Minimization of Residual Monomer Content of Superabsorbent Hydrogels via Alteration of Initiating System

Production of superabsorbent polymer hydrogels with minimized residual monomer content is an essential prerequisite particularly in their related hygienic, pharmaceutical, and food packaging products. Effect of two thermodissociating initiators and an innovative two-step initiation approach on the residual monomer content of acrylic acid-based SAP was preliminarily investigated. Ammonium persulfate (APS) and 4,4'-azobis(4-cyanopentanoic acid) (ACPA) were used as water-soluble initiators for the aqueous solution polymerization. FTIR spectroscopy was used for the structural characterization. It was found that APS was more effective than ACPA, and residual monomer was determined in the range of 2200-3000 and 8900-16,600 ppm for APS- and ACPA-initiated polymerization products, respectively. Residual monomer resulted from APS/tetramethyl ethylenediamine (TMEDA) initiation system was measured to be about 4500 +/- 117 ppm for one step initiation. However, a two-step initiation strategy using the APS-TMEDA was exposed to be a very effective method to decrease residual monomer to 212 +/- 6 ppm. The variation of the hydrogel properties (i.e., gel content, swelling capacity, and the residual monomer content) versus the initiator system and concentration was discussed based on the basic literature and supported by some rheological evidences obtained from rheoanalysis of water-swollen samples. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2716-2723, 2011