Intramolecular and intermolecular association during chemical cross-linking of dilute solutions of different polysaccharides under the influence of shear flow.

Effects of shear flow on intramolecular and intermolecular associations of dilute aqueous alkali solutions of dextran, hydroxyethylcellulose (HEC), and a hydrophobically modified analogue (HM-HEC) in the presence of a chemical cross-linker agent were characterized with the aid of viscometry and rheo-small-angle light scattering (rheo-SALS) methods. The picture that emerges at short times in the course of cross-linking of the polymer solutions under the influence of a constant shear rate is that HEC coils contract because of intramolecular cross-linking, whereas the HM-HEC species show an incipient association and the dextran molecules are unaffected. At longer times, interchain cross-linking of the polymers promoted the growth of large flocs, which were disrupted by shear forces when they were sufficiently large. These findings are novel, and both the building up of aggregates and disaggregation are well substantiated by the SALS results.