Tuning the swelling and rheological attributes of bentonite clay modified starch grafted polyacrylic acid based hydrogel

Abstract Bentonite clay is used to tune the swelling, stimuli responsiveness (sorption and thermal) and the rheological characteristics of starch grafted polyacrylic acid based hydrogel. Here, polyacrylic acid moiety is grafted on the polysaccharide backbone of starch via radical polymerization. N,N′-methylene bisacrylamide is used as comonomer-crosslinker to obtain the crosslinked hydrogel matrix. Maximum swelling percentage is found to be 12,020% and 13,000% at 298 K and 277 K respectively. In addition, the storage modulus is enhanced by 3.55 times compared to the sample with no clay. Few models have been hypothesized to simulate these observations. The effects of external stimuli like temperature, pH and ion concentration have been studied. A conspicuous change in thermal response (like thermophillic to thermophobic) is noticed with the incorporation of bentonite clay. Thermophilic behaviour is observed for the clay concentration of 0 wt% and 5 wt%. At 10 wt% and beyond, the thermophobic behaviour is found. The hydrogels are further characterized by FTIR, XRD, TGA and SEM.