Flow field-flow fractionation of polyacrylamides: Commercial flocculants

The coupling of flow field-flow fractionation (flow FFF) and a multiangle laser light-scattering (MALLS) detector enables absolute measurements of weight-averaged molecular mass distributions for polymer solutions. The technique, applied recently to polyacrylamide (PAAm) standards, has been extended to commercial nonionic flocculants in an aqueous environment. A mass distribution is achieved in less than 2 hours per sample, which offers a significant improvement over size-exclusion chromatography in terms of throughput. While the fractionation of commercial PAAm solutions generally follows the same pattern as for lower molecular mass standards, there is also strong evidence of polymer agglomeration. In some samples these agglomerates are of sufficient size to interfere with the fractionation due to the parallel separation mechanisms of the FFF. The extent of agglomerate formation was dependent upon solution age and may be a factor in age-related loss of flocculant activity. Significant dispersion of such species was achieved by dilution of polymer in salt solutions prior to injection into the FFF cell.