| The super absorbent polymer (SAP) was synthesized through a rapid solution polymerization of sweet potato starch grafted acrylic acid under normal atmospheric conditions. The optimization conditions were carried out, and the properties of SAP were studied on its absorbency , retentiveness, the biodegradability and the slow urea releasing.The initiator systems of K2S2O8, (NH4)2S2O8, and (NH4)2Ce(NO3)6, as well as different cross-link agents, were compared. The factors influencing the absorption ratio of deionized water (RADW), such as the method of starch gelatinization, the volume of water, the neutralization degree of acrylic acid, were investigated. Based on these, the addition order of material, starch grafted acrylic acid and acrylamide, the reaction added by kaolin were studied. The results suggested that the maximum absorbency in deionized water was 1000g/g water. The optimization conditions were the quantity of starch, monomer, water and initiator were 4g ,39.8ml (70% neutralization degree),40ml,0.06g,respectively. It also showed that adding acrylamide or caolin had no result on increasing the absorbency of deionized water.The water of absorption of the SAP in various salt solution of different ionic strengths, the effect of diameter of SAP particle on the RADW, the water retentiveness under variable conditions, and the biodegradability of the SAP under controlled condition were also measured. The results indicated that: the absorbency of SAP was 85g/g in 1% NaCl solution, the water retentiveness amounted to 60% (70℃, 12h) and 18% (110℃,12h), or 96.3% under 5000r/s centrifugation. RADW dropped with the increase of particle size in certain range of diameter of SAP particle, 45 % and 34% of SAP degradability were observed under fungal-growth and soil-burial tests.The synthesis of SAP by adding urea in the graft co-polymerization was studied, and it showed that the more the urea was added, the lower RADW of SAP was. The results proved SAP has the ability of controlled release of urea.
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