Rheological characterization of the galactomannan from Leucaena leucocephala seed

A water soluble galactomannan isolated from Leucaena leucocephala seeds gave an intrinsic viscosity of 3.5 dl/g and viscosity average molecular mass, Mv, of 6.98 × 105 g/mol. This was in reasonably good agreement with the value of the weight average molecular mass, Mw, of 5.44 ± 0.20 × 105 g/mol determined by GPC-MALLS coupled to RI. The onset of polymer coil overlap occurred at c*[η] of 2.1, with slope of 3.0 above and 1.3 below the point of polymer coil overlap. The shear viscosity of the polysaccharide was temperature dependent and decreased with increasing temperature. The activation energy for viscous flow of 3.0% polysaccharide concentration obtained by Arrhenius plot of zero shear viscosity as a function of temperature was 26.4 kJ/mol. Both the storage modulus (G′) and loss modulus (G″) showed strong dependence on frequency indicating the presence of entangled coils. The Cox–Merz plot gave close superimposition of the complex and shear viscosities.