Flow‐induced crystallization by surface growth of polyethylene fibers

Rietveld, J.; McHugh, A. J.

doi:10.1002/pol.1983.180210818

Cited by 4 publications

(2 citation statements)

References 15 publications

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“…The growth phenomena observed here should not be confused with observations on the stretching of swollen gels as possibly related to surface growth phenomena (16, 20-23). Though the merits of the surface growth experiments are unquestionable, the growth process from a seed in Poiseuille flow accurately exemplifies and examines the phenomena of flow-induced crystallization whereas surface growth does not (8).…”

Section: Discussionmentioning

confidence: 99%

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Flow‐induced fibrillar formation process in poiseuille flow

Rietveld¹,

McHugh²

1983

J. Polym. Sci. B Polym. Lett. Ed.

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Section: Discussionmentioning

confidence: 99%

“…The polyethylene seeds positioned in the Poiseuille flow field were grown from a 0.25% by weight solution of Hostalen CUR 412 in xylene at 106.6"C, via the surface growth method in a Couette apparatus with a Teflon rotor (8). The seeds averaged 0.02 mm X 0.04 mm in cross section and extended 10 mm into the flow tube.…”

Section: Methodsmentioning

confidence: 99%

Flow‐induced fibrillar formation process in poiseuille flow

Rietveld¹,

McHugh²

1983

J. Polym. Sci. B Polym. Lett. Ed.

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Low density foams produced from sheared ultra‐high‐molecular‐weight polyethylene gels

Matthews¹,

Hoffman²

1990

Polymer Engineering & Sci

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Low‐density foam (0.02–0.09 g/cc) was produced from gels of ultrahigh molecular weight (UHMW) polyethylenes in solvents with melting points above ambient. The hot PE solutions were stirred at high speed to induce extended chain crystalline gels. These gels were subsequently cooled to allow the solvent to solidify and then the solvent was extracted with alcohol or sublimed. This resulted in a tough, low density foam or a collapsed mass depending mainly on the concentration of the polymer. Shrinkage was significant until polymer concentrations reached 4–5%. Foam cell size varied between 5–30 μm, or 25–75 μm depending on the method of preparation. Polarizing microscopy revealed both spherulitic and row‐nucleated structures depending on the thermal history followed during the sample preparation. We were also interested in whether or not small particles could be used to influence the nucleation and growth of the solution crystallization process. These particles could be suspended in the gel and stabilized in something like a colloidal necklace as has been proposed recently. We successfully incorporated small (0.5 μm) tungsten particles in UHMWPE gels which remained in the foam on extraction of the solvent. Polyethylene containing carbon black particles produced less successful results. These effects may be related to absorption associated with gelation of UHMWPE.

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Polyethylene fiber formation in tubular flow. I. Observations of growth pattern and fiber properties

Rietveld

McHugh

1985

J. Polym. Sci. Polym. Phys. Ed.

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The process of seeded growth of fibrillar polyethylene crystals has been studied in a tubular flow geometry for 0.01‐wt % solutions of a high‐molecular‐weight polyethylene in xylene. The transformation sequence has been followed visually by using polarized‐light illumination in conjunction with a video camera. Data are presented to show that transformation is initiated by the formation of a concentrated, unoriented, amorphous precursor fiber within which oriented birefringent crystals subsequently grow in consequence of the stresses transmitted by the flowing solution. Time constants for the precursor formation, birefringence initiation, and completion of birefringence were measured as functions of temperature and flow rate over a range of growth conditions. Wide‐angle x‐ray diffraction, overall birefringence, and optical hot‐stage melting data were also obtained on the grown fibers. The net result of these observations is to conclude that fibrillar crystal growth during flow is always preceded by the formation of a liquidlike phase transformation which produces the concentrated, unoriented precursor. Subsequent orientation is in consequence of stress‐induced crystallization with overall fiber orientation showing an increase with solution flow rate at a fixed temperature and a decrease with temperature at a fixed flow rate. At higher temperatures and lower flow rates, birefringence develops in an oscillatory fashion, indicating a remelting process possibly due to slippage of trapped chain entanglements formed by flow. A discussion is given of the implications of these observations for the understanding of flow‐induced structure development, phase transformation, and oriented crystallization; this is expanded upon in a companion paper, Part II.

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Flow‐induced crystallization by surface growth of polyethylene fibers

Cited by 4 publications

References 15 publications

Flow‐induced fibrillar formation process in poiseuille flow

Flow‐induced fibrillar formation process in poiseuille flow

Low density foams produced from sheared ultra‐high‐molecular‐weight polyethylene gels

Polyethylene fiber formation in tubular flow. I. Observations of growth pattern and fiber properties

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