CN114805859B - A kind of preparation method of heat setting chitosan hydrogel - Google Patents

Abstract

The preparation method of the heat-setting chitosan hydrogel comprises the following steps: s1: chitosan with deacetylation degree more than 95% is dissolved in acetic acid solution with volume concentration of 1% or hydrochloric acid solution with molar concentration of 1% to prepare chitosan solution with concentration of (1-3) wt%; s2: adding NaOH solution into chitosan solution under stirring, and stirring uniformly, wherein the concentration of NaOH added per ml of 1.1 wt% chitosan solution is (1.25-25) x 10 ^‑6 mol; s3: adding a metal nitrate solution into the system obtained in the step S2; s4: and (3) heating the system obtained in the step (S3) to more than 80 ℃ and less than 100 ℃ to obtain the heat-set chitosan hydrogel. The invention has few reports on forming gel by heating and reducing temperature to form the thermo-reversible gel of sol, and the application space of the hydrogel is further widened by forming the hydrogel under the heating state.

Description

A kind of preparation method of heat setting chitosan hydrogel

technical field

The invention relates to a preparation method of hydrogel, in particular to a preparation method of heat-setting chitosan hydrogel, and belongs to the field of chemical technology.

Background technique

Hydrogel is a three-dimensional network structure cross-linked product that can absorb and retain a large amount of water. It has good biocompatibility, stimuli responsiveness and easy functionalization. It is widely used in biochemistry, medicine and health, agriculture and environmental protection. The field has a wide range of applications. A thermoreversible gel is a gel that can melt and reform in response to temperature. Most thermoreversible gels are characterized by changing from sol to gel as the temperature decreases, and from gel to sol when heated again, which is thermoreversible. According to the source of gel molecules, hydrogels can be divided into natural hydrogels and synthetic hydrogels. Among them, the materials of artificially synthesized hydrogels can also be divided into natural polymers and artificially synthesized molecules. Synthetic molecules are often obtained through petrochemical refining or organic synthesis and polymerization. The preparation process is cumbersome, expensive, and non-renewable. Therefore, it is of great significance to develop hydrogels based on natural renewable polymers.

Contents of the invention

The object of the present invention is to develop thermosetting hydrogels based on naturally renewable polymers.

For realizing the purpose of the present invention, adopted following technical scheme: a kind of preparation method of heat-setting chitosan hydrogel adopts the following steps:

S1: Dissolve chitosan with a deacetylation degree of more than 95% in acetic acid solution with a volume concentration of 1% or hydrochloric acid solution with a molar concentration of 1%, and prepare chitosan with a concentration of (1-3) wt% solution, the viscosity of chitosan is 100-200 mpa.s;

S2: Add NaOH solution to the chitosan solution while stirring, and stir evenly. The NaOH added dropwise per milliliter and per 1 wt% chitosan solution is equivalent to (1.25-25)×10 ^-6 mol, and the concentration of NaOH solution is 0.4-0.7M;

S3: Add metal nitrate solution to the system obtained in step S2, and stir evenly; the metal nitrate solution includes Ni(NO ₃ ) ₂ , Cu(NO ₃ ) ₂ , Zn(NO ₃ ) ₂ , Cd(NO ₃ ) ₂ , Co(NO ₃ ) ₂ solution, the concentration of metal nitrate solution is 0.4-0.7M, the amount of nitrate added per milliliter of 2.0 wt% chitosan solution is (0.9-1.1)×10 ^-4 mol;

S4: heating the system obtained in step S3 to above 80° C. and below 100° C. to obtain heat-set chitosan hydrogel.

Further; cooling the heat-set chitosan hydrogel obtained in step S4 to normal temperature, the heat-set chitosan hydrogel becomes a sol with good fluidity.

Further; the metal nitrate solution is Ni(NO ₃ ) ₂ solution, the following preparation method is adopted: dissolving chitosan with a deacetylation degree of more than 95% in an acetic acid solution with a volume concentration of 1%, and preparing a concentration of For 2.0 wt% chitosan solution, take 2 mL of the prepared solution, stir and add 30 μL of 0.5 M NaOH solution, stir well, then add 400 μL of 0.5 M Ni(NO ₃ ) ₂ solution, stir well , and then heated to 95°C to obtain heat-set chitosan hydrogel.

Further; the gelation time of the heat-set chitosan hydrogel is less than or equal to 3min.

Further; the heat-set chitosan hydrogel is clear and transparent, and can be cycled more than 100 times.

The positive and beneficial technical effect of the present invention is that chitosan is a kind of basic amino polysaccharide formed by deacetylation reaction of natural chitin, which widely exists in nature. The invention uses natural chitosan as raw material, acetic acid and hydrochloric acid as solvent, adds metal ions, and prepares completely reversible heat-setting hydrogel by raising the solution temperature. The results show that when the temperature rises, the protonated amino groups in chitosan molecules can dissociate hydrogen ions, resulting in a decrease in pH, and the free amino groups can complex with metal ions, thereby cross-linking to form a highly elastic thermally reversible hydrogel glue. The heat setting gel is clear and transparent and can be cycled more than 100 times. Thermoreversible gel is a gel that can be melted and transformed according to temperature. The current thermoreversible gel is characterized by changing from sol to gel as the temperature decreases, and from gel to gel when heated again. Sols are thermally reversible. However, there are few reports on thermally reversible gels that form gels by heating and turn into sols when cooled in the present invention. The formation of hydrogels under heating further expands the application space of hydrogels. .

Description of drawings

Figure 1 is a photograph of different hydrogels.

Figure 2 is a graph showing the effect of temperature on the pH of the gel precursor solution.

Fig. 3 is a graph showing the relationship between rheology and temperature of chitosan-nickel ion solution.

Detailed ways

In order to more fully explain the implementation of the present invention, the implementation examples of the present invention are provided, and these implementation examples are only illustrations of the present invention, and do not limit the scope of the present invention.

Example 1:

Dissolve chitosan with a deacetylation degree of more than 95% in acetic acid solution with a volume concentration of 1% to prepare a chitosan solution with a concentration of 2.0 wt%. Take 2 mL of the prepared solution and slowly add 30 μL of the solution under stirring. 0.5 M NaOH solution, stir well, then add 400 μL of 0.5 M Ni(NO ₃ ) ₂ solution, stir well. Then heated to about 95°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Example 2:

Dissolve chitosan with a deacetylation degree of more than 95% in acetic acid solution with a volume concentration of 1%, and prepare a chitosan solution with a concentration of 2.0 wt%. Take 3 mL of the prepared solution, and slowly add 15 μL of the solution under stirring. 0.5 M NaOH solution, stirred evenly, then added 600 μL of 0.5 M Cu(NO ₃ ) ₂ solution, and stirred evenly. Then heated to about 85°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Example 3:

Dissolve chitosan with a deacetylation degree of more than 95% in acetic acid solution with a volume concentration of 1% to prepare a chitosan solution with a concentration of 2.0 wt%. Take 2 mL of the prepared solution and slowly add 100 μL of the solution under stirring. 0.5 M NaOH solution, stirred evenly, then added 400 μL of 0.5 M Zn(NO ₃ ) ₂ solution, stirred evenly. Then heated to about 95°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Example 4:

Dissolve chitosan with a deacetylation degree of more than 95% in acetic acid solution with a volume concentration of 1% to prepare a chitosan solution with a concentration of 2.0 wt%. Take 3 mL of the prepared solution and slowly add 300 μL of the solution under stirring. 0.5 M NaOH solution, stirred evenly, then added 600 μL of 0.5 M Co(NO ₃ ) ₂ solution, and stirred evenly. Then heated to about 90°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Example 5:

Dissolve chitosan with a deacetylation degree of more than 95% in hydrochloric acid solution with a molar concentration of 1%, and prepare a chitosan solution with a concentration of 1.0 wt%. Take 2 mL of the prepared solution, and slowly add 80 μL of the solution under stirring. 0.5 M NaOH solution, stir well, then add 200 μL of 0.5 M Zn(NO ₃ ) ₂ solution, stir well. Then heated to about 90°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Embodiment 6:

Dissolve chitosan with a deacetylation degree of more than 95% in hydrochloric acid solution with a molar concentration of 1%, and prepare a chitosan solution with a concentration of 3wt%. Take 2mL of the prepared solution and slowly add 200 μL of 0.5 M NaOH solution, stirred evenly, and then 600 μL of 0.5 M Ni(NO ₃ ) ₂ solution was added, and stirred evenly. Then heated to about 95°C to obtain clear transparent high elastic hydrogel. The gel slowly returned to the original solution after cooling at room temperature.

Fig. 1 is the gel photograph that the present invention obtains.

Mechanism analysis of the present invention: Fig. 2 is the figure that is used for the mechanism of the present invention to explore and explain, among the figure CS is chitosan, UP is heating up, and down is cooling down, and what adopt is hydrochloric acid to dissolve chitosan. Figure 2 is only for illustrating the mechanism of the present invention. In Figure 2, when the chitosan (protonated) solution is at 40°C, the amino groups on the chitosan mainly exist in the form of ammonium salts, and the interaction between ammonium salts and nickel ions is very low. The solution is therefore in a fluid state, and the pH at this point is about 3.5. As the temperature gradually rises, the ammonium salt on the protonated chitosan molecule dissociates to generate free amino groups and H ⁺ , H ⁺ makes the pH of the solution drop, and at the same time, the free amino groups can form with nickel ions in the solution Intensely complexed, cross-linked to form a dynamic molecular network. When nickel ions are added and the temperature rises to a certain critical point, there are enough cross-linking points formed by the complexation of nickel ions and amino groups, and the polymer network binds water molecules to form a highly elastic hydrogel. When the temperature is lowered, the above process is completely reversible, and the free H ⁺ recombines with the amino group to form an ammonium salt. The nickel ions are released back into the solution, turning the gel into a solution state.

Fig. 3 is the relationship between rheology and temperature of chitosan-nickel ion solution. At room temperature, the interaction between protonated chitosan and nickel ions is very weak and cannot form crosslinks, so it is in a solution state. At this time, the loss modulus (G") of the sample is greater than the storage modulus (G'). When the temperature rises to a certain critical point (about 68°C), the ammonium salt on the chitosan molecule dissociates and free The amino group of the sample forms a strong cross-linking reaction with nickel ions to form a gel. At this time, the storage modulus (G') of the sample is greater than the loss modulus (G).

Claims (4)

1. a preparation method of heat-set chitosan hydrogel, is characterized in that: adopt following preparation method: the chitosan that deacetylation degree reaches more than 95% is dissolved in the acetic acid solution that volume concentration is 1%, is mixed with concentration For 2.0 wt% chitosan solution, take 2 mL of the prepared solution, stir and add 30 μL of 0.5 M NaOH solution, stir well, then add 400 μL of 0.5 M Ni(NO ₃ ) ₂ solution, stir well , and then heated to 95°C to obtain heat-set chitosan hydrogel. 2. the preparation method of a kind of heat-setting chitosan hydrogel according to claim 1 is characterized in that: heat-setting chitosan hydrogel is cooled to normal temperature, and heat-setting chitosan hydrogel becomes fluidity good of Sol. 3. The preparation method of a kind of heat-setting chitosan hydrogel according to claim 1, characterized in that: the gelation time of the heat-setting chitosan hydrogel is less than or equal to 3min. 4. The preparation method of a kind of heat-setting chitosan hydrogel according to claim 1, characterized in that: the heat-setting chitosan hydrogel is clear and transparent, and the number of cycles can be greater than 100 times.