Orientation development and crystallization in melt spinning of fibers

Extensional, flow-induced crystallization (FIC) of a high-density polyethylene (HDPE) melt has been studied using a four-roll mill flow cell. Simultaneous measurement of the birefringence and scattering dichroism are used to quantify the crystallization process during and following transient flow deformation in planar extensional flow. Suspension of the HDPE phase as a droplet in a linear low-density polyethylene carrier phase prevents die blockage on crystallization and allows measurement of the flow kinematics. Initial crystallization rates following a transient flow deformation show a stress-strain dependence. Crystallization induction times during flow correlate with the extension rate during the transient flow deformation. Measurement of the HDPE melt steady and oscillatory flow rheological properties, along with measurements of time constants following step-shear and extensional strains, allow determination of the viscoelastic properties which enhance FIC. Parameters obtained from these experiments are used in a phenomenological model for FIC which allows qualitative and semiquantitative analysis of the data trends, particularly the relaxation behavior of the birefringence during flow cessation/crystallization.

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“…The intensity is essentially constant during flow, whereas, at the point of flow crystallization. The positional dependence of the (9) and (10).…”

Section: Rheological Measurementsmentioning

confidence: 99%

Transient flow-induced crystallization of a polyethylene melt

Bushman

McHugh

1997

J. Appl. Polym. Sci.

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“…The molecular orientation of a fiber developed during the melt-spinning process is strongly affected by the spinning conditions and also by the polymer-chain properties, including the crystallization behavior. 31 The presence of nanoclay alters the chain rigidity and polymer rheology, so this may hinder the alignment of molecules by spin tension at give spinning speed. 32,33 In addition, changes in the crystallization behavior caused by nanoclay addition could influence the molecular orientation development because crystallization and orientation development occur simultaneously during spinning and they are highly interrelated.…”

Section: Birefringencementioning

confidence: 99%

Structure and tensile properties of Nanoclay–Polypropylene fibers produced by melt spinning

Rangasamy

Shim

Pourdeyhimi

2011

J of Applied Polymer Sci

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Nanocomposite fibers of polypropylene and montmorillonite-based organoclay were produced by a melt-spinning process, and their structures and mechanical properties were studied. The addition of nanoclay in polypropylene increased the rate of crystallization and altered the microstructures of the fibers. Increases in the crystal size and a reduction in the molecular orientation were observed in the nanoclay-polypropylene composite fibers. The tensile properties of nanoclay composite fibers were also studied, and decreases in the fiber modulus and tenacity and increases in the strain at break were observed.

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“…The melt spinning of polyethylene, 8 -10,14 polypropylene, 10,11 poly(ethylene terephthalate), 14 poly-(vinylidene fluoride), 16,17 and polyamides, 18 including nylon 6, 12,13,19 -22 have been studied using rotating anode or synchrotron X-ray sources. A thorough review of the orientation development and crystallization behavior during the melt spinning of polymer fibers 23 summarizes much of the work listed above.…”

Section: Introductionmentioning

confidence: 99%