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Many polysaccharides with varying shear stability have been grafted with polyacrylamide branches to enhance their turbulent drag‐reducing and flocculating characteristics. Their aqueous solutions have been studied by shear and extensional rheometric techniques. All the solutions of grafted carboxymethyl cellulose, guar gum, starch, and sodium alginate exhibit shear‐thinning non‐Newtonian behavior. The viscosities are higher than those of ungrafted polysaccharides. The solutions of grafted carboxymethyl cellulose, guar gum and sodium alginate are spinnable. When subjected to uniaxial stretching in a stretching device, the formation of a thread and reduction of the thread diameter with time were observed. The stretching device was used to measure the relaxation time, which was found to be the largest (∼26 ms), on the order of flexible polyacrylamide, for the grafted carboxymethyl cellulose. Though a polyacrylamide solution degrades through nozzle flow and completely loses its extensional properties, a solution of grafted carboxymethyl cellulose retains about half its relaxation time because of the shear stability of polysaccharide chains and their structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3200–3209, 2000

ABSTRACT:Various polysaccharides, such as starch and its constituent amylopectin, are used as flocculants in industrial effluent treatment. Grafting them with polyacrylamide branches enhances their flocculating and turbulent drag-reducing characteristics drastically. Aqueous solutions of the graft copolymer of amylopectin with polyacrylamide show a shear thinning non-Newtonian behavior. It is also expected that the solutions exhibit extensional effects. When the aqueous solution at 1000 ppm was subjected to a stretching device, the formation of a thread and reduction of the thread diameter with time were observed. The extensional relaxation time was thus estimated and compared with that of polyacrylamide. The measured relaxation time indicates that the performance of the rigid branched amylopectin, when grafted with fewer and longer polyacrylamide branches, is overwhelmed by the grafted polyacrylamide chains and the reduction of rigidity by the grafting process itself. This article reports the details of the investigations that led to these conclusions.

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