GAS ATOMIZATION OF POLYMERS - I - FEASIBILITY STUDIES AND PROCESS-DEVELOPMENT

A new gas atomization process (GAP) was explored for mass producing hi gh-quality spherical powders and very high aspect ratio microfibers fr om molten polymers. The process involves the use of high-pressure (7.6 MPa or 1050 psi) nitrogen gas and a specifically designed nozzle to a tomize a molten stream of polymer into fine droplets that cool to form spherical powders. Polyethylene-based powders, ranging in size from 0 to 200 mu m, were efficiently produced in short cycle times by changi ng a few process control variables such as atomization temperature and polymer melt stream size in a contamination-free environment. The cry stallinity of the polymer favored formation of spherical powders. Anal ysis of the experimental data indicated that the maximum weight fracti on of the powders at 0-53 mu m can be produced by atomizing the more c rystalline polymer, using a 3.175-mm melt stream size at 205 degrees C . Using the GAP in an alternative route to mass producing powders from low-molecular-weight, polyethylene-based waxes that cannot be ground eliminates most of the problems of conventional grinding processes. Th ese benefits of the process together with its flexibility, high throug hput, and facile nature can be expected to make it worth considering f or industrial processes that must be safe, be capable of mass producti on, and operate in an environmentally benign fashion. (C) 1998 John Wi ley & Sons, Inc.