Cold-drawn fiber

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. 

The increase in oxygen concentration accompanies the deterioration of fiber physical properties, but the deterioration does not necessarily relate to the increase directly. Factors such as fiber orientation and the conditions, primarily temperature at which the fiber is drawn, can affect the rate of deterioration [113], The reduction of elongation that accompanies exposure to UV light is less for a highly oriented fiber because the photooxidation reaction is initially limited to the fiber surface. The photooxidation reaction is accompanied by the formation of cracks on the thin surface [114]. Cold-drawn fiber reacts throughout, degrades faster, but does not form surface cracks. Fiber wettability increases with increased UV exposure [112], which is additional evidence of the formation of surface oxygen bonds. 

Favorable conditions are met for a cold-drawn fiber or film when its birefringence An = n - nx can be determined (ny and nx denote the refractive indices along and perpendicular to the drawing direction). Here, S can be directly deduced from An, using the relation... 

It has been also well documented that a process zone (PZ) consisting of cold drawn fibers and membranes always precedes the crack in PE. The process of SCG depends, in a large extent, on the properties of PZ material ahead of the crack tip. Closely coupled crack and... 

Fig. 13. Elongation to break as a function of birefringence for undrawn, hot-drawn, and cold-drawn annealed fibers (6) , undrawn , cold-drawn,...

Hard, waxlike, crys-stalline fibers may be cold drawn above M.W. 90002-10... 

Figure 6. X-ray fiber diagram of poly(5-methyl-1,4-hexadiene) prepared with a Etj,AlCl/S-TiCl, catalyst at 0°C in pentane solvent. Compression molded sample cold drawn to four times its original length.

Such fibers can be produced, for example, as a copolymer composed from 80% ethene and 20% acrylic acid is extruded through a spin-nerette die into a 500 p diameter strand at 125°C and then drawn to a 10 ju diameter filament. The filament contains an orientation resembling to a cold-drawn filament (9). After several intermediate steps, eventually microporous chopped fibers are obtained that are useful as intermediates for forming high melting aluminum salt derivative fibers. This is effected by contacting the fibers with an aqueous solution of 0.5% aluminum sulfate. 

Slit and Split Films. Thick incUistiial-giade yams aic often pioduccd by slitting films, providing a less expensive alternative to melt spun fiber. Cast film is slit in the machine direction by parallel rotary knives. The resulting tape can then be cold drawn in an oven in a manner similar to melt spun fibers to produce the final fiber. 

Figure 9. Unrealistic resolution with unconstrained optimization. Corrected equatorial trace of a polypropylene fiber specimen cold drawn X-5-5. Total theoretical trace comprised of unrealistic profiles.

Figure 11. Good resolution with constrained optimization and addition of a paracrystalline peak. Corrected equatorial trace of a polypropylene fiber specimen cold drawn X-5.5. Total theoretical trace now comprised of realistic crystalline peaks 110, 040, 130, 111, 131, 041, and paracrystalline peak at 15.5°. Compare...

As noted in Fig. 14.1 (a), commercial fibers of semicrystallme polymers are always cold-drawn after spinning to achieve further structuring through further macromolecular orientation and crystalline morphological changes, many of which are retained because of the low temperature of the cold-drawing processes. A typical stress-strain curve for a polycrystalline polymer at a temperature Tg < T < Tm appears in Fig. 14.6. 

Fiber textures vary in perfection, i.e., in the scatter of the direction about the fiber axis, and both single and double fiber textures have been observed. Thus, cold-drawn aluminum wire has almost a single [ill] texture, but copper, also FCC, has a double [111] + [100] texture i.e., in drawn copper wire there are two sets of grains, the fiber axis of one set being [111] and that of the other set [100]. 

Applications. Poly (thiol esters) can be good starting materials for producing fibers when the esters have an inherent viscosity 77 >0.3 g/dl (27) or >0.75 g/dl (16). They can be cold-drawn to oriented fibers involving a three- to fivefold or even higher increase in length. 

The incorporation of P-1 into monofilament by compounding with PPH powder and extrusion was effective only partially in reducing draw-initiated oxidation. After X3 cold draw (at 25°C) the observed -OOH level was 0.3 X 10 3M, in the presence of 0.1 wt % P-1, in comparison with 1.1 X 10 3M for the stabilizer-free fiber. Furthermore, this lower level of draw-induced degradation still had a large photosensitizing effect, even in the presence of the stabilizer. After 200 hr of UV exposure in the xenon arc, the P-1 concentration was reduced by more than 20 fold in the cold-drawn filament and photooxidation was accelerating rapidly, whereas for the undrawn filament no P-1 loss was visible, and photooxidation was undetectable. 

Wide-angle X-ray scattering and DSC measurements of cold drawn PEN stretched from an amorphous fiber that is spun at low speeds indicate that the strain-induced crystallization can occur at a temperature be-... 

Samples that were hot-drawn or cold-drawn and annealed displayed a well-formed mono-clinic structure. Cold-drawing transformed the monoclinic form of the spun fibers into a more oriented but disordered structure. The x-ray pattern exhibited a high degree of line... 

Densities of the hot-drawn and cold-drawn and annealed fibers were slightly higher than those of the spun fibers. Crystalline fractions of around 61% were observed. 

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