KR20030038892A - Biodegradable interpolymer of gamma-poly(glutamic acid) and chitosan and manufactured film using the same - Google Patents

Abstract

PURPOSE: A biodegradable copolymer of γ-polyglutamic acid and chitosan and a film prepared by using the copolymer are provided, to improve biodegradability, tensile strength and elongation and to reduce the solubility to water. CONSTITUTION: The biodegradable copolymer is a copolymer of γ-polyglutamic acid and chitosan, wherein the copolymer is preferably represented by the formula 1. The degree of deacetylation of the chitosan is 80-100 %, and the viscosity of the chitosan is 100-150 cps. Preferably the γ-polyglutamic acid and chitosan is separated from Bacillus licheniformis. The film prepared by using the copolymer has a tensile strength of 50-100 MPa, an elongation of 10-20 %, a solubility to water of 1.0-10.0 %, and a moisture absorption ratio of 1.0-20.0 %.

Description

Biodegradable copolymer of gammapolyglutamic acid and chitosan and film prepared using the same {Biodegradable interpolymer of gamma-poly (glutamic acid) and chitosan and manufactured film using the same}

The present invention relates to a biodegradable copolymer and a film prepared using the same, and more particularly, to a copolymer made of a polymer material having excellent physical properties and capable of biodegradation, and a film produced using the same.

As science and technology progress, various synthetic polymer materials have been developed. The synthetic polymer material is a simple household tool, packaging film, agricultural film, etc., due to the ease of processing, various physical properties due to chemical structural differences, and low price, such as automobile, aircraft composite materials, medical advanced materials such as artificial heart, etc. It is used in various raw materials. However, most of these synthetic polymer materials are not decomposed when disposed in a natural state such as soil after use, causing serious environmental pollution problems.

As such, as the environmental pollution caused by the synthetic polymer material becomes serious, there is an increasing demand for polymer material that can be easily decomposed in the industry, and by mixing a small amount of natural biodegradable polymer such as cellulose or starch into the existing synthetic polymer material Attempts have been made to facilitate degradation by microbial methods.

However, the biodegradable polymer material made by mixing with starch not only has a significant decrease in physical properties, but also has a problem in that it does not completely decompose in the ecosystem but collapses into fine pieces and still exists in the ecosystem.

Therefore, in recent years, natural polysaccharides, natural polymers such as chitin, or polymers produced from microorganisms such as PHA (poly-hydroxyalkanoate) based polysaccharides have been a trend.

On the other hand, biochemical polymer materials such as PLA (poly lactic acid), which have similar characteristics to the existing synthetic polymer polyethylene and are capable of mass production, have been developed. Biochemical polymers are synthesized from raw materials such as amino acids, sugars and the like produced at low cost by fermentation technology, and have been evaluated as ideal biodegradable polymers due to easy control of functions. The polymer material is environmentally friendly and has a feature of high biodegradability compared to other biodegradable polymer materials, but has a problem that the price is four times more expensive than the existing polymer materials.

In addition, Korean Patent Application No. 1994-19856 discloses an example in which a polymer is prepared by mixing chitosan and cellulose, which are natural substances, and then a biodegradable film is prepared. Korean Patent Application No. 1994-26030 discloses chitosan and starch. Composite films made of polymers have been disclosed.

However, these chitosan-based films are biodegradable and inexpensive, but their physical properties are not as good as those of conventional synthetic polymer products. In addition, starch added to chitosan is difficult to apply commercially due to low elongation. .

The present invention has been made to solve the above problems, the technical problem to be achieved by the present invention is a copolymer made of a polymer material having excellent physical properties and easy to apply commercially and biodegradable and produced using the same To provide a film.

In order to achieve the above object, the present invention provides a copolymer of gamma polyglutamic acid and chitosan, represented by the following formula (1).

Hereinafter, the present invention will be described in detail.

Gamma polyglutamic acid (γ-poly (glutamic acid; hereafter referred to as "γ-PGA") is a biopolymer having a molecular weight of about 1 million daltons isolated from microbial culture, which is water-soluble, has anions, and is edible. This has the feature of being possible. Although γ-PGA is a natural polyamide, it has a unique structure different from most proteins. That is, proteins generally have a peptide bond between the α-carboxylic group and the α-amino group, but γ-PGA is a covalent bond between the α-amino group and the γ-carboxyl group by glutamic acid, a repeating unit. As a peptide bond. Such γ-PGA is known to be highly useful in industrial fields such as medicine and food (King et al ., J. Polymer Sci. Part A: Polymer chemistry , 36: 1995-1999, 1998).

On the other hand, chitin is a chain polymer in which N-acetyl-D-glucosamine is polymerized by β- (1 → 4) linkage (poly-β- (1.4) -N-acetyl D-glucosamine) is a natural polymer contained in the cell walls of fungi such as shells, fungi, yeasts, and mushrooms. However, chitin has a crystal structure composed of hydrogen bonds between intermolecular and intermolecular, and is difficult to dissolve in most solvents. Deacetylation of such chitin yields chitosan, which is a chain polymer polysaccharide (β- (1) in which D-glucosamine is polymerized by a β- (1 → 4) bond. , 4) -2-amino-2-deoxy-β-D-glucan), has a relatively high solubility in water. Chitosan dissolves in water under acidic protonation of the amine group at the C-2 position.

The degree of deacetylation indicates the amount of amino group that becomes positive (+) when solubilized, and is an important factor in determining the quality of chitosan along with the molecular weight of chitosan. That is, 80% of deacetylation means that 20% of chitin and 80% of chitosan are mixed.

In the present invention, it is characterized in that the copolymer consisting of the γ-PGA and chitosan. The copolymers according to the invention are negatively charged (-COO) resulting from the extra carboxyl reactor in γ-PGA.^-Positive charge (-NH) produced by the protonation of the amino reactors in₃ ⁺) It is formed by the action of electrostatic interaction in the liver.

Chitosan used in the preparation of the copolymer of the present invention is a deacetylation of chitin, it is preferable to use a deacetylation degree of 80-100%. If the deacetylation degree is less than 80, the solubility of the chitosan and the amount of charge are reduced, so it is preferable not to use less than 80.

In addition, the chitosan used in the preparation of the copolymer of the present invention preferably has a viscosity of 100-150 cps. When the viscosity of the chitosan is less than 100 cps, the molecular weight is too small, and if the viscosity exceeds 150 cps, it is preferable to use chitosan having a viscosity in the above range because problems may occur in mixing, homogenization, and solubilization.

In addition, the chitosan used in the preparation of the copolymer of the present invention is preferably low ash concentration. Ash is the amount of ash remaining after burning at high temperatures. If the ash concentration is too high, it means that the chitosan material contains a large amount of impurities, so it is preferable to use chitosan having a low ash concentration.

Specifically, the copolymer of the present invention has a deacetylation degree of 96.7%, ash concentration of 0.08%, 1% chitosan solution with a viscosity of 120 cps, solubility in 0.25% acetic acid, 75.1%, insoluble in 0.25% acetic acid. Chitosan with 1.1% and 8% moisture content was used.

On the other hand, γ-PGA used in the preparation of the copolymer according to the present invention, it is preferable to use the purified γ-PGA separated from the culture solution of Bacillus licheniformis ( Bacillus licheniformis ). The γ-PGA may be separated and purified by a general method known in the art, and a polymer having a molecular weight of about 800,000 to 1.2 million daltons is usually obtained.

In addition, the present invention is characterized by providing a film made of the copolymer of the chitosan and γ-PGA.

In one embodiment of the present invention, a biodegradable film was prepared using the copolymer prepared with the chitosan and γ-PGA. In preparing the film, a plasticizer such as glycerol and sorbitol, which are conventional additives, may be blended. Plasticizers are materials which are excellent in workability by being added to rigid polymers to have plasticity and are generally used in the production of polymer films.

The film made of the copolymer of chitosan and γ-PGA according to the present invention preferably has a tensile strength of 50-100 Mpa, an elongation of 10-20%, a solubility of 1.0-10.0%, and an absorption of 1.0-20.0%.

Since the film made of the copolymer according to the present invention is harmless to the human body, it may be used for medical, drug delivery, drug coating, and the like.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

<Example 1>

Biodegradable Copolymer and Preparation of Film Using the Same

1-1) Preparation of γ-PGA and Chitosan Samples

After culturing Bacillus licheniformis ( Bacillus licheniformis , ATCC 9945a), γ-PGA was purified by the following method.

NaCl was added to the Bacillus licheniformis culture to 6% and shaken at high speed for 1 minute using a blender. The mixed solution was centrifuged at 10,000 × g for 30 minutes to obtain a culture medium from which the cell cells were removed. Three times of 95% ethanol was added to the culture medium to precipitate γ-PGA. Γ-PGA obtained as a precipitate was redissolved in distilled water and then filtered through a filter of 0.45 μm (pore size) to remove residual solids, and dialyzed with distilled water to remove low molecular weight substances having a molecular weight of 30,000 Daltons or less. 10N hydrochloric acid was added to the solution to adjust the pH of the γ-PGA aqueous solution to 1.5, and then 1: 1 mixed solvent of n-propanol and ether was added thereto to precipitate γ-PGA. . The precipitated γ-PGA was recovered and dried, and then dissolved in 100 mM sodium acetate solution (pH 5.0) to be used in subsequent experiments. The molecular weight of the isolated and purified γ-PGA was about 1 million Daltons.

In addition, chitosan was prepared by the following method.

Crab shells were ground to a size of 5-10 mesh, washed with water, and ethanol was treated at 80 ° C. for 2 hours to remove pigments. Then 1N KOH was treated for 2 hours at 80 ℃ to remove the protein, washed again with water. 1N HCl was treated at room temperature for 1 hour to remove inorganics, and then washed with water to obtain chitin. The chitin prepared as described above was deacetylated for 24 hours at 50 ° C. with 55% KOH to prepare chitosan, and the properties of the chitosan thus prepared are shown in Table 1 below.

characteristic Solubility in 0.25% acetic acid (%) % Insoluble for 0.25% acetic acid Ash content (%) Deacetylation degree (%) moisture(%) 1% chitosan viscosity (cps) 75.1 1.1 0.08 96.7 8 120

1-2) Copolymer of γ-PGA and Chitosan and Preparation of Film Using the Same

A copolymer was prepared by blending a 10% γ-PGA aqueous solution prepared in Example 1-1 and a 2% chitosan solution and solution polymerization at 20 ° C.

The copolymer solution was cast on a glass plate, and the glass plate was left at room temperature for 2 days, and then dried at 70 ° C to prepare a film. As a plasticizer, 99.5% pure glycerol (TEDIA Company, INC., USA) was added at a level of 0.3%.

Comparative Example 1

Preparation of Chitosan Film

After dissolving the lactic acid (Lactic acid, Hayashi Pure Chemical Industries Ltd.) to a final concentration of chitosan of 2% (w / w), the undissolved precipitate was removed by filtration using a 0.45 μm filter. . Glycerol (glycerol, Sigma) and sorbitol (sorbitol, Sigma) were added as a plasticizer and stirred well, then cast on a flat glass plate and left at room temperature for 2 days, and dried at 70 ℃ for 24 hours to prepare a chitosan film.

Comparative Example 2

Preparation of γ-PGA Film

2 g of γ-PGA was added to 100 ml of 100 mM sodium acetate (pH 5.0), 0.3 g of glycerol was added as a plasticizer, and the solution was cast on a flat glass plate and left at room temperature for 2 days. Time drying resulted in γ-PGA film.

<Example 2>

Physical Characterization of Copolymer Films of γ-PGA and Chitosan

Experiments were performed to compare the physical properties between the copolymer film according to the present invention prepared as in Example 1, the existing polyethylene film, chitosan film (Comparative Example 1) and γ-PGA film (Comparative Example 2).

2-1) Tensile strength and elongation rate measurement

Each film was preconditioned for 24 hours at a temperature of 65% relative humidity and 20 ° C., and then cut into 10 × 2.5 cm size and tensioned using a texture analyzer (TA-XT2, Haslemere Surrey, England). Strength and elongation were measured. The initial gripping distance (distance between grips) was 5 cm and the cross head was 500 mm / min. The tensile strength (MPa) of the film was calculated by dividing the maximum tension until the film was cut by the cross section of the initial film, and the elongation (%) of the film was calculated by extending the length of the film to the distance between the initial grips. It is expressed as a percentage, and the results are shown in Tables 2 and 3 below.

Conventional polyethylene film Comparative Example 1 Comparative Example 2 Example 1 Tensile Strength (MPa) 2.9 17.2 10.8 85.5

Conventional Polyethylene Film Comparative Example 1 Comparative Example 2 Example 1 Elongation (%) 95.4 53.4 80.2 12.5

As shown in Table 2 above, the force (tensile strength) required for stretching was the smallest (2.9 MPa) for polyethylene film, followed by the γ-PGA film (10.8 MPa), followed by the chitosan film (17.2 MPa). The copolymer film of 85.5 MPa was used the most force. That is, it was confirmed that the tensile strength of the copolymer film of the present invention is high.

In addition, as shown in Table 3, the elongation of the existing polyethylene film was 95.4%, followed by γ-PGA (80.2%), chitosan film (53.4%), the copolymer film of the present invention was the least 12.5% Increased. That is, it was confirmed that the copolymer film of the present invention did not easily stretch.

2-2) Measurement of solubility (water resistance) and water absorption (water content) of film

In order to confirm the solubility (water resistance) of the copolymer film in water, the weight was measured at a standard state (20 ° C., relative humidity 65%), followed by stirring for 24 hours in water at room temperature (20 ° C.). The film was dried and weighed in a standard state to determine the amount of film dissolved in water. The solubility of the film was taken as a percentage of the initial dry amount of the amount dissolved in water, and the results are shown in Table 4 below.

In addition, the water absorption rate (water content) was calculated from the weight after leaving for 24 hours at a standard state (20 ℃, 65% relative humidity) and the weight after drying for 30 minutes at 100 ℃, the results are shown in Table 5 below.

Conventional Polyethylene Film Comparative Example 1 Comparative Example 2 Example 1 Solubility (%) 0 47.7 100 6.8

Conventional Polyethylene Film Comparative Example 1 Comparative Example 2 Example 1 Absorption rate (%) 0 44.5 72.3 18.4

As shown in Table 4, γ-PGA was completely dissolved in distilled water with 100% solubility, chitosan film showed a weight loss of 47.7%, but the copolymer film of the present invention showed a weight loss of 6.8%. . That is, it was confirmed that the copolymer film of the present invention has a property that is not easily dissolved in water.

In addition, as a result of measuring the change in weight increased by absorbing moisture in the air at a standard condition (20 ° C., 65% relative humidity), as shown in Table 5, 72.3% of the γ-PGA film and the chitosan film were The weight gain of 44.5% was shown, but the copolymer film of the present invention showed a weight gain of 18.4%. That is, it was confirmed that the copolymer film of the present invention does not readily absorb moisture.

As described above, as a result of comparing the tensile strength, elongation rate, solubility and water absorption of the existing polyethylene film and the copolymer film of the present invention, the existing polyethylene film is not easily dissolved in water compared to the copolymer film of the present invention, It was good, but the difference was small. However, it was confirmed that the copolymer film of the present invention is much superior in terms of tensile strength and elongation, which are important in film quality evaluation.

<Example 3>

Determination of Biodegradability of Copolymer Films of γ-PGA and Chitosan

As described above, the biodegradability of the copolymer film according to the present invention was found to be excellent in quality.

First, the mixture of the soil and the copolymer film prepared according to the present invention in the Erlenmeyer flask was put, sealed with a rubber stopper, and two glass tubes were plugged into the rubber stopper. As a control, only the soil was used without the copolymer film. The NaOH solution was passed through one glass tube to slowly blow carbon dioxide-depleted air into the soil in the flask with an air pump, and the other glass tube allowed the air that had entered the soil to slowly come out of the flask. At this time, if the film or carbon compound (organic matter) in the soil is decomposed carbon dioxide is emitted through the glass tube. The air exited was then passed through another NaOH solution to capture carbon dioxide gas. Therefore, it is possible to test whether the film (or organic matter) is decomposed from the amount of carbon dioxide collected.

As a result, as shown in Table 6, it was confirmed that the generation of high carbon dioxide compared to the control. That is, it was found that the copolymer film prepared in the present invention can be decomposed in a natural state.

CO2 emissions in aerobic soil environments Housing time (unit: days) One 2 4 8 16 32 Accumulated Carbon Dioxide (mg) Copolymer Film (Example 1) 100 150 220 300 470 600 Control 80 120 150 160 170 170

The copolymer of γ-PGA and chitosan according to the present invention has excellent biodegradability and physical properties, and is easily applied in commercial fields such as medical, food, and chemical products. In addition, the film made of the copolymer is not only excellent in physical properties such as tensile strength, elongation, but also has the advantage of low solubility in water.

Claims (10)

Copolymer of gamma polyglutamic acid and chitosan. The copolymer of gamma polyglutamic acid and chitosan according to claim 1, represented by the following general formula (1). <Formula 1> The copolymer according to claim 1, wherein the degree of deacetylation of the chitosan is 80-100%. The copolymer of claim 1, wherein the chitosan has a viscosity of 100-150 cps. The copolymer of claim 1, wherein the gamma polyglutamic acid is separated from Bacillus licheniformis . A biodegradable film made from the copolymer of claim 1. 7. The biodegradable film of claim 6, wherein the tensile strength is 50-100 MPa. The biodegradable film according to claim 6, wherein the elongation is 10-20%. The biodegradable film according to claim 6, wherein the solubility in water is 1.0-10.0%. The biodegradable film according to claim 6, wherein the water absorption is 1.0-20.0%.