Synthesis and swelling properties of silk sericin-g-poly(acrylic acid/attapulgite) composite superabsorbent

A composite superabsorbent silk sericin-g-poly(acrylic acid/attapulgite) was synthesized by the aqueous solution copolymerization method with potassium persulfate–sodium sulfite as the redox initiation system and N,N′-methylenebisacrylamide as the crosslinker. The structure of the attapulgite, silk sericin and the product was characterized via Fourier transform infrared absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy. The influences of reaction variables on the swelling properties of the composite superabsorbent were studied and optimized. The addition of the natural silk sericin improved the swelling properties of the acrylic acid/attapulgite bipolymer. The maximum swelling capacities of the composite superabsorbent silk sericin-g-poly(acrylic acid/attapulgite) in pure water and in 0.9 % NaCl aqueous solution were 1,236 and 108 g/g, respectively. The optimal conditions were initiator, 0.6 %; acrylic acid, 2.5 M; crosslinker, 0.1 %; silk sericin, 10 %; attapulgite, 12 %; reaction temperature, 65 °C; and time, 4 h.