Rheology, dynamic light scattering and physicochemical characterization of octenyl succinic anhydride (OSA) modified starch in aqueous solution.

Physicochemical and rheological properties of hydrophobically modified starch by octenyl succinic anhydride (OSA) have been evaluated in order to investigate the effects of concentration and temperature on its aggregation phenomenon in an aqueous solution. The analysis of particle size distribution showed the existence of two modes of aggregation by intramolecular bonds, whereas beyond the critical aggregation concentration a second population appears which seems to be induced by the intermolecular interactions. From the rheological analysis of OSA starch solutions, three behaviour classes were observed. The first class presents a non-Newtonian shear-thinning behavior characterized by two Newtonian regions. The second class exhibits a gel like behavior due to the entanglement of the macromolecular chains by intermolecular bonds, where its destructuring makes it possible to find the first morphology of the aggregated macromolecules. The third class exhibits a liquid behavior in a concentrated domain due to the phase separation between the modified and unmodified parts. Otherwise, the thermo-rheological analysis demonstrated indeed the presence of a thermosensitive behavior in tangled solutions of OSA starch.