EFFECT OF SURFACTANT CONCENTRATION, PH, AND SHEAR RATE ON THE RHEOLOGICAL PROPERTIES OF AQUEOUS SYSTEMS OF A HYDROPHOBICALLY-MODIFIED CHITOSAN AND ITS UNMODIFIED ANALOG

Oscillatory shear, shear relaxation and viscosity experiments have bee n carried out on semidilute solutions of chitosan and on a hydrophobic ally modified analogue (HM-chitosan) in 1 % acetic acid. This was done in the presence of various amounts of cetyltrimethylammonium bromide (CTAB) and at different pH values. All the rheological measurements on the HM-chitosan solutions revealed significant polymer-surfactant int eraction and pH effects. The observed rheological effects were least p ronounced at pH approximate to 4, while a strong viscoelastic response was found at pH values of 1 and 5 in HM-chitosan solutions of low sur factant concentration At these conditions, significant shear-thinning effects were observed. In semidilute solutions of unmodified chitosan, the influence of pH, surfactant concentration and shear rate on the r heological properties was moderate or insignificant.