Microporous Membranes of Polyoxymethylene from a Melt-Extrusion Process: (I) Effects of Resin Variables and Extrusion Conditions

A two part study utilizing polyoxymethylene (POM) was undertaken to investigate a three stage process (Melt-Extrusion/Annealing/Uniaxial-Stretching) (MEAUS) employed to produce microporous films. In this first part, three POM resins (D, E & F) were melt-extruded into tubular films (blowup ratio; BUR = 1), where resin D has a higher weight average molecular weight (Mw) than resin E but both possess similar relatively narrow molecular weight distributions (MWD). In contrast, resin F is characterized by a broader MWD while its Mw is slightly lower than resin D. Specific attention was focused upon the morpholog ical and crystal orientation results as a function MWD and Mw. A stacked lamellar morphology was obtained in each case from the melt-extrusion, however, the type of stacked lamellar morphology, planar or twisted, and the orientation state was found to depend upon both the resin characteristics and the melt-extrusion conditions. Atomic force microscopy and wide-angle X-ray scattering were the main techniques utilized to study the melt-extruded films while dynamic melt rheometry in conjunction with the Carreau-Yasuda model aided in differentiating the melt-flow behavior of the three resins. Small-angle light scattering (SALS) was also employed to characterize the morphological state. Matthew B. Johnson Chapter V POM Melt -Extrusion ___________________________________________________________________________ 173 5.