Characterization of Mechanically Alloyed PET/Vectra Blends using X-ray Microscopy

Archie P. Smith, Changhai Bai, Dr. Harald Ade*, Dr. Richard Spontak, Dr. Maurice Balik, and Dr. Carl Koch
Department of Materials Science and Engineering and *Physics, North Carolina State University.


The Problem:
Blends of poly(ethylene terephthalate) (PET) and Vectra had been produced with mechanical alloying in an attempt to produce a plastic which retained the processing characteristics of PET but had the barrier properties of Vectra .  In these blends Vectra was the minority component.  Several different attempts had been made to determine the blend morphology of both the as milled powders and the melt processed samples with only limited success.  Optical microscopy showed the Vectra, due to its birefringence, but had insufficient spatial resolution.  While analysis with TEM could not distinguish the phases without ambiguity.


The Results:
Two different sets of samples were studied.  The first was the as-milled powders.  Here we took the pulverized powders and embedded them in epoxy to microtome them.  Then we studied the thin section with the x-ray microscope.  Shown below is the x-ray micrographs obtained from these powder particles.

Images A and B both show the same powder particle from a 80%/20% PET/Vectra blend that was milled at cryogenic temperatures.  In figure A, both the PET and Vectra appear dark and the outline of the particle in the epoxy if visible.  In image B, the Vectra appears dark relative to both the PET and the epoxy.  These images indicate that the Vectra accumulates at the outside of the PET for this system.  Image C is obtained from within a powder particle composed of an 80%/20% PET/Vectra blend that was milled at ambient temperature.  Here the Vectra again appears dark with respect to the PET and shows that the PET is now finely milled into the PET.  This figure shows that milling at higher temperatures does a better job of mixing the polymers than milling at cold temperatures.  This result is suprising since the polymer are more brittle at lower temperatures.
 

The next question was: "What happens to this morphology when the powders are consolidated back into solids?"  For this experiment, the milled powders were melt extruded to form solid bars and these bars then microtomed.  Below are x-ray micrographs obtained from these samples.

In all of these images the Vectra appears dark relative to the PET (gray) and the white areas are holes in the samples.  All three are PET rich blends with A) 25%, B) 10% and C) 1% by weight concentration Vectra that were all milled at cryogenic temperatures.  The number and size of the vectra domains scales with the Vectra concentration of the blend.  The Vectra particles range in size from approximately 100 nm to greater than 20 microns in size.  These results show that the fine scale dispersion of the Vectra within the PET is retained even after melt processing of the materials.


For more Information
Click here (PDF format, 180 kb) for a reprint of a paper published in Macromolecular Rapid Communications in November 1998  (V19 n11 pg 557).


All materials here copyright 1998 by Dr. Harald Ade and the Polymer X-ray Spectromicroscopy Research Group.  Reproduction without express permission from Dr. Harald Ade is prohibited (single print-out excepted).


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Created 10/14/98 by A. P. Smith, last modified 12/30/98.