3.2. Water solubility
After substitution, CMCH is expected to have better solubility characteristics.
As shown in Table 3, CMCH is soluble in a wide range of pH in acidic and alkaline media while CH is completely soluble only below pH 6.
It can be seen that CMCH is completely soluble at neutral as well as alkaline pH.
The limited solubility of CH (pKa = 6.8) is overcome by introduction of carboxy groups to the backbone of chitosan.
Since all chemical processing of cotton is carried out at neutral or alkaline pH, this is desirable.
The insolubility of CMCH around pH 4–5 could be due to the temperature and solvent mix used in its preparation (Chen & Park, 2003).