Effects of Initial Structure on the Deformation Behavior of PP Hollow Fiber in Continuous Drawing

摘要

The effects of the microcrystalline structure of undrawn fibers on the rheological behavior in the process of the polypropylene (PP) hollow fiber formation system were studied by a simple model describing the continuous drawing process. The predicted and observed drawing behaviors were explained in view of a simple approach based on the concept of strain-rate sensitivity and strain-hardening parameters. Var- ious parametric studies showing the interactive nature of the strain-rate sensitivity and strain-hardening parameters on the drawing behavior were also numerically pel-formed. Strain-rate sensitivity affects mainly the intensity of the neck. and strain hardening has more effects on the position of the inflection point in continuous drawing. Details of the necking mechanism in the drawing process were studied by observing the deformation behavior of the specimens with different initial microcrystalline struc-tures. The distinctive initial structure of undrawn pp hollow fibers can be formed by controlling the quenching condition in melt spinning. It was shown that the water- quenched pp fiber exhibited an unstable smectic form. whereas the stable monoclinic phase was observcd for the fiber prepared without quenching by forced convection. The experimental results of the drawing behavior indicated that the strain-rate sensitivity of the fiber with a smectic fonn was larger than that with the monoclinic form. It was also shown that the hollowness was affected by the quenching condition in melt spinning and the defonnation behavior in the drawing process.