Viscoelastic flow analysis of surface morphology on injection‐molded polypropylene

Abstract

The molecular orientation of a frozen layer in an injection‐molded specimen of a polypropylene–rubber blend was investigated. A typical V‐shaped pattern of birefringence was observed from the surface to the core in a crosscut section. From the comparison of the V‐patterns near the gate to the flow end, it was assumed that a frozen layer formed from the surface to a depth of 0.06 mm in a plaque (3 mm thickness) during the injection molding filling process. Numerical viscoelastic analysis of the fountain flow was carried out using an original 2D unsteady flow simulation program and ignored crystallization. A large extensional deformation formed just when the molten polymer contacted the cavity wall and the deformation immediately froze. A layer with a small birefringence between the surface and the shear‐oriented layer was divided into two parts. The depth profile of birefringence was compared to the principal stress difference calculated by numerical analysis. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Crystallization of polypropylene near the surface in injection‐molded plaques: A comparison of morphology and a numerical analysis

“…The crystallinity stays constant inside the 100-μm depth because the crystallization temperature is expected to be higher than 123 °C. Our previous study suggested that the frozen-in orientation near the surface occurred at high temperature [19]. High orientation near the surface was also observed in this study, even if the crystallinity was low.…”

“…The numerical method was the same as in the previous work [19]. We assumed dimensionless particles in the fluid and tracked their movement and deformation in the non-isothermal transient condition.…”

“…Our purpose in this study was to clarify the skin morphology formation in the [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] μm depth region by a WAXD analysis of three types of nucleated PP and by an original 2-D viscoelastic flow simulation program. Birefringence with a polarizing optical microscope (POM) and micro-beam synchrotron WAXD were utilized for evaluating injection-molding-induced morphology.…”

The unique flow of polypropylene at the weld line behind an obstacle in injection molding

“…Consequently, the Al flakes at the center of the ND ordered perpendicular to the wall surface. In our previous study using an original 2‐D unsteady flow simulation program for a viscoelastic fluid, the formation of a frozen layer in an injection‐molded specimen was described using the fountain‐flow concept [10]. In this model, at the advancing flow front molten polymer moves from the center to the surface and is subjected to large deformation and then quenched at the cold wall surface.…”

Effect of melt flow on morphology and linear thermal expansion of injection-molded ethylene-propylene-diene terpolymer/isotactic polypropylene blends

“…Generally, specimens with a structure of co‐continuous microlayers are fabricated by injection molding. The melt complexly flows during injection molding, which is critical in determining morphology . The molten polymer flows from the middle of the cavity towards the wall and is subjected to extensional deformation.…”