Modification Of Corn Starch And Preparation And Characterization Of Nanoparticles

There has been much interest in the utilization of starch as a biodegradable andrenewable resources of polymer material. However, the application of native starches isstill limited because of their inherit nature. The various modified methods are used tomodify active hydroxyl groups of starch structure in order to enhance its functionality. Inrecent years, the research on nanomaterial has just been unfolding. Compared with otherartificial polymer material, starch nanomaterials have a series of advantages, especially indrug carrier and adsorbent. In this thesis, the chemical modification of corn starch has beenperformed based on the starch macroscopic structure. The anionic groups are introducedinto starch, which can improve the hydrophilicity of starch and achieve more excellentproperties. Then, taking native starch and modified starch as the raw materials, starchnanoparticles are prepared by nanoprecipitation method. In view of micro level, themolecular aggregated structure of starch are controled. The main obtained results are asfollows:1. Cornstarch as raw material, succinic anhydride as the esterifying agent, succinatestarches were prepared by semi-dry process. The various factors influencing themethodology (RSM) were used to predict the relationship between extent of thesuccinylation and independent variables. A multiple quadratic regression equation wasused to fitting function relation between factors and response values to establishmathematical model. Through analyzing response values the optimal process parameterswas obtained. The analysis of variance analysis(ANOVA) of the response suggested the model was a good fit. FT-IR, XRD and SEM were used to characterize the obtainedsuccinate starches. FT-IR spectra of the modified starches suggested that succinyl moietywas incorporated onto the backbone of starch. X-ray diffraction confirmed that thecrystalline structure of starch was not disrupted after the modification, the esterificationreaction mainly occurred in the amorphous region of starch granules. The SEMobservations revealed that the succinylation did not cause any observable change in themorphology of the starch.2. Starch nanoparticles can be prepared through nanoprecipitation technique by thedropwise addition of starch-DMSO solution to excess nonsolvent. The experimentinvestigated the influencing factors on the preparation of nanoparticles size, i.e., selectionof solvent and nonsolvent, the solvent/nonsolvent volume ratio, the starch concentration,and so on. The dispersion performance of nanoparticles in different medium was studiedand nanoparticles could remain stable over a longer time without any stabilizing agent.The structural of nanoparticles was charactered by dynamic light scattering (DLS),SEM and XRD. Results showed that changing the experimental parameters could beprepared and controled the starch particle size. Nanoprecipitation process led to thenanoparticles without changing the chemical structure of starch granules but changing thecrystallinity pattern and forming spherical particles.3. Using corn starch as raw material and water or alkaline water as the solvent,nanoparticles were prepared by nanoprecipitation. When starch paste was dropwiseaddition to ethanol, starch reassembled polymerization to form nanoprecipitation byintermolecular or intramolecular hydrogen bond interaction. The various factors thatinfluence on nanoparticles size were investigated, including the starch slurry concentration,pH, volume of nonsolvent, concentration of alkali and urea content, the amount ofsurfactant and so on. The structure of nanoparticles was charactered by DLS, SEM andXRD. When the nonsolvent contained Tween80, the prepared particle size would increasewith the increase of the concentration, due to its brought the space steric hindrance. 4. Cationic starch and anionic starch with positive and negative charges weresynthetized by chemical modification，then modified starch nanoparticles were prepared byprecipitation method. This paper studied the preparation and characterization of modifiedstarch nanoparticles. Zeta potential of cationic starch nanoparticles increased with theincrease of the degree of substitution, potential positive showed that the particle surfacewith positive charge. Cationic starch nanoparticles can be used to load or adsorb negativelycharged molecules. However, anionic modified starch nanoparticles had obvious negativecharge. FT-IR showed that the modified starch chemical structure were changed, thetypical characteristic peak could be found in the corresponding region. XRD confirmedthat no crystal peaks were in the nanoparticles pattern. SEM showed that the particles hadaggregation to some extent and dry powder state was more obvious.