Synthesis And Application Of A New Wheat Straw Based Superabsorbent

The superabsorbent is a new functional polymer material. It could absorb water with the weight of thousands of its own weight. It has a good water retention capacity, even under pressure. With the advantage of excellent performance, superabsorbent has been widely used in various fields.In the paper, wheat straw was used as the raw material. A new kind of superabsorbent which called as wheat straw-based superabsorbent (WS-SAB) was prepared by grafting acrylic acid, acrylamide and dimethy diallyl ammonium chloride onto the cellulose in the wheat straw with the present of initiator and crosslinker. The effect of various factor on the synthesis were studied by single factor experiment and orthogonal experiment and the best synthesis process was determined. Some modern analytical techniques such as elemental analysis, infrared spectroscopy and scanning electron microcopy were used to characterize WS-SAB.The studies showed that the optimum synthesis conditions were as follow:the reaction temperature was50℃,the reaction time was5h, the mass ratio between the monomers and wheat straw was m(wheat straw):m(AA):m(AM):m(DMDAAC)=1:4:2:1, the amount of initiator and crosslinker were1%and0.2%of the monomer’mass, the neutralization degree of AA was85%. Under this optimal sysnthesis conditions, WS-SAB has the best absorption capacity:133.76g/g in distilled water and33.83g/g in0.9%NaCl solution.The swelling behavior and deswelling behavior of WS-SAB was studied in the paper. The effect of pH, temperature and particle sizes on the swelling behavior and deswelling behavior was discussed. It was found that the temperature was higher, WS-SAB reached absoption balance more quickly with a lower water absoption amount. When the pH was6, WS-SAB had the maximum water absorption capacity. The effect of the salt ions in the swelling capacity was Na+> K+>Mg2+> Ca2+and Cl-> SO42-. The particle size was small, WS-SAB had a quickly water absorption process with a large water absorption capacity.And WS-SAB had a good reswelling capacity.In order to investigate the adsorption properties of element N and P on the WS-SAB, the adsorption of ammonium ions and phosphate ions on the WS-SAB in aqueous solution were studied. With the studied of kinetic model and equilibrium model, the adsorption mechanism were discussed. It found that the adsorption of ammonium ion and phosphate ion on WS-SAB could reach equilibrium within4h, and when the pH were in the range of4-10, the adsorption were kept in a high level. The adsorption of ammonium ions and phosphate ions on WS-SAB were in line with the pseudo second adsorption kinetics model. The Freundich adsorption model could be well fitted with NH4+adsorption, and for the adsorption of PO43-, the Freundich model fit well.WS-SAB could adsorb ammonium ions and phosphate ions, and the adsorption capacity were affected by the factors such as pH, temperature, adsorption time, initial solution concentration and adsorbent dosage.The effect of WS-SAB on the soil properties and soil nitrogen and phosphorus were studied through simulations. The result showed the soil bulk density, pH value, conductivity and water stable aggregate content were changed with the adding of WS-SAB. And this superabsorbent could increase the nitrogen fixation capacity of soil so as to delay the fertilizer effectiveness and achieve the purpose of fertilize retention. WS-SAB could also weak the phosphorus-fixation capacity of soil and increase the phosphorus release rate, thereby improving the utilization of phosphorus.