JP4125047B2 - Hydrophilic cross-linked chitosan foam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrophilic crosslinked chitosan foam. The present invention also relates to a cross-linked chitosan foam having particularly uniform and fine bubbles and excellent touch feeling.
The hydrophilic cross-linked chitosan foam of the present invention is applicable as a sponge-like sheet-like elastic body for cosmetic purposes, and is suitably used for cosmetic pack base materials, facial and body cleaning tools, cosmetic puffs and the like. The
[0002]
[Prior art]
A method for obtaining a water-insoluble chitosan crosslinked product by dissolving chitosan in an acid aqueous solution to crosslink with an appropriate crosslinking agent using the amino group of chitosan as a functional group and then removing water is already known.
As a method for dissolving chitosan in an aqueous solvent, acetic acid is generally used. However, a crosslinked chitosan obtained by cross-linking chitosan dissolved in acetic acid and then drying it has an acetic acid odor, and is therefore commercially available. It will be inferior.
There are diisocyanates and dialdehydes as cross-linking agents having the amino group of chitosan as a functional group. However, diisocyanates are generally highly reactive and react with the solvent water in aqueous solutions. However, if the reaction proceeds and the mixture is not rapidly mixed, there will be variations in the cross-linked product, which is difficult to operate. In the case of dialdehyde, generally, there are many strong odors, and there is a problem that odor remains in the chitosan crosslinked product obtained by crosslinking chitosan and then drying, resulting in poor merchantability.
In addition, natural polymer compounds such as starch and gelatin are dissolved in water and gelled by addition of a crosslinking agent, pH change, temperature change, etc., and the resulting hydrogel product is freeze-dried to effect freezing. A method of obtaining a foamed body having ice crystal portions as bubbles is known.
In a general freeze-drying method, vacuum drying is performed after freezing in a freezer at −30 to −40 ° C. At this freezing temperature, there is a large time difference between the moisture near the surface of the hydrogel and the moisture near the center, and the ice crystals formed near the surface grow and freeze with little moisture near the center. Complete.
When the above frozen product is vacuum-dried to sublimate ice crystals, non-uniform and large bubbles are formed, resulting in a foam having an undesirable appearance.
[0003]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to improve the above-mentioned drawbacks of the conventional chitosan gelled foam, that is, the odor caused by the inorganic or organic acid added for the dissolution of chitosan and the crosslinking agent for the gelation. It is to provide a hydrophilic cross-linked chitosan foam that is highly safe to living organisms, has uniform air bubbles, has a preferable appearance, and is excellent in touch.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have found that the above problem can be solved by rapidly freezing at a temperature of −50 ° C. or lower and vacuum drying.
That is, the present invention is as follows.
(1) A hydrous solution in which chitosan is dispersed in water and diluted hydrochloric acid or organic acid without odor is added and dissolved in a pH range of 5.0 to 6.0, and the solution is crosslinked with an aliphatic diepoxy compound. A hydrophilic cross-linked chitosan foam characterized in that a gelled product is formed by freeze-drying.
The preferred embodiments of the present invention will be further described below.
(2) The hydrophilic crosslinked chitosan foam according to (1), wherein the aliphatic diepoxy compound is polyethylene glycol diglycidyl ether.
(3) The hydrophilic crosslinked chitosan foam as described in (2) above, wherein the polyethylene glycol diglycidyl ether is ethylene glycol diglycidyl ether.
(4) The hydrophilic gel described in (1) to (3), which is formed by rapidly freezing the hydrated gelled product under a condition of −50 ° C. or less and then vacuum drying. Cross-linked chitosan foam.
[0005]
First, the hydrophilic cross-linked chitosan foam of the present invention uses dilute hydrochloric acid or an organic acid having no odor as an acid for dissolving the chitosan so that the pH is 5.0 to 6.0 equivalent to the skin. Adjust to prepare an aqueous chitosan solution. The chitosan solution is crosslinked with an aliphatic diepoxy compound, which is a highly safe crosslinking agent for a living body, to form a hydrogel product. The hydrogel product is formed by lyophilization. Preferably, a uniform and dense ice crystal is formed by rapidly freezing at a temperature of −50 ° C. or lower, followed by vacuum drying, and the ice crystal is sublimated to form bubbles, thereby forming a uniform and dense ice crystal. A foam having a cellular structure is obtained.
When hydrochloric acid is used for dissolving chitosan, the odor of hydrochloric acid disappears upon drying after crosslinking, so that an odorless foam can be obtained.
Compared with foams obtained by the usual freeze-drying method, there is no odor, it is safe for the living body, and it has excellent appearance and feel, and is a sponge-like elastic sheet that is gentle on the skin. As a result, it is possible to obtain a hydrophilic cross-linked chitosan foam having a high level of commercial properties and having uniform bubbles.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the hydrophilic crosslinked chitosan foam of the present invention will be described in detail.
The hydrophilic cross-linked chitosan foam of the present invention is characterized by no odor remaining and high safety for a living body.
In the production of the hydrophilic crosslinked chitosan foam of the present invention, dilute hydrochloric acid or odor is used as an acid (inorganic acid or organic acid) added to swell and dissolve chitosan in water so that no odor remains after vacuum drying. As the organic acid that does not remain, citric acid, gluconic acid, succinic acid, lactic acid, fumaric acid, malic acid and the like are used.
[0007]
The pH of the chitosan suspension is adjusted to pH 5.0 to 6.0, preferably pH 5.0 to 5.5 using the above acid aqueous solution in a suspension in which chitosan is dispersed in water.
When the pH of the chitosan suspension is less than 5.0, the obtained foam is strongly irritating to the skin, and when it exceeds 6.0, the chitosan is not sufficiently dissolved and the crosslinking reaction cannot be performed. is there. The above pH range is suitable for the reaction between the amino group of chitosan and the crosslinking agent, and is the same range as the skin. When hydrochloric acid is used, the hydrochloric acid odor disappears upon drying after crosslinking.
[0008]
The concentration of chitosan in the chitosan solution is not particularly limited, but a preferable concentration is in the range of 1 to 10% by weight.
If it is less than 1% by weight, the strength of the obtained foam is weak and unsuitable for practical use. If it exceeds 10% by weight, the viscosity when dissolved in an acid aqueous solution is high, and the crosslinking reaction cannot be made uniform. Unsuitable.
[0009]
In the production of the hydrophilic cross-linked chitosan foam of the present invention, the cross-linking method for obtaining a water-containing gelled product from the chitosan solution dissolved in water described above improves the safety to the living body simultaneously with the odor. In contrast, an aliphatic diepoxy compound is added as a highly safe crosslinking agent, and the mixture is reacted under the conditions of pH, temperature, and time according to the crosslinking agent to perform a gelation treatment.
Examples of the aliphatic diepoxy compound include polyethylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, hexanediol diglycidyl ether, and the like. Most preferred is ethylene glycol diglycidyl ether.
Although the addition amount of a crosslinking agent does not have limitation in particular, Generally, it is preferable that the glycidyl group of a diepoxy compound is 1-20 mol% with respect to the amino group of chitosan.
[0010]
Next, as described above, the hydrophilic cross-linked chitosan foam of the present invention contains at least a cross-linking agent in a chitosan solution dissolved in water, and gels the solution by adjusting the pH and temperature conditions. By performing freeze-drying on the water-containing gelled product, it is possible to obtain a foam in which the ice crystal portion at the time of freezing is a bubble.
The hydrophilic cross-linked chitosan foam having uniform and fine bubbles, which is a preferred embodiment of the hydrophilic cross-linked chitosan foam of the present invention, is rapidly frozen under the condition of −50 ° C. or lower in the above lyophilization, and then subjected to vacuum. It is characterized by drying.
Examples of the method of rapidly freezing at −50 ° C. or less include, for example, direct contact with dry ice, immersion in dry ice / methanol or liquid nitrogen, collision of cold air at −50 ° C. or less, or dynamic magnetic field Among them, there may be mentioned a method of freezing all at once in a supercooled state under a temperature of −50 ° C. or less while giving weak vibration and suppressing ice crystallization.
In order to obtain a hydrophilic cross-linked chitosan foam having a sheet-like uniform cell with excellent merchantability, the sheet-like water-containing gelled product is rapidly frozen under a condition of −50 ° C. or lower, or blocked. A foam obtained by a normal freeze-drying method is obtained by rapidly freezing the hydrated gel-like product at -50 ° C. or less and then vacuum-drying the sheet sliced to a desired thickness. Compared to the above, a sponge-like sheet-like elastic body excellent in appearance and feel and gentle to the skin can be obtained, and a hydrophilic cross-linked chitosan foam having uniform air bubbles can be obtained which has a high commercial value for cosmetics.
[0011]
Further, at the same time as freezing at a time in the supercooled state, the freezing time is preferably within 1 hour, more preferably within 30 minutes.
When it is longer than 1 hour, ice crystals grow, and after vacuum drying, coarse bubbles are formed, which is inappropriate.
The degree of vacuum at the time of vacuum drying needs to be a vacuum of 60 Pa or less so that ice crystals do not melt.
[0012]
In the production of the hydrophilic crosslinked chitosan foam of the present invention, the chitosan solution may further contain additives such as a plasticizer and a sheet strength improver as necessary.
For example, a fibrous water-insoluble additive may be mixed in order to increase the strength of the foam, and a plasticizer such as glycerin may be mixed in order to give flexibility to the foam during drying.
[0013]
Examples of the plasticizer include glycerin, PEG, PPG, PEG, or a fatty acid ester of PPG. It is added to plasticize the hydrophilic crosslinked chitosan foam during drying.
Although there is no limitation in particular as an addition amount, Generally it is preferable that it is 10 to 50 weight% with respect to the chitosan weight.
[0014]
Examples of the sheet strength improver include cellulose and silk fiber. It is added to improve the sheet strength when drying the hydrophilic crosslinked chitosan foam.
Although there is no limitation in particular as an addition amount, Generally it is preferable that it is 10 to 50 weight% with respect to the chitosan weight.
[0015]
【Example】
The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited to these examples.
[Example 1]
(Preparation of sheet-like chitosan foam)
1 kg of distilled water 1 kg of crab-derived chitosan with an average particle size of 100 μm and a deacetylation rate of 85% and cellulose powder (KC Flock W-100 manufactured by Nippon Paper Industries Co., Ltd.) for improving sheet strength during drying After being well dispersed, 1N hydrochloric acid was gradually added to adjust the pH to 5.3, 7.5 g of glycerin was added as a plasticizer at the time of drying, and the mixture was stirred well and mixed. After leaving the above mixture in a 60 ° C. water bath for 1 hour, ethylene glycol diglycidyl ether (epoxy equivalent = 113) was added to the calculated value so that the degree of crosslinking was 5%, and the mixture was rapidly stirred and mixed well. Thereafter, deaeration was performed for 100 G × 10 minutes using a centrifuge. The degassed mixture was poured into a polyethylene tray measuring 80 mm × 120 mm × 20 mm deep (0.1 mm thickness) carefully so as not to entrain air bubbles to a thickness of 2 mm. The tray into which the mixture was poured was allowed to stand on a 60 ° C. water bath for 3 hours, and then allowed to cool at room temperature to obtain a water-containing gelled product of epoxy-crosslinked chitosan.
[0016]
The obtained hydrogel tray was placed on a copper plate laid on dry ice, a copper plate was laid on the upper surface of the tray, and the ice was rapidly frozen in a state where dry ice was placed thereon. The frozen hydrogel was vacuum dried at room temperature for 40 hours using a vacuum dryer to obtain a chitosan foam. The obtained chitosan foam was excellent in water retention with an odorless surface and a smooth feel, having a thickness of approximately 1.8 mm, an apparent density of 0.06 g / cm ³ and a water absorption of 19 times its own weight. It was a foam.
[0017]
[Example 2]
Instead of the ethylene glycol diglycidyl ether (epoxy equivalent = 113) used in Example 1, the degree of cross-linking is 5% using a polyethylene glycol diglycidyl ether (epoxy equivalent = 268) having 9 molecules of ethylene glycol as a calculated value. The same operation as in Example 1 was carried out except that.
The obtained chitosan foam was excellent in water retention with an odorless and smooth surface condition, having a thickness of approximately 1.5 mm, an apparent density of 0.08 g / cm ³ and a water absorption of 15 times its own weight. It was a foam.
[0018]
[Comparative Example 1}
The same operation as in Example 1 was performed except that reagent-grade acetic acid was used instead of 1N hydrochloric acid used in Example 1. The obtained chitosan foam had a strong acetic acid odor and was inferior in commercial properties.
[0019]
[Comparative Example 2]
The same operation as in Example 1 was performed except that a reagent-grade 25% glutaraldehyde solution was used instead of the ethylene glycol diglycidyl ether used in Example 1. The obtained chitosan foam had a strong aldehyde odor and poor merchantability.
[0020]
As is clear from the above results, the hydrophilic crosslinked chitosan foam of Example 1 according to the present invention obtained satisfactory results, but the chitosan foam of each comparative example was unsatisfactory in some properties. Met.
[0021]
【The invention's effect】
As described above, the hydrophilic cross-linked chitosan foam of the present invention first uses dilute hydrochloric acid or an organic acid having no odor as an acid for dissolving chitosan so as not to leave an odor, and has a pH of 5. Adjust to 0-6.0 to prepare an aqueous chitosan solution. The chitosan solution is crosslinked with an aliphatic diepoxy compound to form a hydrogel product. The hydrogel product is formed by lyophilization. Preferably, a foam having a uniform and dense cell structure is obtained by rapidly freezing at a temperature of −50 ° C. or less to form uniform and dense ice crystals and then vacuum drying.
Compared with foams obtained by the usual freeze-drying method, there is no odor, it is safe for the living body, and it is excellent in appearance and feel, and is a sponge-like elastic sheet that is gentle on the skin. As a product, it is possible to obtain a hydrophilic cross-linked chitosan foam having uniform air bubbles with high commercial properties.

Claims (4)

Diluted hydrochloric acid or citric acid, gluconic acid, succinic acid, lactic acid, fumaric acid or malic acid is added to a suspension of chitosan dispersed in water and dissolved in a pH range of 5.0 to 6.0. A hydrophilic cross-linked chitosan foam characterized in that it is formed by freeze-drying a hydrogel product that has been cross-linked with a system diepoxy compound.   The hydrophilic crosslinked chitosan foam according to claim 1, wherein the aliphatic diepoxy compound is polyethylene glycol diglycidyl ether.   The hydrophilic crosslinked chitosan foam according to claim 1, wherein the aliphatic diepoxy compound is ethylene glycol diglycidyl ether.   The hydrophilic property according to any one of claims 1 to 3, wherein the water-containing gelled product is formed by rapid freezing under conditions of -50 ° C or lower and then vacuum drying. Cross-linked chitosan foam.