Cryomilling of Thermoplastic Powder for Prepreg Applications

Abstract : The U.S. Army uses thermoplastic (TP) polyetherimide (PEI) prepreg for the manufacture of high-performance composite tank ammunition components. To manufacture the material, manufacturers typically use powder coating, in which TP powder is electrostatically deposited onto a fiber tow. Powder size and distribution have been major factors that determine the quality of prepreg. Cryomilling offers a powerful approach to produce powders with small particle size in bulk quantities by mechanical milling of starting powders with large particle size in a cryogen, such as liquid nitrogen. In this work, starting with 350- m powders, we use cryomilling to produce PEI powders suitable for prepregging with particle sizes of less than 20 m. For size characterization of the powders, wet sieving was found to be the most effective technique. Using this method, we determined that a milling time of 8 h at 400 rpm is sufficient to yield approximately 70% by mass of particles under 20 m.