The relationship between chitosan viscosity and its degree of deacetylation (DD) is complex and influenced by several factors, but the key points of interaction include the following:
1. Degree of Deacetylation (DD)
The DD of chitosan refers to the proportion of deacetylated glucosamine units in the polymer chain. A higher DD means more free amino groups (-NH₂) are present, making the chitosan more cationic and water-soluble under acidic conditions.
2. Viscosity
The viscosity of chitosan solutions depends on its molecular weight, polymer chain conformation, and interactions within the solution. Chitosan with higher molecular weight generally has a higher intrinsic viscosity.
Relationship
- Direct Relationship (Moderate DD Range): At moderate DD levels (typically around 70-85%), an increase in DD can lead to stronger intramolecular and intermolecular hydrogen bonding due to the increase in free amino groups. This can enhance the rigidity of the polymer chains, potentially increasing the viscosity under certain conditions.
- Inverse Relationship (Very High DD): At very high DD levels (e.g., >90%), the polymer becomes more hydrophilic due to an abundance of free amino groups. This can reduce the interaction between chains, leading to a decrease in viscosity.
Impact of Molecular Weight: The molecular weight of chitosan also heavily influences the viscosity. For a given DD, chitosan with a higher molecular weight will exhibit higher viscosity.
3. Other Influencing Factors
Several factors modulate this relationship:
- Solvent pH: Chitosan is only soluble in acidic solutions where it forms a cationic polymer. The pH of the solvent impacts the protonation of amino groups, affecting the chain conformation and thus the viscosity.
- Concentration: Higher polymer concentrations generally increase viscosity.
- Temperature: Higher temperatures reduce solution viscosity by lowering hydrogen bonding.
Summary
The relationship between chitosan viscosity and its DD is not linear but depends on a combination of DD, molecular weight, and environmental factors. Generally:
Moderate DD increases viscosity up to a certain point.
Very high DD can lead to a decrease in viscosity due to increased hydrophilicity and reduced chain interactions.
Orison Chemicals Limited offer different DD and Viscosity of Chitosan
We can produce chitosan with different deacetylation degrees and viscosities according to different needs of customers: high DD, high viscosity chitosan; medium DD, medium viscosity; high DD, low viscosity.
