RHEOLOGICAL PROPERTIES OF SEED GALACTOMANNAN FROM CASSIA-NODOSA BUCH-HEM

The solution properties of the galactomannan polysaccharide isolated from the seed of Cassia nodosa have been determined for a wide range of concentrations. The gum used has a mannose-to-galactose ratio of about 3.5, <($$)over bar>M(W) = 7.01 x 10(5) and an intrinsic viscosity of 1210 ml/g. The transition from dilute to semi-dilute regime, determined from viscometry, occurs at a critical concentration C*(c) similar to 2.5 +/- 0.5/[eta] which is Similar to the values obtained for some galactomannans and other polysaccharides although it is higher than the value obtained for more rigid polysaccharides. The slope of the log-log plot of specific viscosity versus C at zero shear rate is 6.5 in the more concentrated regime. These rheological studies clearly reveal the characteristics of a coil in dilute solutions. However, the large dependence of the viscosity on the coil overlap parameter is probably due to interactions because of low galactose content. The concentrated domain is characterized for polymer concentrations higher than 15 g/l where the rheological behaviour reached that of a pseudonetwork (weak gel-like behaviour).