Studies On Transesterification, Structure, Properties Of PET/PEN Melt Blended Materials

Poly(ethylene-2,6,-naphthalate) (PEN) is a newly developed polyester. The chemical structure of PEN can be described by replacing the benzene ring in poly(ethyiene terephthalate) (PET) with the stiffer naphthalene ring. Due to its high performance, PEN is expected to be an excellent candidate for a variety of industrial applications. When PEN and PET were melt blended, however, transesterification between two homopolymers would take place and the resultant product may be not crystallizable. This is not appropriate for modifying the physical properties of PET/PEN blended samples. In this study, Strategy for inhibiting the ester exchange reaction was examined firstly. Both chemical and physical methods were used to achieve this goal. Their effect was studied in detail.Transesterification reaction, structure and properties of PET/PEN melt blended samples were studied by 1H NMR, WAXS, DSC, DMTA and mechanical tests. The result of 1H NMR measurement indicated that it is difficult to inhibit the transesterification by adding various chemical reagents or changing the content of reagent in PET/PEN melt blended system. The ratio of two polymers in the melt blended samples did not affect the level of the transesterification, but the ester exchange reaction was controlled by the selected melt blending time and blending temperature significantly. When melt blending temperature was selected at 300癈 and melt blending time was less than 2 min, The transesterification between PET and PEN molecules almost did not take place. Such prepared PET/PEN blended samples were hot drawn and the structure of two series samples with and without the hot drawing was studied. The result of WAXS and DSC measurements showed that the PET/PEN melt blended samples were amorphous before being hot drawn. But they were able to be crystallized, when they were heated and/or hot drawn. The results of mechanical test showed the properties of PET/PEN melt blended samples were associated with the composition of PET/PEN melt blended samples. When the content of PEN in the melt blended samples was increased, the mechanical properties of samples were modified and its modulus was increased. The modulus of PET and PEN homopolymers was found to be higher than the melt blended samples, It may be attributed to that the crystallization of PET/PEN melt blended samples were not superior to pure PET and PEN. The modulus of PET/PEN melt blended samples, however, was almost proportional to the content of PEN in the melt blended samples.