Abstract
This paper presents the morphology and the mechanism of microcellular polyethylene terephthalate (PET) prepared by compression moulding. The microstructures of foamed PET and crystallinity were investigated by optical microscopy, field emission SEM and wide angle X-ray diffraction, and the mechanism of microcellular foaming process was also discussed. The results showed that a peculiar structure was successfully obtained by compression moulding, which looked like oriented elliptical cells aligned along the surface of the sheet due to the biaxial orientations and the restriction by regular crystal planes of PET sheet. A cell nucleation model of PET sheet was formed. The deformed bubble growth (from spherical initial nuclei to ellipsoidal ones) was due to constraint of crystalline planes and competition of bubble growth among neighbouring bubbles. Cooling and decreasing the gas dissolution were found important for bubble shaping in the final phase of bubble growth.
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