Amorphous orientation functions

Noncrystalline domains in fibers are not stmctureless, but the stmctural organization of the polymer chains or chain segments is difficult to evaluate, just as it is difficult to evaluate the stmcture of Hquids. No direct methods are available, but various combinations of physicochemical methods such as x-ray diffraction, birefringence, density, mechanical response, and thermal behavior, have been used to deduce physical quantities that can be used to describe the stmcture of the noncrystalline domains. Among these quantities are the amorphous orientation function and the amorphous density, which can be related to some of the important physical properties of fibers. 

Table 6 Amorphous Orientation Function (fa) of Differently Drawn PET Fibers...

Draw ratio Density of the amorphous material da) (g/cm-" ) Amorphous orientation function fa) Crystallite length Oc) (nm) Long period (L) (nm) Degree of crystallinity (X=>) Substructure parameter (A) Axial elastic modulus ... 

Fibers of a diversified draw ratio in the range 2.0-5.2 X were considered, determining the following parameters of their fine structure the crystalline and amorphous orientation functions,and/a, degree of crystallinity, X, and critical dissolution time (CDS) in seconds. The results obtained are listed in Table 11. 

Annealing temperature rc) Annealing time (min) Birefringence (An) Anid Volume crystallinity (%) TTM fraction Critical dissolve time (s) Amorphous orientation function (/ )... 

FIGURE 3.57 High-temperature endotherm peak, 7 2m versus amorphous orientation function (o) drawn fiber (x) heat-set fiber. (From Samuels, R.J. J. Polym. ScL, Polym. Phys., 1975, 13, 1417. With permission.)... 

Fig. 12. Amorphous orientation functions, determined from the infra-red peaks at the indicated frequencies, plotted against extension ratio for low density polyethylene...

The peaks at 1078, 1303,1352 and 1368 cm originate entirely from the amorphous phase and the respective D— )/( )-f 2) values were obtained directly. For the 2016 cm" peak, which contains both an amorphous and a crystalline component, the ( )—l)/(Z)-i-2) values are appropriate to the amorphous component only. They were obtained from the measured net D values for the 2016 cm" peak, in combination with X-ray data and dichroic data on the 1894 cm" crystalline band. Details of tte method used for resolving the amorphous orientation function are given by Read and Stein. ... 

A comparison of Figs. 12 and 11 shows that the amorphous orientation functions are generally lower than the crystal orientation functions at low extensions. Figure 12 also reveals a qualitative correspondence between the experimental f M values and the theoretical values in Table 1, as might be expected if eapproximately valid for the amorphous regions of the polymer. The negative fj values for the 1078... 

Time dependent dichroic measurements during the stress relaxation of low density polyethylene have been reported by Gotoh et alP and more recently by Fukui et alP and by Uemura and Stein. Fukui and coworkers determined both crystalline and amorphous orientation functions at a constant strain between 2-5 and 5%. At room temperature, values of —f and —f>, estimated from data on the 730 and 720 cm" bands respectively, increased with time towards steady values which were attained after about 10 s. These time dependencies were considered to largely determine the observed time dependence of the strain-optical coefficient. Values of f from the 1352 cm" band showed little time dependence, but the amorphous orientation was estimated to contribute the larger amount to the magnitude of the strain-optical coefficient. 

Miller et al. have recently reported infra-red dichroic data obtained for high density polyethylene crystallised under the orientation and pressure effects of a pressure capillary viscometer. Their data for a number of crystalline bands (including the 1894 cm" absorption) showed that the crystal c-axes were almost perfectly oriented (f 1) in the initial extrusion direction. The amorphous orientation functions were generally lower, but corresponded to an extension ratio between 2 and 7 when compared with the above results of Read and Stein and of Glenz and Peterlin. Further evidence was also obtained for the relatively high orientation of the amorphous component of the 2016 cm" band (U = 0-66-0-72). 

Strain Higher crystallization rate crystallization at low temperature dependent on amorphous orientation function, temperature, and strain rate 15-23... 

It is relatively difficult to make a direct determination of the amorphous orientation function of a semicrystalline polymer. Determination by X-ray diffraction recording the azimuthal angle dependence of the amorphous halo and infrared dichroism of an amorphous absorption band may be useful in addition to the indirect method suggested above. 

A.9 Orientation of a Polymer Melt in Shear Flow. LDPE (NPE-953) is extruded through a film die at 170 °C at a wall shear stress of 1.2 x 10 Pa. The film die consists of parallel plates having a width of 1.0 m and a height of 0.05 cm. Determine the amorphous orientation function as a function of distance from the center to the die wall in the region where steady shear flow exists. 

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