Breathable polymer films produced by the microlayer coextrusion process

Fabrication of a breathable film by the microlayer coextrusion process is d escribed. Poly(ethylene oxide) (PEO) was microlayered with a filled polyole fin, either CaCO3-filled polyethylene or CaCO3-filled polypropylene. The th ickness of individual layers was varied by increasing the total number of l ayers in the microlayered film from 8 to 4096. The water vapor transport ra te (WVTR) was measured for microlayer films that varied in composition and number of layers. Especially with the PP(CaCO3)/PEO system, systematic vari ation in composition and number of layers made it possible to obtain large changes in the WVTR. The results were related to the tortuousity of the pat hway through the microlayer. The filled polyolefins acted as a barrier to w ater vapor transport through the hydrophilic PEG. As the individual layers were made thinner by increasing the total number of layers, the polyolefin layers changed from continuous to discontinuous. Tortuousity concepts were used to correlate the increase in WVTR with an effective aspect ratio of th e discontinuous polyolefin layers. In addition to high WVTR values, the bre athable films produced by microlayering PEO with a filled polyolefin exhibi ted excellent mechanical properties. (C) 2000 John Wiley & Sons, Inc.