Shear and extensional rheological investigations in solutions of grafted and ungrafted polysaccharides

Many polysaccharides with varying shear stability have been grafted with po lyacrylamide branches to enhance their turbulent drag-reducing and floccula ting characteristics. Their aqueous solutions have been studied by sheer an d extensional rheometric techniques. All the solutions of grafted carboxyme thyl cellulose, guar gum, starch, and sodium alginate exhibit shear-thinnin g non-Newtonian behavior. The viscosities are higher than those of ungrafte d polysaccharides. The solutions of grafted carboxymethyl cellulose, guar g um and sodium alginate are spinnable. When subjected to uniaxial stretching in a stretching device, the formation of a thread and reduction of the thr ead diameter with time were observed. The stretching device was used to mea sure the relaxation time, which was found to be the largest (similar to 26 ms), on the order of flexible polyacrylamide, for the grafted carboxymethyl cellulose. Though a polyacrylamide solution degrades through nozzle flow a nd completely loses its extensional properties, a solution of grafted carbo xymethyl cellulose retains about half its relaxation time because of the sh ear stability of polysaccharide chains and their structure. (C) 2000 John W iley & Sons, Inc.