Rheological properties of Cedrela odorata gum exudate aqueous dispersions

Rheological studies of Cedrela odorata gum aqueous dispersions demonstrated viscoelastic properties. Mechanical spectra derived from small amplitude oscillatory shear (SAOS) results support the onset of gel-like structure at given conditions (10% w/v, 20 degrees C). The increase in the storage and loss moduli, along with the drop in their frequency dependence, observed at higher gum concentrations, indicates a slower relaxation mechanism, which may be related to the increasing number and structural complexity of transient junction zones among macromolecules. The transition from gel-like to sol-like structure, at higher temperature, was detected from SAOS results. The flow behaviour of the aqueous gum dispersions under steady shear is highly non-Newtonian and can be modelled by the Sisko equation. The Cox-Merz rule was found to fail at critical gum concentration for the onset of gel-like behaviour and also at a temperature slightly above the gel-sol transition. C. odorata gum aqueous dispersions may have interesting applications as stabilisers of emulsions and suspensions on account of their theological behaviour. (C) 2008 Elsevier Ltd. All rights reserved.