Axial‐feed thermoforming of oriented polypropylene tubes

Abstract

The effect of newly developed axial feed thermoforming process (AFTF) on mechanical properties and morphology were investigated to gain a better understanding of structure-properties-process relationship. The starting material for AFTF is an oriented polypropylene tube (OPP) produced in uniaxial direction by using solid state extrusion process. Morphological changes from solid-state extrusion are briefly reported. A die-less bulge testing system was designed to bulge OPP tube at a high temperature in biaxial direction. Wide-angle X-ray diffraction, field emission scanning electron microscope, and optical microscopy were used to characterize the microstructure of the extruded and bulged samples of OPP. In addition, tensile tests were carried out at room temperature of samples machined from the extruded and bulged tubes along the axial and hoop directions. The results show that tensile strength increases with draw ratio in extruded samples as well as improvements in ductility were obtained in die-less bulge tests with an increase in axial feed.

Orientation development in solid‐state extrusion and hot forming of polypropylene tubes

“…For thermoplastic polymers such as PP studied in this work, however, the formed tubes become more isotropic with increased axial feed due to the reorientation of molecular chains as shown in Figs. 21 and 22 [11]. The observed microstructure development is consistent with anisotropic mechanical properties of extruded tubes and more isotropic properties of the bulged tubes.…”

“…The lower actuator was used in tandem with the pressure intensifier to apply the pressure inside the tube. Further details were provided in an earlier paper [11]. The axial feed of the tube results on strain paths in the tension compression side of the forming limit diagram (FLD).…”

“…Research activities in the area of polymer forming by the current authors have demonstrated that structural‐oriented polypropylene (OPP) tubes can be formed at higher temperatures by processes such as axial‐feed hot oil or gas forming [10, 11]. This process typically results in strain paths that lie in the tensile‐compressive quadrant of the forming limit diagram.…”