Evolution of Density Fluctuations to Lamellar Crystals in Linear Polyethylene

Published

November 8, 1999

Author(s)

Y A. Akpalu, Eric J. Amis

Abstract

Structure formation during the isothermal crystallization of a linear polyethylene (M_w = 32,1000 g/ mol, M_w/M_n = 1.1) has been monitored by simultaneous real time small-angle x-ray scattering (SAXS) and wide angle x-ray scattering (WAXS) with synchrotron radiation. Changes in the crystalline and amorphous scattering in WAXS occur simultaneously with the changes observed in the SAXS intensity profile, suggesting that the resulting scattering is a consequence of forming crystals. At the early stage of crystal growth, the SAXS intensity at q< 0.02 ^-1 increased while that at higher wavevectors remained constant. Meanwhile, the apparent crystallinity from WAXS increased to about 10% before two peaks in the SAXS intensity profile could be resolved. As lamellar stacks are developed, the period corresponding tot he first SAXS peak, L1, decreases initially. After reaching a minimum, L1 further increases with crystallization time. On the other hand, the period corresponding to the second SAXS peak increases with crystallization time. At late times, the rate of increase is very slow. Changes in the crystallinity obtained from WAXS and the total scattering power from SAXS were evaluated and compared with a model for the crystallizing system which accounts for changes in the fraction of lamellar aggregates. The relative importance of two secondary crystallization processes, namely the formation of new lamellar stacks and increase in the crystallinity within lamellae, were evaluated during and after primary crystallization.

Citation

Journal of Chemical Physics

Volume

111

Issue

No. 118

Pub Type

Journals

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Keywords

crystallization, polyethylene, SAXS/WAXS

Citation

Akpalu, Y. and Amis, E. (1999), Evolution of Density Fluctuations to Lamellar Crystals in Linear Polyethylene, Journal of Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851565 (Accessed April 24, 2024)