Effects of Process Temperatures on the Flow-Induced Crystallization of Isotactic Polypropylene/Poly(ethylene terephthalate) Blends in Microinjection Molding

Zhao, Zhongguo; Qi, Yang; Gong, Pengjian; Sun, Huaqin; Wu, Pingping; Huang, Yajiang; Liao, Xia

doi:10.1021/acs.iecr.7b02189

Cited by 19 publications

(22 citation statements)

References 62 publications

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“…The results showed that the yield strength and tensile modulus of the PP/PC MFCs improved by 66% and 17%, respectively, compared to that of the HDPE/PC blends molded by the common injection molding (CIM). Zhao et al [33] reported that the increased mold temperature could induce the formation of the lamella, fan-shaped β-crystals and transcrystals around the in situ poly(ethylene terephthalate) (PET) microfibrils. However, there are also some studies about the negative effects of the injection molding process.…”

Section: Introductionmentioning

confidence: 99%

“…However, there are also some studies about the negative effects of the injection molding process. For example, the injection molding process caused a reduction in the microfibrilar aspect ratio [20,33,34], which was a key to determining the performances of the MFCs. Moreover, little attention extensively focused on the effects of the dispersed phases formed in the process of the microfibrillation on the crystal structure and performance of the matrix in the polymer blends.…”

Section: Introductionmentioning

confidence: 99%

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The Formation of a Highly Oriented Structure and Improvement of Properties in PP/PA6 Polymer Blends during Extrusion-Stretching

et al. 2020

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During the “slit die extrusion-hot stretching” process, highly oriented polyamide 6 (PA6) dispersed phase was produced and retained in the polypropylene (PP) matrix directly. By adjusting the stretching forces, the PA6 spherical phase evolved into the ellipsoid, rod-like microfibril with a decreasing average diameter; then, the PA6 microfibrils broke. Moreover, the effects of the PA6 phases formed in the process of the microfibrillation on PP’s crystallization behaviors were studied systematically. As the stretching forces increased, the crystallization ability and orientation degree of PP crystals improved significantly. Differential scanning calorimetry and polarizing optical microscopy confirmed the formation of PP spherulite, fan-shaped lamellae and a transcrystalline layer under the induction of the PA6 phases with different morphology. In the PP/PA6 microfibrilar composites (MFCs), PP crystals showed smaller average size, more crystals and stronger interface adhesion due to more excellent heterogeneous nucleation ability of the PA6 microfibrils, which made contributions to the improvement of the melt elasticity responses and oxygen barrier properties of the PP/PA6 polymer blends.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Formation of a Highly Oriented Structure and Improvement of Properties in PP/PA6 Polymer Blends during Extrusion-Stretching

et al. 2020

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“…In the present work, µIM is adopted to adjust the microstructure of iPP/PET blends, and so called "in-situ PET microfibrils" can be formed during this µIM process. In our previous report [17,18], the formation of PET microfibers was affected by the mold temperature and melt temperature under microinjection molding conditions. Both increasing the melt temperature and decreasing the mold temperature are beneficial to form well-defined, long, PET microfibers.…”

Section: Introductionmentioning

confidence: 91%

Crystallization and Microstructure Evolution of Microinjection Molded Isotactic Polypropylene with the Assistance of Poly(Ethylene Terephthalate)

Zhao

Zhang

et al. 2020

Polymers

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In this work, a series of isotactic polypropylene/poly(ethylene terephthalate) (iPP/PET) samples were prepared by microinjection molding (μIM) and mini-injection molding (IM). The properties of the samples were investigated in detail by differential scanning calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Polarized light microscope (PLM) and scanning electron microscopy (SEM). Results showed that the difference in thermomechanical history between both processing methods leads to the formation of different microstructures in corresponding iPP/PET moldings. For example, the dispersed spherical PET phase deforms and emerges into continuous in-situ microfibrils due to the intensive shearing flow field and temperature field in μIM. Additionally, the incorporation of PET facilitates both the laminar branching and the reservation of oriented molecular chains, thereby leading to forming a typical hybrid structure (i.e., fan-shaped β-crystals and transcrystalline). Furthermore, more compact and higher degrees of oriented structure can be obtained via increasing the content of PET. Such hybrid structure leads to a remarkable enhancement of mechanical property in terms of μIM samples.

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“…Investigations of the morphology evolution mechanism, including chain orientation and crystallization, formed by MIM are relatively rare. Most of these primarily concentrated on the effect of MIM processing parameters on morphology evolution . Researches have shown that the morphology through the thickness of the micropart normally exhibited a similar skin‐core structure as the morphology of the macropart, but micropart presented a large fraction of shear layer in comparison to macropart .…”

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

Polymers for Advanced Techs

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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

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Effects of Process Temperatures on the Flow-Induced Crystallization of Isotactic Polypropylene/Poly(ethylene terephthalate) Blends in Microinjection Molding

Cited by 19 publications

References 62 publications

The Formation of a Highly Oriented Structure and Improvement of Properties in PP/PA6 Polymer Blends during Extrusion-Stretching

The Formation of a Highly Oriented Structure and Improvement of Properties in PP/PA6 Polymer Blends during Extrusion-Stretching

Crystallization and Microstructure Evolution of Microinjection Molded Isotactic Polypropylene with the Assistance of Poly(Ethylene Terephthalate)

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

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