The effect of anionicity on mechanical degradation of polyacrylamide-type flocculants

The effect of ultrasonication, screening and shearing on five polyacrylamide-based flocculants of similar molecular weight but different degrees of anionicity (DA) was studied through measurement of intrinsic viscosity ([i]) and size exclusion chromatography (SEC) to investigate the influence of DA on the degradation of polymers. It was found that screening did not affect the [i] of the polymers while the effect of shearing was most noticeable in the cases of non-ionic and most anionic flocculants. Furthermore, ultrasonication caused a sharp decrease in the [i] which indicates a rapid degradation of the polymers. The results suggested that degradation of the polymers as a result of ultrasonication was irreversible since after a 24 hour resting period, the [i] did not recover to the values obtained for the untreated samples. Using a ratio of the [i] in distilled water to that in a dilute electrolyte as a measure of the relative flexibility of the flocculant chain, it was shown that the most flexible flocculants resisted ultrasonication and degradation better than those with rigid chains. Results from SEC confirmed that the degradation of polymers due to ultrasonication was a result of breakage of the polymer chains into sections of lower molecular weights.