Determination of the Charge Density of Anionic Polyacrylamide

Although there are starch based flocculants available, it is the various polyacrylamide compounds that are most commonly used in the mining and petroleum industries. It is primarily used as a method for enhancing the sedimentation of solids in the water treatment processes as well as a mobility control agent in enhanced oil recovery processes. It is most commonly the non-ionic and anionic polyacrylamide compounds which are used in these industries. The charge density of the polyacrylamide will have an effect on its efficacy in these given implementations.

There are a number of methods which are traditionally used to determine the carboxylate content of the polyacrylamide. They are conductometric and potentiometric titrations as well as infrared spectroscopy. However, the titration methods are time consuming and the infrared spectroscopy is limited by poorly resolved spectra of carboxylate carbonyl and the amide carboxyl adsorption peaks.

W.M Leung, D.E. Axelson and D. Syme have proposed alternative methods for determining the charge densities of anionic polyacrylamide which promise to be more precise and faster. The proposed method makes use of nuclear magnetic resonance spectroscopy and differential scanning calorimetry.

They found that the 13C resonances from the amide carbonyl carbons in the anionic polyacrylamide appeared in the form of sharp singlets which were not sensitive to tacticity effects. It was also found that broadening and splitting occurred due to monomer distribution effects in partially hydrolysed samples. Similar effects were noted with the CH and CH2 compounds.

As such, it is theorized that the comonomer content and thus the charge densities of anionic polyacrylamides may be measured by careful consideration of the relative peak intensities in the carbonyl or methane carbon regions. Further study is required in order to formalize the optimum delays for the spectroscopy and calorimetry to deliver consistent and accurate results. It was observed that recycle delays of three seconds or less may be too short.

Further information on the study and its results can be found at link.springer.com/article/10.1007/BF01412958.

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