JP2005225935A - Chitosan dispersion liquid, preparation method therefor and manufacturing method for chitosan film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare an aqueous liquid which has a film-forming property derived from chitosan and gives little harm derived from an acid, a preparation method therefor and a manufacturing method for a chitosan film with a low acid component content. <P>SOLUTION: A chitosan emulsion is prepared by dispersing chitosan in a weakly acidic aqueous solution by the action of a surfactant, wherein the weakly acidic aqueous solution is an aqueous acid solution with a pH of 4-7. In the manufacturing method for the chitosan film, the acidic solution of chitosan is treated with the surfactant to obtain an emulsion wherein the chitosan is dispersed in the aqueous acid solution by the action of the surfactant, the acid component is subsequently removed from the aqueous acid solution to obtain the weakly acidic aqueous solution, and a film is formed from the emulsion to form the chitosan film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dispersion of chitosan having a low acid component in the liquid, a method for producing the same, and a method for producing a chitosan film having a low acid component concentration in the film.

  Chitin is a natural polymer produced by many organisms, including shrimps and crabs, insects, shellfish, and mushrooms. Annual production on the earth is estimated to be 100 billion tons, and is attracting attention as a natural material derived from abundant biomass resources. Chitin is a polymer of N-acetyl-D-glucosamine and is a mucopolysaccharide having a structure similar to cellulose. Industrially, chitin is produced by treating a complex with calcium carbonate in the outer shell of shrimp, crab, etc. by treating with hydrochloric acid. When chitin is hydrolyzed with an alkali, the acetyl group is removed and the chitin is converted into chitosan mainly composed of D-glucosamine units. Chemical formulas of chitosan are shown together with those of cellulose and chitin having a structure similar to Chemical Formula 1.

  In general, the degree of deacetylation varies, and those having a degree of deacetylation of 50% or less are called chitin, and those having a degree of deacetylation of 50% or more and soluble in an acid are called chitosan. Chitin is soluble only in special solvents such as formic acid because it has a crystalline structure with strong hydrogen bonds formed in the molecule. Chitosan dissolves in an acidic aqueous solution containing a weak acid because an amino group present in the side chain easily reacts with an acid to form a salt. Moreover, it has various functionality derived from an amino group, and can be used in a wide range of applications. Research and development of applied products such as fibers, paper, medical materials, health food supplements, etc. that utilize the bioactivity of chitin or chitosan are underway.

Chitosan is used in cosmetic materials and food additives, for example, and has antithrombogenic and hemostatic effects. Therefore, it is used as a medical material for clothing, textile materials, fabrics and textile materials because of its antibacterial and antifungal action and the effect of protecting against pathogenic bacteria. Used alone or in combination with other materials. In addition, since it has a strong chemical affinity with cellulose because of its close chemical structure, it is being studied for applications in wallpaper and wood adhesive applications.

  To form a chitosan film, the chitosan is dissolved with an acid, and a chitosan acid solution layer is formed on the object by casting, coating, spraying, dipping, etc. A chitosan film is formed by evaporating water and dehydrating water by drying or absorbing water to the object to be coated (see Non-Patent Document 1).

  Various inorganic acids and organic acids are known as solvents for dissolving chitosan. Among them, organic acids such as acetic acid, lactic acid, propionic acid, succinic acid and acrylic acid are used as good solvents for chitosan. In particular, acetic acid is most commonly used. For example, to a chitosan aqueous suspension containing 1 to 3% by weight of chitosan powder, acetic acid is added to 1 to 3% by weight and stirred to dissolve. Alternatively, 1 to 3% by weight of chitosan powder is added to an aqueous solution of 1 to 3% by weight of acetic acid and dissolved by stirring. At this time, the hydrogen ion concentration of the aqueous solution becomes pH 2 to 3, indicating strong acidity. However, since the range of use of chitosan is limited by the presence of these acids, development of a method that does not cause acid damage is required.

  In order to coagulate chitosan from an acetic acid solution of chitosan, it is necessary to evaporate acetic acid or neutralize with alkali. The former leads to an environmental load, and the latter causes an increase in cost. There is a report (see Non-Patent Document 2) that solves the above problems by using carbon dioxide gas to produce a chitosan film, but it is not common.

For this reason, the chitosan film formed using the above chitosan acid solution contains a lot of strong acid components, and when the acid solution layer is formed on the object to be coated and over time due to moisture absorption from the chitosan film after film formation. The leaking acid component has an adverse effect on the workpiece. Therefore, there is a risk of rough skin when applied to applications that touch human skin, and there is a risk of rusting iron nails when used as an adhesive. This acid problem has become a major obstacle to the development of potential applications that can take advantage of the superior properties of chitosan.
Chitin Chitosan Study Group, “Application of chitin and chitosan”, Technique Hall Publishing, p. 99-122 (1994) Yasuo SAKAI, Koichi HAYANO, Hiroe YOSHIOKA, and Hisashi YOSHIOKA, Polymer Journal, Vol. 33, no. 8, p640-642 (2001)

  The problem to be solved by the present invention is to provide an aqueous dispersion with little harm of acid of chitosan, and a chitosan film having a low acid component content, and a method for producing them.

  As a result of earnest research in view of the above problems, the present inventor has made a weakly acidic aqueous solution of chitosan that is capable of effectively utilizing the various effects of chitosan and that has a small dispersion of chitosan. The inventors have found that the problem can be solved by removing the acid in the acid solution, which is the dispersion medium, and have completed the invention.

  The invention according to claim 1 is a chitosan dispersion in which chitosan is dispersed in a weakly acidic aqueous solution with a surfactant. Since chitosan is hydrated, chitosan hydrate becomes fine particles and is dispersed in the form of an emulsion. Since the acid in the aqueous solution layer of this medium is dilute, the acid component leaking from the chitosan film after film formation is significantly reduced when the emulsion layer is formed on the object to be coated, and the adverse effect of the acid on the object to be coated is remarkably reduced. Can be reduced. In addition, there is an advantage that a wide range of components can be used for components added to the emulsion for use in various applications.

The invention according to claim 2 is the chitosan dispersion according to claim 1, wherein the weakly acidic aqueous solution is an acidic aqueous solution having a pH of 4 to 7.
Since it is an acidic aqueous solution having a pH of 4 to 7, the action due to the leakage of the acid component at the time of forming the dispersion emulsion liquid film and / or after the film formation is mild, the action on the human body is gentle, and there is little risk of damage.

According to the third aspect of the present invention, chitosan is dissolved in an acid aqueous solution, and then a surfactant is allowed to act to obtain a dispersion in which chitosan is dispersed in the acid aqueous medium by the surfactant, and then the acid aqueous solution. A method for producing a chitosan dispersion in which chitosan is dispersed in a weakly acidic aqueous solution by a surfactant, wherein the acid component is removed from the medium.
According to the present invention, an acid aqueous solution of chitosan can be prepared by a normal method and apparatus. Moreover, since it is dispersed using a surfactant, a stable emulsion in which chitosan is dispersed in an aqueous acid solution can be prepared. Next, since the acid component is removed from the aqueous acid solution of the dispersion medium, a chitosan dispersion with less acid damage can be produced.

The invention according to claim 4 is characterized in that the means for removing the acid component from the acid aqueous medium uses an ion exchange resin, and chitosan is dispersed in the weakly acidic aqueous solution by the surfactant. This is a method for producing a chitosan dispersion.
According to the present invention, an acid component can be removed from an acid aqueous solution, which is a dispersion medium of chitosan, using an ion exchange resin with a simple apparatus and operation. Further, at that time, the dispersion liquid is not contaminated and unnecessary impurities are not mixed, and a by-product is not generated. The ion exchange resin can be used repeatedly by removing the adsorbed acid after taking it out of the emulsion.

According to a fifth aspect of the present invention, in the method for producing a chitosan film, a surfactant is allowed to act on an acid solution of chitosan to obtain a dispersion in which chitosan is dispersed in an acid aqueous medium by the surfactant, and then the chitosan film is formed. A method for producing a chitosan film is characterized in that a chitosan film is formed by removing an acid component from an acid aqueous medium of a dispersion and then forming a chitosan film from the dispersion from which the acid component has been removed.
According to the present invention, since the acid component is removed from the aqueous acid solution that is the dispersion medium, the content of the acid component in the aqueous acid solution that is the dispersion medium is low, and the dispersion layer is formed on the object by applying the chitosan dispersion liquid or the like. During formation and after chitosan film formation, contamination by acid components and leakage are small, and damage by acid is reduced.

The invention according to claim 6 is the method for producing a chitosan film according to claim 5, wherein the means for removing the acid component from the acid aqueous medium uses an ion exchange resin.
According to the present invention, since an acid component is removed from an acid aqueous solution that is a dispersion medium of a dispersion using an ion exchange resin, the process is simple and the apparatus can be simplified, and the dispersion is contaminated at that time. No extra impurities or by-products are generated. The ion exchange resin is economical because it can be used repeatedly by removing the adsorbed acid after taking it out of the dispersion.

The present invention will be described in detail below.
Usually, chitosan is produced by purifying chitin obtained from α-chitin contained in crab shells, β-chitin contained in squid soft shells, etc., and converting them into chitosan. There is known a method for obtaining an alkali chitosan hydrogel by treating chitin in a 40 to 45 wt% sodium hydroxide solution at 90 to 120 ° C. for 4 to 9 hours. It is also known that chitosan can be obtained by neutralization.

An aqueous chitosan acid solution is obtained by dissolving chitosan with an aqueous acid solution. As described above, hydrochloric acid, acetic acid, lactic acid, propionic acid, succinic acid, acrylic acid, etc. can be used as the acid that dissolves chitosan. Among them, acetic acid is mild in action, and its action on the human body is gentle. This is preferable because the risk of failure is low.

For example, in order to prepare an acid aqueous solution of chitosan, acetic acid is added to 1 to 3% by weight to a chitosan aqueous suspension containing 1 to 3% by weight of chitosan powder and dissolved by stirring. Alternatively, 1 to 3% by weight of chitosan powder is added to 1 to 3% by weight aqueous solution of acetic acid and dissolved by stirring. Since chitosan is a polymer, it seems that water molecules are coordinated to the chitosan molecule, but it is difficult to completely dissolve it, and a part of the gel-like portion remains. At this time, the hydrogen ion concentration of the acid aqueous solution is pH 2 to 3, indicating strong acidity.

  A weakly acidic aqueous solution refers to an acidic aqueous solution whose concentration in the aqueous solution is much lower than the acid concentration required to dissolve chitosan. In other words, it refers to a weakly acidic aqueous solution having a low acid concentration. Therefore, if there is no operation to emulsify using a surfactant, it means an aqueous solution having an acid concentration in which chitosan is precipitated. Those having a low acid concentration that is as stable as possible in dispersion and as neutral as possible in use are preferred. The pH is preferably 4 or more, more preferably 5 or more, still more preferably 6 or more, and the upper limit is a limit value at which the emulsion is stable, preferably 6 to 7.

  The chitosan dispersion refers to a state in which chitosan is dispersed as fine particles in a liquid medium. An emulsion refers to a state in which incompatible or poorly compatible liquid is dispersed in a liquid medium by forming microcells. The suspension refers to a state in which a solid is dispersed in a liquid medium in a fine particle state. What was made into the acid solution of chitosan and disperse | distributed after that turns into a dispersion liquid of the state close | similar to an emulsion. The dispersion is preferably in a stable state, and a stable emulsion can be formed by using, as a surfactant, a molecule having a portion having an affinity for the dispersion medium and the dispersion. The dispersion of the emulsion in the present invention is chitosan, but more strictly, it seems to be a chitosan-water complex in which water molecules are coordinated around chitosan molecules.

As the surfactant in the present invention, those usually used can be used, but nonionic surfactants or cationic surfactants are preferable, and nonionic surfactants are particularly preferable.
For example, when an aqueous acetic acid solution of chitosan is dispersed with a surfactant, it interacts with chitosan while retaining ions. When acetic acid is removed with an ion exchange resin from this state, the ionization of chitosan is reduced, and a nonionic surfactant and chitosan are caused to undergo a hydrophobic bond interaction and dispersed in water as small dispersed particles. It seems that a part of the ammonium side chain generated by the ionization of chitosan remains as it is, and chitosan is dispersed as cationic dispersed particles. The HLB (Hydrophile-Lipophile Balance) value of the surfactant is preferably larger than 6.4, more preferably 12.6 or more.

  Further, the surfactant is generally properly used depending on the application, but the one for the application can be preferably used in the present invention from the viewpoint of safety and the like. For example, glycerol monostearate, polyethylene glycol oleate and the like are preferably used for cosmetics and bathing agents that are in contact with human skin. For food use, sorbitol monostearate is preferably used. The surfactant is used at a normal dose, but is preferably 0.2 to 1.0% by weight, a specific interaction works between the surfactant and chitosan, and the surfactant is 0.2% by weight. It is considered that the fine particle dispersion of chitosan is promoted between the concentration of 0.5% by weight and 0.5% by weight, so that the concentration of the surfactant is more preferably 0.2% by weight to 0.5% by weight.

  An emulsion is prepared from an aqueous chitosan acid solution by adding a surfactant or an aqueous surfactant solution to the aqueous chitosan acid solution and stirring the mixture with a homogenizer or the like.

  Various means such as ion exchange and membrane separation can be used to remove the acid component from the aqueous acid solution, which is the medium of the dispersion using the aqueous acid solution of chitosan, as long as the emulsion is not destroyed. It is preferable to use an ion exchange method using a resin because the operation is simple and effective, and an anion exchange resin is preferred.

  In order to produce a chitosan film from a chitosan emulsion, usual means can be used. For example, when an emulsion layer is formed on an object to be coated by casting, coating, spraying, immersing, etc., low boiling point substances such as water volatilize from the emulsion layer or moisture is wetted on the object to be coated. Thus, the medium is lost and the chitosan-water complex fine particles come into contact with each other to form a film. Furthermore, it is considered that a chitosan film is formed by volatilization of low boiling point substances such as water in the film.

  Emulsions in which chitosan is dispersed in a weakly acidic aqueous solution with a surfactant must have essentially no chitosan properties, film-forming properties, and chemical corrosiveness, irritation, and acid odor to the coating object. In the environmental field, waste liquid coagulants, heavy metal scavengers, sewage treatment agents, precious metal adsorbents, radioactive material adsorbents, in the agricultural field, soil conditioners, insecticides, growth promoters, in industrial fields, woodwork paints, wood In the adhesive and health care fields, it can be suitably used for cosmetics, bathing agents, fiber treatment agents, functional foods, health supplements, anticancer agents and the like.

  In the case of the above emulsion in which the weakly acidic aqueous solution is an acid aqueous solution having a pH of 4 to 7, it is a weak acid and is relatively easily volatilized. The acid smell of the emulsion itself is weak, and it is difficult to remain in the chitosan film, and even if left, it is harmful to the human body. Due to its small number, etc., it is suitable for various uses in the health and medical field and for applications that dislike metal corrosion. In particular, the emulsion medium is preferably an aqueous acetic acid solution.

The chitosan film obtained from the emulsion can be suitably used for artificial skin, sutures, drug capsules, artificial dialysis membranes, sustained-release films and the like.
The chitosan emulsion, in which the acidic aqueous medium of the emulsion is a weak acid aqueous solution having a pH of 4 to 7, is more resistant to the acid remaining in the membrane, especially in the acetic acid aqueous solution chitosan, and has little acid odor even in the remaining state, causing little harm to the human body Among these uses, the chitosan film is preferably used for various uses in the health care field.

  Since the chitosan dispersion according to the present invention has very little acid component in the acidic aqueous solution, the acid component leaked from the chitosan film after the film formation and when the dispersion layer is formed on the object to be coated significantly decreases. Can significantly reduce the adverse effects of acid on the water. In addition, there is an advantage that a wide range of components can be used as components added to the dispersion for use in various applications.

The dispersion of the aqueous acid solution having a pH of 4 to 7 as the dispersion medium of the chitosan dispersion is mild when the dispersion film is formed on the object to be coated and / or the action due to leakage of the acid component after film formation, The action on the human body is gentle and the risk of injury is low. For this reason, necessary additives can be blended based on this emulsion and used for cosmetics, bathing agents, toothpastes and the like.

According to the method for producing a chitosan emulsion according to the present invention, an acidic aqueous solution of chitosan can be prepared by a normal method and apparatus. Moreover, since it is dispersed by a surfactant, a stable emulsion in which chitosan is dispersed in an aqueous acid solution can be prepared.

  According to the method of removing an acid component from an acid aqueous solution that is a dispersion medium of an emulsion using the ion exchange resin according to the present invention, the acid component can be easily removed from the acid aqueous solution of the dispersion medium. Further, at that time, the emulsion is not contaminated or extra impurities are mixed, and no by-product is formed. Since the ion exchange resin can be repeatedly used by removing the adsorbed acid after taking it out of the emulsion, it is economically efficient.

  According to the method for producing a chitosan film according to the present invention, the acid component is removed from the acid aqueous solution that is the dispersion medium of the emulsion, so that the content of the acid component in the acid aqueous solution that is the dispersion medium of the emulsion is low. When the emulsion layer is formed on the object to be coated and after the chitosan film formation, the contamination and leakage due to the acid component are small, and the damage due to the acid is greatly reduced.

  According to the method for producing a chitosan membrane according to the present invention, an acid component is removed from an acid aqueous solution that is a dispersion medium of a dispersion using an ion exchange resin, so that the process is simple and the apparatus can be simplified. At that time, the emulsion is not contaminated and no extra impurities or by-products are formed. Therefore, a chitosan film having a low acid component and high chitosan purity is formed.

  Hereinafter, the present invention will be described in more detail by giving specific examples of the present invention. The present invention is not limited to the following examples.

〔material〕)
(Chitosan)
As chitosan, SK-10 (catalog molecular weight: 8-100,000; degree of deacetylation: 71%) and SK-50 (catalog molecular weight: 400,000-500,000; degree of deacetylation: 87%) Two types were used.
(Characterization of Chitosan)
Table 1 shows the molecular weight and degree of deacetylation of chitosan determined from the GPC and ¹ HNMR NMR measurement results of the chitosan sample. SK-10 was almost the same as the catalog molecular weight, but SK-50 was 170,000, which was about 1/3 of the catalog molecular weight value. It can also be seen that the degree of deacetylation is higher with SK-50.

(Surfactant)
A nonionic surfactant (trade name is Neugen T-143) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used as the surfactant. Its structure is polyoxyethylene lauryl ether [C ₁₂ H ₂₅ O (CH ₂ CH ₂ O) nH], and its Hydrophile-Lipophile Balance (hereinafter abbreviated as “HLB”) value is 12.6.

(Ion exchange resin)
An anion exchange resin (trade name: Diaion PA408) manufactured by Mitsubishi Chemical Corporation was used as the ion exchange resin. Its molecular structural formula is shown in Chemical Formula 2. The total ion exchange capacity is 0.9 meq / ml-R or more, and the apparent density is 725 g / L. Prior to use, it was activated by treatment with aqueous sodium hydroxide.

(Measuring method and measuring device)
Gel permeation chromatography (GPC) was measured by an apparatus combining a BASIC program of a liquid feeding unit LC-10AS manufactured by Shimadzu Corporation, a differential refractometer detector RID-10A, a column oven CTO-10A and a C-R4A. A water-based TSKgel G4000PWXL manufactured by Tosoh Corporation was used for the column. As a solvent, acetic acid-sodium acetate buffer (pH = 4.7), 40 ° C., and 0.6 mm / min were used. The molecular weight of the sample is
The calculated molecular weight was determined using Pullulan (registered trademark) as a standard.

The degree of deacetylation was determined from the spectrum of 500 MHz ¹ H-NMR (Bruker ARX × 500 measuring apparatus) using CF ₃ COOD-D ₂ O (50/50 in vol%) as a solvent.
Dynamic light scattering (DLS) was measured using a super dynamic light scattering photometer DLC7000 manufactured by Otsuka Electronics Co., Ltd. under the conditions of Ar laser and 25 ° C.
Measurement with a scanning electron microscope (SEM) was performed with a Hitachi S-3000N measuring apparatus.

(Preparation of chitosan dispersion with surfactant and deacetication with ion exchange resin)

1.0 g of chitosan SK-10 was dissolved in an aqueous solution containing 3.0 g of acetic acid to prepare 50 g of a chitosan solution. To this solution, 50 g of an aqueous solution of 2% by weight of surfactant Neugen T-143 was added dropwise and mixed and dispersed. The concentrations of chitosan, acetic acid, and surfactant in the mixed solution are 1.0%, 3.0%, and 1.0% by weight of the total solution, respectively. Ion exchange resin Diaion PA408 was added to this mixed solution, and the mixture was stirred at room temperature for 2 hours for ion exchange. At this time, the amount of ion exchange resin was 41 g, which is the same amount of exchange ions as acetate ions, 20.5 g of 0.5 times the amount, and 61.5 g of 1.5 times the amount. Thereafter, the mixture was subjected to suction filtration to remove the ion exchange resin to obtain a chitosan dispersion.

If neutralization is performed by adding alkali directly to an aqueous acetic acid solution of chitosan containing a surfactant, chitosan salting out occurs and uniform dispersion is impossible. However, acetic acid is ion-exchanged and then removed to prevent chitosan precipitation. A liquid could be prepared.

(Separation of chitosan from chitosan dispersion)
By stirring 10.0 g of the obtained chitosan dispersion in 100 ml of ethanol while slowly dropping, chitosan in the dispersion was precipitated. The precipitate was filtered, washed several times with ethanol, and vacuum dried at room temperature for 6 hours. The chitosan content in the chitosan dispersion was determined from the weight.

(Production of chitosan film)
The obtained chitosan dispersion was cast into a petri dish and dried at room temperature for 3 days to obtain a film. The obtained film was immersed in ethanol for several hours and further washed several times with ethanol. Thereafter, it was air-dried overnight at room temperature and then dried under reduced pressure.

 The results are shown in Table 2.

A chitosan dispersion and a chitosan film were obtained in the same manner as in Example 1 except that SK-50 was used instead of chitosan SK-10.
The results are shown in Table 3.

Tables 2 and 3 compare the states of chitosan dispersions obtained by changing the amount of ion exchange resin. Although the pH of the chitosan solution before ion exchange is about 3.5, it can be seen that it rises with ion exchange. However, even when the ion exchange amount of the ion exchange resin is equivalent to the amount of acetic acid in the solution, the pH is 4 or less, and even when the ion exchange amount is increased by 1.5 times, the pH is 5 or less. showed that. The acetic acid odor was strong when the ion exchange amount was below the equivalence point, but the acetic acid odor almost disappeared above the equivalence point, and it was judged that free acetic acid was almost eliminated.

  FIG. 1 shows the relationship between the chitosan content in the chitosan dispersion and the amount of resin, that is, the ion exchange capacity. From this result, when the ion exchange amount is 1: 1 with the amount of acetic acid in the solution for both SK-10 and SK-50, the chitosan dissolved in the acetic acid aqueous solution is quantitatively dissolved in the dispersion. I understand. When the ion exchange amount by the ion exchange resin was smaller or larger than the acetic acid amount, the solubility of SK-50 having a high degree of deacetylation was increased.

  FIG. 2 shows a DLS analysis result of a chitosan acetic acid aqueous solution typical of chitosan and a chitosan dispersion obtained by ion exchange. (A) In an acetic acid aqueous solution of chitosan SK-10, chitosan shows a dispersion having an average particle size of about 1340 nm. In an aqueous acetic acid solution of chitosan SK-50, the particle size was out of the measurement range, and measurement was impossible. Presumably, the particle size is considered to be 3 μm or more. This result suggests that chitosan is ionized by acetic acid and hydrated, causing charge repulsion and maximizing the molecular spread. On the contrary, (b) the dispersion of chitosan SK-10 emulsified with Neugen ET-143% by weight has a small particle size, and it is considered that the chitosan molecule contracted. (C) The dispersion of chitosan SK-50 is a fine particle dispersion with a narrow degree of dispersion. In any case, it can be seen that chitosan is microemulsified in water by this method.

A chitosan dispersion was prepared in the same manner as in Example 1 except that chitosan SK-10 was used and the amount of the surfactant was changed.
When the ion exchange capacity with respect to acetic acid became equivalent, the chitosan solubility in the chitosan dispersion was maximized. Therefore, the influence of the surfactant concentration on chitosan SK-10 was examined using the conditions.

  The results are shown in FIGS. FIG. 3 shows that the highest solubility is exhibited when the concentration of the surfactant is 1.0% by weight. On the contrary, when the surfactant concentration was higher than 1.0% by weight, the solubility of chitosan decreased.

FIG. 4 shows the relationship between the particle size in the chitosan dispersion and the surfactant concentration. When the surfactant concentration was 0.5% by weight or more, the particle size increased as the surfactant concentration increased. Therefore, it is considered that the aggregation of chitosan is promoted when there is too much surfactant. On the other hand, the surfactant concentration was 0.2% by weight and the particle size was 2005 nm, which was larger than the particle size in the aqueous acetic acid solution. As a result, a specific interaction is acting between the surfactant and chitosan, and the dispersion of chitosan fine particles is promoted between the surfactant concentration of 0.2% by weight and 0.5% by weight. Conceivable.

(Formation of cast film of chitosan)
FIG. 5 is an SEM photograph of a film obtained by casting a chitosan dispersion prepared by deaceticating an aqueous acetic acid solution containing 1.0% by weight of Neugen ET-143 of chitosan SK-10 with different ion exchange resin amounts. . The amount of ion exchange resin is (a) 20.5 g (b) 41.0 g (c) 61.5 g. The surface structure differs depending on the amount of ion exchange. The surfactant is washed away with ethanol, but it can be seen that as the amount of ion exchange increases, that is, acetic acid is removed, the size of the particles settled on the surface decreases. This surface particle structure was formed because chitosan-dispersed particles aggregated and became larger.

  FIG. 6 is an SEM photograph of a similarly produced SK-50 film. The amount of ion exchange resin is (a) 20.5 g (b) 41.0 g (c) 61.5 g (d) 61.5 g. Compared to SK-10, SK-50 shows a smoother surface. This also proceeds due to the association of chitosan-dispersed particles, but it is considered that the SK-50 dispersion has a narrow particle size distribution and thus enables fine association. Incidentally, (c) and (d) are SEM photographs taken for the cloudy part and the transparent part in the same film. (D) is a photograph of the peripheral part of the film, and (c) is a photograph of the central part that was finally dried and formed into a film during film production. The cloudiness seems to be due to the aggregation of the surfactant. The white cloudy part becomes transparent when washed with water.

FIG. 7 shows SEM photographs of films obtained from chitosan SK-10 dispersions having different surfactant concentrations. Although depending on the removal rate of water as a solvent, when the concentration of (b) surfactant (Neugen T-143) is 0.5% by weight, the surface particle structure is relatively small. (A) When the surfactant concentration is 0.2% by weight, the dispersion particle size is large, so that the unevenness is large. (C) When the same concentration is 1.0% by weight, it seems to be due to the association of particles remaining on the solidified surface. A heterogeneous structure is observed.
On the other hand, when a dispersion of chitosan SK-10 prepared from an acetic acid aqueous solution containing 1.5% by weight of Neugen T-143 was cast, no film was formed.

(Dispersion with other surfactants)
When sucrose fatty acid ester was used as a nonionic surfactant, or when a weak anionic surfactant was used, a chitosan dispersion could not be obtained even when the same ion exchange method was applied. However, a chitosan dispersion was obtained when a pyridine type cationic surfactant (Katiogen L) was used. In FIG. 8 a) a dispersion obtained from a nonionic surfactant (Neugen ET-83) having a low HLB value (= 6.4) using SK-50 and b) Neugen ET-143 (HLB = 12. The photograph of the chitosan dispersion liquid obtained from 6) and c) cationic surfactant is shown. In a), separation occurs and is in an unstable state, whereas in b) and c), it is in a transparent and stable state. This suggests that highly hydrophilic nonionic or cationic surfactants are effective for the dispersion of chitosan. Moreover, the chitosan dispersion obtained in this study maintained a stable dispersion state and maintained film-forming properties even after being thawed and thawed.

(Distributed structure)
The aqueous acetic acid solution of chitosan increases in hydrophilicity due to cationization of the side chain amino group of chitosan, and molecules are expanded and dissolved in the solution due to repulsion between intramolecular ions. When a nonionic surfactant is added to this, it interacts with chitosan while retaining ions. When acetic acid is removed with an ion exchange resin from this state, the ionization of chitosan is reduced, and a nonionic surfactant and chitosan are caused to undergo a hydrophobic bond interaction and dispersed in water as small dispersed particles. It is considered that a part of the ammonium side chain generated by ionization of chitosan remains as it is, and chitosan is dispersed as cationic dispersed particles. FIG. 9 shows the dispersion structure of chitosan at each stage. In the future, further detailed structure needs to be studied.

  The emulsion in which chitosan is dispersed in a weakly acidic aqueous solution of the present invention with a surfactant is preferably used in the field of health care and the like where the harm of acid is a problem, among the uses in which a chitosan acid solution is used as described above. The chitosan dispersion according to the present invention and the method for producing a chitosan membrane are also suitable for a wide range of applications, especially for health care and the like because a chitosan membrane with little acid component can be easily obtained by a simple operation. It can be suitably used for the production method of intermediate materials for fields.

It is a figure showing the chitosan content in a chitosan dispersion. It is a figure which shows the particle size distribution of the chitosan-water complex in the chitosan emulsion by DSL. (A) It is a figure which shows the particle size distribution of the chitosan-water complex of the acetic acid aqueous solution of chitosan SK-10. (B) It is a figure which shows the particle size distribution of the chitosan-water complex of the dispersion liquid of chitosan SK-10 emulsified with Neugen ET-143. (C) It is a figure which shows the particle size distribution of the chitosan-water complex of the dispersion liquid of chitosan SK-50 emulsified with Neugen ET-143. It is a figure which shows the relationship between chitosan content and surfactant density | concentration in chitosan SK-10 emulsion. It is a figure which shows the relationship between the particle size of chitosan-water composite_body | complex in chitosan SK-10 emulsion, and surfactant concentration. It is a SEM photograph of the film obtained from chitosan SK-10 emulsion at the time of changing the amount of ion exchange resin. (A) SEM photograph of the film at an ion exchange resin amount of 20.5 g. (B) SEM photograph of the film at an ion exchange resin amount of 41.0 g. (C) SEM photograph of the film at an ion exchange resin amount of 61.5 g. It is a SEM photograph of the film obtained from chitosan SK-50 emulsion at the time of changing the amount of ion exchange resin. (A) SEM photograph of the film at an ion exchange resin amount of 20.5 g. (B) SEM photograph of the film at an ion exchange resin amount of 41.0 g. (C) SEM photograph of the film (white part) at an ion exchange resin amount of 61.5 g. (D) SEM photograph of the film (transparent part) at an ion exchange resin amount of 61.5 g. It is a SEM photograph of the film obtained from chitosan SK-10 emulsion at the time of changing surfactant concentration. (A) A film having a surfactant (Neugen T-143) concentration of 0.5% by weight. (B) A film having a surfactant (Neugen T-143) concentration of 0.2% by weight. (C) A film having a surfactant (Neugen T-143) concentration of 1.0% by weight. It is the photograph of the chitosan emulsion in a test tube at the time of changing the kind of surfactant. a) A dispersion obtained by using SK-50 and a nonionic surfactant (Neugen ET-83, HLB = 6.4). b) Dispersion liquid obtained with a nonionic surfactant (Neugen ET-143, HLB = 12.6) using SK-50. c) A dispersion obtained by using SK-50 and a dispersion obtained by using a cationic surfactant (Katiogen L). It is a schematic diagram of the dispersion structure in the various liquids of a chitosan molecule.

Explanation of symbols

A In acetic acid solution.
B In chitosan particles by surfactant in acetic acid solution medium.
C In chitosan particles after removal of acetic acid from emulsion medium by ion exchange resin.

Claims (6)

  A chitosan dispersion obtained by dispersing chitosan in a weakly acidic aqueous solution with a surfactant.   The chitosan dispersion according to claim 1, wherein the weakly acidic aqueous solution is an acidic aqueous solution having a pH of 4 to 7.   Dissolving chitosan in an acid aqueous solution, then allowing a surfactant to act to form a dispersion in which chitosan is dispersed in the acid aqueous medium with the surfactant, and then removing the acid component from the acid aqueous medium A method for producing a chitosan dispersion obtained by dispersing chitosan in a weakly acidic aqueous solution with a surfactant.   The method for producing a chitosan dispersion comprising chitosan dispersed in a weakly acidic aqueous solution by a surfactant according to claim 3, wherein the means for removing the acid component from the aqueous acid solution medium uses an ion exchange resin. . In the method for producing a chitosan film, a surfactant is allowed to act on an acid solution of chitosan to obtain a dispersion in which chitosan is dispersed in an acid aqueous medium with a surfactant, and then an acid solution from the acid aqueous medium of the chitosan dispersion is used. A method for producing a chitosan film, wherein a chitosan film is formed by forming a chitosan film from a dispersion from which an acid component has been removed. 6. The method for producing a chitosan film according to claim 5, wherein the means for removing the acid component from the aqueous acid medium uses an ion exchange resin.