Preparation Of Starch Hydro-alcohol Gel And Porous Starch Material

Starch is a kind of safe,non-toxic and renewable natural polymer material.Porous starch materials have excellent adsorption and biodegradation properties,and have broad application prospects.In this paper,cassava starch was used as raw material and hydro-alcohol system as medium.Porous starch materials were prepared by the sol-gel method and supercritical CO₂drying.The morphology and porous structure of porous starch were characterized by SEM,XRD,specific surface area and pore size instrument.The main research contents are as follows:（1）The effects of hydro-alcohol ratio,solid content,gelatinization time,sol-gel cold storage time,ethanol replacement and replacement time on the volume shrinkage and mass loss rate of starch hydro-alcohol gels were investigated,and the key factors affecting the formation of starch hydro-alcohol gels were studied.（2）The effects of gel solid content,supercritical drying temperature,drying pressure and drying time on the pore structure of porous starch xerogels were studied and the preparation conditions of porous starch xerogels were optimized.（3）Water-absorbent starch microsols were prepared by inverse suspension graft copolymerization,and then the porous starch microspheres were prepared by sol-gel method and supercritical drying method.The effects of monomer ratio,cross-linking agent dosage and supercritical drying conditions on the morphology and porous structure of the microspheres were studied.（4）The adsorption properties of porous starch xerogels and the water absorption of porous starch microspheres were measured.The main conclusion is as follows.The solid content and volume ratio of hydro-alcohol were the key factors affecting the formation of starch hydro-alcohol gels.When the ratio of hydro-alcohol was 19:1,the solid content was 13%,the gelatinization time was 30 min,and the refrigeration time was 5 d,the volume shrinkage and mass loss rate of gel were small,which could form starch hydro-alcohol gels with stable three-dimensional network skeleton,and the gel could also maintain good stability of skeleton structure in the process of ethanol replacement.Under the supercritical temperature of60℃,the pressure of 13 MPa and drying time of 6 h,the porous starch xerogels with micropore structure could be obtained,and the specific surface area and the Pore volume of the porous starch xerogels were 163m²·g^-1and 0.83 cm³·g^-1,respectively.The average pore size was 22.5 nm.SEM analysis showed that adjusting the solid content of gel could improve the grid distribution density of xerogels.XRD results showed that the sporous starch xerogels had a certain crystal structure,which enhanced the stability of starch gels skeleton.The volume ratio of hydro-alcohol 19:1 was used as water phase and cyclohexane as oil phase.The mass ratio of acrylic acid to acrylamide was 8:1 and the amount of crosslinking agent was 0.625%,at the same time,spherical or ellipsoid microgel particles with certain elasticity could be prepared by inverse suspension graft polymerization of starch and acrylic acid and acrylamide,and it was beneficial to obtain porous starch granules with stable particle morphology and stable skeleton structure.The results of SEM and pore structure characterization showed that the suitable drying conditions were helpful to improve the pore structure of porous water-absorbent starch particles.When the supercritical drying temperature was 60℃,the drying pressure was 13 MPa and the drying time was 3 h,the specific surface area and pore volume of porous starch were 32.04 m²·g^-1and 0.117 cm³·g^-1,respectively,and the average pore size was about 13.0 nm.The results of porous starch xerogel adsorption experiment showed that porous starch xerogels had good adsorption performance for soybean oil and Congo red,and the adsorption quantity of soybean oil reached503%,which was higher than that of similar porous starch products.The maximum adsorption quantity of Congo red was 107.41 mg·g^-1,which was in accordance with Freundlich adsorption isotherm model and quasi second order adsorption kinetic model.The maximum water absorption of deionized water and 0.9%Na Cl solution were 521.7 g·g^-1and 72.9g·g^-1,respectively.The adsorption kinetics of porous starch microspheres conformed to the pseudo second order adsorption kinetic model.