| The growth of plants and vegetables is mainly a function of the quantity offertilizer and water. It is very important to improve the utilization of water resourcesand fertilizer nutrients. However, about40–70%of the nitrogen of the applied normalfertilizers is lost to the environment, and cannot be absorbed by plants and vegetables,causing not only large economic and resource losses, but also very seriousenvironmental pollution. It has been reported that about1/3of nitrogen fertilizersenter into the atmosphere, where N2O destroys the ozone layer, and about1/3ofnitrogen fertilizers leach into the water, leading to eutrophication of water resources.As a by-product of corn crops, corn stalk is an abundant biodegradable resourcewhose main components are cellulose, hemicellulose, and lignin. Up to now, most ofthe crop residues have been focused on burying them back to improve the fertility ofthe soil, using them as the materials for the paper industry and producing protein feed,alcohol, and methane by microbial fermentation. Corn stalk can be used as abioabsorbent, due to its large surface area and a number of hydrophilic hydroxylgroups on the macromolecular chains. However, its fertilizer adsorption capacity isstill very low. Therefore, modification of corn stalk is needed to enhance its fertilizeradsorption capacity. Up to now, straw was either gelatinized, or modified by acidor/and base treatment and then grafted with some monomers to prepare strawcomposite superabsorbents. But there are no reports on the phytic acid–modified cornstalk composite superabsorbent (PCS-SA).PCS-SA was prepared by graft copolymerization of acrylamide (AM), vinylpyrrolidone (NVP), and itaconic acid (IA) with phytic acid-modified corn stalk (PCS)in an aqueous solution, using ammonium persulfate and sodium bisulfite as a redoxinitiator. PCS-SA, having rapid fertilizer absorbency rate, high fertilizer absorbency,good fertilizer release property and high fertilizer retention ability, were obtained. Factors influencing the urea absorbency, urea retention, and urea release properties offertilizers of urea and potassium dihydrogen phosphate, such as the amount of cornstalk, the esterification rate of phytic acid-modified corn stalk, the mass ratio ofitaconic acid and vinyl pyrrolidone, the amount of ammonium persulfate，the amountof crosslinking agent and the neutralization degree of itaconic acid, were investigated.Morphologies and structure of the PCS-SA were characterized by SEM and FTIR.The main results were as follows:(1)PCS-SA, synthesized with phytic acid modified-corn stalk amount of15%,had a urea absorption capacity of2.3626g/g, urea absorbency of105g/g within40min,urea release ratio of76.70%in distilled water after3d. PCS-SA had a potassiumdihydrogen phosphate absorption capacity of0.2681g/g, potassium dihydrogenphosphate absorbency of22g/g within40min, potassium dihydrogen phosphaterelease ratio of79.33%in distilled water after1d.(2) PCS-SA, synthesized with phytic acid modified-corn stalk grafting degree of12%, had a urea absorption capacity of2.5633g/g, urea absorbency of151g/g within80min, urea release ratio of72.87%in distilled water after3d. PCS-SA had apotassium dihydrogen phosphate absorption capacity of0.4239g/g, potassiumdihydrogen phosphate absorbency of27g/g within40min, potassium dihydrogenphosphate release ratio of76.64%in distilled water after1d.(3)PCS-SA, synthesized with an IA and VP mass ratio of70:30, had a ureaabsorption capacity of3.8936g/g, urea absorbency of361g/g within40min, urearelease ratio of56.58%in distilled water after3d. PCS-SA had a potassiumdihydrogen phosphate absorption capacity of0.5762g/g, potassium dihydrogenphosphate absorbency of41g/g within50min, potassium dihydrogen phosphaterelease ratio of60.37%in distilled water after1d.(4)PCS-SA, synthesized with the ammonium persulfate amount of1.6%,had aurea absorption capacity of2.5827g/g, urea absorbency of233g/g within50min, urearelease ratio of62.03%in distilled water after3d. PCS-SA had a potassiumdihydrogen phosphate absorption capacity of0.3998g/g, potassium dihydrogenphosphate absorbency of36g/g within30min, potassium dihydrogen phosphaterelease ratio of65.96%in distilled water after1d.(5)PCS-SA, synthesized with crosslinking agent amount of0.2%, had a ureaabsorption capacity of3.7137g/g, urea absorbency of351g/g within30min, urearelease ratio of61.26%in distilled water after3d. PCS-SA had a potassiumdihydrogen phosphate absorption capacity of0.5034g/g, potassium dihydrogen phosphate absorbency of39g/g within40min, potassium dihydrogen phosphaterelease ratio of66.66%in distilled water after1d.(6)PCS-SA, synthesized with itaconic acid neutralization degree of65%, had aurea absorption capacity of3.5778g/g, urea absorbency of350g/g within40min, urearelease ratio of67.64%in distilled water after3d. PCS-SA had a potassiumdihydrogen phosphate absorption capacity of0.4702g/g, potassium dihydrogenphosphate absorbency of37g/g within40min, potassium dihydrogen phosphaterelease ratio of73.73%in distilled water after1d.(7) After polymerization process optimization, the best synthetic formula forpreparation of PCS-SA was as follows: phytic acid modified-corn stalk amount of15%, grafting degree of12%, itaconic acid and vinylpyrrolidone mass ratio of70:30,the ammonium persulfate amount of1.6%, crosslinking agent amount of0.2%anditaconic acid neutralization degree of65%, under which the prepared PCS-SA hadurea, potassium dihydrogen phosphate absorption capacity of3.8936g/g、0.5762g/gand urea solution, potassium dihydrogen phosphate solution absorbency of360.515g/g、40.515g/g, respectively within40min and50min. Release rates of ureasolution absorbency, potassium dihydrogen phosphate solution were about56.58%and60.37%, respectively with3d and1d. In soil after5d, resulting in a significantlydecreased urea release rate and an increasing urea retention of soil. In soil after3d,resulting in a significantly decreased potassium dihydrogen phosphate release rate andan increasing potassium dihydrogen phosphate retention of soil.（8）FTIR spectrum of the PCS-SA appeared characteristic absorption peaks ofphytic acid modified corn stalk, NVP unit, IA unit and AM unit, a preliminaryindicative of the target structure of the synthesized PCS-SA.（9）PCS-SAhad irregular corrugated surfaces, accompanied by a large numberof small pores and gully, which is conducive to the rapid penetration of water andfertilizer solution into the superabsorbent network structure. |
PDF Full Text Request