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.
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.