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

Abstract

Skin morphology formation on injection-molded isotactic polypropylene (PP) was investigated using micro-beam synchrotron wide-angle X-ray diffraction and numerical simulation. The 1-20-μm depth range was characterized with an X-ray beam of 0.273 μm × 0.389 μm in size. From an evaluation of doping nucleating agents (NA) in PP, the NAs did not work at a depth of 1 μm. α-specified NA affected crystallization within a 5-μm depth. β-specified PP showed α-form crystallinity at the 5-20 μm depth. The mesomorphic crystal near the surface showed extremely high orientation. From viscoelastic flow simulation, PP molecules near the surface were oriented in the flow direction by extensional flow in the flow front, but freezing occurred faster than flow-induced crystallization. It was estimated that the delay of crystallization occurred during the transient temperature. The deformation rate did not cause a difference in crystal morphology near the surface, but the cooling rate did.3

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

“…Figure 9 shows a cross‐section of the weld line at a point 100 mm behind the obstacle as observed using POM. White spots appearing in the core layer are β‐form spherulites, which were identified using wide‐angle X‐ray diffraction in our previous study [12]. A skin layer was homogeneously formed at the weld as well as at at other positions, but the amount of β‐form spherulites at the weld line was smaller than those in the other positions.…”

Microinjection molding of microsystem components: new aspects in improving performance

“…Indeed, a number of constitutive models such as the Phan-Thien-Tanner (PTT), Leonov, Giesekus, and Oldroyed-B equations (see [98] for details) are available for describing polymer melts as well as polymer solutions, while judging their suitability for a specific case is not an easy task [99]. To take advantage of the ability to independently describe shear and extensional properties that are of equal importance in the μIM process, the PTT model has been adopted by several research groups [96,100,101]. For instance, more uniform melt fronts in multi-cavities and more agreeable results with the real manufacturing process can be numerically achieved, compared with the viscous model [96].…”

Model and simulation for melt flow in micro-injection molding based on the PTT model

“…This leads to the fact that the PTT model is superior to others in modeling micro-injection flows. In addition, recent works [19,20] have show that this model has the ability to predict flow-induced stresses for non-equilibrium flows in injection molding. Therefore, the PTT model was employed to describe the flow behavior in this work.…”