Preparation And Characterization Of Starch-based Aerogel

In this research,starch-based aerogels were prepared using starch as raw material.Five different starches were used as raw materials,a series of starch aerogels were prepared through the steps of gelatinization,aging,and freeze drying.By controlling the variables of the gelation step in the preparation process,the effects of variables was studied.Cross-linked starch aerogels and starch-cellulose hybrid aerogels were prepared,the properties of aerogel materials were explored,and their application in adsorption was tested.This research used a variety of starches as raw materials to prepare aerogels to explore the effect of starch properties on the structure of aerogels,and tries to select the ideal starch raw materials for the preparation of aerogels.Nowadays,organic aerogels mostly use sodium alginate or cellulose as precursor materials,and there are few studies on starch as a precursor in the preparation of aerogels.This research compared aerogels made of different starches,which were corn starch,waxy corn starch,pea starch,potato starch and waxy potato starch.The results showed that the potato starch aerogel had good water retention,typical aerogel internal structure arrangement,uniform pores,and the best performance overall,which was suitable for further researches.The gelation process was a key step in the preparation process of starch aerogel,which largely determined the internal structure of the aerogels.Control experiments were performed by controlling the refrigerate duration and freezing duration during the gelation process.The experimental results showed that the refrigeration duration has a significant effect on the structure of the aerogel.The aerogel structure was basically completed within 24 hours refrigeration.After that,the internal structure of the aerogel has a lower growth rate.The freezing duration affected the internal structure of the aerogel through the formation of ice crystals.Too long or too short freezing duration was not conducive to the formation of aerogel internal structure.The aging process of starch aerogel was fitted by Avrami equation with gel transmittance index,and the fitting result was good.Then the aerogel was cross-linked to further improve the properties.In the gelatinization process,different ratios of phosphate cross-linking agent were added to study the effect of cross-linking reaction on the structure of aerogel.The results showed that when the proportion of cross-linking agent was 0.1% and the p H of the crosslinking reaction was 9.0,the aerogel has the best internal pore structure.Through TPA texture analysis to measure the mechanical properties of aerogels under different crosslinking conditions,it was found that the cross-linking reaction had a two-stage effect on the structural of aerogels.In the case of low degree of cross-linking,the structure became more stable,and the structure was destroyed to some extent while in the case of higher degree of cross-linking.The cross-linking reaction changed the aerogel structure to affect its swelling characteristics and dye adsorption.Finally,this research also used cellulose to replace part of starches to prepare hybrid aerogels.Specifically,the aerogel was prepared by using cellulose and starch as raw materials and adding N?N?-Methylene-bis-acrylamide as cross-linking agent.The results showed that without adding cross-linking agent,the addition of cellulose had a significant effect on the internal structure of starch aerogel.After the cross-linking agent was added,the aerogel had the densest pore structure under the condition of 3% of the cross-linking agent,and theoretically can provided the largest specific surface area.The addition of cellulose changed the internal structure of the aerogel,and the cellulose itself also provided a larger specific surface area,so that the adsorption capacity of the aerogel increased as the amount of cellulose replacement increased.Although the addition of the cross-linking agent improved the structure,it inhibited the water swelling of the aerogel and increased the aerogel's adsorption capacity first and then decreased.Finally,a test of vitamin E loading was carried out.The results showed that all aerogels showed much higher vitamin E loading capacity than native starch granules,but the aerogel which contained starch,cellulose,and cross-linking agent of 5%,1%,and 3% respectively(S5C1B3),had the lowest loading capacity for vitamin E,while the cross-linked starch aerogel had the highest loading capacity for vitamin E.