The effect of reaction processing on the physical, morphological, and barrier properties of poly(ethylene 2,6-naphthalene dicarboxylate)/poly(ethylene terephthalate) blends

PET/PEN blends have been considered as a new material, combining the economic advantages of PET with the high barrier and thermal properties of PEN, which can extend the limitation of PET packaging applications. However, PET and PEN are inherently incompatible. Extrusion of PET/PEN blends above the melting temperature of both polymers results in transesterification, which was shown to enhance the miscibility of the blend and improve both the clarity and barrier properties of the resultant films. This research focused on the study of the effect of the processing conditions and the blend composition on the transesterification reaction. In addition, the effect of degree of transesterification, the blend composition, and the orientation on the blend characteristics was also studied.; The results showed that the primary factors controlling the transesterification reaction were blending time and temperature, whereas the composition of the blends was found to have little or no effect on the interchange reaction.; The PET/PEN blends with a degree of transesterification of at least 6% were miscible, homogeneous and optically clear. Further the transesterification reaction had less of an effect on the T_g, the barrier, and the mechanical properties. However, the T_m, % crystallinity, density, and molecular weight average were dependent on the degree of transesterification, regardless of how this degree of transesterification was achieved.; The blend composition was a very important factor controlling the thermal, mechanical, and barrier properties of the blends. A depression of the T _m, % crystallinity, and molecular weight was found, when a small amount of PEN was added to the PET rich phase, or vice versa. The T_m, % crystallinity and molecular weight average were lowest, when the PEN composition was 40–50 mole %. Moreover, the density of the blends decreased, as the PEN composition increased. However, the T_g, the gas barrier properties and the tensile strength of the blends improved when the PEN composition increased.; Orientation process enhanced the barrier and the mechanical properties of the blend films. The water vapor, the oxygen, and the carbon dioxide barrier properties of the PET/PEN blend films improved 1.5–2 times, as the blend films were 3 x 3 biaxially oriented. The tensile strength of the oriented blend films was 4 times greater than that of the non-oriented blend films. Moreover, oriented PEN, and the oriented blend films were flexible, while the non-oriented films were very brittle.