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, and F) were melt extruded into tubular films (blowup ratio; BUR = 1), where resin D has a higher weight average molecular weight (M w ) than resin E, but both possess similar and relatively narrow molecular‐weight distributions (MWD). In contrast, resin F is characterized by a distinctly broader MWD while its M w is slightly higher than resin D. Specific attention was focused upon the morphological and crystal orientation results as a function MWD and M w . 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.