Morphological studies were made to investigate the drawablity of melt-quenched (MQ) and slowly cooled (MSC) films of syndiotactic polypropylene (sPP) with a high syndiotactic pentad fraction.Transmission electron microscopy (TEM) using the ruthenium tetraoxide staining and ultrathin sectioning method revealed that amorphous chains as the matrix of MQ film played a role in drawability of the film by their alignment to machine direction MD and partial crystallizations into nanofibrils. On the other hand, the initial strain induced rotations of clusters of long lamellar crystals as the major entity of MSC film, accompanying breaks of long lamellae and formation of crazes and microvoids at the cluster boundary. Compared with a homogeneous thinning of MQ film by drawing, ca. 100 nm-thick layer slips along MD and parallel to the film surface took place in MSC film. This gave rise to formation of V-shaped bent lamellar morphology and their further break into a smaller cluster of stacked lamellae which were aligned oblique by ca. 35 o from MD. With elongation, some nanofibrils formed from chains generated by the partial breaks of lamellae are aligned perpendicular 2 to the remained oblique lamellae and others parallel to MD in region where lamellar morphology almost disappeared. No chain slips in the nanofibrils can be related to a low elongation at break, i. e., a low ductility of sPP films. The lower elongation at break for MSC film than for MQ one can be interpreted by microvoids initially formed in the neck region and later moved to the fully drawn part, the microvoids initiating the break of the drawn film.
A transmission electron microscopy (TEM) study was made to investigate the mechanism of isothermal crystallization from melt for syndiotactic polypropylene (sPP) with a syndiotactic pentad fraction of 0.92. The TEM morphologies of RuO4-stained and ultrathin-sectioned specimens revealed a clear assignment of lamellar crystals with different crystal thicknesses to their corresponding melting temperatures and types of crystal structures. It has been found that isolated, single crystal lamellae with cell III structure were grown at 140 degrees C by a plausible crystal growth mechanism with regime I. Fringed-micellar type of lamellae with cell II structure as thin as c. 4 nm were formed in the interstices of the thick chain-folded lamellae by the subsequent quenching.
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