Influence of injection rate on crystallization of injection-molded β-nucleated isotactic polypropylene

Gao, Xiaoliang; Huang, Zhigao; Zhou, Huamin; Zhang, Yi; Liang, Junjie

doi:10.1002/pen.24398

Cited by 8 publications

(4 citation statements)

References 45 publications

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“…The individual chips continuously bend until the two end chips make contact, intertwining to form the complete spherulite. In comparison with the α phase, the β phase, possessing a smaller spherical crystallite size and blurred crystal boundary, demonstrates higher impact strength and breakdown strength. − The amorphous region in polypropylene, especially at the spherical boundaries, exhibits a low tolerance for high-energy charge carriers, thus forming weak areas that are prone to electrical breakdown. The conducting path is mainly affected by the size of the spherulites, as shallower traps are located at the boundaries of the spherulites.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Energy Storage Properties of Polypropylene through Crystallization Modulation

Zhu,

Chen,

Pan

et al. 2024

ACS Appl. Polym. Mater.

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Polypropylene (PP), renowned for its high breakdown strength (E), low dielectric loss (tan δ), and excellent selfhealing properties, is widely utilized as the state-of-the-art dielectric polymer in power capacitors and green electric vehicles. However, the low dielectric constant (K) and limited discharged energy density (U e ) of polypropylene hinder the development of dielectric capacitors in miniaturization and integration. Here, a scalable polypropylene-based dielectric film with excellent energy storage properties comprising the lanthanide functional fillers (WBG) has been prepared using a melt extrusion process. Remarkably, the composite film with only 0.10 wt % of WBG demonstrates a high U e of 7.05 J/cm 3 and an ultrahigh charge−discharge efficiency (η) of 99.6% at 581.6 MV/m, coupled with long-term cyclic dielectric stability. The enhanced energy storage properties have been systematically analyzed and attributed to the formation of the βcrystalline phase and enhanced polarization induced by WBG. In a practical application demonstration, dielectric capacitors constructed from extruded composite films display stronger brightness, exhibiting a higher capacity than pure PP capacitors. This work provides a strategy to fabricate polypropylene dielectric films with excellent energy storage properties on an industrial scale.

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Section: Introductionmentioning

confidence: 99%

Enhanced Energy Storage Properties of Polypropylene through Crystallization Modulation

Zhu,

Chen,

Pan

et al. 2024

ACS Appl. Polym. Mater.

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“…For crystalline polymers, the PVT relationship diagram is even more complicated because of phase changes (Figure 1a) [15]. Controlling the extent of molded part shrinkage in crystalline polymers is particularly difficult because the processing conditions also affect the degree of crystallinity (DOC) [16][17][18][19], which plays a significant role in determining part shrinkage. To avoid the ambiguity of DOCinduced uncertainties for shrinkage or PVT behavior (Figure 1b), the solidification process during crystallization is often monitored [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Prediction of Part Shrinkage for Injection Molded Crystalline Polymer via Cavity Pressure and Melt Temperature Monitoring

Chen,

Tsai,

Hsieh

et al. 2023

Applied Sciences

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During an injection molding process, different parts of the molded material are subjected to various thermal–mechanical stresses, such as variable pressures, temperatures, and shear stresses. These variations form different pressure–temperature paths on the pressure–volume–temperature diagram. If these paths cannot converge at a specific target volume value during ejection, it often leads to different levels of shrinkage and associated warping, which pose a significant challenge for molders during mold trials and part quality control. The situation is particularly complicated when molding crystalline polymers because the degree of crystallinity depends on the processing conditions and may vary across different locations. In this study, we propose an innovative and practical approach to improving part shrinkage when molding crystalline polymers. For the first time, we utilized melt temperature profile monitoring rather than the previous mold temperature measurement to detect the crystallization process and determine the time taken to complete the crystallization at different melt and mold temperatures. In addition, we used response surface methodology to build a crystallization time prediction model. The feasibility of the prediction model was verified by determining the warpage of parts molded at various cooling times. Based on this model, we varied the packing pressure, packing time, and melt temperatures to determine the correlation with part shrinkage. Through regression analysis, the time-averaged solidification pressure values can accurately control part shrinkage. Two prediction models provide reasonable accuracy and efficiency for part shrinkage control, as demonstrated by subsequent verification experiments.

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“…[1,2] As a typical semicrystalline polymer, iPP has several different crystals: α, β, γ, and smectic crystals. [3][4][5][6] Compared with α-iPP, β-iPP exhibits excellent thermal stability and mechanical properties, which is currently arousing an intense research topic. Compared with α-crystal PP, however, it is difficult to fabricate β-crystal PP because of its thermodynamic metastable state.…”

Section: Introductionmentioning

confidence: 99%

Isothermal crystallization behaviors of isotactic polypropylene with ultrasonically‐modified calcium sulfate whisker as β‐nucleating agent

Shi

Qin

et al. 2022

Polymer Engineering & Sci

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In this work, the effect of calcium sulfate whisker (CSW) and ultrasonicallymodified CSW (UCSW) on the crystal structure and isothermal crystallization of isotactic polypropylene (iPP) is studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM). UCSW obviously increases heterogeneous nucleation. The isothermal crystallization kinetics of pure iPP, iPP/CSW, and iPP/UCSW composites are analyzed by the Avrami method. Although the Avrami exponent (n) of these samples only changed slightly, the half crystallization time (t 1/2 ) indicates that CSW and UCSW decrease the overall crystallization time and increase the crystallization rate (R c ). POM results show that most crystals are β-iPP shaped and the spherulite size decreases significantly with the addition of UCSW. The apparent equilibrium temperature of iPP/UCSW composites is lower than that of pure iPP and iPP/CSW composites. The values of β-iPP fold surface free energy (σ e ) and the nucleation parameter (K g ) are much lower than that of α-iPP for these iPP composites. The content of β-crystal in iPP composites increases due to the addition of UCSW.

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Influence of injection rate on crystallization of injection-molded β-nucleated isotactic polypropylene

Cited by 8 publications

References 45 publications

Enhanced Energy Storage Properties of Polypropylene through Crystallization Modulation

Enhanced Energy Storage Properties of Polypropylene through Crystallization Modulation

Prediction of Part Shrinkage for Injection Molded Crystalline Polymer via Cavity Pressure and Melt Temperature Monitoring

Isothermal crystallization behaviors of isotactic polypropylene with ultrasonically‐modified calcium sulfate whisker as β‐nucleating agent

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