Three-dimensional phase morphologies in HDPE/EVA blends obtained via dynamic injection packing molding

Abstract

The formation of phase morphology of injection molded HDPE/EVA blends, under the effect of shear stress, has been investigated in detail. The shear stress was induced by dynamic packing injection molding, by which a specimen is forced to move repeatedly in the model by two pistons that move reversibly with the same frequency during cooling. Two kinds of EVA with VA content 16wt% (16EVA) and 33wt% (33EVA) were used to investigate the effect of interfacial tension. The phase morphology was viewed both parallel and perpendicular to the shear flow direction, so one can get an overall three-dimensional phase morphology. Low shear stress provided by the pistons has a substantial effect on the phase morphology along the flow direction but is insignificant in the direction perpendicular to the flow direction. Generally, a much elongated and layer-like structure is formed along the flow direction, and spherical droplet-like morphology is formed perpendicular to the flow direction, and the degree of deformation of rubber particles also depends upon their size and elasticity as well as on the interfacial properties between matrix and dispersed phase. For static samples of HDPE/16EVA blends (without shearing), only droplet morphology is formed as 16EVA content increases from10 to 40wt%. However, under the effect of shear stress (dynamic samples), both droplet and cylinder morphologies can be formed depending on the volume ratio. For static samples of HDPE/33EVA blends, not only droplet, but also cylinder and co-continuous morphology (perpendicular to flow direction) can be formed depending on the volume ratio. For dynamic samples of HDPE/33EVA blends, droplet, cylinder and co-continuous network (co-continuous in both parallel and perpendicular to flow direction) can be formed under the effect of shear stress. The formation of phase morphology is discussed based on interfacial interaction, viscosity ratio, shear stress, and phase inversion.