RHEOLOGICAL PROPERTIES OF AQUEOUS SUSPENSIONS OF CHITIN CRYSTALLITES

Rheologically, suspensions of chitin crystallites are found to behave as other molecular liquid crystalline polymers (LCPs). The average hyd rodynamic diameter of the crystallites in the suspension at pH 4 is de termined to be approximately 80 mn using dynamic light scattering. Con ductimetric and pH titration results show that the pK(a) of the crysta llites is 6.3, which is the same as that reported for chitosan. In com bination with phase diagrams, flow properties of isotropic, biphasic, and anisotropic chitin suspensions were investigated. For isotropic su spensions, a classical shear thinning behavior of rodlike particles is observed. In the case of biphasic suspensions, a two-regime curve is observed where tactoids first orient, deform, and then break up under a shearing force. Similar to other LCPs, a three-regime flow curve is found for the anisotropic suspensions. The viscosity-concentration cur ve exhibits a maximum at the phase separation concentration, and this maximum is less distinct with a decrease of the ionic strength. Second ary electroviscous effects due to strong particle-particle interaction s influence the viscosity of the suspensions at higher concentrations. (C) 1996 Academic Press, Inc.