Polyethylene uniaxially oriented

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

The anisotropic master creep curves, and their shift factors for uniaxially oriented semicrystalline polyethylene terephthalate) (PET) are calculated and measured [35] in Figs. 12 and 13. Crystal orientation and shape have a strong effect on the... 

Solid-state extrusion has also yielded some of the highest properties for uniaxially oriented morphologies. Tensile moduli (210 GPa) nearing the theoretical value of a polyethylene single crystal have been attained.f ... 

A uniaxially oriented sample of linear polyethylene (77) also showed the y maximum. In addition, a study (48) has been made on a rodlike sample of Marlex 50 prepared by heating at 175°C. for 119 hours under 40,000-p.s.i.g. pressure it is presumed that this treatment leads to a sample containing principally extended chains. Using a transverse vibration... 

Comment on the work required to orient polyethylene in the solid state (using the data in figure 8.13) compared with that to orient the melt (as in the blown film process) then crystallize the material. Hence explain why oriented polymer film is usually made by the latter process. Comment on the ease of achieving very high levels of uniaxial orientation in the two processes. 

The crystallisation from strained melt as for instance in a blown film or in the jet during fibre spinning produces a row nucleated structure. " Linear nuclei are formed parallel to the strain direction. They contain more or less extended polymer chains. Secondary epitaxial nucleation on the surface of such linear row nuclei produces folded chain lamellae which are oriented perpendicular to the strain (Fig. 6). In such a case the sample exhibits a high uniaxial orientation of chain axes in the strain direction with random orientation of the a- and b-axes perpendicular to it. If the growing lamellae exhibit a helical twist the chain orientation in the strain direction is very soon replaced by the orientation of the axis of maximum growth rate (b-axis in the case of polyethylene) perpendicular to the strain direction and a more random orientation of the remaining two axes (a- and c-axes in the case of polyethylene) with a maximum in the strain direction. Such a row nucleated structure has parallel cylindrical spherulites (cylindrites) as its basic supercrystalline element. 

Fig. 4. CorO for the unique axes of fluorescent VPBO molecules dispersed in uniaxially oriented tapes of polyethylene terephthalate plotted against the birefringence — of the tapes. O, samples drawn at S(PC to draw ratios between 1 and 6 . samples drawn to draw ratio 2 7 at temperatures between 65° and 90°C. (Reproduced by permission from Ref. 18. Copyright I PC Business Press Ltd.)...

In this work uniaxially oriented specimens of polyethylene terephthalate were studied, most of which were from the first series used in the work of Nobbs et al. described in Section 5.3.1. The Raman intensity measurements were made using a Coderg PHO spectrometer and a CRL 52A argon ion laser tuned to 488 nm. The tape samples were mounted parallel to the spectrometer slit. The partially focused laser beam was incident normally on them and the scattered light was collected in directions making approximately 180° with the incident light direction. The incident and scattered light polarisation vectors could be chosen parallel or... 

Fig. 7. Co O and co O plotted against draw ratio, /.. for chain a.xes in uniaxially oriented tapes of polyethylene terephthalate.. cos O and O. cos determined from Raman intensity measurements on the 1616 (vn line. Curves (a) pseudo-affine cyg regate deformation model, atrves (b) affine rubber elasticity model.

Now consider the case of a uniaxially oriented polyethylene film or fibre, with full orientation, where the chain axes are. parallel to the draw direction or fibre axis and consider only the proton pair interaction arising from the CH2 groups. The CH2 groups are now such that the proton pairs lie in a plane perpendicular to the fibre axis. Figure 3 illustrates the situation. The intemuclear vector r makes an angle P with Ho, and an angle <(> with a chosen direction in the plane normal to the fibre axis. The angle between the fibre axis and Ho is y. 

Applied Spectroscopy 51, No.3, March 1997, p.346-9 AMPLITUDE SPECTRUM APPROACH IN DYNAMIC FT-IR SPECTROSCOPY OF UNIAXIALLY ORIENTED POLYETHYLENE TEREPHTHALATE FILMS. I. DRAW RATIO DEPENDENCE... 

Initial die gaps are set to about 20 percent greater than the final film thickness, and then adjusted to accommodate changes in polymer flow which are resin and rate sensitive. Higher screw speeds increase extruder output, overall film thickness, the tendency toward melt fracture, and may alter the flow pattern. Thus, extruder speed is not a recommended control. In contrast, increased chill-roll speeds decrease film thickness, reduce film width due to increased neck in, increase uniaxial orientation, and alter the optimum air gap or drawdown distance. The optimum air gap, which produces the best orientation, crystallization, and surface properties, depends on the material and chill-roll speed. At 23 to 30 m/min (75 to 100 ft/min), the air gap for low-density polyethylene is about 100 mm (4 in), but when the line speed increases, the air gap is found by trial and error, Since the chill-roll speed controls film stretching, the take-off speed has little effect on the film dimensions. 

Polyaniline also presents an additional potential advantage because uniaxially oriented blends of polyaniline doped with dode-cylbenzenesulfonic acid or CSA and common bulk polymers such as polyacrylonitrile, polyethylene, and poly(vinyl alcohol) display a polarizing efficiency over the range from 400 to 4000 cm that matches, or surpasses, that of commercial wire grid polarizers [211]. These characteristics permit the use of polyaniline simultaneously as a polarizer and as an anode. 

Torsion of oriented polymer sheets was undertaken by Raumann [14] to determine the shear compliances S44 and See for uniaxially oriented (transversely isotropic) low-density polyethylene. Torsion of oriented sheets can also be used to determine the shear compliances S44, 555 and See for sheets possessing orthorhombic symmetry. As this situation is more... 

Finally, it is of interest to compare the theoretical values for a uniaxially oriented sheet (calculated by averaging the stiffness values using the Voigt averaging scheme) with those obtained for a die-drawn rod and a sheet made by hot compaction of high modulus polyethylene fibres (Table 8.4). It can be seen that although, as expected, these materials have not reached full axial orientation so that the experimental values of C33 are much less than the theoretical value, the patterns of anisotropy are very similar, and some of the values for the other elastic constants are surprisingly close. 

From values of the interchain and intrachain vibrations, the Debye-Waller coefficients of uniaxially oriented polyethylene at 100° K were calculated as 2wh(1) = 0.034 and 2wh(1I) = 0.021 by Kitagawa (1968). 

Fig. VII.2. Debye-Waller factors (e " ) of the uniaxially oriented polyethylene, plotted versus down scattering energy-transfer calculated for the experimental conditions of Myers, Summ eld, and King (1966) [final neutron energy of 30meV and scattering angle of 90°]. Solid line is for tte longitudinal (cBK,) and broken line for transverse (c LK,) orientation. From Kitagawa (1968)...

The difTeiential cross sections of uniaxially oriented polyethylene for the one-phonon,two-phonon and three-phonon processes were calculated by Kitagawa and Miyazawa (1969b), as shown in Fig. VIL3. In the region below 200 cm, the transverse one-phonon cross section is much larger than the longitudinal one-phonon cross section. On the other... 

Fig. VII.3. Histogram of the differential cross section (in unit of SfJ4n) of uniaxially oriented polyethylene versus energy-transfer (interval of lOcm ). Calculated for the experimental conditions (100° K) of Myers, Summerfield, and King (1966). Solid line is for the longitudinal (c K,) and broken line for the transverse (cTK,) orientation. From Kitagawa and Miyazawa (1968 b)...

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