Mechanochemical Functionalization of Polysaccharides via Catalytic Esterification for the Preparation of Superabsorbent Materials for Plant Growth Applications

In this study we have developed a new approach to synthesize superabsorbent materials via derivatization of polysaccharides of soybean waste (okara) and banana fibres using mechanochemistry. These polysaccharides, in equal weight ratio, were derivatized with succinic anhydride (SA) in the thermo-mechanical reactive extrusion process in the presence of different amounts of catalysts K2CO3 and/or Zn(OAc)2. The reactions were performed at 130–140 °C for 10 min. Sequentially, after removal of unreacted SA, the derivatized polysaccharides were neutralized with NaOH, KOH and/or aq. NH3 to obtain superabsorbent materials. The esterified polysaccharides were crosslinked using glycidyl methacrylate (GMA) and/or N,N′-methylene bisacrylamide (MBA) and the effects were evaluated. The reactions were confirmed by attenuated total reflectance-Fourier transform Infra-red (ATR-FTIR) spectroscopic analysis and structural characterization was done by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Among the catalysts, K2CO3 performed better than Zn(OAc)2, while among crosslinkers, MBA performed better than GMA crosslinker. The esterified polysaccharides showed optimum water absorption of 36.5 ± 2.2 g/g. Then the superabsorbent materials were used to grow maize plants, and the use of 0.4 wt.% functionalized SAPs in soil resulted in statistically significant increase in shoots length as compared to control, although no significant effect was observed on roots length.