On Wed, 18 Apr 2007 23:52:55 +0200, Dr. Hans-Guenter Beyer enriched cyberspace with these bytes:
It has been a couple of years since I did research on producing microcellular foams (not with PE though, sorry), so this is from memory.
Besides the obvious conditions that have to be created for foaming a plastic (e.g. temperature, rheological properties of your material, type of blowing agent etc. etc.), a key factor when shifting from foaming to microcellular foaming is the magnitude of the pressure drop and pressure drop rate when the material exits the die of the extruder. I can't give you any exact figures about these magnitudes, but IIRC the pressure drop may need to be in the hundreds of bar range, and the pressure drop rate in the 1 GPa/s range (again this is from memory so I could be way off with these numbers).
A lot of research was done in the past at MIT when the Mucell technology was developed. Searching literature for articles by Chul Park or Daniel Baldwin is bound to turn up information about microcellular foaming through extrusion.
Jaap van Heemst
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