As a part of continuous efforts to systematically understand the morphological development in water-assisted injection
molding, high density polyethylene with different molecular weights was molded in this study. Unexpectedly, it
was found that shish kebab with high lamellar and molecular orientations was formed in the sample with a lower
molecular weight (LMW) rather than in the higher one, especially in the water channel layer. Present finding is
obviously inconsistent with the general consensus, that is, higher molecular weight (HMW) polymer is much easier
to form preferential orientation in flow field than LMW one. Such anomalous phenomenon is explained by the fact
that even though melts experienced the same processing, lower shear rate is practically achieved in HMW sample
due to its high viscosity. The result indicates that the flow history in industrial processing method is far from that
in laboratory one.
