Preparation method of latex gel-based nanocellulose sustained-release antibacterial film

Abstract

The invention discloses a method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, the method comprising the following steps: (1) preparing nanocellulose microgel by cross-linking carboxyl nanocellulose with polyethyleneimine; (2) preparing Pickering emulsion gel by emulsifying microgel particles with lemon essential oil-paraffin composite oil; (3) casting the emulsion gel into a film after blending with cellulose nanofibrils to prepare an emulsion gel-based nanocellulose sustained-release antibacterial film. The antibacterial film obtained by the method of the present invention is coated with an antibacterial agent and a phase change material, and the antibacterial agent release rate is different at different temperatures, has good sustained-release antibacterial performance, and has a simple preparation process, good raw material biocompatibility, is environmentally friendly, and can be widely used in the field of food.

Description

Technical Field

[0001] The invention belongs to the technical field of antibacterial material preparation, and specifically is a method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film. Background Art

[0002] Nanocellulose has good renewability and biodegradability. The film material prepared with nanocellulose as the substrate has good oxygen barrier properties and has broad application prospects as a green functional packaging material. However, the nanocellulose film itself does not have antibacterial ability, so the development of nanocellulose antibacterial film with antibacterial effect is of great significance to expand its application in the field of food and drug packaging.

[0003] The common method of preparing nanocellulose antibacterial film is to compound antimicrobial agent with nanocellulose based on physical or chemical method. At present, the research of compounding nanocellulose with antimicrobial agent to prepare nanocellulose antibacterial film has achieved certain results. For example, Chinese patent application publication number CN109943977A discloses a method of preparing a nanofiber antibacterial fresh-keeping film by combining microfibrillated nanocellulose and chitin nano whisker as substrate with modified chitosan. Another example is that Chinese patent application publication number CN109134942A discloses a method of preparing a transparent nanocellulose antibacterial paper by using sodium alginate, nanocellulose and glycerol. However, the antimicrobial agent of these existing antibacterial films is usually added by direct embedding method, and there is a common problem of too fast release of antimicrobial agent. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a new method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film. The antibacterial film prepared by the method can achieve the sustained-release effect of the antibacterial agent and prolong the antibacterial effect of the antibacterial film. Moreover, the preparation process is simple and the raw materials are green and environmentally friendly.

[0005] The present invention solves the above technical problems with the following technical solutions:

[0006] The present invention provides a method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, comprising the following steps:

[0007] (1) Preparation of nanocellulose microgel: dispersing carboxyl nanocellulose in deionized water to prepare a carboxyl nanocellulose aqueous dispersion with a mass concentration of 1.0% to 3.0%; adding a 2.0% polyethyleneimine aqueous solution dropwise on the carboxyl nanocellulose aqueous dispersion, wherein the added polyethyleneimine aqueous solution and the carboxyl nanocellulose aqueous dispersion are in a mass ratio of 1 to 3:1, and standing at room temperature for 24 hours to obtain a gel matrix; transferring the gel matrix to a 2.0% polyethyleneimine aqueous solution, soaking and aging for 12 hours, taking it out, soaking it in an EDC / NHS mixed solution for reaction for 24 hours, and obtaining a nanocellulose hydrogel; rinsing the nanocellulose hydrogel twice with an equal mass ratio of deionized water, and then adding an equal mass ratio of deionized water to treat it at a mechanical shear rate of 10,000 rpm for 3 minutes, so that the hydrogel is broken and evenly dispersed in water in the form of particles, and obtaining a nanocellulose microgel;

[0008] (2) Preparing a Pickering emulsion gel: adding a paraffin-lemon essential oil composite oil phase dropwise to the nanocellulose microgel prepared in step (1) and emulsifying the mixture uniformly to prepare a Pickering emulsion gel; wherein the mass ratio of the composite oil phase to the gel aqueous phase is 75-90:10-25, and the mass ratio of the paraffin and lemon essential oil in the paraffin-lemon essential oil composite oil is 20-40:60-80;

[0009] (3) Preparation of sustained-release antibacterial film: The Pickering emulsion gel prepared in step (2) was mixed with a cellulose nanofibril aqueous dispersion having a mass concentration of 1.0% to 2.0% in a mass ratio of 1:1, and after magnetic stirring at a constant speed of 300 rpm for 40 min, poured into a mold, and dried at 25°C and a relative humidity of 50% for 48 h to obtain an emulsion gel-based nanocellulose sustained-release antibacterial film.

[0010] In the step (1), the molecular weight of polyethyleneimine in the polyethyleneimine aqueous solution is 10 kDa to 70 kDa; and the surface carboxyl content of the carboxyl nanocellulose is 1.0 to 1.4 mmol / g.

[0011] The mass ratio of EDC to NHS in the EDC / NHS mixed solution of step (1) is 2.5:1.

[0012] In the step (2), the paraffin-lemon essential oil composite oil phase and the nanocellulose microgel are placed in an emulsifying homogenizer with a rotation speed of 6500 rpm to be emulsified uniformly.

[0013] In the step (2), the main component of the paraffin is C18 normal alkane.

[0014] In the step (3), the cellulose nanofibrils have a diameter less than 100 nm and a length between 1 and 1000 μm.

[0015] The present invention utilizes the negatively charged carboxyl groups on the surface of nanocellulose and the positively charged amino groups on the surface of polyethyleneimine to form a large gel based on electrostatic force, and further uses EDC / NHS treatment to form a chemically bonded and strengthened gel structure. The gel can be broken under mechanical action to obtain micron-sized gel particles, and the microgel can be used as a solid particle emulsifier to disperse lemon essential oil-paraffin composite oil in water to obtain a highly stable water-in-oil type high internal phase Pickering emulsion, and the oil phase encapsulation rate can reach more than 75%, showing a gel state, and the emulsion gel is mixed with cellulose nanofibrils and cast into a film. The essential oil droplets are embedded in the film by the microgel and cellulose nanofibrils. When the temperature is lower than the paraffin phase transition temperature of 30°C, the essential oil is released slowly. When the temperature is higher than 30°C, the essential oil is released faster, thereby achieving efficient sustained-release antibacterial, and the raw materials are green and environmentally friendly, and the preparation process is simple. It is an environmentally friendly, high-performance antibacterial packaging material with extremely high application value.

[0016] The method of the present invention has the following beneficial effects:

[0017] 1. The present invention utilizes nanocellulose microgel to replace traditional surfactants to prepare emulsion gel, thereby achieving efficient encapsulation of essential oils. At the same time, paraffin is melted at a phase change temperature to achieve auxiliary controlled release of antibacterial essential oils.

[0018] 2. The present invention utilizes the chemical bonding of nanocellulose and polyethyleneimine to prepare nanocellulose microgel, and the obtained microgel has excellent interfacial stability and antibacterial properties. The nanocellulose microgel is used as an emulsifier for Pickering emulsion, and the oil phase encapsulation rate can reach more than 75%, and the emulsion is in a gel state. After the emulsion gel is mixed with nanocellulose microfibrils and cast into a film, the oil phase essential oil droplets are embedded in the film by the microgel and nanocellulose microfibrils, which can delay the release of the essential oil, thereby achieving the purpose of continuous and long-term inhibition of bacterial growth. In addition, compared with the existing surfactant-stabilized high internal phase emulsion technology, the present invention uses nanocellulose microgel as a solid particle emulsifier to prepare a high internal phase emulsion with good biosafety and environmental compatibility, avoiding environmental pollution and other problems caused by surfactants.

[0019] 3. The present invention adopts a phase change material paraffin and lemon essential oil composite. Compared with the existing antibacterial film, the emulsion gel in the present invention is coated with paraffin. When the temperature is lower than the phase change temperature of paraffin, the paraffin is solid and can delay the release of essential oil. When the temperature is higher than the phase change temperature, the release of essential oil is accelerated, thereby realizing auxiliary controlled release of antibacterial essential oil. The prepared antibacterial film can realize the sustained release effect of antibacterial agent and prolong the antibacterial effect of the antibacterial film. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. The chemical reagents and raw materials used in the following embodiments are all of analytical grade.

[0021] Example 1

[0022] A method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, the specific steps are as follows:

[0023] (1) Preparation of nanocellulose microgel: Carboxyl nanocellulose with a surface carboxyl content of 1.4 mmol / g was dispersed in deionized water to prepare a carboxyl nanocellulose aqueous dispersion with a mass concentration of 1.0%; a 2.0% polyethyleneimine aqueous solution was added dropwise at a mass ratio of 1:1 on the carboxyl nanocellulose aqueous dispersion, and the mixture was allowed to stand at room temperature for 24 hours to obtain a gel matrix; the gel matrix was transferred to a 2.0% polyethyleneimine aqueous solution and soaked for aging for 12 hours, then taken out and soaked in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 2.5:1) for reaction for 24 hours to obtain a nanocellulose hydrogel; the hydrogel was rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio was added and treated at a mechanical shear rate of 10,000 rpm for 3 minutes, so that the hydrogel was broken and evenly dispersed in water in the form of particles to obtain a nanocellulose microgel; wherein the molecular weight of polyethyleneimine was 50 kDa;

[0024] (2) Preparing a Pickering emulsion gel: In an emulsifying homogenizer at a rotation speed of 6500 rpm, adding a paraffin-lemon essential oil composite oil phase dropwise to the nanocellulose antibacterial microgel prepared in step (1) to prepare a Pickering emulsion gel; wherein the mass ratio of the composite oil phase to the microgel aqueous phase is 90:10, and the mass ratio of paraffin to lemon essential oil in the composite oil is 20:80; the paraffin is preferably a C18 normal alkane;

[0025] (3) Preparation of an emulsion gel-based nanocellulose sustained-release antibacterial film: The Pickering emulsion gel prepared in step (2) was mixed with a nanocellulose microfibril aqueous dispersion having a mass concentration of 1.5% in a mass ratio of 1:1, and after magnetic stirring at a constant speed of 300 rpm for 40 minutes, poured into a mold, and dried at 25° C. and a relative humidity of 50% for 48 hours to obtain an emulsion gel-based nanocellulose sustained-release antibacterial film. The nanocellulose microfibril had a diameter of less than 100 nm and a length of 1-1000 μm.

[0026] The emulsion gel-based nanocellulose sustained-release antibacterial film prepared in this example was covered on an Escherichia coli culture dish at 25°C and 38°C for an antibacterial rate test, and the results showed that: at 25°C, the antibacterial rate was 97.21±0.55% on the 3rd day, 96.33±0.48% on the 5th day, and 94.91±0.33% on the 7th day; at 38°C, the antibacterial rate was 99.26±0.43% on the 3rd day, 98.56±0.53% on the 5th day, and 97.47±0.54% on the 7th day, indicating that the emulsion gel-based nanocellulose sustained-release antibacterial film obtained by the method of the present invention can effectively control the release rate of the antibacterial essential oil and has good sustained-release antibacterial performance.

[0027] Example 2

[0028] A method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, the specific steps are as follows:

[0029] (1) Preparation of nanocellulose microgel: Carboxyl nanocellulose with a surface carboxyl content of 1.0 mmol / g was dispersed in deionized water to prepare a carboxyl nanocellulose aqueous dispersion with a mass concentration of 3.0%; a polyethyleneimine aqueous solution with a mass concentration of 2.0% was added dropwise on the carboxyl nanocellulose aqueous dispersion, the added polyethyleneimine aqueous solution and the carboxyl nanocellulose aqueous dispersion being in a mass ratio of 3:1, and the mixture was allowed to stand at room temperature for 24 hours to obtain a gel matrix; the gel matrix was then transferred to a polyethyleneimine aqueous solution with a mass concentration of 2.0% and immersed in it for aging for 12 hours, and then taken out and immersed in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 2.5:1) for reaction for 24 hours to obtain a nanocellulose hydrogel; the hydrogel was rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio was added and treated at a mechanical shear rate of 10000 rpm for 3 minutes, so that the hydrogel was broken and evenly dispersed in water in the form of particles to obtain a nanocellulose microgel; wherein the molecular weight of polyethyleneimine was 10 kDa;

[0030] (2) Preparing a Pickering emulsion gel: In an emulsifying homogenizer at a rotation speed of 6500 rpm, the paraffin-lemon essential oil composite oil phase is added dropwise to the nanocellulose antibacterial microgel prepared in step (1) to prepare a Pickering emulsion gel; wherein the mass ratio of the composite oil phase to the microgel aqueous phase is 75:25, and the mass ratio of paraffin to lemon essential oil in the composite oil is 40:60; the paraffin is preferably a C18 normal alkane;

[0031] (3) Preparation of an emulsion gel-based nanocellulose sustained-release antibacterial film: The Pickering emulsion gel prepared in step (2) was mixed with a nanocellulose microfibril aqueous dispersion having a mass concentration of 1.0% in a mass ratio of 1:1, stirred at a constant speed of 300 rpm by magnetic force for 40 min, poured into a mold, and dried at 25° C. and a relative humidity of 50% for 48 h to obtain an emulsion gel-based nanocellulose sustained-release antibacterial film. The nanocellulose microfibril had a diameter of less than 100 nm and a length of 1-1000 μm.

[0032] The emulsion gel-based nanocellulose sustained-release antibacterial film prepared in this example was covered on an Escherichia coli culture dish at 25°C and 38°C for an antibacterial rate test, and the results showed that: at 25°C, the antibacterial rate was 96.91±0.46% on the 3rd day, 96.33±0.41% on the 5th day, and 95.71±0.38% on the 7th day; at 38°C, the antibacterial rate was 98.86±0.36% on the 3rd day, 98.16±0.50% on the 5th day, and 97.17±0.52% on the 7th day, indicating that the emulsion gel-based nanocellulose sustained-release antibacterial film obtained by the method of the present invention can effectively control the release rate of the antibacterial essential oil and has good sustained-release antibacterial performance.

[0033] Example 3

[0034] A method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, the specific steps are as follows:

[0035] (1) Preparation of nanocellulose microgel: Carboxyl nanocellulose with a surface carboxyl content of 1.2 mmol / g was dispersed in deionized water to prepare a carboxyl nanocellulose aqueous dispersion with a mass concentration of 2.0%; a polyethyleneimine aqueous solution with a mass concentration of 2.0% was added dropwise on the carboxyl nanocellulose aqueous dispersion, the added polyethyleneimine aqueous solution and the carboxyl nanocellulose aqueous dispersion being in a mass ratio of 2:1, and the mixture was allowed to stand at room temperature for 24 hours to obtain a gel matrix; the gel matrix was then transferred to a polyethyleneimine aqueous solution with a mass concentration of 2.0% and immersed in it for aging for 12 hours, and then taken out and immersed in an EDC / NHS mixed solution (the mass ratio of EDC to NHS was 2.5:1) for reaction for 24 hours to obtain a nanocellulose hydrogel; the hydrogel was rinsed twice with deionized water of the same mass ratio, and then deionized water of the same mass ratio was added and treated at a mechanical shear rate of 10000 rpm for 3 minutes, so that the hydrogel was broken and evenly dispersed in water in the form of particles to obtain a nanocellulose microgel; wherein the molecular weight of polyethyleneimine was 70 kDa;

[0036] (2) Preparing a Pickering emulsion gel: In an emulsifying homogenizer at a rotation speed of 6500 rpm, the paraffin-lemon essential oil composite oil phase is added dropwise to the nanocellulose antibacterial microgel prepared in step (1) to prepare a Pickering emulsion gel; wherein the mass ratio of the composite oil phase to the microgel aqueous phase is 80:20, and the mass ratio of paraffin to lemon essential oil in the composite oil is 30:70; the paraffin is preferably a C18 normal alkane;

[0037] (3) Preparation of an emulsion gel-based nanocellulose sustained-release antibacterial film: The Pickering emulsion gel prepared in step (2) was mixed with a nanocellulose microfibril aqueous dispersion having a mass concentration of 2.0% in a mass ratio of 1:1, stirred with a constant magnetic force at 300 rpm for 40 min, poured into a mold, and dried at 25° C. and a relative humidity of 50% for 48 h to obtain an emulsion gel-based nanocellulose sustained-release antibacterial film. The nanocellulose microfibril had a diameter of less than 100 nm and a length of 1-1000 μm.

[0038] The emulsion gel-based nanocellulose sustained-release antibacterial film prepared in this example was covered on an Escherichia coli culture dish at 25°C and 38°C for an antibacterial rate test, and the results showed that: at 25°C, the antibacterial rate was 97.71±0.37% on the 3rd day, 96.73±0.47% on the 5th day, and 95.28±0.44% on the 7th day; at 38°C, the antibacterial rate was 98.16±0.46% on the 3rd day, 97.77±0.32% on the 5th day, and 97.07±0.43% on the 7th day, indicating that the emulsion gel-based nanocellulose sustained-release antibacterial film obtained by the method of the present invention can effectively control the release rate of the antibacterial essential oil and has good sustained-release antibacterial performance.

Claims

1. A method for preparing an emulsion gel-based nanocellulose sustained-release antibacterial film, characterized in that: The steps include: (1) Preparation of nanocellulose microgel: dispersing carboxyl nanocellulose in deionized water to prepare a carboxyl nanocellulose aqueous dispersion with a mass concentration of 1.0% to 3.0%; adding a 2.0% polyethyleneimine aqueous solution dropwise on the carboxyl nanocellulose aqueous dispersion, wherein the added polyethyleneimine aqueous solution and the carboxyl nanocellulose aqueous dispersion are in a mass ratio of 1 to 3:1, and standing at room temperature for 24 hours to obtain a gel matrix; transferring the gel matrix to a 2.0% polyethyleneimine aqueous solution, soaking and aging for 12 hours, taking it out, soaking it in an EDC / NHS mixed solution for reaction for 24 hours, and obtaining a nanocellulose hydrogel; rinsing the nanocellulose hydrogel twice with an equal mass ratio of deionized water, and then adding an equal mass ratio of deionized water to treat it at a mechanical shear rate of 10,000 rpm for 3 minutes, so that the hydrogel is broken and evenly dispersed in water in the form of particles, and obtaining a nanocellulose microgel; (2) Preparing a Pickering emulsion gel: adding a paraffin-lemon essential oil composite oil phase dropwise to the nanocellulose microgel prepared in step (1) and emulsifying the mixture uniformly to prepare a Pickering emulsion gel; wherein the mass ratio of the composite oil phase to the gel aqueous phase is 75-90:10-25, and the mass ratio of paraffin to lemon essential oil in the paraffin-lemon essential oil composite oil is 20-40:60-80; and the main component of the paraffin is C18 normal alkane; (3) Preparation of sustained-release antibacterial film: The Pickering emulsion gel prepared in step (2) was mixed with a cellulose nanofibril aqueous dispersion having a mass concentration of 1.0% to 2.0% in a mass ratio of 1:1, and after magnetic stirring at a constant speed of 300 rpm for 40 min, poured into a mold, and dried at 25°C and a relative humidity of 50% for 48 h to obtain an emulsion gel-based nanocellulose sustained-release antibacterial film.

2. The method for preparing the emulsion gel-based nanocellulose sustained-release antibacterial film according to claim 1, characterized in that: In step (1), the molecular weight of polyethyleneimine in the polyethyleneimine aqueous solution is 10 kDa to 70 kDa; and the surface carboxyl content of the carboxyl nanocellulose is 1.0 to 1.4 mmol / g.

3. The method for preparing the emulsion gel-based nanocellulose sustained-release antibacterial film according to claim 1, characterized in that: The mass ratio of EDC to NHS in the EDC / NHS mixed solution of step (1) is 2.5:

1.

4. The method for preparing the emulsion gel-based nanocellulose sustained-release antibacterial film according to claim 1, characterized in that: Step (2), placing the paraffin-lemon essential oil composite oil phase and the nanocellulose microgel in an emulsifier homogenizer with a rotation speed of 6500 rpm to emulsify evenly.

5. The method for preparing the emulsion gel-based nanocellulose sustained-release antibacterial film according to claim 1, characterized in that: In step (3), the cellulose nanofibrils have a diameter less than 100 nm and a length between 1 and 1000 μm.