Study On Preparation And Adsorption Capacity Of Starch Microsphere Aerogels

Starch microsphere aerogels are widely used because of their low density,large specific surface area and good biodegradability.Tapioca starch is a suitable raw material for the preparation of starch microsphere aerogels because of its suitable ratio of amylose/amylopectin and high viscosity.In this paper,tapioca starch was used as raw material to prepare starch microsphere aerogels by emulsion-gel method.The effects of molecular weight and amylose content on gel formation and adsorption capacity were evaluated by acid hydrolysis and enzymatic hydrolysis of modified starch.The cross-linking technology was optimized to characterize the properties of cross-linked starch microsphere aerogels,and the adsorption mechanism of the crosslinked starch microsphere aerogels was investigated by applying them to the adsorption of phosphorus and oil,in order to provide a basis for the efficient preparation,performance optimization and application of starch microsphere aerogels.The main conclusions are as follows:(1)Study on preparation,adsorption properties and morphology of starch microsphere aerogelsThe effects of heating temperature,time,concentration and oil-emulsion ratio of starch on the adsorption capacity of microsphere aerogels were studied,the effects of heating time,temperature and starch milk concentration on the adsorption of microsphere aerogel were significant.Response Surface Methodology was optimized as follows:Starch milk concentration 15%,heating temperature 85°C,TIME 90 min,adsorption capacity 0.928±0.008 mg/g,69.80%higher than the original starch.The microsphere aerogels prepared at different heating temperature,time and starch concentration were analyzed by SEM.The results showed that the diameter of microsphere aerogels increased with the heating temperature below 100°C,when the temperature reached 100°C,the starch microspheres formed a coralline surface.(2)Effect of modified starch on the adsorption properties of starch microspheres aerogelsThe adsorbability of the microspheres prepared from acid-hydrolyzed starch decreased significantly(p<0.05),and acidolysis starch was unfavorable to the preparation of starch microspheres.The microsphere aerogels prepared by enzymatic hydrolysis of starch with alpha-amylase at moderate temperature have strong adsorbability.The proper cleavage ofα-1,4 glycosidic bonds is beneficial to the enhancement of the adsorption capacity of starch microsphere aerogels,and the cleavage ofα-1,6 glycosidic bonds can decrease the adsorption capacity of starch microsphere aerogels.Compared with the raw starch,the amylose content of the alpha-amylase starch was decreased by 9.46%,the adsorbability was increased by 25.40%,and the weight and molecular weight of the different amylases were decreased significantly,when the average molecular weight distribution of enzymolysis starch was concentrated around M_W=6.39×10~6 g/mol(the molecular weight was 16.60%lower than that of raw cassava starch),it was suitable for the preparation of microsphere aerogels,and the adsorbability increased significantly.When the p H is 11 and the amount of sodium trimetaphosphate is 2%(starch dry basis),the adsorbability of the crosslinked starch microsphere aerogel is 1.816±0.026 mg/g,which is higher than that of the original starch microsphere aerogel,adsorption capacity increased by 100.60%.(3)Study on the properties of starch microsphere aerogelsThe infrared spectrum analysis showed that the characteristic peaks of starch(cross-linked starch)microspheres aerogel and original starch were similar,but the vibration intensity of the peaks changed,and the group type did not change.The results showed that the cross-linked starch microspheres aerogels were coral-like,which increased the specific surface area and adsorption capacity.The cross-linked starch microsphere aerogels showed excellent pore structure,and the porosity increased to 75.06%,about 2.5 times of the original starch.The results of DSC showed that the endothermic enthalpy of cross-linked starch microspheres aerogels was higher and the degree of retrogradation was higher.(4)Study on the application of starch microsphere aerogelThe cross-linked starch microsphere aerogel was applied to the adsorption of phosphorus in water,and the quasi-primary and quasi-secondary adsorption kinetics,Langmuir and Freundlich isothermal adsorption were simulated.The results showed that starch microsphere aerogels and cross-linked starch microsphere aerogels fit the quasi-second-order adsorption kinetic model,and the adsorption characteristics were mainly chemical adsorption.The effect of cross-linked starch microsphere aerogel on removal of phosphorus was the best.With the increase of the amount of cross-linked starch microsphere aerogel,the removal effect of phosphorus gradually increased,the removal rate of phosphorus was up to 58.48%.Cross-linked starch microspheres aerogel has a bright future in phosphorus removal.Cross-linked starch microsphere aerogel has the best adsorption effect on oil,the adsorption equilibrium time is about 50 min.Cross-linked starch microsphere aerogel can be used for the adsorption and removal of vegetable oil.