Preparation And Properties Of Starch-based Superabsorbent Polymer For Slow Release Of Urea

The coated slow/controlled release fertilizer has the advantages of long controllable release period and high utilization rate,and can improve crop yield.However,the degradation performance of synthetic polymer coating materials is poor,which will bring pollution to the environment,and the development of natural degradable and multifunctional composites as slow release matrix has become a focus in this field.Starch-based superabsorbent polymer is a multi-functional material,has a unique three-dimensional network structure,with excellent water absorption capacity,water and moisture retention,nutrients slow/controlled release.Furthermore,it is environmentally friendly.Therefore,it can be used as a superior urea slow-release matrix.In this study,starch-based superabsorbent polymer embedded with urea was prepared by the innovative mixer reaction system.The chemical composition and morphology of the samples were characterized by infrared spectroscopy,thermogravimetric analysis and scanning electron microscopy respectively;The water absorption and gel strength of the samples were investigated by water absorption test and rheological tests respectively;Finally,the slow release performance was investigated by water dissolution test;Which provides a theoretical basis for the application of starch-based superabsorbent in the field of slow release fertilizer.Research was carried out by the following order: first,according to the different load order of urea,two feasible preparation methods are explored: Method 1 and Method 2 and the urea release model of the system was analyzed.On the basis of this,the slow-release properties of starch-based superabsorbent polymer with different starch chain ratio(G50,maize,waxy)and different cross-linking agent content were compared.Finally,the effects of different initiator contents and different degree of saponification on the slow-release properties of starch-based superabsorbent were studied.Through the research work of this paper,the following conclusions are drawn:1.Two preparation methods were explored through the innovative mixer reaction system.The results showed that the two preparation methods were both applicable in this reaction system,M1-SBSAP prepared by the method 1 showed higher gel strength;M2-SBSAP prepared by the method 2 showed better water absorption capacity.The slow release behavior of urea is divided into three stages: initial stage,sustained release stage and equilibrium stage.The initial stage of nutrient release depends on the water absorption of the absorbent resin;the latter two stages of nutrient release are mainly determined by the gel strength of the sample.2.The results showed that the storage modulus of maize-SBSAP was the highest,followed by G50-SBSAP,and the water absorption performance of G50-SBSAP> waxy-SBSAP> maize-SBSAP was the highest.And the storage modulus of the two is not very different,waxy-SBSAP storage modulus is small,much difference compared with the former,With the release of time prolonging,the gel strength of the sample gradually weakened,showing mechanical relaxation;G50-SBSAP sustained release effect is better than the other two.3.The results showed that the gel strength of the samples increased with the increase of the content of the crosslinking agent.The content of the crosslinking agent increased with the increase of the content of the crosslinking agent.The slow release performance has no significant effect.4.The gel strength and water absorption performance of the samples with different initiator contents and different saponification degree showed no linearity.The experimental results showed that 2.5% CAN and 100% saponified samples had better release performance.