The synthesis of polyethylene terephthalate (PET) has been comprehensively reviewed. Various catalyst compounds based on zinc with different chelating ligands have been synthesized and structurally characterized. All were trialled in PET synthesis and compared with the standard antimony catalyst in both melt and solidstate polymerizations. Among those exhibiting some activity, zinc catechol acetate showed higher catalytic activity, optical clarity and lower colour and DEG content than standard. All zinc compounds were slower than the standard in the solid-state polymerization. Thermal characterization of the polymer samples by DSC showed comparable T g and slightly lower T m for zinc catalysts polymers compared with antimony. Thermogravimetric analysis (TGA) revealed higher thermal stability of the polymer catalyzed by zinc complexes. A part of the work was to synthesize a new nitrogen containing ligand to prevent intermolecular binding and promote solubility. Though the desired compound was not obtained, a new I-pot reaction in which four new bonds were made has been discovered. Study of the mechanism of catalyzed PET polymerization through model molecules was marred by difficulties in formation of crystalline complexes of them with zinc. PET -Clay catalysis and nanocomposite have been investigated. A naturally occurring clay sample was modified with zinc ions and/or quaternary alkyl ammonium salts and tested for catalysis and Clay-PET nanocomposite formation. The zinc-organic modified clay showed catalytic activity higher than antimony. Discoloration as normal in polymer-clay nanocomposite systems was observed. Dispersion of the clay in the PET matrix was investigated by W AXD, SEM and TEM and demonstrated as having partially exfoliated layers. Gas permeability of the nanocomposite showed only minor improvement due to incomplete exfoliation, lack of orientation of intercalated layers, and higher DEG content. Thermal properties by DSC showed a reduction in T g and significant reduction in Tm, also due to the higher DEG content (6.39%). TGA results showed a comparable thermal stability between the nanocomposite and the neat sample. Mechanical properties were investigated. The PET-Clay sample exhibited ca. 9% higher flexural modulus compared with the standard sample, and a reduction ca. 30 and 34% in the storage modulus and loss modulus respectively due to the higher content of DEG.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:627991 |
| Date | January 2009 |
| Creators | Alfarhood, Bander F. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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