A study of structure evolution during deformation and subsequent heat-setting process in poly(ethylene terephthalate) and poly(ether imide) binary miscible blends

Fundamental aspects of the structure evolution during the process of uniaxial stretching of Poly(ethylene terephthalate) (PET)/Poly(ether imide) (PEI) blend films and the subsequent process of heat-setting have been investigated using a variety of characterization techniques.; Refractive index results reveal that (i) PET/PEI 100/0, 90/10, and 70/30 films are optically transversely isotropic on stretching in uniaxial free width (UFW) mode; (ii) however, uniaxially stretched 100/0 films tend to deviate from transverse isotropy due to the increased levels of preferential alignment of phenyl groups at high stretch ratios (∼5). This preferential orientation of phenyl planes is disrupted in the presence of PEI molecules; (iii) 100/0 and 90/10 are anisotropic, stretched in uniaxial constant width (UCW) mode while 70/30 retains transverse isotropy; (iv) both pure PET and PET/PEI films follow Cauchy's dispersion relation.; Based on a consistent correlation among the results, the structure evolution in the films during stretching at respective T_g + 10°C is envisioned by three distinct categories: PET/PEI 100/0, 90/10, and 70/30. In 100/0, amorphous orientation takes place rapidly, followed by rapid crystallization. In 90/10, PET and PEI intermingled molecules keep orienting steadily with suppressed crystallization of PET due to both the dilution effect and insufficient stress level to overcome it.; Prior to the study of structure evolution during the heat-setting process, a new concept on the deformation temperature has been introduced for miscible blend films in order to sort out the effect of stress level on the structure evolution by imparting the apparently similar deformation behavior to the films. Using this concept, not only did we generalize the deformation behavior of the films with different PEI composition, but also we could demonstrate that viscosity increased with increasing PEI at the respective T _g's.; During the heat-setting process, crystallization is dominant in 100/0, achieving the major portion of the crystallinity at early stages, and hence the c-axis orientation tends to remain constant throughout the heat-setting process. However, due to the dilution effect in 90/10 and 70/30, crystallization is suppressed and relaxation becomes, dominant at early stages. As a result, relaxation occurs simultaneously with crystallization throughout the heat-setting process, giving rise to a decrease in the c-axis orientation as the heat-setting time increases. The dilution effect in 70/30 induces the disruption of (100) planes, which allows for the transverse isotropy. (Abstract shortened by UMI.)...