| Abstract: | Hydrogels with moderate water retention capacity and salt stability have been prepared from starch, oxidized starch, and amylopectin all crosslinked with epichlorohydrin. The swelling power was measured in water and in various salt solutions of different concentrations. The swelling capacity decreases with increasing both the crosslinker and the polymer concentration. The plateau modulus (G′p) of the prepared gels was determined from complex dynamic viscosity measurements. G′p was measured as a function of the epichlorohydrin and polymer concentrations. The loss modulus (G″) for the prepared gels was also measured and was always found to be almost zero. The molecular weight between two entanglement points (mesh width) was estimated from the G′p values. The ratio between the number of elastically effective entanglement points, calculated from the G′p values, and that calculated from complete conversion of the cross-linker was also estimated for various gels. It was found that this ratio is very small (0.2–0.7%) for gels prepared with 10 wt-% starch, it increases however to 13% at higher starch concentration of 25 wt-%. |
