Fourier‐transform infrared study of coextrusion‐drawn poly(ethylene terephthalate)

The effects of initial morphology and extrusion temperature on the orientational anisotropy and conformational changes on coextrusion drawing of poly(ethylene terephthalate) (PET) have been determined by Fourier‐transform polarized infrared spectroscopy. The samples were drawn from both amorphous and semicrystalline (50%) PET at 50 and 90°C. A strong influence of coextrusion drawing temperature was observed for overall chain orientation evaluated from the dichroic ratio of the 795‐cm−1 band for the samples prepared from the amorphous state: this dependence was less prominent in samples drawn from the semicrystalline state. Under the same drawing conditions, the dichroic ratio for the 973‐cm−1 trans band for samples prepared from the amorphous state was higher than from the semicrystalline state. Furthermore, in all samples, the relative intensity of this band was almost proportional to the degree of crystallinity. In all samples, the gauche content, evaluated from the 896‐cm−1 band, decreased with increasing draw ratio. However, the dichroic ratio of this band was near unity regardless of draw ratio, initial morphology, or extrusion temperature. From these results it is considered that all gauche units in the amorphous phase are almost isotropic in the extrusion‐drawn samples with overall orientation arising largely from the crystalline chains possessing totally the trans conformation (973 cm−1) in its content. In order to evaluate the deformation mechanism of the coextrusion drawing method, the relationship between the bulk and film surface orientation is also reported.