Preparation Of Layered Double Hydroxides And Carbon Nanotubes / Polymer Nanocomposites, Structure, And Performance Studies

Polymer/inorganic nanocomposites possess unique and excellent mechanical, thermal, electronic, optical and physico-chemical properties, typically not shared by its conventional microscopic counterparts, which is attributed to the fine and nanoscale dispersion of inorganic nanoparticles in polymer matrices. Moreover, unexpected properties are obtained from the addition of inorganic nanoparticles to a polymer matrix. Therefore, the preparation /fabrication and utilization of high performance and multifunctional nanocomposites are meeting new chances and great challenges.In this thesis, both layered double hydroxide (LDH) and carbon nanotube reinforced polymer nanocomposites were studied. On the one hand, the preparation and characterization of polymer/LDH nanocomposites were described. The fabrications of nylon 6 (PA6)/CoAl-LDH binary nanocomposites and poly(s-caprolactone) (PCL)/ CoAl-LDH binary nanocomposites were prepared via two methods:in situ polymerization and solution intercalation. In addition, high performance nylon 6/CoAl-LDH/CNT ternary nanocomposites were also prepared through a synergistic effect of 2D LDH nanoplatelets and 1D CNT. On the other hand, the multipurpose organically modified CNT was achieved via a combination of the 1,3-dipolar cycloaddition reaction and Curtius rearrangement, and its application of this novel functionalization approach of CNT to the preparation of nylon 6 nanocomposites was explored.The main contents and conclusions of the thesis are as follows: 1. Firstly, the organo-modified CoAl-LDH (OCoAl-LDH) was prepared. Then, a series of novel exfoliated CoAl-LDH/nylon 6 nanocomposites with different CoAl-LDH loadings have been successfully obtained via in situ polymerization. Compared with neat PA6, the tensile modulus, the yield strength and the hardness of the nanocomposites were improved by about 100% 75%, and 25%, respectively, with incorporation of only 1 wt% CoAl-LDH. Moreover, the thermal stability of exfoliated PA6 nanocomposites was also improved because of fine dispersion of CoAl-LDH nanolayers in the matrix.2. The highly exfoliated CoAl-LDH/polycaprolactone (PCL) nanocomposites were successfully synthesized by simple solution intercalation of PCL into the galleries of organically modified CoAl-LDH under refluxing in cyclohexanone. The TGA, dynamic FTIR spectra and 2D-IR were used to study the degradation mechanism of PCL/LDH nanocomposites. It has been found that the observed decrease of degradation temperature for the nanocomposites is mainly because a lot of hydroxyl groups on the LDH surfaces can hydrolytically cleave the ester groups of PCL chains. The DSC data showed that the exfoliated LDH nanolayers have strong heterogeneous nucleation effect on the crystallization of PCL thus leading to an increase of the crystallization rate.3. The nonisothermal melt crystallization behavior of neat PCL and its LDH nanocomposites and the effect of LDH incorporation on the crystalline morphology of PCL were extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. Both the Ozawa approach and the Avrami equation failed to describe the nonisothermal crystallization kinetics behavior of PCL and its nanocomposites, whereas the combination of Avrami and Ozawa analyses (Mo model) can be successfully employed to describe the nonisothermal melt crystallization behavior of neat PCL and the nanocomposites. The results revealed that very small amounts of LDH could accelerate the crystallization process of PCL and the increase of the crystallization rates was attributed to the nucleating effect of the LDH nanoparticles. Polarized optical microscopy (POM) observations also support the DSC results. In addition, the activation energies of nonisothermal melt crystallization for neat PCL and its LDH nanocomposites were determined using Kissinger, Takhor and Augis-Bennett models.4. The preparation of nylon 6-functionalized SWNT was accomplished by using the grafting-from strategy via four-step processes:(1) the reaction of N-methylglycine and 3,4-dihydroxybenzaldehyde can introduce phenolic substituents onto SWNT via a simple and fast microwave-assisted method (and the resulting product was denoted as SWNT-f-OH); (2) SWNT-f-OH and trimellitic anhydride were stirred at room temperature, the resulting product was denoted as SWNT-f-COOH; (3) caprolactam-functionalized SWNT was obtained through the Curtius rearrangement in the presence of caprolactam, the resulting product was denoted as SWNT-f-caprolactam; (4) the nylon-functionalized SWNT can be finally produced through anion polymerization between SWNT-f-caprolactam and caprolactam. TGA data showed that the final product, nylon-functionalized SWNT, possesses a grafted polymer weight percentage of ca.45%.5. High-performance nylon 6/LDH/CNT ternary nanocomposites have been successfully prepared by in situ polymerization. A uniform distribution and fine dispersion for both CNT and LDH in nylon 6 have been achieved and evidenced. A significant synergistic effect of both 2D LDH nanoplatelets and 1D CNT on reinforcing nylon 6 matrix has been observed. With incorporation of 1 wt% LDH and 0.5 wt% CNT, the tensile strength and Young's modulus are significantly improved by about 128% and 230%, respectively, compared with neat nylon 6. This reinforcement effect could be understood by assuming the formation of 3D conjugated nanofiller networks (with 1D CNT inserted into the interlayer spacing of 2D LDH nanoplatelets), as indicated by melt rheological measurements.