Preparation, properties and application of pH/thermo-sensitive PNIPA/CS semi-IPN hydrogel beads

Several novel semi-interpenetrating polymer network hydrogel beads (PNIPA/CS) composed of the temperature sensitive poly(N-isopropylacrylamid) and the pH-sensitive chitosan (CS) were prepared by inverse suspension polymerization. It was found that the introduction of CS doesn't change the low critical solution temperature (LCST) of the hydrogels, i.e., the prepared PNIPA/CSs maintain the same LCST as that of the PNIPA hydrogel, all of them are around 33°C. The hydrogel beads prepared are sensitive to both temperature and pH value evidently. The influences of the temperature, pH value and component of the hydrogels on the swelling behavior of the prepared hydrogel beads were studied. The results show that the content of CS affects the swelling ratio of PNIPA/CSs obviously, and the swelling ratio reaches its maximum when pH is 3. The experiments also show that the hydrogel beads prepared have reversible swelling character in response to the temperature. Besides, the experiments of using the prepared hydrogel beads to adsorb and then release the lactic acid were conducted, and it was found that when the mass ratio of PNIPA to CS is 10, the maximum adsorption is 168.29 mg·(g dry gel)^-1, and the release ratio is 31.74%.