Melt spinning of fibers

Fig. 12.14 Effect of the method of measurement on the value of D/Do for HDPE. Curve 1, frozen extrudates Curve 2, extrudates annealed at 160°C in hot silicon oil Curve 3, photographs of extrudates emerging from capillary Curve 4, photographs of extrudates in hot silicon oil. [Reprinted by permission from J. L. White and J. F. Roman, Extrudate Swell During the Melt Spinning of Fibers-Influence of Rheological Properties and Take-up Force, J. Appl. Polym. Sci., 20, 1005 (1976).]...

J. L. White and J. F. Roman, Extrudate Swell During the Melt Spinning of Fibers—Influence of Rheological Properties and Take-up Force, J. Appl. Polym. Sci., 20, 1005 (1976). 

During the melt spinning of fibers such as polyamides, polyesters, and polypropylenes, the extruder pumps the melt or slurry through a spinneret die and into a containment box where the melt is cooled. The fiber is then drawn and wound on a bobbin. The process produces high levels of uniaxial orientation and facilitates crystallization of the fibers. 

PVDF and PP sutures have very similar melting temperatures (165-175°C), but distinctively different level of crystallinity. PVDF has a level of crystallinity 59% 7%,whilePPhas43% 3%. Because ofthe lack ofan a alkyl group, PVDF could be sterilized by the conventional /-irradiation method, while PP requires the use ethylene oxide gas. Thus, PVDF could take advantage of the effidenqr and convenience of /-irradiation sterilization. like PP sutures, PVDF sutures should not have any Oj element in their chemical structure. However the surface of PVDF and PP sutures showed oxidation products as confirmed by electron spectroscopy for chemical analysis. The amounts of O2 element on the surface of PVDF and PP sutures were 7.4% and 7.9%, respectively. However, bulk FUR data failed to reveal such oxidation products. This suggests that oxidation of PVDF and PP is introduced during melt spinning of fibers and is mainly restricted to the surface of suture fibers. 

Ordinary thermal processing of plastics almost invariably produces some orientation effects. Depending on the end use of a material such effects can be advantages as in melt spinning of fibers or extremely undesirable whereever isotropic performance is required. Many studies on the effects of orientation on the properties of polymers have b n reported and reviewed (38,92,271—273). 

White J L and Roman J F (1976), Extrudate swell during the melt spinning of fibers—influence of rheological prop>erties and take-up force . Journal of Applied Polymer Science, 20,1005-1023. 

The die swell effect is neglected here as was done in the fiber-spinning analysis. In film casting no significant cooling is obtained between the face of the die and the chill-roll (see Section 5.2), whereas in the melt spinning of fibers cooling was very important. If the z component of the film velocity at the die lips is v o and at the freeze line is v, then the draw ratio, T)r, is defined as (see Eq. 9.27)... 

White, J. L., Dynamics and Structure Development During Melt Spinning of Fibers, J. Soc. Rheol. Japan, 4, 137-148, 1976. 

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