Preparation and Characterization of Layered Silicate Polyethylene Terephthalate Nanocomposite by in Situ Polymerization

A series of experiments on the synthesis of poly (ethylene terephthalate) (PET)/organo-montmorillonite (MMT) nanocomposites were carried out in a pressurized reactor using alkyl ammonium exchanged smectite clays, (Closite ۳۰B).Given the degradation of organoclay at high temperatures, the in situ polymerization process was carried out at mild temperatures ranging from ۲۱۰ to ۲۳۰°C for ۴۰ minutes followed by solid state polymerization (SSP) at ۲۴۵°C for ۳۰ minutes at a pressure of ۵ mbar. The nanocomposites were prepared using different weight percentages (۱-۵)of organoclay. The reaction completed when the mixing torque ceased to change as recorded by the auto data acquisition system of the pressure reactor. The DSC analysis provided information on the course of the thermal characterization of the PET nanocomposites versus regular PET. As shown by the results of DSC cooling scan, all the PET nanocomposite samples have higher crystallization temperatures (Tc) and faster crystallization rates (∆HC/t) compared to regular PET. Furthermore, the opposite behavior is observed for t۱/۲. This is due to the fact that the nucleation of organoclay nanoparticles reduces the crystallite size in the PET nanocomposites. The XRD results indicated that the peaks in the ۲θ angle from ۱° to ۷° were disappeared, which is an indication of an exfoliated MMT.In addition, The atomic force microscope (AFM) results showed broken mirror like lamellae, confirming the exfoliated results of the XRD analysis. The peaks are indexed according to the ۲θ angle from ۱۰° to ۳۰° known assignments of the triclinic unit cell dimensions for PET. The comparative crystallite size of the PET nanocomposites samples (۱-۵%wt organoclay) can be deduced from the peak ratio change of ۲θ angle from ۱۰° to ۳۰°. Heat distortion (or deflection) temperature (HDT) was enhanced by increasing the amount of organoclay in PET nanocomposites compared to regular PET. The tensile test results of ۲%wt organoclay show an increase of ۵۸% in the tensile strength of this sample. As a result of MMT agglomeration, due to the high temperature instability of Closite ۳۰B, the relative oxygen pressure drop data shows fluctuations. However, as an overall trend, PET nanocomposite gives about ۵۰% greater reduction in O۲ pressure drop or relative oxygen permeability compared with a homo structure.

Keywords:

Poly (Ethylene Terephthalate) , Montmorillonite , Nanocomposite , Exfoliated , In situ Polymerization