Polymer nanocomposites are prepared by dispersing small quantities (0.5-10% by weight) of nano-sized particles which have high aspect ratios (100-1500) and high surface area (in excess of 750-800 m2/g) into the polymer matrices. Polymer nanocomposites offer improvements over conventional composites in mechanical, thermal and barrier properties without substantially increasing the density or affecting the light transmission properties of the base polymer.
The objective of this project is to develop a new process for preparation of polyethylene terephthalate (PET)/montmorillonite (MMT/Na+MMT) nanocomposite and to characterize it. During the study, we tried to disperse natural clay (Na+MMT) in PET polymer monomers by different methods. Natural MMT clay has been chosen to prepare PET nanocomposites because previous studies with organoclays have shown that organically modified clays get thermally degraded at PET preparation and processing temperatures (~280 °C) and because of degradation, PET nanocomposites do not show expected improvement in properties. PET nanocomposites were prepared by dispersing pristine MMT (Na+MMT) clays into ethylene glycol (esterification-ES clay addition) and bishydroxy ethylene terephthalate (polycondensation-PC clay addition). Thermal, mechanical and barrier properties of these nanocomposites have been studied in comparison to those of neat PET.
Differential scanning calorimetry (DSC) results were used to study thermal properties and it was observed that regardless of weight percentage of Na+MMT clay in PET matrices, there were no significant changes in glass transition temperatures (Tg) or melting temperatures (Tm) of the nanocomposites compared to neat PET. It was observed, however, that crystallization rate had increased at higher clay loading because of agglomeration of clay in the PET polymer matrices. For 0.5 wt% ES clay addition PET nanocomposite, tensile strength and tensile modulus observed to be increased by 85% and 92% respectively compared to that of neat PET. As clay percentage increased further, decrease in mechanical properties was noticed because of agglomeration of clay. Compared with neat PET, 0.5 wt% ES clay addition nanocomposite showed 30-40% increase in oxygen barrier properties. Different theoretical models were used to calculate values of tensile modulus and oxygen permeation for given clay content in the PET matrix and compared with experimental values of PET/ Na+MMT nanocomposites. It is concluded that the ES clay addition method resulted into better dispersion of Na+MMT clay into the PET matrices than the PC clay addition method. It is very easy and efficient method to prepare PET/Na+MMT nanocomposites and results into the nanocomposites having better properties than that of neat PET without organic modification of natural MMT.