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

TLDR

Microparts produced by micro‑injection molding can develop distinct morphological features compared to macroparts made by conventional injection molding, affecting their physical properties. The study aimed to compare the morphology of isotactic polypropylene microparts and macroparts. The comparison was performed using polarized light microscopy, scanning electron microscopy, differential scanning calorimetry, and wide‑angle X‑ray diffraction. Microparts exhibited a skin–core structure with a larger shear layer, highly oriented shish‑kebab lamellae, more homogeneous lamellae thickness, higher crystallinity and β‑crystal content, and stronger chain orientation than macroparts, which showed a larger core layer and random lamellae orientation. © 2011 John Wiley & Sons, Ltd.

Abstract

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 µm thickness and macroparts with 2000 µm 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 β‐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. Copyright © 2011 John Wiley & Sons, Ltd.