ABSTRACT:Blends of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalene dicarboxylate) (PET/PEN) have exhibited properties that are of commercial interest to the packaging industry. Melt processing of PET with PEN results in transesterification reactions. The blend properties are controlled by the kinetics of these reactions. The chemical kinetics equations have been modified to predict theoretical processing temperatures required for different blend compositions to achieve critical levels of transesterification. These values are found to be in close agreement with the experimentally observed values obtained for blends processed in a twin-screw extruder. The critical transesterification temperature is dependent on the equilibrium melting point of the miscible blend and the nature of the PET and PEN resins used for preparing the blend.

Blends and copolyesters of poly(ethylene terephthalate)/ poly(ethylene 2,6-naphthalene dicarboxylate), PET/PEN, have shown promise in high performance container applications. In the first part of this series on the processing characteristics of PET/PEN blends, we investigated the applicability of reaction kinetics to predict the critical transesterification temperature during processing and the influence of the equilibrium melting point of the miscible blends on the critical transesterification temperature. In the present work, we have studied both the rheology and degradation kinetics of the blends 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 PEN in terms of thermal and thermal-oxidative degradation. Addition of low amounts of PEN to PET causes a depression in melt viscosity. A critical composition of 10% PEN by weight is required before an

ABSTRACT:The injection molding and orientation characteristics of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)/ poly(ethylene 2,6-naphthalene dicarboxylate) (PET/PEN) blends are discussed. Injection molding was carried out to produce preforms with good optical clarity. The difference between the processing temperature and the equilibrium melting point of the materials, their crystallizability, and their levels of transesterification are major factors controlling optical clarity in the preforms. Free blow experiments were conducted on the injection-molded preforms to study changes in the blow-up ratio (BUR) as a function of molecular weight, blend composition, level of transesterification, and the difference between the orientation temperature and the glass-transition temperature (T − T g ). Results indicate that for a given value of intrinsic viscosity and T − T g , the blends will require higher stretch ratios than that of PET to achieve equivalent levels of strain-induced crystallization. The BUR for a given blend composition is independent of the degree of randomness after a critical level of transesterification