Crystallization-Induced Fluid Flow in Polymer Melts Undergoing Solidification

Published

February 19, 2007

Author(s)

Donghua Xu, Z G. Wang, Jack F. Douglas

Abstract

The formation of semi-crystalline plastic polymer materials often occurs under confinement conditions where high pressure imprinting or casting in a mold are involved. To gain insight into this highly non-equilibrium process, we examine the nature of the fluid flow that occurs in the non-crystallized regions of polymer melts during spherulitic crystallization by following the movement of tracer particles (carbon black; CB) in model confined polymer (isotactic polypropylene; iPP) films using optical microscopy. We observe a relatively rapid (average particle velocity 13 micron / min at 138 degrees C, compared to a spherulite growth rate of 0.86 micron /min) particle movement in the melt until the spherulites become geometrically percolated, whereupon the crystallization-induced flow becomes sharply attenuated.We interpret this transient flow to arise from the buildup of local stresses (at centers of negative hydrostatic pressure arising from local crystallization) under confinement conditions. Crystallization-induced fluid flow is expected to significantly influence the crystal morphology, defect formation and ultimate properties of plastic materials forming by injection molding, pressure imprinting and other processing conditions.

Citation

Macromolecules

Volume

40

Pub Type

Journals

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Keywords

crystallization, fluid flow, injection molding, spherulite formation, yield

Citation

Xu, D. , Wang, Z. and Douglas, J. (2007), Crystallization-Induced Fluid Flow in Polymer Melts Undergoing Solidification, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852674 (Accessed April 18, 2024)