Swelling behavior of protein‐based superabsorbent hydrogels treated with ethanol

A fish protein‐based superabsorbent hydrogel has been synthesized by modifying 80% of the ϵ‐amino groups of the protein with ethylenediaminetetraacetic dianhydride followed by crosslinking the remaining ϵ‐amino groups with glutaraldehyde. The hydrogel thus prepared was capable of absorbing about 200 g water per g dry gel after centrifuging at 214 g . Denaturation of the gel by treatment with absolute ethanol increased the equilibrium water uptake of the gel from 200 to 425 g water per g of dry gel. The saline uptake of the gel also increased from 24 g saline (0.1 M NaCl) for the control gel to 35 g saline per g dry gel for the ethanol‐treated gel. Analysis of the structural state of protein chains in the crosslinked swollen gel network using circular dichroism spectroscopy showed that, whereas the protein chains in the control gel were predominantly in β‐turn form, those in the ethanol‐treated sample were mainly in the α‐helical form. In addition to improving the swelling properties, the ethanol treatment offered the following advantages: 1. It dehydrated the gel and thereby eliminated the need for drying the gel. 2. It extracted low molecular weight off‐odor compounds from the protein gel. 3. It could also extract any residual unreacted glutaraldehyde (believed to be carcinogenic) that might be present in the gel. The ethanol used in the process can be easily recovered and recycled in the process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2190–2196, 2001