Uniaxial stretching

We carried out thermodynamic studies on the crystallization from melts of flexible-chain polymers uniaxially stretched at various degrees of molecular orientation in the melt and studied the effect of the stretching stress on thermodynamic parameters such as degree of... 

Figure 8 Five independent spectra of a uniaxially stretched PE sample (draw ratio of 11.7). Reproduced with permission from Pigeon et al. [47]. Copyright 1991 American Chemical Society.

In anisotropic samples, it is convenient to concentrate on the principal directions of deformation. In uniaxial stretch, the parallel and perpendicular radii are given by... 

R > is the mean square end-to-end distance of the polymer chain. Consider a sample stretched by a factor Ay in the Y direction and Az in the Z direction. A general deformation can be easily treated, but for simplicity only uniaxial stretching or isotropic swelling will be examined. Note that under conditions of uniaxial deformation, the volume of the sample changes very little. This change may be ignored, and it becomes convenient to set Az = A and Ax — Ay. ... 

Only a few results are shown, others are easily calculated using equations from the previous section. The data in the Table refer to uniaxial stretching only. However, in pn isotropically swollen network, the calculate values of (R /RO -i are identical with the values of (R /R° ) 5 given in the Table. Of course A has not the same precise sense in the two experiments. 

The first SANS experiments on end-linked elastomers with a well-defined functionality were carried out by Hinkley et al, (22). Hydroxy-terminated polybutadiene was crosslinked by a trifunctional isocyanate, and the resultant polymer was uniaxially stretched. 

Simulation of the Birefringence of Uniaxially Stretched Polyethylene Melts. 

Many semicrystalline polymers are polymorphic and exist in different crystal forms. When PBT fiber is uniaxially stretched [75], the contracted gauche-trans-gauche a-crystal chain is extended to a fully trans conformation of a y-crystal. Above 20% strain, the crystal form is 100% y-crystal with a longer c-axis triclinic cell dimension. Thus, it is reasonable to ask whether the... 

Polypropylene and polyethylene microporous films obtained by this method are available from Cel-gard48.5o,54,55 Ube. The dry process is technologically convenient because no solvents are required. However, only a uniaxial stretching method has been successful to date, and as a result, the pores are slitlike in shape and the mechanical properties of films are anisotropic. The tensile strength in the lateral direction is relatively low. 

Figure 12.21 (A) NIR spectra of a 0% HOPE film before and after uniaxial stretching (B) weighted difference...

The extruded fiber is then often uniaxially stretched by take-up rollers rotating at different speeds. The fiber stretching encourages the polymer chains to align on a molecular level producing increased strength in the direction of the pull. 

Figure 8.31 The result of subtracting a spectrum of polyethylene film obtained after uniaxial stretching from the spectrum of the same film before uniaxial stretching.

Figure 3.5 (a) Preparation method of a typical expanded polypropylene film membrane, in this case Celgard . (b) Scanning electron micrograph of the microdefects formed on uniaxial stretching of films [6]... 

A second class of polarizers uses dichroism to produce linearly polarized light. Techniques to produce dichroic polarizing sheets were pioneered by Land [52], These are made by dissolving a strongly dichroic, small molecule into an amorphous, transparent polymer. The dichroic molecules are then oriented by a uniaxial stretching of the polymer matrix. Since this is accomplished below the polymers glass transition temperature, this ori-... 

Y. Zhao, B. Jasse, and L. Monnerie, Orientation and relaxation in uniaxially stretched poly(methyl methacrylate)-poly(ethylene oxide) blends, Polymer, 30, 1643 (1989). 

Extensional, elongational or shear-free flows play a dominant role in the post die-forming step, such as stretching of melt strands in spinning, uniaxial stretching of molten films... 

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