Fibers stretched

The development of the internal orientation in formation in the fiber of a specific directional system, arranged relative to the fiber axis, of structural elements takes place as a result of fiber stretching in the production process. The orientation system of structural elements being formed is characterized by a rotational symmetry of the spatial location of structural elements in relation to the fiber axis. Depending on the type of structural elements being taken into account, we can speak of crystalline, amorphous, or overall orientation. The first case has to do with the orientation of crystallites, the second—with the orientation of segments of molecules occurring in the noncrystalline material, and the third—with all kinds of structural constitutive elements. 

The quantitative assessment of the degree of crystallite orientation by x-ray examination is not free of ambiguity. From a comparative analysis [23] in which results obtained from the consideration of (105) and from three different variations of equatorial reflection were compared, the conclusion was that the first procedure can lead to underrated results, i.e., to the underestimation of the orientation. However, it can be assumed that this does not result from an incorrect procedure, but from ignoring the fact that the adjacent (105) reflex can overlap. The absence of the plate effect of the orientation is characteristic of the orientation of crystallites in PET fibers. The evidence of this absence is the nearly identical azimuthal intensity distributions of the diffracted radiation in the reflexes originating from different families of lattice planes. The lack of the plate effect of orientation in the case of PET fiber stretching has to do with the rod mechanism of the crystallite orientation. 

Contrary to widespread opinion, the value of Ea is not a constant quantity. As was proved previously [52], the value of E is variable, since it depends on the ordering of macromolecules in the amorphous material of the fiber. At the same time, one can suppose that this ordering will be affected by the specificity of the fine structure of the fiber, and particularly by the type of substructure of the fiber. The relationship determining the modulus Ea appropriate for a definite type of fiber substructure can be derived from Eq. (11) when appropriate values of A are assumed. In the case of the microfibrillar substructure, i.e., for A < I, typical of PET fibers stretched, but not subjected to annealing, this equation has the form [52] ... 

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. 

If orientation is assumed to occur only in one dimension (an oversimplification), birefringence and several related phenomena (infrared dichroism, etc.) measure the quantity , which is the average angle 8 between the molecular chain direction and that of the orienting force, such as the fiber stretch axis. It is convenient to introduce an orientation function [12]... 

Figure 7.9. Relationship between mechanical properties and fibril length (L) for self-assembled collagen fibers. Plot of UTS (A) and elastic slope (B) versus L in im for self-assembled type I collagen fibers stretched in tension at strain rate of 50%/min. Points with fibril lengths less than 20 pm are for uncrosslinked self-assembled type I collagen fibers and the points above 20 pm are for crosslinked fibers. The correlation coefficient for the best fit line is given by R2.

Retractive forces in animal fibers stretched into the Hookean region of the stress-strain curve are generally attributed to the stretching of chemical bonds and hence to an increase in the internal energy of the fiber (Ast-bury and Haggith, 1953 Peters, 1956). 

Heart failure is due to defects in cardiac contractility (the vigor of heart muscle), leading to inadequate cardiac output. Signs and symptoms include decreased exercise tolerance and muscle fatigue, coupled with the results of compensatory responses (neural and humoral) evoked by decreases in mean BP. Increased SANS activity leads to tachycardia, increased arteriolar tone T afterload, 4- output, 4 renal perfusion), and increased venous tone (T preload, T fiber stretch). Activation of the renin-angiotensin system results in edema, dyspnea, and pulmonary congestion. Intrinsic compensation results in myocardial hypertrophy. These effects are summarized in Figure IH-4-1. 

The uniform oxidation of the cold-drawn filament results in a high overall degree of oxidation and associated backbone scission before surface deterioration reaches the level at which spontaneous restructuring and crack formation can occur. Lateral cohesion of these fibers was much greater than for the highly oriented filaments. For example, the latter could be easily peeled, whereas the cold-drawn fiber stretched rather than fibrillated after notching. 

These drugs cause dilation of veins. Venodilation results in a decrease in preload, and decreased ventricular filling, which decreases the load to the myocardium and increases myocardial efficiency (i.e., by Starling s law). The decrease in preload contributes to a decreased fiber stretch, and optimal actin-myosin interaction, which results in increased contractile force and increased myocardial efficiency. 

As one might anticipate, hair fiber stiffness also varies with relative humidity it decreases with increasing relative humidity (see Figure 8-23). We might conclude that hair fiber stiffness generally parallels fiber-stretching properties with respect to treatments. This conclusion is probably correct however, further empirical tests should be made before this conclusion becomes accepted. 

TAN 07] Tanaka T., Yabe T., Termachi S., et al, Mechanical properties and enzymatic degradation of poly[(R)-3-hydroxybutyrate] fibers stretched after isothermal crystallization neaxJg , Polymer Degradation and Stability, vol. 92, no. 6, 1016-1024, 2007. 

In strain-induced crystallization the polyester material is stretched at a suitable rate and temperature to achieve crystallization within the polyester. With polyester compositions dealt with here, typical temperatures are about 80°C-140°C typical stretch rates are about 300 to about 1500%/s. The stretch ratio suitable is about 8 to about 24. For fiber stretching or orientation, the stretch ratio of about 2 to about 8 is suitable. 

Fiber stretch, cold Pulling operation with little or no heat on fibers to increase tensile strength. 

Figure 5 shows the scanning electron micrograph and WAXD pattern of four times one-step-drawn commercial-P(3HB) fibers after isothermal crystallization (Tanaka et al. 2007c). The surfaces of the fibers after isothermal crystallization had many fine voids that were evenly distributed throughout the fiber (Fig. 5a). The WAXD patterns of four times one-step-drawn P(3HB) fibers stretched at a crystallization time of over 24 h showed sharp reflections of both the a-structure and the P-strnctnre (Fig. 5b).

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