1, the total concentration of metal ions in the mixed solution is 0.5-0.6 mol / L, the concentration of sodium hydroxide in the mixed alkaline solution of sodium hydroxide and sodium carbonate is 1.5-2 mol / L, and the concentration of sodium carbonate is 0.5-0.7 mol / L, and the pH value of the mixed alkaline solution is adjusted to 10.5 with dilute hydrochloric acid or sodium hydroxide solution. The zinc nitrate, aluminum nitrate, sodium hydroxide, and sodium carbonate used are all analytical grade reagents, and the conductivity of the deionized water used in the preparation of the solution is not higher than 1 μS / cm;

[0069] Coprecipitation reaction: Under vigorous stirring conditions (stirring speed of 350r / min), the metal salt mixed solution was added dropwise to the mixed alkaline solution at a rate of 5-8mL / min. The reaction system temperature was maintained at 70°C during the addition process and stirring was continued for 9 hours. During this process, precise control of the dropping rate, stirring speed and reaction temperature is crucial for the production of LDH nanosheets with good performance;

[0070] Washing and drying: After the reaction is completed, the product is separated by centrifugation and repeatedly washed with deionized water 4-5 times until no nitrate ions are detected in the washing liquid (tested with silver nitrate solution). The washed product is then dried at 65°C for 12-15 hours and finally ground into powder to obtain zinc-aluminum layered double hydroxide (LDH) nanosheets;

[0071] Step 5: Essential Oil Loading

[0072] The lavender essential oil obtained in step 2 and the LDH nanosheets prepared in step 4 are mixed in a mass ratio of 1:6, and added to an ultrasonic dispersion container containing an appropriate amount of deionized water. The temperature of the ultrasonic dispersion container is controlled at 25° C. by a circulating cold water bath. The ultrasonic power is 220 W and the dispersion time is 50 minutes. Under the action of ultrasonic dispersion, the lavender essential oil can be evenly loaded onto the LDH nanosheets to form essential oil-loaded LDH nanosheets;

[0073] Step 6: Mixing and modification

[0074] The essential oil-loaded LDH nanosheets and the nanocellulose prepared in step 3 were added to a jacketed stainless steel reactor in a mass ratio of 1:7. Circulating water was introduced into the jacket for temperature control. The temperature fluctuation range did not exceed ±2°C during the reaction. An appropriate amount of deionized water was added to adjust the solid content of the mixed system to 3wt%. The mixture was stirred in the reactor at a speed of 400 r / min for 1.5 hours to fully mix the two to form a mixture with a pH-responsive sustained-release function.

[0075] Step 7: Post-processing

[0076] The mixed product obtained in step six is washed with deionized water. During washing, the mixed product is mixed with deionized water in a mass ratio of 1:6, stirred for 10-15 minutes, and then centrifuged. After washing, the product is pre-frozen at -45°C for 2.5 hours for freeze-drying pretreatment, and then vacuum-dried at 42°C and maintained at a vacuum degree of 10-20 Pa for 20 hours to remove moisture and obtain pH-responsive sustained-release antibacterial nanocellulose.

[0077] Specifically, biodegradable antibacterial surgical sutures

[0078] Preparation method: Antibacterial nanocellulose and polylactic acid are blended in a mass ratio of 3:7, and fibers with a diameter of 15 μm are prepared by electrospinning, which are then shaped into lines by hot pressing.

[0079] performance:

[0080] Initial breaking strength: 320MPa (wet state), able to withstand a certain amount of tension during surgery to ensure the effectiveness of suturing.

[0081] Antibacterial effectiveness period: 4 weeks (simulated wound environment), providing antibacterial protection for wounds for a longer period of time and reducing the risk of infection.

[0082] Complete degradation time: 5 months, avoiding the trouble of removing traditional sutures and reducing patients' pain.

[0083] Advantages: No need to remove stitches, reducing patient pain; natural essential oil ingredients promote wound healing and improve patient recovery efficiency.

[0084] Specifically, artificial skin scaffold

[0085] Preparation method: Antibacterial nanocellulose and collagen were mixed in a ratio of 1:3 and freeze-dried into a porous scaffold (porosity 85%).

[0086] performance:

[0087] Cell adhesion rate: 98% (L929 fibroblasts), which is beneficial to cell attachment and growth, and promotes the repair of skin tissue.

[0088] Moisture permeability: 2500g / m 2 / 24h, can maintain a moist environment for the wound and promote wound healing.

[0089] Antibacterial persistence: 6 weeks (simulating wound infection environment), inhibiting bacterial growth for a long time and preventing wound infection.

[0090] Advantages: Bionic skin structure, with both antibacterial and repair-promoting functions, suitable for deep burn treatment, providing patients with better treatment options.

[0091] As attached Figure 2As shown, combining the contents of the above three groups of embodiments, it can be concluded that the active ingredients of lavender essential oil are retained by supercritical CO2 extraction technology, and combined with the layered double hydroxide nanosheet loaded sustained-release system, the long-term controllable release of antibacterial ingredients in the acidic wound environment is successfully achieved, breaking through the limitations of traditional antibacterial materials with short aging and single function, and meeting the needs of high-end medical scenarios such as surgical implants and long-term dressings. The whole process green process (such as bioethanol termination reaction, CO2 recycling rate>95%) ensures material safety. The combination of natural bamboo pulp cellulose and lavender essential oil gives the product biocompatibility and environmental protection characteristics. Through the optimization of process parameters (such as extraction pressure 22-25MPa, homogenization pressure 110-120MPa), the wet tensile strength of the material reaches 178-185MPa, and the moisture permeability is 2500g / m 2 / 24h, its comprehensive performance is better than that of similar chemical antibacterial materials. It not only increases the added value of natural plant resources, but also provides innovative products such as degradable surgical sutures and artificial skin scaffolds for the medical and health field, promoting the application of green materials in high-end medical care, and has significant technological innovation and industrial transformation potential.

[0092] Although the present invention is disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing antibacterial nanocellulose modified with natural plant essential oils, characterized in that: The preparation method comprises the following specific steps: Step 1: Select fresh narrow-leaved lavender flowers as natural plants, rinse them with clean water to remove impurities, dry the surface moisture after rinsing, and then use a chopper to crush the flowers; Step 2: extracting refined lavender essential oil from lavender powder using supercritical CO2 extraction; Step 3: Using natural bamboo pulp cellulose as raw material, nanocellulose is prepared by TEMPO oxidation combined with high-pressure homogenization treatment; Step 4: preparing zinc-aluminum layered double hydroxide nanosheets by coprecipitation method; Step 5: mixing the refined lavender essential oil obtained in step 2 with the zinc-aluminum layered double hydroxide nanosheets prepared in step 4, adding the mixture into an ultrasonic dispersion container containing deionized water for ultrasonic dispersion, so that the lavender essential oil is evenly loaded onto the zinc-aluminum layered double hydroxide nanosheets to form essential oil-loaded zinc-aluminum layered double hydroxide nanosheets; Step 6: adding the essential oil-loaded zinc-aluminum layered double hydroxide nanosheets and the nanocellulose prepared in step 3 into a reactor and mixing them, adding deionized water and stirring to form a mixture with a pH-responsive sustained-release function; Step 7: The mixture obtained in step 6 is washed with deionized water, stirred and centrifuged after washing, and then the product is freeze-dried and pre-treated, and then vacuum-dried to obtain pH-responsive sustained-release antibacterial nanocellulose.

2. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step 1, the selected lavender flowers are picked 3-5 days after the flowering period and are processed within 2-4 hours after picking. The lavender flowers are crushed and sieved with a 2mm-3mm filter. After the lavender flowers are rinsed, natural bamboo fiber absorbent paper is used to absorb surface moisture.

3. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step 2, the specific extraction process is as follows: The lavender powder is evenly loaded into a supercritical extraction kettle, with the loading amount being 60%-70% of the volume of the extraction kettle. Purified CO2 gas is introduced into the extraction kettle, so that the pressure in the extraction kettle is gradually increased to 22MPa-25MPa within 15min-20min. At the same time, the temperature of the extraction kettle is adjusted to 38°C-41°C through a circulating hot water bath, so that the CO2 extracts the powder under a supercritical state. The extraction time is 2.5h-3h. During this period, the material in the extraction kettle is stirred at a speed of 80r / min-100r / min by a stirring device. After the extraction is completed, the supercritical CO2 fluid rich in lavender essential oil is introduced into the separation kettle through a pipeline, and the essential oil and CO2 are separated by adjusting the pressure and temperature in the separation kettle.

4. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 3, characterized in that: In the step 2, the specific operation of separating the essential oil and CO2 by adjusting the pressure and temperature in the separation kettle is as follows: first, the pressure of the separation kettle is reduced to 7MPa-8MPa within 10min-15min, and the temperature is maintained at 38°C-40°C, so that the lavender essential oil is precipitated from the supercritical CO2 fluid to obtain crude lavender essential oil, and then the crude lavender essential oil is filtered, and filtered at -0.08MPa to -0.1MPa using a polyethersulfone microporous filter membrane with a pore size of 0.45μm-0.6μm to obtain refined lavender essential oil.

5. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In step 3, the specific process for preparing nanocellulose by TEMPO oxidation combined with high-pressure homogenization is as follows: Natural bamboo pulp cellulose is placed in deionized water to prepare a suspension with a mass fraction of 2%-3%. TEMPO reagent is added to the suspension in an amount of 0.2%-0.4% of the mass of the cellulose. At the same time, 1.2%-1.5% of NaBr is added as an auxiliary agent and stirred evenly. Under stirring, 11%-13% NaClO solution is slowly added dropwise to carry out oxidation reaction. The dropwise addition speed is controlled at 1mL / min-2mL / min and the reaction time is 2.5h-3h. During the reaction, 1M sodium hydroxide solution is used to maintain the pH value of the reaction system at 10-10.

5. After the oxidation reaction is completed, ethanol produced by the biological fermentation method is added in a ratio of 1:3-4 by volume of ethanol to the reaction system to terminate the reaction, and then the reaction product is separated by centrifugation and repeatedly washed with deionized water 3-4 times until the pH value of the washing liquid is 6.7-7.

2. The washed product is redispersed in deionized water to prepare a suspension with a mass fraction of 1%-2%, and then the suspension is treated by a high-pressure homogenizer. The pressure of the high-pressure homogenization treatment is 110MPa-120MPa, and the treatment is circulated 3-4 times, with each treatment time being 25S-30S, so that the cellulose is further refined into nanocellulose.

6. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step 4, the specific process for preparing zinc-aluminum layered double hydroxide nanosheets is as follows: a mixed solution of zinc nitrate and aluminum nitrate and a mixed alkaline solution of sodium hydroxide and sodium carbonate are prepared respectively, the molar ratio of zinc nitrate to aluminum nitrate is 2.5-3:1, the total concentration of metal ions in the mixed solution is 0.5 mol / L-0.6 mol / L, the concentration of sodium hydroxide in the mixed alkaline solution of sodium hydroxide and sodium carbonate is 1.5 mol / L-2 mol / L, and the concentration of sodium carbonate is 0.5 mol / L-0.7 mol / L, and the pH value of the mixed alkaline solution is adjusted to 10.5 with dilute hydrochloric acid or sodium hydroxide solution. -10.7, under the stirring condition of 300r / min-400r / min, the metal salt mixed solution is added dropwise to the mixed alkali solution at a rate of 5mL / min-8mL / min, the reaction system temperature is maintained at 70℃-72℃ during the addition process, and stirring is continued for 9h-10h. After the reaction is completed, the product is separated by centrifugation and repeatedly washed with deionized water for 4-5 times until no nitrate ions are detected in the washing liquid by testing with silver nitrate solution. The washed product is dried at 60℃-70℃ for 12h-15h, and then ground into powder to obtain zinc-aluminum layered double hydroxide nanosheets.

7. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step 5, the refined lavender essential oil and the aluminum-type layered double hydroxide nanosheets are mixed in a mass ratio of 1:6-7, the temperature of the ultrasonic dispersion container is controlled at 23°C-27°C by a circulating cold water bath, and the ultrasonic power is 220W for dispersion, and the dispersion time is 50min-60min.

8. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step six, the zinc-aluminum layered double hydroxide nanosheets loaded with essential oil and the nanocellulose prepared in the step three are mixed in a mass ratio of 1:7-8, deionized water is added to make the solid content of the mixed system 2wt%-4wt%, and the mixture is stirred in a reactor at a speed of 350r / min-450r / min for 1.2h-2h.

9. A method for preparing natural plant essential oil-modified antibacterial nanocellulose according to claim 1, characterized in that: In the step seven, the mixture obtained in step six is washed with deionized water 3-4 times, and the mixed product is mixed with deionized water at a mass ratio of 1:5-8 during each washing, stirred for 10min-15min, and then centrifuged. The freeze-drying pretreatment is pre-freezing at -45°C to -40°C for 2.5h-3h, and then vacuum drying at 42°C-45°C for 20h-23h.

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