Construction Of Relationship Between Structures&Properties Of Starch-based Hydrogel And Slow Release Of Urea

Hydrogels are three-dimensional matrix constituted by linear or/and branched hydrophilic polymers that are chemically cross-linked,with the ability to absorb large quantities of water.Hydrogels are gradually being applied into agriculture as soil conditioners and nutrient carriers to support the plant growth in the past few decades.However,the high production cost and the non-biodegradability of traditional petroleum based hydrogels has restricted their application at large scale in agriculture.The introduction of it contributes a lot to great reduction of production cost,which natural renewable starch as a raw material and the reactive extrusion to the production of hydrogel.Starch-based hydrogels have attracted increasingly attention for application in controlled release fertilizers.However,there is currently a lack of knowledge on ways to characterize this system.In this work,we employed a hot-compression vulcanizer to in-situ synthesize monolithic urea-embedded grafted starch hydrogels with a slab geometry,which facilitates the subsequent measurement of gel strength and urea release kinetics.However,in the production and actual use of starch-based hydrogels,the toughness of hydrogel will affect the cycle of agricultural and the length of time for the controlled release fertilizer.Therefore,the research on the modulus(rheological kinetics)exhibited by starch graft copolymerization plays a very important role in regulating the reactive extrusion of urea-loaded hydrogels.In this work,we employed a hot-compression vulcanizer to in-situ synthesize monolithic urea-embedded grafted starch hydrogels with a slab geometry.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:1.We employed a hot-compression vulcanizer to in-situ synthesize monolithic urea-embedded grafted starch hydrogels with a slab geometry.Starch-based superabsorbent polymer embedded with urea was prepared.The samples exhibit good rheological behavior and have a high modulus.The swollen hydrogel for a longer period of time can also maintain a high modulus,such modulus behavior is helpful for practical use in agriculture.The release behavior of urea mainly shows zero-order release kinetics.The crosslink density mainly affects the initial release rate.As the crosslink density increases,the hydrogel exhibits high gel strength and the initial release rate decreases.2.The starch-based hydrogels constructed with different urea content showed different gel strength and slow-release effect.Below 60 % of urea content,the modulus and sustained release show a linear relationship.As the content of uremia increases,the modulus decreases due to a decrease in the degree of crosslinking.3.The results showed that with increasing gel strength,which was induced by decreasing urea load,increasing monomer/starch ratio,or increasing cross-linker content,resulted in a reduced burst release of urea at initial.The burst release at initial could be attributed to the heterogeneous network structure of statistical starch-based hydrogels and the accumulation of saturated urea on their surface.However,the gel strength produced little effect on the urea steady state release rate with a linear cumulative curve during the intermediate period.This zero-order urea release kinetics for starch-based hydrogel delivery systems would be of great beneficial to plant growth.This new technique has opened agate for further studying.