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  • Molecular Diversity Preservation International  (5)
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  • 1
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    Growing Nano-SiO2 on the Surface of Aramid Fibers Assisted by Supercritical CO2 to Enhance the Thermal Stability, Interfacial Shear Strength, and UV Resistance (2019)
    Molecular Diversity Preservation International
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    Publication Date: 2019-08-26
    Description: Aramid fibers (AFs) with their high Young′s modulus and tenacity are easy to degrade seriously with ultraviolet (UV) radiation that leads to reduction in their performance, causing premature failure and limiting their outdoor end use. Herein, we report a method to synthesize nano-SiO2 on AFs surfaces in supercritical carbon dioxide (Sc-CO2) to simultaneously improve their UV resistance, thermal stability, and interfacial shear strength (IFSS). The effects of different pressures (10, 12, 14, 16 MPa) on the growth of nanoparticles were investigated. The untreated and modified fibers were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was found that the nano-SiO2-decorated fibers exhibited improvement of thermal stability and mechanical properties, and the IFSS of the nano-SiO2 modified fibers increases by up to 64% compared with the untreated fibers. After exposure to 216 h of UV radiation, the AFs-UV shows a less decrease in tensile strength, elongation to break and tensile modulus, retaining only 73%, 91%, and 85% of the pristine AFs, respectively, while those of AFs-SiO2-14MPa-UV retain 91.5%, 98%, and 95.5%. In short, this study presents a green method for growing nano-SiO2 on the surface of AFs by Sc-CO2 to enhance the thermal stability, IFSS, and UV resistance.
    Electronic ISSN: 2073-4360
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 2
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    Effect of Different Pressures of Supercritical Carbon Dioxide on the Microstructure of PAN Fibers during the Hot-Drawing Process (2019)
    Molecular Diversity Preservation International
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    Publication Date: 2019-03-01
    Description: The hot-drawing process of polyacrylonitrile (PAN) fibers is an important step during the production of PAN-based carbon fibers. In this study, supercritical carbon dioxide (Sc-CO2) was used as one kind of media for thermal stretching of PAN fibers to study the effect of different pressures of Sc-CO2 on crystallinity, degree of orientation and mechanical property of PAN fibers during the hot-drawing process. The changes of microstructure and mechanical properties in the PAN fibers were investigated by wide-angle X-ray diffraction, small angle X-ray scattering and monofilament strength analysis. The results showed that as the pressure increased, the crystallinity and degree of orientation of PAN fibers increased. Furthermore, when the pressure was 10 MPa, the crystallinity increased from 69.78% to 79.99%, which was the maximum crystallinity among the different pressures. However, when the pressure was further increased, the crystallinity and degree of orientation of the fibers were reduced. The test results of the mechanical properties were consistent with the trends of crystallinity and degree of orientation, showing that when the pressure was 10 MPa, the tensile strength of the fibers increased from 4.59 cN·dtex−1 to 7.06 cN·dtex−1 and the modulus increased from 101.54 cN·dtex−1 to 129.55 cN·dtex−1.
    Electronic ISSN: 2073-4360
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 3
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    Recyclable Choline Nicotinate and Ferulate Aqueous Solutions as Efficient Lignin Solvents (2018)
    Molecular Diversity Preservation International
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    Publication Date: 2018-07-30
    Description: Four novel choline carboxylate aqueous solution systems were developed by mixing H2O with choline nicotinate [Ch][Na], choline ferulate [Ch][Fa], choline vanillate [Ch][Va] and choline syringate [Ch][Sa]. The solubility of lignin in the four solvents was determined at 25 °C. The influence of the molar ratio of H2O to [Ch][Na] ([Ch][Fa], [Ch][Va] and [Ch][Sa]) and the anionic structure on lignin solubility were systematically investigated. It was found that, the anionic structure and H2O content significantly affected lignin dissolution. Interestingly, H2O/[Ch][Na] and H2O/[Ch][Fa] solvents show efficient capacity for lignin dissolution even at room temperatures. The dissolution of lignin in H2O/[Ch][Na] and H2O/[Ch][Fa] solvents is mainly ascribed to the interaction of lignin with the alkyl chain in the anion and cation dissociated from [Ch][Na]([Ch][Fa]) by H2O. In addition, the recycling of the lignin solvent was examined, and the structure and thermostability of the lignin regenerated from the solvent were also estimated.
    Electronic ISSN: 2073-4360
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 4
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    Study on the Changes of Structures and Properties of PAN Fibers during the Cyclic Reaction in Supercritical Carbon Dioxide (2019)
    Molecular Diversity Preservation International
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    Publication Date: 2019-03-01
    Description: Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO2) medium was studied. The thermal behaviors of the PAN fibers were investigated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The cyclization reaction was sensitive to the heating temperature and gas atmosphere. The FT-IR results of the PAN fibers treated in the Sc-CO2 confirmed that the degree of cyclization increased with the increase of the cyclization temperature. Compared with the PAN fibers treated in the air, the PAN fibers treated in the Sc-CO2 showed a higher degree of cyclization even at the same temperature. These findings might be related to the osmotic action of Sc-CO2 causing the fibers to be further arranged in a regular manner, which was favorable for the cyclization reaction. Moreover, as one kind of high diffusion and high heat transfer media, the heat release during the cyclization of PAN fibers could be quickly removed by Sc-CO2, which achieved the progress of the rapid-entry cyclization reaction.
    Electronic ISSN: 2073-4360
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 5
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    Comparison Study of Induction Motor Models Considering Iron Loss for Electric Drives (2019)
    Molecular Diversity Preservation International
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    Publication Date: 2019-02-05
    Description: In a variety of motor models, the effects of iron-loss (ILS) on motor control accuracy and efficiency are generally ignored. This makes it difficult for the motor control system to obtain accurate control parameters (especially on high speed and low load conditions), and limits the improvement of motor control accuracy. This paper aims to clarify the influence of different ILS modeling and observation methods on motor control performance. Three equivalent models of motors with iron losses are compared. These models are: A parallel model, a series model and the simplified traditional model. Three tests are conducted to obtain the effect of ILS perturbation on ILS estimation results, and then to derive the sensitivity of the motor state and torque to the perturbation. These test conditions include: Ideal no-load, heavy-load, locked-rotor, and ILS perturbations during speed regulation. Simulation results show that the impedance and excitation characteristics of the series model and the parallel model are similar, and the traditional model has the best speed regulation smoothness. The ILS estimation errors of the series model is nearly constant and easy to compensate. For accurate ILS observation results, the series model can achieve better control accuracy.
    Electronic ISSN: 1996-1073
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Molecular Diversity Preservation International
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