Preparation And Characterization Of Starch-based Water-absorbing Microspheres

Starch is one of the most abundant renewable resources in nature,it has been widely used in various industries because of its rich resources and low price.However,the application of starch is limited because of its poor heat resistance and acid resistance as well as easy to gelatinization.Therefore,it is of great significance to modify the raw starch,overcome its inherent shortcomings and broaden its application fields.In this thesis,the raw starch was modified by carboxyl methylation,cross-linking and the formation of the interpenetrating networks to improve its own chemical and physical properties,while giving them new functions,which lays a foundation for preparing high-performance starch based water absorbent microspheres.The process of preparing sodium carboxymethyl starch by carboxyl methylation of raw starch was studied by dry process and solvent method respectively.The optimum process conditions were obtained by controlling the single variable and optimizing the reaction parameters.It is found that compared with dry process,sodium carboxymethyl starch(CMS)prepared by solvent method has higher degree of substitution and better water absorption.The preparation technology and influencing factors of crosslinked sodium carboxymethyl starch microspheres were studied.The effects of reaction parameters on the properties of the crosslinked microspheres were investigated systematically from four factors,such as ethanol concentration,cross-linking agent dosage,starch milk concentration and reaction time.The optimum process conditions are as follows: the reaction temperature is 50 ℃,the concentration of ethanol is 40%,the amount of crosslinking agent is 3%,the concentration of starch is 2%,and the reaction time is 4h.Under these conditions,the water absorption of crosslinked starch microspheres can reach12056%.CMS/AA/PVP interpenetrating networks water-absorbing resin microsphere was synthesized by aqueous solution polymerization.The effects of CMS dosage,PVP dosage,KPS dosage and NMBA dosage on the properties of CMS/AA/PVP water-absorbing resin microspheres were systematically studied.The optimum process conditions are as follows:CMS dosage is 20%(based on the quality of acrylic acid,the same below),PVP dosage is10%,KPS dosage is 1.5% and NMBA dosage is 0.15%.Under these conditions,CMS/AA/PVP interpenetrating networks water-absorbing resin microsphere has good regularity,and its water absorption can be as high as 36025%.