KR101620626B1 - Porous composite material from cellulose and method of making the same - Google Patents

Abstract

The present invention relates to a porous fibrous structure derived from a cellulose-based material and a method for producing the same and, more particularly, to a production method including a step of augmenting an internal pore by immersing a cellulose-based material in a polar solvent, substituting the polar solvent with a non-polar solvent, and performing drying by a critical point drying method and a porous fibrous structure that is produced by the method. According to the present invention, a cellulose-derived fibrous structure can be produced into the porous fibrous structure without being contracted after being expanded by the use of the polar solvent. The porous fibrous structure that is produced in this manner is environment-friendly and lightweight, and thus can be utilized in the materials sector as a stiffener for various biocomposite materials. In addition, the porous fibrous structure can be utilized in fields of separation membrane that have purposes such as gas separation, gas adsorption, and pervaporation.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous fibrous structure derived from cellulose and a method for producing the porous fibrous structure. [0002] POROUS COMPOSITE MATERIAL FROM CELLULOSE AND METHOD OF MAKING THE SAME [

The present invention relates to a porous fibrous structure derived from a cellulosic material and a method for producing the porous fibrous structure. More specifically, the present invention relates to a porous fibrous structure obtained by immersing a cellulosic material in a polar solvent to increase internal voids, replacing a polar solvent with a non- Drying the porous fibrous structure, and a porous fibrous structure prepared thereby.

As the global exhaustion of fossil fuels and concerns over environmental pollution increase, the concept of renewable and alternative energy that produces stable and sustainable energy is becoming a hot topic. As part of such alternative energy development, technologies for producing bioenergy and chemical products from biomass are attracting attention.

Biomass refers to a carbon assimilation process that fixes carbon dioxide by using sunlight, that is, a saccharide biosynthesized through a photosynthesis process, and the whole organism including the biosubstance. The fibrosome biomass has advantages such as abundant amount, So that it can be used not only as a fuel such as ethanol and butanol but also as various materials.

Among the fiber-based biomass is lignocelluloses, one of the cellulosic biomass represented by the most abundant and reproducible plant resources on the planet. Lignocellulose is a complex of lignin, a refractory aromatic polymer, and carbohydrates cellulose and hemicellulose (Perlack et al., 2005), and the main components such as cellulose, hemicellulose, and lignin are firmly bound have. Through various pretreatment methods, these three components can be separated from each other. Of the components of the fibrous biomass, cellulose is stable to heat and soluble in acid, hemicellulose is unstable in heat and soluble in acid . On the other hand, lignin is stable to heat and soluble in alkali.

The structure of the lignocellulose is that the lignin is bonded to the hemicellulose through the covalent bond and the hemicellulose is connected to the cellulose through the hydrogen bond so that the cellulosic microfibril, which is a straight straight line, And the hemicellulose is surrounded by a covalent linkage of lignin. It has a form to protect cellulose, which is the main carbohydrate of plants.

Cellulose, which is an important component in lignocellulose, is a linear polysaccharide of a stable form in which glucose is linked by a β1,4 bond. It is physically and chemically much more natural in nature than a helical amylose in which glucose is linked by α1,4 bonds It has a strong structure. Cellulose has inter- and intra-hydrogen bonds in its structure. It is a simple polysaccharide which constitutes the main component of the cell wall of the higher plants. It is the most abundant carbohydrate on the planet, accounting for 30 ~ 50% of the plant.

Since cellulose such as cellulose is hardly degraded in the human digestive tract, it has been thought that it is not worth as a food in the past. Recently, however, its effect as a functional dietary fiber such as a sucking action has been attracting attention. A new processed food containing starch and fibrin is also being developed with emphasis on this point. Because it is insoluble in water, it is used in food processing in derivative form.

In addition to being used as food, there are membrane fields for gas separation, dialysis evaporation, water treatment and the like in a variety of applications where cellulose can be used. For this purpose, it is possible to increase the surface area of cellulose, thereby making it easier to use. It is possible to increase the surface area by breaking hydrogen bonds through contact with a polar solvent such as water, but at the same time, There is a need for a drying method.

In order to achieve this purpose, freeze drying or critical point drying (CPD) methods may be considered instead of conventional air drying or oven drying. Freeze-drying is a method in which an aqueous solution or a material containing a large amount of water is frozen and decompressed to sublimate ice to remove moisture to obtain a dried material, which is known to have no significant effect on the increase of the surface area of cellulose. On the other hand, critical point drying is a method of drying the sample at a critical point (neither gas nor liquid) in which the surface tension does not act in order to prevent deformation of the sample caused by surface tension of the liquid during drying of the sample.

During the critical point drying process, the gas is not liquefied even when compressed at a certain temperature (critical temperature) or above. At the critical temperature, the pressure is constant depending on the type of gas and is called the boundary point. In this boundary point, since the interface between the liquid layer and the base layer is lost, there is an advantage that deformation of the sample due to the surface tension can be prevented.

When cellulose is contacted with a polar solvent such as water, some hydrogen bond breaks and expands. Since expanded cellulose has many pores, it can be used in various fields as a wide surface area structure. However, when the polar solvent such as water is removed, the expanded structure contracts due to the restoration of the hydrogen bond, and the pore collapse occurs, and the cellulosic state of the expanded structure is not maintained. In the case of drying in air or oven drying after contact with a polar solvent, the surface area is not increased due to restoration of hydrogen bonding of cellulose, and therefore, a method is required to maintain the cellulose having an expanded structure even after drying.

In order to maintain the cellulose having such an expanded structure as it is, a method of manufacturing a porous fibrous structure without changing the structure by using a critical point drying method in the state of expanding with a polar solvent and replacing with a nonpolar solvent Respectively. And then further pretreated with an alkaline reducing water or an acidic aqueous solution to obtain a further expanded porous fibrous structure.

It is an object of the present invention to provide a method for producing a cellulose-derived porous fibrous structure which is extractable from a fibrous biomass and has a stable structure from an abundant cellulose, so that it can be utilized in various industries.

In order to solve the above-mentioned problems, the present invention provides a method of manufacturing a magnetic recording medium, comprising the steps of: a) immersing a fibrous material in a polar solvent to increase internal voids; b) replacing the polar solvent present in the internal voids of the fibrous material with a non-polar solvent; And c) drying the fibrous material substituted with the nonpolar solvent by controlling the pressure at a critical point by using a critical fluid, and drying the fibrous material.

The fibrous material in step a) may be a material containing a fibrous subcellular cellulose.

The polar solvent in step a) may be neutral water, formamide, ethylene glycol, dimethylformamide (DMF), pyridine, formic acid, N-methylmorphol N-methylmorpholine N-oxide (NMMO), an ionic liquid, or a combination thereof.

The replacement with the nonpolar solvent in step b) may be carried out by b1) immersing in acetone, b2) immersion in ethanol, immersion in acetone, or b3) immersion in ethanol, followed by immersion in amyl acetate.

The critical fluid in step c) may be carbon dioxide or freon.

The critical temperature of step c) may be 35 to 37 占 폚 when the critical fluid is carbon dioxide.

Adjusting the pressure in step c) may be a method of applying 500 psi pressure after the critical fluid is carbon dioxide, followed by an additional 1200 psi pressure or a method of applying only 500 psi pressure.

Before step a), d) treating the fibrous material with a pretreatment solvent to facilitate internal void formation.

The pretreatment solvent may be an acidic aqueous solution or an alkaline aqueous solution.

The acidic aqueous solution may be a 0.5 to 3 wt% sulfuric acid aqueous solution.

The alkaline aqueous solution may be an alkaline reducing water having a pH of 10 or more or an aqueous solution of sodium hydroxide of 0.5 to 4% by weight obtained by electrolysis of water.

The present invention also provides a porous fibrous structure produced by any one of the above production methods.

A functional material may be impregnated or coated on the inner pores or the outer surface of the porous fibrous structure.

According to the present invention as described above, the fibrous structure derived from cellulose can be made into a porous fibrous structure without being contracted after swelling with a polar solvent. The porous fibrous structure thus produced is characterized by being environmentally friendly and lightweight, and thus can be utilized as a reinforcing material for various biocomposites in the field of materials. In addition, the porous fibrous structure can be utilized in the separation membrane for gas separation, gas adsorption, dialysis, and evaporation.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart of a process for making a porous fibrous structure.
Fig. 2 is a photograph of the surface of a porous fibrous structure prepared without pretreatment. a) is a magnification of 50,000 times, and b) is a magnification of 100,000 times.
FIG. 3 is a photograph showing a surface of a porous fibrous structure pretreated with an alkali-reduced water and oven-dried. a) is a photograph at an enlargement magnification of 20,000 times, and b) is a photograph at an enlargement magnification of 100,000 times.
FIG. 4 is a photograph of a surface of a porous fibrous structure pretreated with alkali-reduced water and lyophilized. a) is a photograph at an enlargement magnification of 20,000 times, and b) is a photograph at an enlargement magnification of 100,000 times.
FIG. 5 is a photograph of a surface of a porous fibrous structure pretreated with an alkali-reduced water and dried by a critical-point drying method. a) is a photograph at an enlargement magnification of 20,000 times, and b) is a photograph at an enlargement magnification of 100,000 times.

Hereinafter, the present invention will be described in detail.

In one aspect, the present invention provides a process for preparing a fibrous material, comprising: a) immersing a fibrous material in a polar solvent to increase internal voids; b) replacing the polar solvent present in the internal voids of the fibrous material with a non-polar solvent; And c) drying the fibrous material substituted with the nonpolar solvent by controlling the pressure at a critical point by using a critical fluid, and drying the fibrous material.

The fibrous material in step (a) is characterized by being a material containing a fibrous cellulosic material.

The polar solvent in step a) may be neutral water, formamide, ethylene glycol, dimethylformamide (DMF), pyridine, formic acid, N-methylmorphol N-methylmorpholine N-oxide (NMMO), an ionic liquid, or a combination thereof.

The replacement with the nonpolar solvent in step b) is carried out by b1) immersing in acetone, b2) immersing in ethanol, immersing in acetone, or b3) immersing in ethanol, and immersing in amyl acetate.

The critical fluid in the step c) is characterized by being carbon dioxide or freon.

In the step c), the critical temperature is 35 to 37 DEG C when the critical fluid is carbon dioxide. The critical temperature of a critical fluid for critical point drying is not liquefied even when it is compressed at that temperature. At the critical temperature, the pressure is constant according to the kind of gas and is called the boundary point. At this boundary point, the interface between the liquid layer and the base layer disappears, so that deformation of the sample due to surface tension can be prevented.

The control of the pressure in step c) is characterized in that when the critical fluid is carbon dioxide, a pressure of 500 psi is applied, then a pressure of 1200 psi is further applied, or a method of applying only 500 psi pressure. In the microvoids of fibrous materials substituted with nonpolar solvents, there are polar solvents that are not substituted with some nonpolar solvents. The polar solvent remaining in the micropores as well as the nonpolar solvent can be additionally removed while the pressure is increased to 500 psi. While the pressure increases again to 1200 psi, the carbon dioxide vaporizes and is dried to obtain a fibrous structure. On the other hand, when the polar solvent remaining in the nonpolar solvent and some microvoids is removed from the sample by increasing the pressure only up to 500 psi, drying by conventional air drying or oven drying can lower the applied pressure when considering industrial use have.

Before step a), d) treating the fibrous material with a pretreatment solvent to facilitate internal void formation.

The pretreatment solvent is an acidic aqueous solution or an alkaline aqueous solution.

The acidic aqueous solution is a 0.5 to 3 wt% sulfuric acid aqueous solution. An aqueous 0.9 to 1.1 wt% sulfuric acid solution is preferably used.

The alkaline aqueous solution is characterized by being an alkaline reducing water having a pH of 10 or more or an aqueous solution of sodium hydroxide of 0.5 to 4% by weight obtained by electrolysis of water. Preferably, alkaline reducing water having a pH of 12 or more or aqueous solution of sodium hydroxide having a concentration of 2.8 to 3.2% by weight is used.

In another aspect, the present invention provides a porous fibrous structure produced by any one of the above production methods.

And a functional material is impregnated or coated on the inner pore or the outer surface of the porous fibrous structure.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

Example 1. Preparation of porous fibrous structure

The porous fibrous structure was manufactured through the same process as shown in Fig. The concrete manufacturing process was verified by establishing the effects of each step through the following experiments.

Experimental Example 1. Surface area change according to pretreatment method

For fibrous materials such as cellulosic biomass, pretreatment solutions are used to facilitate hydrogen bonding of the fibrous material prior to expansion and drying. The solution which can be a pretreatment solution may be an acidic solution and an alkaline solution. The effect of each solution was measured experimentally.

Treated with alkali reducing water (pH 12; Zen ducks, Daejeon), dilute sulfuric acid and NaOH for eucalyptus cellulosic biomass (Guangzhou Research Institute, China) The porous fibrous structure thus obtained was dried according to the critical point drying method, and various indexes such as surface area change and pore size, etc. were measured, Respectively.

(1) Alkali-reduced water pretreatment

When water is electrolyzed, alkaline water is produced in the cathode, and acidic water is produced in the anode, which is referred to as 'electrolytic reduced water (electrolytic water)'. Alkali-reduced water is usually a strong alkaline water with a pH of 11 or higher. In order to manufacture the electrolytic cell, a flow type electrolytic water producing apparatus using a flow type electrolytic cell is generally used in which electrolysis is performed in one or two stages and the anode and the cathode are separated into diaphragms. Strong acidic water (pH 3 or lower) and strong alkaline water (pH 11 or higher) were obtained in the first stage electrolysis using NaCl or K ₂ CO ₃ as the electrolytic solution, Two-step electrolysis is performed to produce alkaline water, and a strong alkaline water of pH 12 can be obtained.

A strong alkaline-reduced water of pH 12, prepared in this manner, was purchased from Zen Dacs and treated for 1 hour with a cellulose-based biomass, eucalyptus (Guangzhou Institute, China), and the treatment temperature was 180 ° C. After the treatment with alkaline reducing water, a swelling due to a polar solvent is also performed. Thereafter, a step of immersing in a non-polar solvent (30, 50, 70, 90, 95, 100% ethanol and acetone for 15 minutes each) , And dried according to the critical point drying method. Specifically, 5 g of the sample was converted into a non-polar solvent, and then the non-polar solvent acetone was removed by drying at a critical point (36 ° C.) using carbon dioxide, followed by drying.

(2) Pretreatment of diluted sulfuric acid

Diluted sulfuric acid treatment was carried out for 2 hours with 1% sulfuric acid (H ₂ SO ₄ ) in eucalyptus cellulose (Biotechnology, Guangzhou, China) at a treatment temperature of 121 ° C. After dilute sulfuric acid treatment, it was diluted with a polar solvent. After that, the solution was immersed in a non-polar solvent (30, 50, 70, 90, 95, 100% ethanol and acetone for 15 min each) , And dried according to the critical point drying method.

(3) Sodium Hydroxide - Steam pretreatment

Sodium hydroxide vapor pretreatment was carried out by immersing the cellulosic biomass eucalyptus (Guangzhou Laboratories, China) in 3% NaOH for 12 hours and then steamed at 160 ° C for 12 minutes. After the steam treatment, a swelling due to a polar solvent is also performed. Subsequently, after the process of converting to a non-polar solvent (immersing for 15 minutes in each of 30, 50, 70, 90, 95 and 100% ethanol and acetone sequentially) Dried according to the critical point drying method.

(4) Comparison of final porous fibrous structure according to pretreatment type

Table 1 below shows that when pretreated with alkaline-reduced water, the surface area was 195 times that of the fibrous structure sample without pretreatment, 71 times that of the pretreated with dilute sulfuric acid, and that when pretreated with NaOH-steam , It is found that it is increased by 156 times. The volume of pore was also significantly increased compared to the case without pretreatment. Therefore, it is preferable to perform the pretreatment of the fibrous biomass such as cellulose, followed by the treatment with a polar solvent, the solvent substitution with a non-polar solvent, and the critical point drying using carbon dioxide in sequence, as compared with the case of performing critical- It can be seen that this is a very effective method for the production of fibrous structures.

[Table 1: Comparison of pretreatment with alkaline reducing water and other polar solvents]

Experimental Example 2: Surface area change according to difference in drying method

The eucalyptus (Guangzhou Research Institute, China), a fiber-based biomass expanded by releasing hydrogen bonds in the course of pretreatment with alkali reducing water (pH 12; Zen Dacs, Daejeon) (Oven drying, lyophilization, critical point drying), and the surface area was changed according to the drying method.

(1) Three drying methods

In the oven drying method, 5 g of the sample pretreated with alkali reduced water was dried in an oven at 50 ° C for 48 hours. In the freeze-drying method, 5 g of a sample pretreated with an alkali-reduced water was frozen at -60 ° C for 48 hours and then dried in a freeze dryer for 72 hours. In the critical point drying method, 5 g of the sample pretreated with alkali-reduced water was first subjected to a step of converting into a non-polar solvent (sequentially immersed in 30, 50, 70, 90, 95, 100% ethanol and acetone for 15 minutes each) The critical point drying (36 ℃) was applied to remove acetone and drying. Another example of the critical point drying method is a method in which a sample is passed through ethanol and replaced with amyl acetate and then placed in an internal pressure-tightly closed container, liquefied carbon dioxide is injected, the temperature is raised to about 40 DEG C to bring it into a boundary state, It is possible to do it. Critical point drying can also be carried out using Freon instead of carbon dioxide.

(2) Comparison of the final porous fibrous structure according to drying process

The results of Table 2 below are the average values of the measured values. In the case of oven drying, the surface area was 0.5-1.3 m ² / g, the pore volume was 0.002-0.005 cm ³ / g and the surface area was 1.04-2.44 m ² / g, pore volume was 0.005-0.015 cm ³ / g, surface area was 58.5-161.5 m ² / g, and pore volume was 0.103-0.249 cm ³ / g for critical point drying.

It was confirmed that the surface area of the porous fibrous structure prepared by the critical point drying was increased by 178 times as compared to that prepared by oven drying and 66 times as compared with that prepared by freeze drying. Therefore, it has been confirmed that the method of pretreatment, expanding with a polar solvent, substituting a polar solvent with a non-polar solvent, and applying critical point drying using carbon dioxide is more effective for producing a porous fibrous structure than other drying methods.

[Table 2. Comparison of results of oven drying, freeze drying and drying by critical point drying method]

Example 2. Confirmation of surface appearance of porous fibrous structure

Three methods of drying (oven drying, freeze-drying) were carried out on eucalyptus (Guangzhou Research Institute, China), a fiber-based biomass expanded by releasing hydrogen bonds in the course of pretreatment with alkali reducing water (pH 12; , Critical point drying), and then the surface morphology according to the drying method was observed with an electron microscope. The specific drying process of the three drying methods (oven drying, freeze drying, critical point drying) was carried out in the same manner as Experimental Example 2.

2 shows the case of drying without pretreatment, but the surface of the sample is smooth in both the photograph of the magnification of 50,000 magnification and the enlarged magnification of 100,000 times. 3, 4, and 5, it can be seen that when the sample is pretreated with alkali-reduced water and dried, the surface of the sample is relatively coarse, whether it is a 20,000 magnification photograph or a 100,000 magnification photograph. Compared to the untreated sample, the sample pretreated with the alkaline-reduced water has white organic matter (lignin), which appears to have been discharged out of the surface of the pretreated sample.

In the case of drying by the critical point drying method (see Fig. 5), the oven drying (see Fig. 3) and the freeze drying (see Fig. 4) are densely arranged. For white organics (lignin), higher amounts of lignin are observed in the photographs in the order of oven drying <freeze drying <critical-point drying. In the case of oven drying, the organic materials return to the inside due to the shrinkage phenomenon caused by the drying process, and a relatively small amount of organic matter is exhibited. In the case of freeze drying, the organic material is seen but the internal surface shrinkage occurs. Drying of the critical point can be seen in that the organic matter is dried out without deformation due to shrinkage while the organic matter is out, and a large amount of organic matter is observed, thereby maintaining a high surface area and volume.

Having described specific portions of the present invention in detail, it will be apparent to those skilled in the art that this specific description is only a preferred embodiment and that the scope of the present invention is not limited thereby. It will be obvious. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (12)

a) immersing the fibrous material in a polar solvent to increase the internal void;
b) replacing the polar solvent present in the internal voids of the fibrous material with a non-polar solvent; And
c) drying the fibrous material substituted with the nonpolar solvent by controlling the pressure at a critical point using a critical fluid and drying the fibrous material.
The method according to claim 1, wherein the fibrous material in step a)
Wherein the porous fibrous structure is a material containing a fibrous cellulosic material.
The method according to claim 1, wherein the polar solvent in step a)
It is also possible to use neutral water, formamide, ethylene glycol, dimethylformamide (DMF), pyridine, formic acid, N-methylmorpholine-N-oxide N-oxide, NMMO), an ionic liquid, or a combination thereof.
The process according to claim 1, wherein the substitution with the nonpolar solvent in step b)
b1) immersing in acetone,
b2) immersing in ethanol and then immersing in acetone,
b3) immersing in ethanol and immersing in amyl acetate.
2. The method of claim 1, wherein the critical fluid in step c)
Carbon dioxide, or fluorine.
2. The method of claim 1, wherein adjusting the pressure in step c)
Wherein when the critical fluid is carbon dioxide, a pressure of 500 psi is applied, and then a pressure of 1200 psi is further applied, or a method of applying only 500 psi pressure.
The method according to claim 1, wherein, prior to step a)
d) treating the fibrous material with a pretreatment solvent to facilitate formation of internal voids.
8. The method according to claim 7,
Wherein the porous fibrous structure is an acidic aqueous solution or an alkaline aqueous solution.
9. The method according to claim 8,
0.5 to 3% by weight aqueous solution of sulfuric acid.
9. The method according to claim 8, wherein the alkaline aqueous solution comprises:
Characterized in that it is an alkaline reducing water having a pH of 10 or more or an aqueous solution of sodium hydroxide of 0.5 to 4% by weight obtained by electrolysis of water.
The porous fibrous structure according to any one of claims 1 to 10, which has a surface area of 58.5 to 161.5 m ² / g and a pore volume of 0.103 to 249 cm ³ / g.
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