Preparation And Properties Of Starch Nanocrystals/Natural Polymer Composite Films

Polymer-matrix nanocomposites, as an important part in nanotechnology field, are developing rapidly and have potential applications. Especially, the technology of nano-particles prepared from natural polymer opens a new research direction for nanocomposites. In this thesis, the starch nanocrystals were prepared from natural starch. Then, the environment-friendly starch nanocrystals/soybean protein isolate(SPI) and starch nanocrystals/Carboxymethyl chitosan (CM-CH) composite films were prepared by solution blend method. The structures and properties of the nano-composite were studied.Starch nanocrystals were prepared by sulfuric acid hydrolysis of waxy maize amylopectin. The remaining starch granules after acid hydrolysis were characterized by X-ray diffraction(XRD) and Transmission electron microscopy (TEM). The results indicated that the crystallinity of granules increases and the crystallite size and interplanar spacing decrease with the increasing of acid hydrolysis time. Starch nanocrystals with size between 40nm to 100nm and crystallinity of 62.97% were obtained after 6 days of hydrolysis. The yield of starch nanocrystals is about 24.1wt%.The Starch Nanocrystals/Soybean Protein Isolate(SPI) composite films filled with different content of starch nanocrystals were prepared by solution blend method, and their properties were studied, the results showed that when the content of starch nanocrystals was lower, they had a better improvement and reinforcement function for properties of the composite films, such as the mechanical properties and barrier properties.The FT-IR analysis of composite films suggested there was strong interaction between the nanocrytal and SPI. When the starch nanocrystals content was 20wt%, the tensile strength(TS) of composite films increased by 7 times, elongation at break(EB) is 70.6%. The films'hygroscopicity and Water Vapor Permeation ratio reduced to the lowest and displayed good barrier properties.Starch Nanocrystals/Carboxymethyl Chitosan composite films were prepared. The structure of composite films was characterized by FT-IR, XRD and SEM. The results indicated there was strong interaction and good compatibility between starch nanocrystals and carboxymethyl chitosan in composite films. The transmittance of composite films decreased with the increasing of starch nanocrystals content, while the starch nanocrystals content was 40wt%, the transmittance decreased to the minimum value 69.3%. The mechanical properties of composite films were improved with filled proper starch nanocrystals. When the starch nanocrystals content was 30wt%, the tensile strength(TS) of composite films approached 28.8MPa, which was the two times higher than that of the carboxymethyl chitosan film without filling starch nanocrystals, and the elongation at break(EB%) of composite films was 92.4%, that indicated composites films had a good extensibility. The barrier properties of composite films were improved with the increasing of starch nanocrystals content.