| The melt recrystallization of vacuum carbon coated melt-drawn iPP thin film was studied by means of transmission electron microscopy combined with electron diffraction.When the melt temperature is below 200?,the carbon-coated melt-drawn highly oriented iPP thin films melt-recrystallized always in an oriented way with well ordered edge-on crystalline lamellae perpendicular to the drawing direction by varing melting temperature,melting time and recrystallization temperature.This is related to the strong fixing effect of the vacuum evaporated carbon film on the oriented iPP chain stems on the surface layer.Since these fixed iPP chain stems are originally included in the a-iPP crystal lattice,they serve as a-iPP nuclei during the recrystallization process and induce highly oriented iPP lamellae composed of only a-iPP crystals.This indicates that the frequently reported orientation-induced ?-iPP crystallization is a nucleation controlled process.Moreover,by comparing the original oriented structure of melt-drawn iPP films with the recrystallized ones,it is concluded that the characteristic wide angle laimellar branching is severely suppressed in elongation-induced crystallization,while takes place evidently during melt-recrystallization.When melting the sample at 300?,a part of molecular chains released from the carbon layer and relaxed completely.Therefore,flat-on lamellae formed.At low crystallization temperature,e.g.,120?,both edge-on and flat-on lamellae were observed.At elevated crystallization temperature,e.g.,150?,the flat-on iPP crystals show more or less a regular lath shape.At the same time,quadrites originating from homoepitaxy of ?-iPP were seen.These results indicate an inhomogeneous fixing effect of the vacuum evaporated carbon layer on the oriented iPP thin film,which is also confirmed by dissolution test.It was further found that all of the three kind iPP crystals have a fixed mutual orientation.While a portion lamellae in the quadrites possess the same molecular chain orientation as the parallel aligned edge-on lamellae,the flat-on iPP crystals arranged with their a-axis along the molecular chain direction of the parallel aligned edge-on lamellae.This suggest that both the quadrites and flat-on crystals of iPP are initiated by the parallel aligned edge-on lamellae. |
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