Synthesis, swelling and responsive properties of a new composite hydrogel based on hydroxyethyl cellulose and medicinal stone

In this study, a series of pH- and saline-responsive composite hydrogels were prepared by a facile free-radical graft copolymerization amongst hydroxyethyl cellulose (HEC), sodium acrylate (NaA) and medicinal stone (MS). Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric/Differential thermal analysis (TG/DTA) confirmed NaA was grafted onto HEC and MS participate in polymerization, and presented the improved thermal stability. Field emission scanning electron micro-scope (FESEM), Energy dispersive spectroscopy (EDS), Elemental map (EM) and Transmission electron microscopy (TEM) analyses revealed a better distribution of MS in the HEC-g-PNaA matrix. Introducing 10 wt% MS greatly enhanced the swelling capacity by 400% (from 162 to 810 g/g), and also enhanced by 117% (from 162 to 352 g/g) even MS content reached 50 wt%. Also, the initial swelling rate was improved by incorporating MS, but decreased with enhancing the ion strength. The highly reversible On-Off switching pH- and saline-responsive region of the hydrogel was clearly extended after forming composite. In addition, the intriguing “overflowing” swelling behaviour was observed in aqueous solution of dimethyl sulfoxide (DMSO).