Morphological comparison of isotactic polypropylene parts prepared by micro‐injection molding and conventional injection molding

Abstract

The morphological feature of microparts evolved during micro-injection molding may differ from that of the macroparts prepared by conventional injection molding, resulting in specific physical properties. In this study, isotactic polypropylene (iPP) microparts with 200 mm thickness and macroparts with 2000 mm thickness were prepared, and their morphological comparison was investigated by means of polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and wide-angle X-ray diffraction (WAXD). The results presented some similarities and differences. PLM observations showed that the through-the thickness-morphology of micropart exhibited a similar ''skin-core'' structure as macropart, but presented a large fraction of shear layer in comparison to the macropart which presented a large fraction of core layer. The SEM observation of shear layer of micropart featured highly oriented shish-kebab structure. The micropart had a more homogeneous distribution of lamellae thickness. The degree of crystallinity of the micropart was found to be higher than that of the macropart. High content of b-crystal was found in micropart. The 2D WAXD pattern of the core layer of macropart showed full Debye rings indicating a random orientation, while the arcing of the shear layer indicates a pronounced orientation. The most pronounced arcing of the micropart indicates the most pronounced orientation of iPP chains within lamellae.

Morphology evolution and crystalline structure of controlled‐rheology polypropylene in micro‐injection molding

“…Molecular weight distribution curves of controlled-rheology polypropylene specimens. This figure is available in colour online at wileyonlinelibrary.com/journal/pat by simple one-dimensional heat conduction equation [eqn (8)] [48] :…”

Cavitation Behavior of Semi-Crystalline Polymers during Uniaxial Stretching Studied by Synchrotron Small-Angle X-Ray Scattering

“…As to microinjection molding, the flow field in the cavity is quite strong due to the small cavity size especially for the first two cases. Therefore, a larger fraction of the skin layer is formed compared to common injection molding part [36], which means that a larger fraction of oriented structures exists in the microinjection-molded sample compared to the macroinjection-molded one.…”

Effects of ultrahigh molecular weight polyethylene and mould temperature on morphological evolution of isotactic polypropylene at micro-injection moulding condition

“…MIM refers not only to actual reductions in the size of parts but also to the extreme processing environment involved in this process, such as extremely high shear rate, high temperature gradient, high injection pressure and high injection rate (can reach 800 mm/s or higher), etc. This can affect the crystallization behaviour of semicrystalline polymers, that is, the nucleation and growth of crystalline lamellae, resulting in a specific morphology that differs from that of macroparts prepared via conventional injection moulding [6,7].…”