Adding Supercritical [CO.sub.2] Aids Polymer Blending.

Adding 2% of high-pressure carbon dioxide during blending of polystyrene and acrylic (PMMA) resins in a twin-screw extruder results in a much finer mix of the two immiscible polymers, reports a paper given at this spring's SPE ANTEC 2000 conference in Orlando, Fla. Authors M.D. Elkovitch, L.J. Lee, and D.L. Tomasko from the Chemical Engineering Dept. at Ohio State Univ. in Columbus said [CO.sub.2] can reduce the viscosities of PMMA and PS by up to 80% and up to 70%, respectively [CO.sub.2] under supercritical conditions of temperature and pressure can act like a solvent. The result is sharply reduced size of the dispersed phase in the blend. Adding small amounts of fillers or compatibilizers is necessary to minimize de-mixing after the [CO.sub.2] is vented, they report.

This development holds the promise of creating new kinds of blends and is also said to be a low-cost, benign way to process thermally sensitive polymers.