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Improvement of Physical and Mechanical Properties of Poly (Ethylene Terephthalate) (PET) by Incorporating Metal-organic Framework (MOF) Nanoparticles

Samieifakhr, Mohammad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54607 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Shojaei, Akbar; Molavi, Hossein
  7. Abstract:
  8. Over the past decade, MOFs have been extensively studied due to their very high specific surface area and porous structure. Among a wide range of MOFs, UiO-66 has produced widespread attention for its excellent solvent resistance and high thermal stability. This nanoparticle is formed by 12 coordinates between Zr6O4(OH)4 unit and terephthalic acid ligand, and it seems that the similarity of its organic ligand with one of the PET-forming monomers makes them highly compatible. In this study, for the first time, the role of UiO-66 nanoparticles in improving the amount and rate of crystallization and mechanical and rheological properties of PET was investigated using the melt mixing method. For this purpose, samples containing 0.25 wt%, 0.5 wt%, 1 wt%, and 2 wt% of UiO-66 nanoparticles were prepared via melt mixing in a co-rotating twin-screw extruder and a compression molding machine. FESEM images prepared from the samples show the uniform dispersion of nanoparticles inside the polymer matrix and the success of the melt mixing method in the proper dispersion of the nanoparticles. DSC results show that the degree of crystallinity increased with the addition of UiO-66. The sample containing 1 wt% of nanoparticles with 38.1% crystallinity had the highest increase compared to pure PET with 31.7%. Similarly, the rate of crystallization is significantly increased by decreasing the crystallinity half-life, indicating that UiO-66 acts as a nucleating agent to create heterogeneous nucleation and increase the crystallization rate. Along with the increase in crystallinity, the modulus has also increased so that in nanocomposite containing 2 wt% of nanoparticles, we saw about 40% increase in elastic modulus. The elongation at break of nanocomposites increased by adding up to 0.5 wt% of nanoparticles and then decreased. A significant increase in elongation at break at 0.5 wt% is consistent with a significant decrease in Tg temperature. This indicates a very high softening of the sample, which could be attributed to the optimal spacing of nanoparticles in the polymer matrix. The impact strength of PET / UiO-66 nanocomposites is significantly increased by adding up to 0.5 wt% and then decreased. Still, the 2 wt% sample also has a higher impact strength than the pure polymer. The glass transition temperature and elongation at break results illustrated that UiO-66 with its flexible structure, has acted as a toughening agent. The storage and loss modulus show similar rheological behavior, decreasing with the increasing amount of nanoparticles at all frequencies. It is observed that viscose behavior is dominant in all frequencies investigated. The reduction of the storage modulus with increasing UiO-66 indicates the connection between polymer matrix chains and nanoparticles and their chemical compatibility. The complex viscosity of nanocomposites has been reduced by increasing frequency, indicating non-Newtonian and shear thinning behavior. The further decrease in viscosity with the increasing amount of nanoparticles was due to the flexible and porous structure of UiO-66, which resulted in easier deformation. Finally, the 0.5 wt% sample can be considered optimal due to the better melt mixing and uniform dispersion on UiO-66 nanoparticles, more flexible structure and maximum toughness, and particular rheological behavior
  9. Keywords:
  10. Nanocomposite ; Polyethylene Terephthalate ; Metal-Organic Framework ; UiO-66 Hybrid Nanoparticles ; Melt Mixing Conditions

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