Filling behavior, morphology evolution and crystallization behavior of microinjection molded poly(lactic acid)/hydroxyapatite nanocomposites

A series of polycarbonate (PC)/multiwalled carbon nanotubes (CNT) nanocomposites were prepared by diluting a commercially available masterbatch using a neat PC resin in a lab‐scale batch mixer. The obtained nanocomposites were subjected to microinjection molding to fabricate microparts, which have a 3‐step decrease in thickness along the flow direction, under a defined set of processing conditions. The obtained microparts were mechanically divided into 3 different sections, namely, thick, middle, and thin sections, based on thickness. Morphology observations and electrical conductivity measurements were conducted to explore the evolution of microstructure within subsequent microparts. Additionally, a comparison of the electrical and morphological properties of stepped microparts of various thermoplastic polymers filled with CNT was studied. Results suggested that the selection of host polymers influences the dispersion of nanotubes within subsequent moldings, thereby affecting the electrical properties. The thermal stability of subsequent moldings deteriorated upon the addition of CNT, suggesting that the addition of CNT and the thermomechanical history experienced by the polymer melts in microinjection molding might cause a chain scission effect on PC. Raman spectroscopy analysis was used to study the orientation and properties of CNT in microparts.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microinjection molding of multiwalled carbon nanotubes (CNT)–filled polycarbonate nanocomposites and comparison with electrical and morphological properties of various other CNT‐filled thermoplastic micromoldings

Zhou

Hrymak

Kamal

2018

“…Microinjection molding (MIM) is currently one of the most promising processing methods for fabricating polymeric microparts, such as biochips, microgears, microheat exchangers, and so on . MIM process not only reduces the actual dimensions of the molded products, but also involves extreme and complicated thermomechanical history, including high‐temperature gradient, extremely high shear rate, high injection pressure, and so on .…”

Section: Introductionmentioning

confidence: 99%

Influence of scale effect and injection speed on morphology and structure of the microinjection molded isotactic polypropylene parts

Wang

Jiang

et al. 2020

The morphology and microstructure as well as their forming mechanism of the parts in microinjection molding process are critical. In this work, the coupling effect of scale factor and injection speed on the morphology of the microparts was systematically investigated. Neat isotactic polypropylene parts with thicknesses of 1 mm, 200 μm, and 100 μm were molded at different injection speeds. Polarized light microscope and wide-angle X-ray diffraction were used to inspect the microstructures along the sample thickness. In this way, three kinds of typical morphology were observed in the parts, including typical skin-core structure for the parts with the thickness of 1 mm, noncore shear layer structure for the parts with the thickness of 200 μm, and special skin-core structure with large fraction of columnar crystal for the parts with the thickness of 100 μm. Most interestingly, it was intuitively and straightforward found that the wall slip occurs when the injection speed exceeds a certain value. Specifically, opposite morphological change trend can be obtained when the parts were molded at different levels of injection speeds. Based on these experimental observations, the formation mechanism was proposed to interpret the morphological evolution. Our work provides a new insight for better understanding the morphology evolution mechanism for microinjection molding parts. K E Y W O R D Scolumnar crystal structure, microinjection molding, morphology and structure, noncore structure, wall slip 1 | INTRODUCTION Microinjection molding (MIM) is currently one of the most promising processing methods for fabricating polymeric microparts, such as biochips, microgears, microheat exchangers, and so on. 1-3 MIM process not only reduces the actual dimensions of the molded products, but also involves extreme and complicated thermomechanical history, including high-temperature gradient, extremely high shear rate, high injection pressure, and so on. 4-6 These special phenomena can affect the crystallization behavior of the semicrystalline polymers during the MIM manufacturing process. It is for this reason that the morphologies of the obtained products were different from traditional injection molding. 7-10 As is known to all, morphologies and physical properties (mechanical, optical, electrical, transport, and chemical) 11-14 are closely correlated for polymeric parts. Hence, the first step toward highperformance MIM parts is to thoroughly and systematically investigate the morphology evolution mechanism.At present, researches of MIM techniques have mainly focused on specific injection machines, 13,15 numerical simulation, 16-20 and replicating capability analysis. [21][22][23][24] Investigations of the morphology

“…Microinjection molding parts are significantly different from those obtained by the conventional injection molding process, especially given their characteristic micro-structural features and layered induced morphology. 5 An in-depth investigation on the induced morphology distribution within the mold under the conventional injection molding process was conducted by Pantani et al 6 Microinjection molding employs high injection velocity to avoid premature solidification of the molten polymer. Thus, high shear rates are employed causing high-temperature rise.…”

mentioning

confidence: 99%

Simulation of crystallization evolution of polyoxymethylene during microinjection molding cycle

Benayad

Boutaous

Otmani

et al. 2019

A mathematical model coupled with a numerical investigation of the evolving material properties due to thermal and flow effects and in particular the evolution of the crystallinity during the full microinjection molding cycle of poly (oxymethylene) POM is presented using a multi‐scale approach. A parametric analysis is performed, including all the steps of the process using an asymmetrical stepped contracting part. The velocity and temperature fields are discussed. A parabolic distribution of the velocity across the part thickness, and a temperature rise in the thin zone toward the wall have been obtained. It is attributed to the viscous energy dissipation during the filling phase, but also to the involved characteristic times for the thermal behavior of the material. Depending on the molding conditions and the locations within the micro‐part, different evolution of crystallization rates are obtained leading to at least three to five morphological layers, obtained in the same part configuration of a previously work, allowing a clear understanding of the process‐material interaction.