Lamellar orientation, nucleator effect

Dibenzylidene sorbitol exists in the form of fibrils and usually acts as an effective nucleating agent to facilitate crystallization of poly-(olefin)s during manufacturing (12). In particular, when the dibenzylidene sorbitol concentration reaches a critical value, the fibrils will self-organize into a three-dimensional network when there is a decrease of temperature, but before crystallization takes place. The network of the fibrils may facilitate the subsequent process of nu-cleation and crystallization growth. An oriented deformation of the dibenzylidene sorbitol network could act as a template for anisotropic crystallization of PP, which then results in a high lamellar orientation level. 

The adsorption of semicrystalline polymers at the polymer melt-solid interface is another interesting question to be answered. When a monolayer of semicrystalline polymer molecules is prepared on a solid surface, nucleation and crystal growth can be very different from that found in the bulk due to confinement effects [72-78]. Polymer chains in the vicinity of the solid surface tend to crystallize into lamellar crystals with either flat-on or edge-on orientations, depending on specific interactions with solids [79-81]. Among a variety of morphologies reported in the literature, the formation of dendrites or seaweed structures via the so-called diffusion-limited aggregation (DLA) process was the most commonly observed in semicrystalline polymer monolayers [76, 82]. 

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