Synthesis And Properties Of Tertiary Aminoalkylated Starch Based PH-sensitive Hydrogels

Intelligent or smart hydrogels have shown a sudden change with response to the external stimuli, such as pH, temperature, electric field, magnetic field, solvent, salt and so on. Among them, pH-sensitive hydrogels have attracted considerable interests because it is easy to obtain. In this study, hydroxyethyl starch, for which has a good solubility and be with good biocompatibility and biodegradability, is used to prepare pH sensitive starch dervatives by functionalized modification. And next, these starch derivatives are used to prepare a series of tertiary aminoalkylated starch based pH-sensitive hydrogels.In this work, pH sensitive 3-dialkylamino-2-hydroxypropyl-hydroxyethyl starch (TAS) with different carbon number of alkylamino groups and different molar degree of substitution (MS) were synthesized.1H-NMR was uesd to determine the structure of TAS and calculate its MS. The value of hydrogen dissociation ability (pka) and the phase transition pH (pHt) were obtained by the potentiometric-conductometric titration curves and transmittance curves.Novel pH-sensitive gels (TASEDGE, TASPEDGE and TASECH) were prepared using DP-TAS with MS 0.84 as raw materials (DP-TAS-0.84), high reactive ethylene glycol diglycidyl ether (EDGE), polyethylene glycol diglycidyl ether (PEDGE) or epichlorohydrin (ECH) as crosslinkers respectively. The reaction variables, including the dosage of solvent, NaOH and crosslinkers, were optimized through orthogonal and single factor experiments. Scanning electron microscopy (SEM) photos using for observing the internal morphology and porosity of these hydrogels confirmed the gels are porous materials. The swelling ratio (SR) at different pH conditions and the pH circulation performance of hydrogels were studied. In addition, the effects of some variables on SR, including the concentration of NaCl solutions, MS of TAS and the crosslinking agents were investigated. The results showed that the SR decreases with the increasing of the pH. The change of SR is not obvious when the pH is 4 to 8. But from 2 to 4, the change of SR is very remarkable. Among these, the SR of TASECH gel is 220.5 g/g when pH is 1. The concentration of NaCl solutions has an effect on the SR, it instantaneously drops with the increasing of ionic strength. But when the NaCl concentration exceeds 0.05 mol/L, the SR changes little. The SR increases with the increasing of the MS. The difference of crosslinking agents also have an effect on the SR. The SR of these three kinds of hydrogels are 24.89 g/g,30.67 g/g,40.23 g/g in neutral condition.Applied them to dye adsorption. The parameters on the adsorption property, including initial dye concentration, volume of dye, pH of dye solution, adsorption time, temperature, MS and the concentration of NaCl were studied in detail. And the gels’adsorption-desorption for dye is also studied. The results showed that the adsorption capacity increases with the increasing of the initial dye concentration, volume of dye, temperature, adsorption time and the MS. On the contrary, it decreases with the increasing of pH and NaCl concentration. The dyes structure has an effect on the adsorption efficiency, but they are all above 90%. The differences between crosslinking agents have a influence on the adsorption efficiency as well. And applied TASEDGE gels to the acid yellow wastewater treatment, the adsorption efficiency reached 67%.