| With the deterioration of global climatic conditions and the prominence of environmental problems,how to develop and utilize biodegradable materials is extremely important to reduce environmental pollution and promote sustainable development.Starch is a kind of natural polymer widely existing in plants,which is rich in sources,green,non-toxic and cheap,and has a wide range of applications in industrial production.Starch nanocrystal(SNC),a novel two-dimensional nanometer material,is obtained by acid hydrolysis,and has the advantages of high modulus,high strength,high crystallinity and biodegradability.Therefore,it can be used as a good modification reagent to improve the properties of the polymer.Poly(fi-hydroxybutyrate))(PHB)is an energy substance in microorganisms,which has good biocompatibility and biodegradability,can be used as environment-friendly medical materials and food packaging materials.Therefore,the biodegradable PHB can be compounded with SNC in order to prepare fully biodegradable green composites,and the crystalline structure and sphero-crystal morphology of PHB can be controlled by adjusting the surface properties of SNC.This thesis focuses on the preparation and modification of starch nanocrystals and the structure and properties of starch nanocrystals/poly(?-hydroxybutyrate)composites,in order to clarify the effect of starch nanocrystals on the structure and properties of polymer composites.The specific contents are as follows:The main results are as follows(1)Starch nanocrystals were prepared by sulfuric acid hydrolysis,and the hydroxyl groups on the surface of starch nanocrystals were acetylated.The changes of morphology,structure and properties of starch after acidolysis and acetylation modification were studied The morphology of corn starch,starch nanocrystals and acetylated starch nanocrystals were observed by scanning electron microscope(SEM)and transmission electron microscope(TEM).The chemical structure and crystal structure were studied by FT-IR,1H-NMR and XRD,and the surface properties,thermal properties and mechanical properties were studied.(2)Poly(?-hydroxybutyrate)/starch nanocrystalline composites were prepared by solution blending.The effects of starch nanocrystals and acetylated starch nanocrystals(aSNC)on the crystallization behavior of PHB were studied.In addition,the different roles of the two kinds of nanoparticles in the nucleation and spherulite growth of PHB were well explained by the secondary nucleation theory,and the interfacial interaction between the two nanoparticles and PHB matrix was evaluated by calculating the interaction energy parameters.The reasons for the different effects of SNC and aSNC on the crystallization behavior of PHB were analyzed from the aspects of crystallization temperature Tc,crystal structure,spherulite morphology,banding change and so on(3)PHB/PBS blends and PHB/PBS/SNC ternary composites were prepared by solution blending and melt extrusion.The changes of two-phase morphology,crystal structure,crystallization temperature and mechanical properties of PHB/PBS blends before and after adding SNC were studied.The dispersion of SNC in PHB/PBS blends was studied,and the interaction between SNC and PHB and PBS was further discussed.The addition of starch nanocrystals has different responses to the crystallization temperature of PHB and PBS However,the crystallization temperature of PHB is highly dependent on the SNC loadings,whereas that of PBS not.In this paper,a new method for evaluating the dispersion of nano-modified fillers in blends is proposed:the dispersion of nanoparticles in incompatible phases can be predicted by studying the dependence of polymers on crystallization temperature.This method is suitable for semi-crystalline incompatible blends filled with nanocrystals. |
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