1. Chitosan Solution Preparation

It seems like your chitosan solution is being prepared with citric acid and ascorbic acid, which are acidic and can lower the pH. The acidification helps dissolve chitosan, but when the solution is added to Carbopol gel, which typically requires neutralization to form a gel, the difference in pH could be causing the separation and the sponge-like texture.

• Tip 1: Pre-neutralize the chitosan solution before adding it to Carbopol.You can try adjusting the pH of the chitosan solution after dissolving it in the acid to around 4.5 to 5.5 using a mild base (like sodium bicarbonate) before adding it to the Carbopol gel. Neutralizing with NaOH directly might be too harsh for the chitosan, causing it to degrade. Instead, use sodium bicarbonate or a buffered solution to gradually increase the pH, keeping the chitosan stable.

2. Addition of Chitosan to Carbopol Gel

Carbopol gels form when the polymer is neutralized, but the method of adding the chitosan solution is crucial to avoid phase separation.

• Tip 2: Add chitosan solution slowly and in small amounts.When incorporating the chitosan solution, do it slowly while continuously stirring the Carbopol gel. This will give the chitosan time to disperse and prevent clumping. It's also helpful to pre-gel the Carbopol by dispersing it in water and then neutralizing it with NaOH before adding the chitosan solution. This will help the gel network form first, making it more stable when adding the chitosan.

3. Viscosity and Gelation Control

Chitosan has its own viscosity, and Carbopol's gel strength is also dependent on the neutralization level. If you’re seeing a sponge-like texture, it might be due to incompatibility in the viscosity or crosslinking behavior.

• Tip 3: Consider adjusting the Carbopol concentration.If you find that the gel is too stiff or unstable after adding chitosan, try reducing the Carbopol concentration slightly, as Carbopol gel at higher concentrations may not be able to accommodate chitosan effectively without separation.
• Tip 4: Try a co-solvent.If the solution continues to separate, you might want to experiment with a co-solvent (e.g., glycerin or propylene glycol) to improve the homogeneity between chitosan and the Carbopol gel. These ingredients can help stabilize the gel matrix and prevent separation.

4. Temperature Considerations

• Tip 5: Use controlled temperatures during mixing.If you’re using heat to dissolve the chitosan or gel the Carbopol, ensure that you’re keeping the temperature low to prevent thermal degradation of chitosan, especially when neutralizing. If your solution is getting too warm, try performing the process at room temperature or with gentle heating.

5. Other Additives

• Tip 6: Incorporate surfactants or stabilizers.Adding a small amount of a mild surfactant (such as Polysorbate 80 or PEG-400) might help improve the dispersion of chitosan in the Carbopol gel without causing separation or degradation.

To Summarize:

• Neutralize the chitosan solution with a gentle buffer (like sodium bicarbonate) to keep it stable.
• Slowly incorporate chitosan into the Carbopol gel with continuous stirring.
• Adjust the Carbopol concentration or use a co-solvent to help stabilize the mixture.
• Control the temperature and avoid excessive heat.
• Consider adding mild surfactants or stabilizers for improved dispersion.