The nucleated isotactic polypropylene (iPP) was
molded by water-assisted injection molding. The crystalline
morphology and orientation distribution were
studied. The results show that shear brought by melt
filling and pressurized water penetration can separately
induce the formation of oriented structures in
skin region (i.e., the region near mold cavity wall) and
the water channel region. For virgin iPP, slightly oriented
lamellae appear exclusively in the above aforementioned
regions. However, shish-kebab structure
occurs not only in skin and water channel region of the
iPP containing moderate content of nucleator (0.2 wt%)
but also in the whole region of the iPP containing a
higher content of nucleator (1 wt%). It is well known
that nucleator cannot directly induce the development
of shish-kebab in the absence of shear, thus the results
indicate: shear flow actually distributes over a much
broader range than expected; in shear field, nucleator
is significantly helpful for the shear which is not sufficient
to solely induce oriented structure to promote the
formation of the oriented structure.
