Orientation of uniaxially stretched poly(ethylene naphthalene 2,6‐dicarboxylate) films by polarized infrared spectroscopy

Abstract

Poly(ethylene naphthalene‐2,6‐dicarboxylate) has been uniaxially stretched at different draw ratios and at two different temperatures below and above its glass transition (Tg ∼ 120 °C) respectively, at 100 and 160 °C. Crystallinity has been evaluated from calorimetric analyses and compared to the values deduced by FTIR spectroscopic data. As expected, the obtained results are quite similar and show that films stretched at lower temperature (100 °C) are more crystalline than those stretched at 160 °C. Optical anisotropy associated with orientation has been evaluated by birefringence and show that films stretched at 100 °C are more birefringent than those stretched at 160 °C as a result of a higher chain relaxation above Tg. Polarized FTIR was also performed to evaluate the individual orientation of amorphous and crystalline phases by calculating dichroic ratios R and orientation functions 〈P2(cos θ)〉 and also show that amorphous and crystalline phases are more oriented in the case of films stretched below Tg. Nevertheless, the orientation of the amorphous phase is always weaker than that of the crystalline phase. Films stretched at 100 °C show a rapid increase in orientation (and crystallinity) with draw ratio and 〈P2(cos θ)〉 reaches a limit value when draw ratio becomes higher than 3.5. Films drawn at 160 °C are less oriented and their orientation is increasing progressively with draw ratio without showing a plateau. A careful measurement of the IR absorbance was necessary to evaluate the structural angles of the transition moments to the molecular chain axis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1950–1958, 2007

Effect of orientation and crystallization on dielectric and mechanical relaxations in uniaxially stretched poly(ethylene naphthalene 2,6 dicarboxylate)(PEN) films

“…Films drawn at 160°C exhibit a linear crystallinity evolution with draw ratio [15,20]. On the contrary, as seen in Table 2, the crystallinity ratio of films drawn at 100°C rises immediately to a plateau value when the draw ratio becomes higher than 3.…”

“…As displayed in Table 2, PEN samples drawn below T g (100°C) are more crystalline than those stretched above T g (160°C) in relation with a higher chain orientation revealed by birefringence and polarized infrared analysis [28] and also pole figures deduced from X-ray diffraction (not shown here). For films stretched in the glassy state, a decrease of T g is representative of a large increase of molecular mobility.…”

“…The T g evolution of PEN films stretched below and above T g has been detailed in previous works [15,20]. As can be seen in Fig.…”

“…4. The F RAF has been evaluated from DRS data using the following equations: An increase of rigid amorphous fraction is generally observed when crystallinity increases [15,20] except for values estimated from b-relaxation that show a negligible F RAF evolution. Note that rigid amorphous fractions could not be estimated in the case of films drawn in the glassy state because they exhibit a highly mobile deformed amorphous state that can not be compared to the amorphous sample (i.e.…”

“…The experimental draw ratios obtained are gathered in Table 1. The experimental procedure to determine these draw ratios have been described elsewhere [15,20].…”