| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 101 === In this study, magnesium/aluminum layered double hydroxide (MgAl LDH) with a molar ratio of Mg/Al = 2 was synthesized by the co-precipitation method. In order to improve the compatibility between polymer and LDH, the surface of LDH was organo-modified by sodium dodecyl sulfate (SDS). Poly(butylene succinate) (B100) and its copolyesters with minor amounts of 2-methyl-1,3-propylene succinate (BM90 and BM80) were blended with 1, 3, or 5 wt% of SDS modified LDH, respectively, by the melt intercalation at 120, 100, and 90 °C and at a rotor speed of 50 rpm for 3 min. The physical properties of these biodegradable nanocomposites were characterized before studying their crystallization and melting behaviors. X-ray diffraction patterns and transmission electron micrographs indicated that the LDHs were intercalated and exfoliated, island-type exfoliated, and island-type exfoliated into the B100, BM90, and BM80 matrix, respectively, when the content of LDHs was 3 wt%. TGA results revealed that the thermal stability of the resultant nanocomposites was reduced after the addition of LDH. DSC heating thermograms of the amorphous nanocomposites (at a heating rate of 10 °C/min under nitrogen atmosphere) indicated that the cold crystallization ability and the degree of crystallinity of these nanocomposites decreased as the amount of LDH increased. Dynamic mechanical properties of the fabricated 3 wt% nanocomposites (at a heating rate of 2 °C/min) showed significant enhancements in the storage modulus compared with the neat matrix and 1 or 5 wt% nanocomposites.
The effect of LDH-SDS on the isothermal crystallization behavior of B100, BM90, and BM80 was investigated using a differential scanning calorimeter (DSC) and polarized light microscopy (PLM). The Avrami equation successfully describes the isothermal crystallization kinetics of these nanocomposites and the value of Avrami exponent was between 2.32 and 3.15. The rate constant was significantly reduced when the amount of LDH was 3 wt%. Besides, it was found that the incorporation of LDH-SDS has little effect on the crystalline structure as well as the melting behavior of B100, BM90, and BM80. PLM micrographs revealed that smaller and less perfect crystals were formed in the nanocomposites because of the steric hindrance of the matrix diffusion, i.e. reducing the transportation ability of polymer chains during the crystallization. Finally, the overall results suggest that LDH-SDS at nanometer level acted as non-nucleating agent and decelerated the overall crystallization process of B100, BM90, and BM80.
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