Swelling behaviors and gel strength studies of wheat straw-composite superabsorbent

A novel wheat straw-composite superabsorbent with high gel strength and high water absorbency was prepared by graft polymerization with acrylic acid, acrylamide and maleic anhydride-modified wheat straw, using N,N-methylene-bis-acrylamide as a crosslinker and ammonium persulfate and sodium bisulfite as redox initiators. Factors influencing water absorbency and gel strength of the superabsorbent composite, such as amount of maleic anhydride-modified wheat straw, crosslinker amount and initiator amount, were investigated. Morphologies and structure of the wheat straw-composite superabsorbent were characterized by Fourier transform infrared spectroscopy, scanning electron microscope and X-ray diffraction. Composite superabsorbent with modified wheat straw as high as 25 wt% still has water absorbency of 435 g/g. Fourier transform infrared spectroscopy spectra indicate the structure of wheat straw graft copolymer. Scanning electron microscope data show that the discontinuous sheet structures of wheat straw disappear and gel aggregates with many large microporous holes and small capillary pores are formed after wheat straw graft modification. The wheat straw-composite superabsorbent has better thermal stability than those of raw wheat straw and maleic anhydride-modified wheat straw.