Synthesis And Properties Of Organic/Inorganic Nanocomposites Hydrogels With Semi-IPN Structure

In the last two decades, polymer/clay nanocomposites have been extensively investigated as advanced composite materials because these nanocomposites exhibit markedly improved mechanical property and reduce the cost of the manufacture. Among all the polymer/clay nanocomposites, the nanocomposite hydrogels based on bentonite have been more widely investigated. The properties of the hydrogels, e.g. salt-resistance, swelling capacity, absorbency rate, mechanical strength and thermal stability can be significantly enhanced by incorporation of bentonite into the polymer network, due to the natural activity and the low cost of the bentonite.Na-bentonite was modified by cationic polyelectrolyte though solution intercalation. The XRD pattern and TEM image indicated that the cationic polyelectrolyte was intercalated into the interlayer space of the Na-bentonite, the interlayer distance was enlarged, no basal reflection was observed in the XRD pattern and an exfoliated nanocomposite was obtained. The molecular weight of the cationic polyelectrolyte has a significant effect on the interlayer space of the nanocomposites. An exfoliated or intercalated structure can be obtained by controlling the molecular weight of the cationic polyelectrolyte.In order to improve the hydrogel strength and salt resistance, we prepared a novel amphoteric nanocomposite hydrogel with semi-interpenetrating polymer network (semi-IPN) which is composed of starch-g-acrylic acid (AA) and Na-BENT modified with linear polycations poly(dimethyldiallylammonium chloride )(PDMDAAC). The influences of the synthesis conditions on the swelling capacity of amphoteric superabsorbent composites were investigated in details. The results showed that the nanocomposite hydrogel has the swelling capacity of 858 g/g in deionized water. The hydrogel kept a high swelling in a wide pH range range of 4 to 13, and good salt tolerance. Swelling capacity was 72 g/g at the pH 13 and 81 g/g in 0.1 mol/L NaCl solution. Besides, the compressive strength of the hydrogel reached 28 kPa even under a more than 99% of water content.Amphoteric semi-IPN nanocomposite hydrogels with define porous structure composites of starch-g-acrylic acid/PDMDAAC/Na-bentonite were prepared in the presence of poly(ethylene glycol) (PEG) as the pore-forming agent. The influences of the PEG molecular weight, the amount of the PEG and the synthesis condition on porous structure are investigated. The PEG-modified hydrogels are characterized by swelling rate and swelling kinetics. The porous hydrogels reached its equilibrium swelling within 10 min.The urea and formaldehyde were used to modify Na-BENT by intercalative condensation, as the results of XRD and TEM showed an exfoliated nanocomposite FU/BENT was obtained. Then semi-IPN nanocomposite hydrogels prepared by interpenetrating with poly(acrylic acid) (PAA). The influences of the amount of Na-BENT on the swelling behavior of nanocomposite hydrogels were studied in details. When the amount of Na-BENT was 5 wt.%, the hydrogel has the swelling capacity of 983 g/g in deionized water. The nanocomposite hydrogel kept a high swelling in a wide pH range of 4 to 13 and good salt tolerance. Swelling capacity kept 126 g/g at the pH 131 g/g and in 0.1 mol/L saline solutions, respectively.