Superabsorbent polymers (SAPs) were prepared from cassava starch by graft copolymerization of acrylamide on to starch using ceric ammonium nitrate (CAN) as free radical initiator, followed by alkali saponification. The reaction parameters such as concentration of acrylamide, concentration of CAN, temperature, and duration of polymerization reaction were optimized for maximum water absorbency using a 4‐factor 3‐level Box‐Behnken design. The highest values of percentage grafting and absorbency obtained were 174.8% and 425.2 g/g, respectively. The polymers were characterized by determination of grafting efficiency, N‐content, acrylamide content, FTIR analysis, SEM and XRD analyses. Thermogravimetric analysis (TG) showed that the SAP has higher thermal stability. The rate of water absorbency and the swelling behaviour of the SAP under different conditions of pH, and different salts were determined. The de‐swelling pattern of the hydrogels over different time durations was also determined.

Superabsorbent polymers (SAPs) are macromolecules with the ability to absorb water and release it slowly to the surroundings. SAP hydrogels can be used as soil moisture conditioners which act as water reservoirs and release water depending upon the need of plant roots. In the present study, a cassava starch based superabsorbent hydrogel was evaluated as a soil conditioner and its effect on physical, chemical, and biological properties of the soil as well as on plant growth parameters was studied. Amendment of the soil with the starch based SAP hydrogel significantly altered the physical and chemical properties of the soil. Bulk density of the soil was decreased, whereas water holding capacity and porosity were increased on SAP treatment. There was an improvement in the soil status of major, secondary and micronutrients and organic carbon in the SAP amended soil. An increase in bacteria (16%) and fungi counts (18%) as well as superior plant growth were observed for the treatment with SAP and irrigated at an interval of 3 days, compared to those of control without SAP. Soil amendment with starch based SAP hydrogel was found to be beneficial for maintaining the physicochemical and biological soil properties as well as plant growth.

Superabsorbent polymers (SAPs) are hydrophilic polymeric networks that can absorb, swell and retain large quantity of water and other physiological fluids. In this paper, the water sorption pattern and kinetics of cassava starch based SAP hydrogels were studied under different conditions of swelling such as soaking duration, pH, presence of salts, and particle size of the hydrogel. The kinetics was studied using Voigt‐based viscoelastic model to determine the rate parameter and the swelling rate (SR). It was noted that under all conditions, the water sorption followed a second order kinetics. The absorbency was directly proportional to the rate of swelling. But when the sample was allowed to swell in aqueous solutions of CaCl2 and AlCl3, the absorbency as well as the SR was irregular. The particle size also had significant effect on water absorption by the SAP and the polymer with smaller particles showed more absorption than those with larger particle size. The solvent induced phase transition of the superabsorbent hydrogel was also studied.

Cassava starch-graft-poly(acrylamide) superabsorbent polymers (SAPs) with varying absorbencies were synthesized. Weight average molecular weight (M w ) of the hydrolyzed starch-graft-copolymers ranged from 1.6 3 10 6 to 2.8 3 10 6 g/mol, the largest being shown by the sample with highest percentage grafting. The storage (G 0 ) and loss modulus (G 00 ) of hydrogels were determined as a function of frequency. G 00 was larger than G 0 for the hydrogels with higher absorbencies and exhibited a liquid-like behavior. However, hydrogels with lower absorbencies showed a reverse viscoelastic behavior. The viscosity of hydrogels determined using a Brookfield viscometer at different shear rates was found to be larger for the hydrogels with higher absorbencies. The melting temperature (T m ) and enthalpy change of fusion (DH f ) of the SAPs ranged from 149.7 to 177.7 C and 65 to 494.9 J/g, respectively and showed a positive correlation with grafting parameters and M w . Heavy metal ion removal capacity of hydrogel followed the order Cu 21 > Pb 21 > Zn 21 .

Graft copolymerization of poly(acrylonitrile) onto cassava starch was carried out with potassium persulphate (PPS) as the free radical initiator using a response surface Box-Behnken design. Different levels of monomer concentration, initiator concentration, and temperature were used, and regression models were generated in terms of these factors, which can be used to predict the grafting level and efficiency at a given level of the factors. The grafted starches were characterized by FTIR, XRD, and SEM analyses and determination of %grafting (%G), N-content, thermal properties, water and saline solution retention, and rheological properties. Under the conditions used, %G was found to depend only on the temperature used for the reaction. The maximum %G of 120.1 was obtained for the sample synthesized under the following conditions: weight of AN ¼ 0.753 mol/10 g starch, weight of PPS ¼ 0.284 g and temperature ¼ 55 C, and the grafting efficiency was 30.03%. The absorption bands at 2243 cm À1 for the nitrile group (ACN) in the FTIR spectra of the products confirmed the grafting reaction. There was a decrease in crystallinity and disappearance of the granular structure after grafting of the starch. The melting temperatures of the graft copolymers determined by differential scanning calorimetry analysis were higher than that of the native starch. The grafted starches exhibited very high thermal stability as observed from the thermogravimetric analysis. The superabsorbent polymer prepared from the grafted starch by alkali saponification exhibited a maximum water absorbency of 636 g/g. V C 2011Wiley Periodicals, Inc. J Appl Polym Sci 122: [1546][1547][1548][1549][1550][1551][1552][1553][1554][1555] 2011