Preparation Of Functional Starch Nanocrystals And Application In Biodegradable Materials

In this paper, functional starch nanocrystals were prepared by emulsion polymerization and crosslinking reaction. After using the measurements of cold field emission scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Hydrogen nuclear magnetic resonance (1H NMR), the morphology and the structure of functional starch nanocrystals were studied, and the dispersibilities in polar solvents and nonpolar solvents were observed with the method of wettability experiments. The results of cold field emission scanning electron microscope (SEM) showed that particle dispersibilities of functional starch nanocrystals were improved and their particle sizes were enlarged. Fourier transform infrared spectroscopy (FT-IR) and Hydrogen nuclear magnetic resonance (1H NMR) indicated that polystyrene was grafted onto the surface of starch nanocrystals and epichlorohydrin (ECH) was crosslinked with hydroxyl radical on the surface of starch nanocrystals. The consequences of X-ray diffraction (XRD) demonstrated that the crystals of starch nanocrystals after functionalization were not altered. Meanwhile, the employments of wettability experiments illustrated that functional starch nanocrystals were of good amphipathicity.Functional starch nanocrystals/polylactic acid nanocomposites were prepared through blending functional starch nanocrystals with polylactic acid nanocomposites. The utilization of cold field emission scanning electron microscope (SEM) was to reveal interfacial compatibility of functional starch nanocrystals/polylactic acid nanocomposites, and molecular structure and crystal of functional starch nanocrystals/polylactic acid nanocomposites were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Thermal properties of functional starch nanocrystals/polylactic acid nanocomposites were analyzed with the employment of differential scanning calorimetry (DSC) and mechanical performances and water vapor permeability were also investigated. The experimental results concluded that the structure of polylactic acid matrix was unchanged after the addition of functional starch nanocrystals with the content of 1%-8%. The results of differential scanning calorimetry (DSC) confirmed that glass transition temperature of polylactic acid was reduced about 10℃ because of the addition of functional starch nanocrystals, while the influence on melting temperature of polylactic acid was few.Mechanics performance tests signified that when the additive content of crosslinked starch nanocrystals was 3%, the strength and the toughness of functional starch nanocrystals/polylactic acid nanocomposites were increased outstandingly, which compared to pure polylactic acid, tensile strength was increased about 12%, tensile modulus 35%, and breaking elongation 16%. When the additive content of polystyrene grafted starch nanocrystals was 1%, tensile strength and tensile modulus were all improved, however, breaking elongation was nearly unchanged, and tensile modulus was increased all the way along with the increase of additive amount of polystyrene grafted starch nanocrystals, whose value was increased about 20% when the addition was 8%.The morphology of fracture surface of functional starch nanocrystals/polylactic acid nanocomposites displayed that when the additive content of crosslinked starch nanocrystals was 3%, crosslinked starch nanocrystals were dispersed well in polylactic acid matrix and there existed small embossments on fracture surface, which illustrated that there was good interaction between crosslinked starch nanocrystals and polylactic acid matrix, and when the additive amount of crosslinked starch nanocrystals was reached 8%, crosslinked starch nanocrystals were aggregated distinctly in polylactic acid. With the increasing additive amount of polystyrene grafted starch nanocrystals, polystyrene grafted starch nanocrystals were appeared partial phase separation, and glazing holes were arided on the fracture surface.Water vapor permeability exhibited that functional starch nanocrystals reduced water vapor permeability of polylactic acid validly, and were with good gas barrier performance. Water vapor permeability of crosslinked starchy nanocrystals/polylactic acid nanocomposites with the additive crosslinked starch nanocrystals amount of 3% was reduced about 21.17%。...