Structural development and mechanical properties of polyethylene naphthalate/polyethylene terephthalate blends during uniaxial drawing

The blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) were obtained by melt blending at 310°C for 2 min and quenching into an ice water. Mechanical properties and structural formation of unoriented amorphous PEN/PET blend films during drawing at 85, 100 and 130°C were studied by tensile tests and in situ X-ray measurements. The results obtained were compared with the pure PEN and PET. T film could not be drawn due to partial melt at above 100°C and a lower drawing rate but the film blended with PEN was possible to be drawn. The crystallization of PEN/PET blend during drawing proceeded gradually due to the effect of PET at 100°C though the crystalline reflections in the crystallization of pure PEN appeared suddenly by necking. This was evidenced by the formation of α-form crystalline reflections of PEN as detected by in situ X-ray measurements.