阅读说明：本技术 一种壳聚糖在弱碱性水溶液中的溶解方法 (Method for dissolving chitosan in alkalescent aqueous solution ) 是由 蔡杰 钟奕 张俐娜 于 2019-02-01 设计创作，主要内容包括：本发明公开了一种壳聚糖在弱碱性水溶液中的溶解方法。将壳聚糖加入到碳酸氢盐的水溶液中,直接搅拌溶解壳聚糖；或者将壳聚糖先用稀酸溶解后再用碱中和后,无需分离,继续加入碳酸氢盐,搅拌溶解壳聚糖；将壳聚糖加入到碱液或碳酸盐的水溶液中,通入二氧化碳,生成碳酸氢盐来溶解壳聚糖；将甲壳素和碱液混合后,加热进行脱乙酰化反应生成壳聚糖,将混合物的碱液调整到一定浓度后,通入二氧化碳,生成碳酸氢盐来溶解壳聚糖。加入尿素、硫脲等稳定剂有助于提高弱碱性水溶液的溶解能力。利用本发明公开的溶剂组合和溶解方法可以高效、节能的得到弱碱性的壳聚糖溶液。有利于拓展壳聚糖的应用范围。(The invention discloses a method for dissolving chitosan in a weakly alkaline aqueous solution. Adding chitosan into a bicarbonate water solution, and directly stirring to dissolve the chitosan; or dissolving chitosan with dilute acid, neutralizing with alkali, adding bicarbonate, and stirring to dissolve chitosan; adding chitosan into an aqueous solution of alkali liquor or carbonate, and introducing carbon dioxide to generate bicarbonate to dissolve the chitosan; mixing chitin and alkali liquor, heating for deacetylation reaction to generate chitosan, adjusting the alkali liquor of the mixture to a certain concentration, and introducing carbon dioxide to generate bicarbonate to dissolve the chitosan. The addition of stabilizers such as urea and thiourea is helpful for improving the dissolving capacity of the weakly alkaline aqueous solution. The solvent combination and the dissolving method disclosed by the invention can be used for efficiently and energy-saving obtaining of the weakly alkaline chitosan solution. Is favorable for expanding the application range of the chitosan.)

1. A method for dissolving chitosan in a weak alkaline aqueous solution is characterized by comprising the following steps:

(1) preparing a weakly alkaline aqueous solution, wherein the weakly alkaline aqueous solution consists of bicarbonate, a stabilizer and water; wherein the final concentration of bicarbonate is 0.2-1.5 mol/kg^-1The final concentration of the stabilizer is 0.3-5.0 mol/kg^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the two, and the balance water;

(2) and (2) adding chitosan into the alkalescent aqueous solution obtained in the step (1), continuously stirring for more than 30 minutes under the condition that the freezing point is 35 ℃, dissolving the chitosan, and defoaming to obtain a transparent chitosan solution.

2. The dissolution method according to claim 1, wherein the final concentration of bicarbonate in the weakly alkaline aqueous solution prepared in the step (1) is in the range of 0.3 to 1.2 mol-kg^-1The final concentration of the stabilizer is 1.0 to 4.0 mol/kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea and the balance water.

3. A method for dissolving chitosan in a weak alkaline aqueous solution is characterized by comprising the following steps:

(1) dissolving chitosan in a stabilizer at a concentration of 0.1-1.0 mol/kg^-1Adding a proper amount of alkali to the inorganic or organic acid aqueous solution to adjust the pH of the solution to be neutral, and separating out chitosan; the stabilizer is 0.3-5.0 mol/kg of final concentration^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the two; the alkali for adjusting the pH of the solution is any one of alkali hydroxide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal bicarbonate, alkaline earth metal bicarbonate, ammonia water, ammonium carbonate and ammonium bicarbonate or a mixture of the alkali hydroxide, the alkali metal carbonate, the alkaline earth metal bicarbonate and the ammonia water; the inorganic or organic acid is preferably acetic acid, hydrochloric acid, citric acid, etc.;

(2) adding bicarbonate into the mixture of chitosan and water in the step (1), continuously stirring for more than 10 minutes under the condition of the freezing point to 35 ℃, dissolving the chitosan, and defoaming to obtain a transparent chitosan solution; the final concentration of the bicarbonate is 0.2-1.5 mol/kg^-1。

4. The dissolution method according to claim 3, wherein the stabilizer is added in the step (1) to a final concentration of preferably 1.0 to 4.0 mol-kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea; the final concentration of the bicarbonate in the step (2) is 0.3-1.2 mol/kg^-1。

5. A method for dissolving chitosan in a weak alkaline aqueous solution is characterized by comprising the following steps:

(1) preparing an alkaline aqueous solution, wherein the alkaline aqueous solution consists of alkaline hydroxide or carbonate, a stabilizing agent and water; wherein the final concentration of the alkali hydroxide is 0.2 to 1.5 mol/kg^-1The final concentration of carbonate is 0.10 to 0.75 mol/kg^-1The final concentration of the stabilizer is 0.3-5.0 mol/kg^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the thiourea and the water;

(2) adding chitosan into the alkaline aqueous solution obtained in the step (1), introducing carbon dioxide, continuously stirring for more than 30 minutes under the condition that the freezing point is 35 ℃, dissolving the chitosan when the pH value of the solution is about 7-10, and defoaming to obtain a transparent chitosan solution;

the alkaline hydroxide is metal hydroxide, ammonium hydroxide, quaternary ammonium base, preferably sodium hydroxide, potassium hydroxide, ammonium hydroxide or a mixture thereof; the carbonate is preferably sodium carbonate, potassium carbonate, ammonium carbonate, or a mixture thereof.

6. The dissolution method according to claim 5, wherein the final concentration of the alkali hydroxide in the aqueous alkali solution prepared in the step (1) is 0.3 to 1.2mol kg^-1The final concentration of carbonate is 0.15-0.6 mol/kg^-1The final concentration range of the stabilizer is that the mass molarity is 1.0-4.0 mol/kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea and the balance water.

7. A method for dissolving chitosan in a weak alkaline aqueous solution is characterized by comprising the following steps:

(1) chitin and the mass molar concentration of 8.0-12.5 mol/kg^-1Mixing sodium hydroxide aqueous solution or potassium hydroxide aqueous solution, heating to perform deacetylation reaction to generate chitosan;

(2) adjusting the final concentration of sodium hydroxide or potassium hydroxide in the mixture obtained in (1) to 0.2-1.5 mol ·kg^-1Reducing the temperature of the mixture to between the freezing point and 35 ℃, adding a stabilizer, introducing carbon dioxide at room temperature, converting sodium hydroxide or potassium hydroxide into bicarbonate when the pH value of the solution is about 7-10, stirring for more than 30 minutes to dissolve chitosan, and defoaming to obtain a transparent chitosan solution; the stabilizer is 0.3-5.0 mol/kg of final concentration^-1Urea or 0.3-1.2 mol/kg^-1One or a mixture of two of thiourea; preferably, the final concentration of the stabilizer is 1.0-4.0 mol/kg^-1Urea or 0.4-1.0 mol/kg^-1One or a mixture of two of thiourea; preferably, the final concentration of the bicarbonate is 0.3-1.2 mol-kg^-1。

8. The dissolution process according to claim 7, characterized in that: the method for adjusting the concentration of sodium hydroxide or potassium hydroxide in the mixture in the step (2) comprises the following steps: filtering and squeezing the mixture obtained in the step (1) to remove excessive sodium hydroxide or potassium hydroxide aqueous solution, and adding a proper amount of water to ensure that the final concentration of the sodium hydroxide or the potassium hydroxide in the mixture is 0.2-1.5 mol/kg^-1。

9. The dissolution method according to any one of claims 1 to 8, wherein the bicarbonate comprises an alkali metal bicarbonate, an alkaline earth metal bicarbonate, or ammonium bicarbonate, preferably one or more of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, or magnesium bicarbonate.

10. A weakly alkaline aqueous chitosan solution prepared by the method of dissolving chitosan according to any one of claims 1 to 9 in a weakly alkaline aqueous solution.

11. A chitosan molded product and a derivative thereof prepared by using the chitosan solution obtained by the dissolution method according to any one of claims 1 to 9.

Technical Field

The invention belongs to the field of natural polymers, and particularly relates to a method for dissolving chitosan.

Background

The chitosan is a deacetylated product of chitin, and when the deacetylation degree of the chitin is more than 55%, the chitin is converted into chitosan which can be dissolved in an acidic aqueous solution. The chitosan has good biocompatibility and biodegradability, can promote wound healing, and has hemostatic effect. The chitosan solution obtained by dissolving the chitosan can be used for preparing new materials such as chitosan fiber, chitosan film, chitosan hydrogel, chitosan aerogel, chitosan microspheres and the like, and has good application prospect in the fields of separation and adsorption, biomedical materials, flexible electronic devices, heat insulation materials and the like.

Chitosan has a large number of hydrogen bonds both intra-and intermolecular, and is therefore difficult to dissolve in water and common organic solvents. The traditional method is to use low-concentration acetic acid or hydrochloric acid aqueous solution to dissolve chitosan, but chitosan is easy to degrade molecular chains of chitosan in acidic aqueous solution. Recently, some alkaline aqueous solvents have been developed to dissolve chitosan. The current alkaline aqueous solvents used to dissolve chitosan include lithium hydroxide-sodium hydroxide-urea combination (patent 201110099176.3), lithium hydroxide-potassium hydroxide-urea combination (patent 201310405191.5), sodium hydroxide-urea combination (Zhang W, Xia W.Disolution and stability of lithium in a soluble hydroxide/urea solution [ J ]. Journal of Applied Polymer Science,2014,131(3): 1082. multidot. 1090.) and lithium hydroxide-urea combination (Li C, Han Q, Guan Y, et al. Michael reaction of chitosan with acrylic acid in an aqueous alkali solution [ J ]. Polymer Bulletin,2015,72(8): 2087. multidot. 5.). The specific dissolving method is that firstly the chitosan is added into the alkaline hydrosolvents for soaking, then the mixture is frozen and frozen, finally the mixture is unfrozen and stirred at room temperature, and the chitosan is completely dissolved after one or more times of freezing-unfreezing. The freezing-thawing process consumes a large amount of energy, which is very disadvantageous for industrial applications, and thus, the efficiency of preparing the chitosan alkaline aqueous solution is to be improved.

At present, no report on the dissolution of chitosan in a weakly alkaline aqueous solvent exists. Compared with strong alkaline aqueous solvent and acidic aqueous solvent, the chitosan is more stable in weak alkaline aqueous solution, and the degradation of chitosan molecular chains is not easy to occur. In addition, the weakly alkaline water solvent has no corrosivity to equipment, is safer and more environment-friendly, and is very valuable for industrial application.

Disclosure of Invention

The invention aims to solve the defects in the prior art and provide a novel solvent combination and a dissolving method for obtaining the chitosan solution with high efficiency and energy saving.

The technical scheme provided by the invention is as follows:

in a first aspect, a method for dissolving chitosan in a weakly alkaline aqueous solution is provided, which comprises the following steps:

(1) preparing a weakly alkaline aqueous solution, wherein the weakly alkaline aqueous solution consists of bicarbonate, a stabilizer and water; wherein the final concentration of bicarbonate is: 0.2 to 1.5 mol/kg^-1The final concentration of the stabilizer is 0.3-5.0 mol/kg^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the two, and the balance water;

(2) and (2) adding chitosan into the alkalescent aqueous solution obtained in the step (1), continuously stirring for more than 30 minutes under the condition that the freezing point is 35 ℃, dissolving the chitosan, and defoaming to obtain a transparent chitosan solution.

Preferably, the final concentration of bicarbonate is 0.3 to 1.2mol kg^-1The final concentration of the stabilizer is 1.0 to 4.0 mol/kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea and the balance water.

In a second aspect, there is provided a method for dissolving chitosan in a weakly alkaline aqueous solution, comprising the steps of:

(1) dissolving chitosan in a stabilizer at a concentration of 0.1-1.0 mol/kg^-1Adding a proper amount of alkali to the inorganic or organic acid aqueous solution to adjust the pH of the solution to be neutral, and separating out chitosan; the stabilizer is 0.3-5.0 mol/kg of final concentration^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the two; the alkali for adjusting the pH of the solution is any one of alkali hydroxide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal bicarbonate, alkaline earth metal bicarbonate, ammonia water, ammonium carbonate and ammonium bicarbonate or a mixture of the alkali hydroxide, the alkali metal carbonate, the alkaline earth metal bicarbonate and the ammonia water; the inorganic or organic acid is preferably acetic acid, hydrochloric acid, or lemonAcids, and the like;

(2) adding bicarbonate into the mixture of chitosan and water in the step (1), continuously stirring for more than 10 minutes under the condition of the freezing point to 35 ℃, dissolving chitosan, and defoaming to obtain a transparent chitosan solution; the final concentration of the bicarbonate is 0.2-1.5 mol/kg^-1。

Preferably, the final concentration of the stabilizer added in the step (1) is 1.0-4.0 mol kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea; the final concentration of the bicarbonate in the step (2) is 0.3-1.2 mol/kg^-1。

In a third aspect, a method for dissolving chitosan in a weakly alkaline aqueous solution is provided, which comprises the following steps:

(1) preparing an alkaline aqueous solution, wherein the alkaline aqueous solution consists of alkaline hydroxide or carbonate, a stabilizer and water; wherein the final concentration of the alkaline hydroxide is: 0.2 to 1.5 mol/kg^-1The final concentration of carbonate is 0.1 to 0.75 mol/kg^-1The final concentration of the stabilizer is 0.3-5.0 mol/kg^-1Urea or 0.3-1.2 mol/kg^-1Thiourea or a mixture of the thiourea and the water;

(2) adding chitosan into the alkaline aqueous solution obtained in the step (1), introducing carbon dioxide, continuously stirring for more than 30 minutes under the condition that the freezing point is 35 ℃, converting alkaline hydroxide or carbonate into bicarbonate when the pH value of the solution is about 7-10, dissolving the chitosan, and defoaming to obtain a transparent chitosan solution;

the alkaline hydroxide is metal hydroxide, ammonium hydroxide and quaternary ammonium base, preferably sodium hydroxide, potassium hydroxide, ammonium hydroxide or a mixture thereof; the carbonate is preferably sodium carbonate, potassium carbonate, ammonium carbonate, or a mixture thereof.

Preferably, the final concentration of the alkaline hydroxide in the alkaline aqueous solution prepared in the step (1) is 0.3-1.2 mol/kg^-1The final concentration of carbonate is 0.15-0.6 mol/kg^-1The final concentration of the stabilizer is 1.0-4.0 mol/kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea and the balance water.

In a fourth aspect, a method for dissolving chitosan in a weakly alkaline aqueous solution is provided, which comprises the following steps:

(1) chitin and the mass molar concentration of 8.0-12.5 mol/kg^-1Mixing the sodium hydroxide aqueous solution or the potassium hydroxide aqueous solution, and heating to perform deacetylation reaction to generate chitosan;

(2) adjusting the concentration of sodium hydroxide or potassium hydroxide in the mixture obtained in (1) to 0.2-1.5 mol/kg^-1Reducing the temperature of the mixture to between the freezing point and 35 ℃, adding a stabilizer, introducing carbon dioxide at room temperature, converting sodium hydroxide or potassium hydroxide into bicarbonate when the pH value of the solution is about 7-10, stirring for more than 30 minutes to dissolve chitosan, and defoaming to obtain a transparent chitosan solution; the stabilizer is 0.3-5.0 mol/kg of final concentration^-1Urea or 0.3-1.2 mol/kg^-1One or a mixture of two of thiourea.

Preferably, the method for adjusting the concentration of sodium hydroxide or potassium hydroxide in the mixture in step (2) comprises: filtering and squeezing the mixture obtained in the step (1) to remove excessive sodium hydroxide or potassium hydroxide aqueous solution, and adding a proper amount of water to ensure that the final concentration of the sodium hydroxide or the potassium hydroxide in the mixture is 0.2-1.5 mol/kg^-1。

Preferably, the final concentration of the stabilizer added in the step (2) is 1.0-4.0 mol kg^-1Urea or 0.4-1.0 mol/kg^-1Thiourea; the final concentration of the bicarbonate in the step (2) is 0.3-1.2 mol/kg^-1。

In the method for dissolving chitosan in weakly alkaline aqueous solution of the present invention, the bicarbonate comprises alkali metal bicarbonate, alkaline earth metal bicarbonate, and ammonium bicarbonate, and preferably one or more of sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, and magnesium bicarbonate.

In a fifth aspect, there is provided a weakly alkaline aqueous solution of chitosan prepared by the above method for dissolving chitosan in a weakly alkaline aqueous solution.

In a sixth aspect, there are provided a chitosan molded article and a derivative thereof prepared from the above weak alkaline aqueous solution of chitosan.

The chitosan formed product and the derivative thereof prepared from the chitosan weakly alkaline aqueous solution are obtained by processing and modifying the chitosan weakly alkaline solution obtained by the method for dissolving chitosan in the weakly alkaline aqueous solution according to the preparation method of films, plates, tubes, cubes, granules and fibrous materials.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention provides a method for preparing weakly alkaline chitosan aqueous solution in an environment-friendly and energy-saving way. The chitosan solution can be used for preparing any form of chitosan molded product: such as films, plates, tubes, cubes, granules and fibers, and can be processed into various chitosan derivatives. The invention has the advantages that the adopted solvent is a weakly alkaline aqueous solvent, the chitosan molecular chain is not easy to degrade, and the corrosion is avoided. Meanwhile, the dissolving method is green and environment-friendly, does not need freezing and unfreezing in the dissolving process, is suitable for industrial production and practical application, and has wide application prospect.

Detailed Description

Further features and advantages of the present invention will be understood from the following detailed description. The examples provided are merely illustrative of the method of the present invention and do not limit the remainder of the disclosure in any way.

The chitosan used in the following examples is extracted from natural shrimp shell, crab shell, squid parietal bone, diatom, insects and other organisms containing alpha-chitin and beta-chitin, and the specific extraction steps are soaking with alkaline solution to remove protein, soaking with acid solution to remove inorganic salt, decolorizing with oxidant, washing with water and drying to obtain purified chitin. The chitosan is prepared by deacetylation reaction of chitin in sodium hydroxide or potassium hydroxide aqueous solution, or is a pure chitosan product purchased from a reagent company.