Acetylation Modification Of Starch Substrate And Preparation And Characterization Of Nanometer Microspheres

Due to the degradability and reproducibility of starch,researchers selected it as one of the important high polymer materials.However,the inherent characteristics of starch restrict it in practical application.Via various modify methods to decorate the active polyhydroxy functional groups on the starch structure,its applicability was enhanced and subsequently the application scope for raw material of starch can be effectively extended.Acetylation is one of the most common methods,which employs the ester group to the three alcoholic hydroxyl groups on the starch molecule to display its lyophobic characteristic.With suitable process technologies,the acetylated starch can be made into thin film,which owns the advantages of hydrophobicity and biodegradability.Furthermore,with method of precipitation,the acetylated starch can be made into micro and nano pellet,which obtains excellent performance on the drug carrier and absorbent and earns more competitive advantage and application scope when compared with other kinds of high polymer materials.In this work,the acetylated hydrophobic starch was acquired and the influence of reaction condition on its degree of substitution was determined via single factor experiment.The application of acetylated starch was also studied.On the one hand,the acetylated starch was made into micro and nano pellet with method of precipitation.Via comprehensive analysis on its structure and surface topography,the variations of starch molecule structure,crystal form and morphology features in the formation process were therefore determined.On the other hand,the acetylated starch was prepared into lyophobic thin film with tape casting process.With the measurement and analysis on the mechanical properties and lyophobic characteristic of thin film,the direct impacts of substitution degree of acetylated starch on the mechanical tensile property,transparency and lyophobic performance of thin film were finally determined.The specific investigations in this work can be shown as follows:1.The acetylated starch was obtained with corn starch as raw material,acetic oxide as esterifying agent,and methanesulfonic acid as catalyst.The influences of reaction-consuming time,reaction temperature and rotation speed on the DS of acetylated starch were determined.With the reaction-consuming time 3h,reaction temperature 75 ? and rotation speed 750 rpm,the acetylated lyophobic starch was acquired with DS=2.89.With the aid of FT-IR,XRD and SEM,the structure analysis of classical sample was performed.The results show that when DS=2.89,the OH stretching region of samples was almost totally replaced and the strong lyophobic characteristic of starch was shown.The crystal form of starch was transformed from A type to V type.In the inner part of starch,the crystal region was partially and totally transformed into amorphous region.2.With nanoprecipitation method,the acetylated starch with different substitution degrees was made into starch nano pellet.Structure analysis for classical samples was performed with the aid of FT-IR,XRD and SEM.In the preparation process of nano pellet of acetylated starch via nanoprecipitation method with DMSO as solvent,the chemical structure of molecular chain of starch was not changed.However,the crystal form was damaged and therefore,all the nano pellet of acetylated starch showed V type,which implied that the crystal region has been totally transformed into amorphous region in the inner part of acetylated starch.With the increase of substitution degree,dispersibility and size homogeneity were further improved as well as smooth surface was achieved.All of them were made into nano pellets.3.The acetylated starch was made into lyophobic thin film with tape casting process.The mechanical tensile property,transparency and lyophobic characteristic were analyzed with electronic universal texting machine and spectrophotometer,etc.Testing results showed that the tensile strength was further improved with the increase of substitution degrees of starch.However,a crosscurrent trend was observed for elongation at break.With the increase of substitution degree,the film forming quality and homogeneity for the lyophobic thin film were further improved.Furthermore,smooth surface was achieved and the lyophobic characteristic was enhanced.