Preparation of hydrogels via cross-linking of partially hydrolyzed polyacrylamides with potassium persulfate at moderate temperatures

A series of hydrogels were prepared by cross- linking of a low molecular weight partially hydrolyzed polyacrylamide (HPAM) in aqueous solutions, with potassium persulfate (KPS) as cross linker at moderate temperatures between 60-80⁰C.The minimum concentration of polymer solution for consistent gel formation is 1.5wt%, and the time to obtain the stronger gel decreases with increasing the KPS/HPAM ratio and concentration of HPAM. Increasing the concentration of polymer solutions shifts the onset of gel formation to the lower KPS/HPAM ratios. Increasing the KPS/HPAM ratio at constant weight percent of HPAM decreases the water absorbency, and increasing the polymer content at any KPS/HPAM ratio increases the water absorption .Gel fraction increases with increasing the weight percent of polymer. Increasing the KPS/HPAM ratio has the similar effect on variations of the gel fraction. A gel, prepared at 60⁰C based on the 2 wt% copolymer solution and crosslinker/ copolymer ratio of 1/3 is an optimum gel in terms of gel strength, water absorbency and gel fraction. The Proposed mechanism of gel formation is cross-linking through macroradical combination. FTIR analysis confirms the absence of imidization during gel formation .The Conversion time of gelant solutions to consistent gel is decreased 2 times for every 10⁰C increase of temperature. Fluctuations in the water absorbency of hydrogels which prepared at different temperatures can be explained with competition between degradation and radical combination. Hydrogels prepared at different temperatures and similar KPS/HPAM ratio, have no significant difference in gel fraction.

Author(s): Mehrdad Ghazinezhad, Yauheni V. Hryniuk and Leonid P. Krul

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