Abstract
Polarized infrared (IR) reflectance measurements were performed on polyoxymethylene (POM) prepared by the extrusion method, and an abnormally high reflectance of ∼90% was observed along the extruded direction in the 1000 cm−1–900 cm−1 region. High reflectivity was found in samples made by the conventional injection molding. However, the response of the extrusion sample was higher than that of the injection sample, which can be attributed to the Reststrahlen band. The relative permittivity calculated from the polarized reflection spectrum of the extruded direction shows a notably deep negative region in this high reflectance frequency. Using x rays, by differential scanning calorimetry, and by field emission scanning electron microscopy characterization, the difference in crystallinity and morphology from the extrusion and the injection molding plate was investigated, and the difference in IR optical response was discussed. The conventional IR band assignment of POM was also discussed.
Highlights
Polyoxymethylene (POM) is an industrially important polymer used in gears and bearings due to its toughness and self-lubrication
One of the most notable phenomena is the significant change in the IR spectral shape observed by the KBr or Nujol method, which includes the powdering process, but little change is observed in these powdered samples with Raman and wide angle x-ray scattering (WAXS) measurements.[10]
Iguchi and Murase found a new morphological structure of the extended-chain crystal (ECC) in POM, as opposed to the conventional folded-chain crystal (FCC) structure, which is achieved by crystallizing a dilute POM in a bromobenzene solution or by injection molding.[14]
Summary
Polyoxymethylene (POM) is an industrially important polymer used in gears and bearings due to its toughness and self-lubrication. Because POM has a simple molecular structure, it is an important substance from the viewpoint of basic science. It is well known that POM has a 9/5 or 29/16 helical trigonal crystal structure.[1,2] Until now, structures have been investigated by infrared (IR) spectroscopy, Raman spectroscopy, wide angle x-ray scattering (WAXS), differential scanning calorimetry (DSC), etc., and structural changes due to heat or mechanical processing have been investigated from the molecular to the mesoscopic level.[3–9] One of the most notable phenomena is the significant change in the IR spectral shape observed by the KBr or Nujol method, which includes the powdering process, but little change is observed in these powdered samples with Raman and WAXS measurements.[10]. The A2 mode undergoes a large high wavenumber shift when the FCC-type structure appears. This shift comes from the theory that this mode of vibration has a relatively strong dipole–dipole interaction in POM.[15,16]
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