Processing characteristics of blends of Poly(ethylene terephthalate) (PET) and Poly(ethylene naphthalate) (PEN)

Blends of Poly(ethylene terephthalate) (PET) and Poly(ethylene naphthalate) (PEN) have exhibited properties that are of commercial interest to the packaging industry. Melt processing of PET with PEN results in transesterification reactions. The kinetics of these reactions as well as their effect on blend properties like glass transition temperature, crystallization and haze has been widely studied. These studies show that the blend properties become independent of the reaction once a certain critical level of transesterification has been achieved. However, there is little data available on the injection molding and stretch blow molding characteristics of these blends. In this dissertation, it was proposed to study the processing characteristics (primarily stretch blow molding) of the PET/PEN blends after the blends attain the critical transesterification level. Modifications to the chemical kinetic equations have been made to predict a theoretical processing temperature for different compositions of the blends to achieve critical transesterification. These values were found to be in close agreement with the experimentally observed values when blends were processed in a twin screw extruder. The processes of extrusion and injection molding involve the melting of the polymer at high temperature. Subsequently, an understanding of the melt rheology and the different degradation processes that occur is important. An instron capillary rheometer was used to study the melt viscosity as a function of temperature and shear rate. The flow behavior of blends containing 10, 20 and 40% PEN by weight was very similar to that of PET. A model equation has been developed to describe the dependence of the melt viscosity on shear rate and temperature. Melt viscosity measurements using a cone and plate viscometer showed that addition of low amounts of PEN to PET causes a depression in the melt viscosity. A critical composition of 10% PEN by weight is required before we observe an increase in blend viscosity.; Degradation kinetics (thermal and thermal-oxidative) was studied as a function of material composition. Melt viscosity loss was measured as a function of time and temperature. Activation energies for degradation were calculated from experimental data. Results show that blends containing a minimum of 10% PEN by weight are as stable as pure PEN. Optically clear performs were injection molded from the PET/PEN blends. The optical clarity is primarily dependent on the processing temperature, the level of transesterification in the blends and the crystallizability of the polymers.; Free blow experiments were conducted to study the strain hardening property of the blends. The blow up ratio for the blends was modeled as a function of the PEN composition, molecular weight, the difference between the stretching temperature and the glass transition temperature and the degree of randomness in the blends. Results show that for a given IV, the blow up ratio increases with increasing PEN composition in the blends. In order for us to maintain the same blow up ratio as that of PET of a given molecular weight, the blends must have higher molecular weights greater than PET. Finally, the preforms were stretch blow molded into containers using a conventional PET mold and the physical properties of the containers made from different materials were studied to optimize the resin properties.