Effect of Multi-Level Microstructure on Local and Bulk Mechanical Properties in Micro-Injection Molded PC/PET Blend

Abstract

This study introduces a method to investigate the relationship between the multi-level microstructures and mechanical properties of polymer blends prepared by micro-injection molding (µIM). Special morphological features were systematically researched. Polycarbonate (PC), poly(ethylene terephthalate) (PET), and PC/PET microparts all exhibit typical “skin-core” morphologies. The thickness of the core layer is much greater than that of the skin layer, and the thickness of the skin layer gradually decreases along the flow direction. Photoacoustic Fourier transform infrared spectroscopy records reveal that the PC molecular chain has the biggest orientation degree, followed by PC/PET and PET chains under the same µIM processing conditions. Moreover, the molecular chains orientation in the skin layer is more than 50% that in the core layer. Nanoindentation tests are conducted to study local mechanical properties. The higher modulus in the shear layer is affected to a greater extent by high shear action in comparison with the frozen and core layers. Uniaxial tensile testing demonstrates that the tensile strength of PC/PET micropart is 15.5% higher than that of the PET micropart, while the toughness is 16% higher than that of the PC microparts. In-situ, high- speed tensile imaging, combined with scanning electron microscopy micrographs of the fracture section, are used to study the fracture behaviors of the microparts. The results gathered in this paper may provide a theoretical basis and data to support the feasibility and efficiency of micro-injection molded polymer blends.