Molecular weight and aggregation of Erwinia gum in aqueous solutions

Erwinia (E) gum is composed of glucose, fucose, galactose and glucuronic acid. The weight-average molecular weights M-w, number-average molecular weights M-n and intrinsic viscosities [eta] of the four fractions and the unfractionated E gum in aqueous solutions at desired temperatures were studied by light scattering, membrane osmometry, size exclusion chromatography (SEC) and viscometry. The experimental results prove that E gum formed aggregates in the aqueous solution at 25 degrees C and the aggregates were broken gradually with increasing temperature. The dissociation of the aggregates of E gum in the aqueous solution started at 36 degrees C, and was completed at around 90 degrees C. The [eta] values of E gum and its fractions are much higher than those of the conventional polymers with the similar molecular weights, and decrease with increasing NaCl concentration.