Formation mechanism of crystal morphologies in LLDPE/HDPE blends investigated via water‐assisted and conventional injection molding

The LLDPE/HDPE blends with two different weight ratios as well as pure LLDPE were molded by means of water‐assisted and conventional injection molding (WAIM and CIM) in terms of their different thermal fields. The formation of the crystal morphology in the molded parts was investigated by a scanning electron microscope. The results showed that banded spherulites formed in the WAIM and CIM pure LLDPE parts. Banded spherulites of LLDPE coexisted with the randomly oriented lamellae of HDPE for LLDPE/HDPE blend parts with lower HDPE content at higher cooling rates, whereas a banding to nonbanding morphological transition occurred for LLDPE component (particularly for blend with higher HDPE content) at lower cooling rates. The heterogeneous nucleation effect of HDPE component on LLDPE component was responsible for the banding to nonbanding morphological transition by hindering the twist of LLDPE lamellae. It was interesting to find that the thermal effect, rather than the shear effect, was the main factor for the formation of crystal morphologies in both CIM and WAIM blend parts. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers