KR101135683B1 - Manufacturing Method For Nanofiber of Cellulose Acetate and Montmorillonite Prepared By Electrospinning, And The Nanofiber Using The Same - Google Patents

Abstract

The present invention relates to a method for producing nanofibers of cellulose acetate and montmorillonite using electrospinning and nanofibers produced thereby. More specifically, the present invention comprises the steps of i) preparing a mixed solution of cellulose acetate solution and montmorillonite solution, and ii) electrospinning the mixed solution prepared in the first step. It relates to a nanofiber manufacturing method and a nanofiber produced thereby comprising a second step.

Electrospinning, Cellulose Acetate, Montmorillonite

Description

Manufacturing Method For Nanofiber of Cellulose Acetate and Montmorillonite Prepared By Electrospinning, And The Nanofiber Using The Same}

The present invention relates to a method for producing nanofibers of cellulose acetate and montmorillonite using electrospinning and nanofibers produced thereby. More specifically, the present invention comprises the steps of i) preparing a mixed solution of cellulose acetate solution and montmorillonite solution, and ii) electrospinning the mixed solution prepared in the first step. It relates to a nanofiber manufacturing method and a nanofiber produced thereby comprising a second step.

Recently, it has high specific surface area and porosity, and its application in various fields such as sensor, filtration, membrane, tissue engineering, drug delivery, etc. Electrospinning technology is drawing attention as a technique for producing possible nanofiber non-woven fabrics.

Electrospinning technology is known as an efficient way to produce fibers from microscale to nanoscale from various polymers such as cellulose acetate (CA), polystyrene, polybutadiene, polycaprolactone (PCL), etc. .

In brief, the principle of electrospinning is that, first, a high voltage of 10-30 kV is applied to the capillary containing the polymer solution, and when the applied voltage is high enough to overcome the surface tension of the polymer solution, the charged fine solution The spray will be released towards the target. The spray thus released is sprayed at the target point and collected into a network of small fibers at the target.

One of the most important characteristics of this electrospinning is the diameter of the fiber, which depends largely on the jet content as well as the polymer content since nanofibers are produced by evaporation and solidification of polymer solution jets.

On the other hand, cellulose is naturally the most abundant polymer material, has a macromolecular structure with various functions, and has linearity, flexibility, durability, biodegradabili ty, Despite having various advantages such as chemical resistance, physical strength, non-toxicity, and low cost, there is a problem that the solubility in organic solvents is insufficient due to the supra molecular architecture of cellulose.

However, cellulose acetate (CA), which is one of the derivatives of cellulose, exhibits high solubility in organic solvents with all of the above mentioned advantages, thereby showing sufficient electrospinning ability.

Cellulose acetate is applied in various fields such as membranes, plastic products, packing films, and the like, and the electrospun cellulose acetate fibers can further expand the application ranges.

On the other hand, some researchers have used different solvent systems, such as acetone, acetic acid, N, N-dimethylacetamide (DMAc), and mixed solutions thereof to relate the properties of cellulose acetate solutions and the electrospun cellulose acetate fiber structure therefrom. We have concluded that a mixture of acetone / DMAc (2: 1) is the best solution for electrospinning of CA (Zong XH et al., Structure and morphology changes during in vitro degradation of electrospun poly). Biomacromolecules 2003 (glycolide-co-lactide ) nanofiber membrane; 4:. 416- 423).

In addition, other researchers studied the electrospinning of cellulose acetate nanofibers using a mixed solvent of acetic acid / water, and showed that by introducing a new solvent system, electrospun long and uniform cellulose acetate nanofibers could be electrospun. (SO Han et al, Electrospinning of cellulose acetate nanofibers using a mixed solvent of acetic acid / water:.. Effect of solvent composition on the fiber diameter Materials letters 2008; 62: 759-762)

On the other hand, nanocomposite of cellulose acetate reinforced with montmorillonite (MMT) has been spotlighted because it can greatly improve the material properties of polymer composites even with very small amounts of montmorillonite, and the nanocomposites are polymer materials or Compared with general micro and macro composites, it shows several advantages such as improved mechanical properties, reduced flammability, and improved barrier property.

Nanocomposites of cellulose acetate and montmorillonite having the above advantages have been produced by solution casting or injection molding methods, but a manufacturing method that can have more improved material properties, in particular electrospinning The method of manufacturing by applying has not yet been studied.

Thus, the present inventors have prepared a method for producing nanofibers composed of acetate and montmorillonite using electrospinning technology to show improved morphological, thermal, structural, and mechanical properties than conventional cellulose acetate / montmorillonite composite fibers. To develop nanofibers.

It is an object of the present invention to provide a method for producing nanofibers composed of acetate and montmorillonite using electrospinning techniques and nanofibers produced thereby to show improved morphological, thermal, structural and mechanical properties. .

In order to achieve the object as described above, the present invention comprises the following steps: i) preparing a mixed solution of a cellulose acetate solution and a montmorillonite solution; And ii) a second step of electrospinning the mixed solution prepared in the first step.

In addition, in order to achieve the object as described above, the present invention comprises the following steps: i) preparing a mixed solution of cellulose acetate solution and montmorillonite solution; And ii) a second step of electrospinning the mixed solution prepared in the first step.

Here, the cellulose acetate solution is preferably used to dissolve 18 ~ 23 wt% of cellulose acetate in a mixed solvent of acetic acid and water, it is preferable that the acetic acid ratio of the mixed solvent is 70 ~ 80wt%.

In addition, the montmorillonite solution is prepared by the ultrasonic treatment (ultrasonic treatment) of 3 to 15wt% montmorillonite aqueous solution, preferably 3 to 7wt% montmorillonite aqueous solution.

In addition, the step of stirring the mixed solution of the cellulose acetate solution and the montmorillonite solution before the electrospinning step of the second step.

Nanofibers of the present invention prepared by the above method may have a tensile strength of 1.5 ~ 3.5 (kgf / mm ² ).

By using the nanofiber manufacturing method applying the electrospinning technology to the mixed solution of cellulose acetate and montmorillonite of the present invention, a nanofiber showing improved morphological, thermal, structural and mechanical properties than the conventional nanofibers using cellulose acetate can do.

The method for producing nanofibers of cellulose acetate and montmorillonite using electrospinning according to the present invention and the nanofibers produced thereby will be described in detail below with reference to the following drawings.

1 is a graph showing the change in viscosity of the CA solution according to the CA content, Figure 2 is the MMT content (1-pure CA, 2-CA / MMT-1, 3-CA / MMT-3, 4-CA in the CA solution) / MMT-5, 5-CA / MMT-7, 6-CA / MMT-9) is a graph showing the change in conductivity (conductivity).

3A to 3C, 4A to 4C, 5A to 5C, 6A to 6C, 7A to 7C, and 8A to 8C are CA, CA / MMT-1, CA / MMT-3, and CA / MMT, respectively. SEM image and EDX spectra results graph of -5, CA / MMT-7, CA / MMT-9 nanofibers, FIG. 9 shows various MMT contents (1-pure MMT, 2-pure CA, 3-CA / MMT-1 , 4-CA / MMT-3, 5-CA / MMT-5, 6-CA / MMT-7, 7-CA / MMT-9).

10 and 11 are TEM images of CA / MMT nanofibers and EDX spectra and TEM images of respective constituent elements (C, O, Al, and Si), and FIGS. 12 and 13 are electrospun fibers (a- Pure MMT, b-pure CA, c-CA / MMT-1, d-CA / MMT-3, e-CA / MMT-5, f-CA / MMT-7, g-CA / MMT-9) TGA and DTG results graph to show stability.

In addition, Figure 14 is a graph of tensile strength test results of CA nanofibers (CA, CA / MMT-1, CA / MMT-3, CA / MMT-5, and CA / MMT-7) of various MMT content.

Nanofiber manufacturing method of the present invention i) preparing a mixed solution of cellulose acetate (cellulose aceta te) solution and montmorillonite (montmorillonite) solution; And ii) a second step of electrospinning the mixed solution prepared in the first step.

Here, the cellulose acetate solution of the first step, in order to have a suitable viscosity and stable spray during electrospinning, it is preferable to use a solution of 18-23 wt% of cellulose acetate in a mixed solvent of acetic acid and water. .

At this time, the mixed solvent of acetic acid and water is preferably used in the acetic acid ratio of 70 ~ 80wt% of the mixed solvent in order to maintain the long and uniform electrospun nanofibers, more preferably the mixing ratio of acetic acid and water is 75 : 25 can be used.

On the other hand, the montmorillonite solution of the first step may use an aqueous solution having a montmorillonite content of 3 ~ 15wt% in order to have a high thermal stability and tensile strength with a fine and uniform nanofiber tissue composition, 120% In order to obtain high physical and chemical property improvement effects such as the above tensile strength improvement, an aqueous solution having a montmorillonite content of preferably 3 to 7 wt% can be used.

At this time, the montmorillonite aqueous solution is preferably prepared by dispersing the montmorillonite powder of the appropriate content in water, followed by ultrasonic treatment (ultrasonic treatment) for a suitable time depending on the application field.

In addition, in order to improve the physical, chemical, and mechanical properties of the finally produced nanofibers, the mixed solution of the cellulose acetate solution and the montmorillonite solution after the ultrasonic treatment before the second step of the electrospinning step is 20 to 20 ~. The process of stirring for 30 hours can be further roughened.

Nanofibers prepared through the mixed solution preparation step and the electrospinning step as described above have a much finer and more uniform diameter than common cellulose acetate nanofibers, and have a high tensile strength of 1.5 to 3.5 (kgf / mm ² ) ( tensile strength), which shows about 120% or more improvement in tensile strength over conventionally manufactured nanofibers.

Hereinafter, one embodiment of the nanofiber manufacturing method of the present invention and looks at the various physical properties of the nanofibers produced through it.

[Example]

1. Preparation of mixed solution

Cellulose acetate (hereafter CA) (Aldrich Co., USA, acetyl content 39.8%, MW = 30,000) and montmorillonite (hereafter MMT, cloisite 93A, Southern Clay products Co., USA), and acetic acid (> 99%, DC Chemical Co., Korea) were prepared respectively.

The acetic acid and water were mixed at a weight ratio of 75:25 to prepare a mixed solution containing acetic acid and water (hereinafter, acetic acid / water (75/25)).

CA / MMT solutions were prepared using an ultrasonic treatment method. First, the MMT powder is prepared by drying at 80 ° C. for 24 hours in vacuum before use, and the CA solution is prepared by dissolving 18 wt% of CA in acetic acid / water (75/25) at 65 ° C. to 75 ° C. for 5 hours. It was. In addition, the amount of MMT prepared in advance was sonicated for 2 hours and then stirred for one day and dispersed in water.

The CA solution thus prepared was mixed with MMT solution having different contents of 1, 3, 5, 7, 9 wt% to prepare a CA / MMT solution. Hereinafter, CA / MMT nanofibers electrospun from the solutions were prepared by CA / MMT-1 and CA / MMT-3. Referred to as CA / MMT-5, CA / MMT-7, CA / MMT-9.

2. through electrospinning CA Of MMT  Preparation of Nanofibers

Electrospinning is a single syringe with needle (ID = 0.84mm), ground electrode (d = 21.5cm) consisting of aluminum sheet formed on a drum with adjustable rotation speed, and high voltage power (Chung pa) EMT, Co., Korea).

Each solution was fed at a rate of 2 ml / h using a syringe pump and electrospun at a voltage of 27 kV (positive voltage). At this time, the distance from the tip (tip) to the collector is 10cm, all electrospinning process was carried out at 19 ℃.

3. Characteristics of Mixed Solution-Viscosity ( viscosity ) And conductivity ( conductivity )

Viscosity and conductivity of CA and CA / MMT solutions were measured at 16 ° C. using a Brookfield digital viscometer (Model-DV-prime) and a conductivity meter (Isteck model 455C), respectively.

The present inventors measured the viscosity of CA and CA / MMT solutions in order to examine the appropriate concentration of CA solution in electrospinning and the effect of MMT addition on electrospinning. 1 shows the viscosity of CA and CA / MMT solutions of varying CA concentrations in the range of 13-23 wt% under acetic acid / water (75/25) solvent system.

The viscosity of the CA and CA / MMT solutions shows a similar pattern, and when 5 wt% of MMT is added to the CA solution, the addition of MMT has relatively little effect on the viscosity in CA solutions with concentrations below 18 wt%. Did not give. On the other hand, in the CA solution having a concentration of more than 18 wt%, the viscosity of CA and CA / MMT-5 showed a relatively fast increase.

In addition, 18 wt% of CA and CA / MMT solutions were very stable during the electrospinning process, and by using an acetic acid / water (75/25) mixed solvent system, continuous electrospinning was possible. Therefore, the present inventors used nanofibers electrospun from 18 wt% CA solution as standard nanofibers to examine the effect of the following MMT addition.

FIG. 2 is a graph showing the conductivity of CA / MMT solutions with different MMT concentrations of 1, 3, 5, 7, 9 wt% in 18 wt% CA solution. The conductivity did not change in the range of MMT 1-5 wt% addition, but increased rapidly when MMT was added at a concentration of 7 wt% or more.

This suggests that low concentrations of MMT increase mobility, but high MMT concentrations, such as 7 wt%, result in an increase in conductivity and repulsion in the CA / MMT solution due to the charge of the MMT itself. It can be seen that induces the formation of beads and micronization of the nanofibers diameter.

4. Characteristics of Electrospun Nanofibers

1) morphology of nanofibers

The surface morphology of CA and CA / MMT nanofibers was measured using a scanning electron microscope (SEM, S-470, Hitachi, Japan), and an acceleration voltage of 15-25 kV was used.

3A-3C, 4A-4C, 5A-5C, 6A-6C, 7A-7C, 8A-8C are based on 18 wt% CA in a solvent system of acetic acid / water (75/25) CAs electrospun from CA / MMT solutions with different MMT contents (CA, CA / MMT-1, CA / MMT-3, CA / MMT-5, CA / MMT-7, CA / MMT-9) SEM images and EDAX analysis graphs of the fibers and CA / MMT fibers are shown.

CA nanofibers are electrospun to form a fibrous network having a fine diameter in the range of 150 ~ 350nm, it can be seen that the diameter of the nanofibers are gradually reduced as MMT is added to the CA. In particular, when electrospinning using CA / MMT-5 (FIGS. 6A and 6B), it was confirmed that a very uniform nanofiber net was obtained, but CA / MMT-7 (FIGS. 7A and 7B), CA / MMT- As shown in FIG. 9 (FIGS. 8A and 8B), when the high concentration of MMT is contained, the diameters of the electrospun nanofibers become smaller and smaller, forming non-uniform nanonets. In addition, it can also be seen that the Si and Al peaks increase as the amount of MMT added increases from EDAX analysis graphs (FIGS. 3c, 4c, 5c, 6c, 7c, and 8c) of CA / MMT nanofibers.

This phenomenon increases the charge density of the spray from which the addition of the quaternary ammonium salt of MMT is released, and thus the strong extensibility of the spray due to the self-repulsion of excess charges under strong electromagnetic fields. It can be seen that the diameter of the electrospun fibers is reduced as a result. That is, an increase in the conductivity of the CA / MMT solution having a high concentration of MMT causes a decrease in the diameter of the CA / MMT nanofibers.

2) Crystallinity of Nanofibers

Crystallinity of CA and CA / MMT nanofibers was determined by X-ray diffraction using a diffractometer (D.MAX-2500 diffractometer, Rich. Rigaku, Co, Japan) with Cu-kσ emission (1000 mA, 40 kV). XRD).

FIG. 9 is an x-ray diffraction pattern of MMT, CA, and CA / MMT, in which changes in inter-layer spacings were measured through XRD analysis. CA nanofibers did not show any peaks in XRD, but pure MMT showed (001) diffraction peaks at 3.8 °.

In addition, the diffraction peaks in CA / MMT-1 and CA / MMT-3 disappeared, indicating that most of the MMT was stripped and dispersed in the CA matrix. However, in CA / MMT-5, CA / MMT-7 and CA / MMT-9, wide and thin diffraction peaks were observed at 3.5 ° due to the relatively high dose of MMT layers. These diffraction peaks shift towards lower 0.3 theta values by the addition of MMT, which means that the polymer chains form clay galleries, expanding the clay structure.

3) TEM results of nanofibers

FIG. 10 is a TEM microscope image and EDAX result graph of CA / MMT-5, and FIG. 11 is an image showing distribution of elements (C, O, Al, and Si) constituting the nanofibers. MMT layers peeled from the figures were distributed into the CA / MMT nanofibers, and the presence of MMT agglomerates was also observed in the TEM image of CA / MMT-5.

4) Thermal Properties of Nanofibers

In order to analyze the thermal properties of electrospun nanofibers, a thermogravimetric analyzer (TGA Q 500, TA Instruments) was introduced, in which nitrogen gas was introduced at 100 ml / min and heated at an elevated temperature of 10 ° C./min. And DTG (Derivative thermo gravimetric) curves were recorded.

12, 13 shows electrospun fibers (a-pure MMT, b-pure CA, c-CA / MMT-1, d-CA / MMT-3, e-CA / MMT-5, f-CA / MMT -7, graph of TGA and DTG results to show thermal stability of g-CA / MMT-9).

As can be seen from the figures, both MMT and CA nanofibers start decomposition at 250 ° C. and have maximum decomposition temperatures of 390 ° C. and 350 ° C., respectively. In addition, MMT and CA nanofibers remaining after thermal decomposition at 500 ° C. were 70% and 15%, respectively. The decomposition peaks of CA / MMT nanofibers were divided into two types, and had the highest decomposition temperature around 300 ° C and 350 ° C, respectively.

It can be seen from the figures that the high concentration of MMT in CA nanofibers lowers the decomposition start temperature of CA / MMT nanofibers. This is because the alkyl ammonium cations of MMT are thermally unstable, suggesting that nanofibers containing them decompose at relatively low temperatures. This property reduces the thermal stability of MMT-added CA nanofibers, but the silicate clay layer acts as an excellent insulation and material-transportation barrier, resulting in thermal decomposition. It serves to prevent the release of volatile substances.

5) Tensile strength of nanofibers

Tensile strength of the electrospun nanofibers was measured under tensile strength load conditions using a tensile strength tester (model 4467, Instron Co., USA) according to the ASTM D-638 method. The crosshead speed was 5 mm / min, at least 20 measurements were taken for each sample, and the average value was obtained from the measurement results.

14 is a graph showing the tensile strength of CA / MMT nanofibers having different MMT content, it can be seen that the tensile strength of the CA nanofiber increases by adding MMT, the embodiment showing the highest tensile strength is 18 CA / MMT-5 with 5 wt% MMT added to wt% CA solution, showing a 120% increased tensile strength of 3.3 MPa.

The decrease in tensile strength when MMT is added in excess of 5wt% seems to be related to the lack of interfacial interaction between clay and matrix polymers, resulting in many defects in surface area. Agglomerations are caused.

As such, by using the nanofiber manufacturing method applying the electrospinning technique to the mixed solution of cellulose acetate and montmorillonite of the present invention, nanofibers exhibiting improved morphological, structural and mechanical properties are compared to those of nanofibers using cellulose acetate. It can manufacture.

The present invention is not limited to the above specific embodiments and descriptions, and various modifications can be made by those skilled in the art without departing from the gist of the invention as claimed in the claims. Such variations are within the protection scope of the present invention.

Figure 1-Graph showing the change in viscosity of the CA solution according to the CA content

Figure 2-MMT content in CA solution (1-pure CA, 2-CA / MMT-1, 3-CA / MMT-3, 4-CA / MMT-5, 5-CA / MMT-7, 6-CA / Graph showing the change in conductivity according to MMT-9)

3A-3C-SEM image and EDX spectra results graph of CA nanofibers

4A-4C-SEM image and EDX spectra results graph of CA / MMT-1 nanofibers

5A-5C-SEM image and EDX spectra results graph of CA / MMT-3 nanofibers

6A-6C-SEM image and EDX spectra results graph of CA / MMT-5 nanofibers

7A-7C-SEM image and EDX spectra results graph of CA / MMT-7 nanofibers

8A-8C-SEM image and EDX spectra results graph of CA / MMT-9 nanofibers

 Figure 9-Various MMT contents (1-pure MMT, 2-pure CA, 3-CA / MMT-1. 4-CA / MMT-3, 5-CA / MMT-5, 6-CA / MMT-7, 7 -Graph showing XRD pattern of CA nanofibers with CA / MMT-9)

10-Graph showing TEM image and EDX spectra of CA / MMT nanofibers

FIG. 11-TEM image of each element (C, O, Al, Si) of CA / MMT nanofibers

12, 13-Electrospun fibers (a-pure MMT, b-pure CA, c-CA / MMT-1, d-CA / MMT-3, e-CA / MMT-5, f-CA / MMT -7, graph of TGA and DTG results to show thermal stability of g-CA / MMT-9)

14-Tensile strength test results graph of CA nanofibers of various MMT content (CA, CA / MMT-1, CA / MMT-3, CA / MMT-5, and CA / MMT-7)

Claims (15)

i) preparing a mixed solution of a cellulose acetate solution and a montmorillonite solution; And ii) a second step of electrospinning the mixed solution prepared in the first step; Nanofiber manufacturing method comprising a. The method of claim 1, wherein the cellulose acetate solution of the first step is a method for producing nanofibers, characterized in that 18 to 23 wt% of cellulose acetate is dissolved in a mixed solvent of acetic acid and water. The method of manufacturing nanofibers according to claim 2, wherein the acetic acid ratio of the mixed solvent is 70 to 80 wt%. The method of claim 1, wherein the montmorillonite solution of the first step is a 3 to 15 wt% montmorillonite aqueous solution. 5. The method of claim 4, wherein the montmorillonite solution is an aqueous solution of montmorillonite of 3 to 7 wt%. The method of claim 4, wherein the montmorillonite aqueous solution is ultrasonically treated. The method of manufacturing nanofibers according to claim 1, further comprising the step of stirring the mixed solution before the electrospinning step of the second step. i) preparing a mixed solution of a cellulose acetate solution and a montmorillonite solution; And ii) a second step of electrospinning the mixed solution prepared in the first step. The nanofiber of claim 8, wherein the nanofiber has a tensile strength of 1.5 to 3.5 (kgf / mm ² ). The nanofiber of claim 8, wherein the cellulose acetate solution is dissolved in a mixed solvent of acetic acid and water in an amount of 18 to 23 wt% of cellulose acetate. 11. The nanofiber according to claim 10, wherein the acetic acid ratio of the mixed solvent is 70 to 80 wt%. The nanofiber of claim 8, wherein the montmorillonite solution of the first step is an aqueous solution of montmorillonite of 3 to 15 wt%. The nanofiber of claim 12, wherein the montmorillonite solution of the first step is an aqueous montmorillonite solution of 3 to 7 wt%. The nanofiber of claim 12, wherein the montmorillonite aqueous solution is ultrasonically treated. The nanofiber of claim 8, further comprising the step of stirring the mixed solution before the electrospinning step of the second step.

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