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Ultrasound Assisted Extrusion and Properties of Polycarbonate/Carbon Nanotubes Composites and Cast Films

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2017, Doctor of Philosophy, University of Akron, Polymer Engineering.
Dispersion and distribution of carbon nanotubes (CNT) play a vital role in transferring the extraordinary properties of CNT to polymer composites. This research aimed to investigate ultrasound assisted twin screw extrusion technology on improving the dispersion and distribution of multi-walled (MWNT) and single-walled (SWNT) carbon nanotubes in polycarbonate (PC) composites and cast films. Concentrations of MWNT and SWNT were up to 1.5 wt% and 0.3 wt%, respectively. The effects of ultrasonic amplitude, molecular weight of PC, processing parameters (flow rate and screw configuration), intrinsic properties of CNT on the performance of end products were systematically studied. Electrical, rheological, morphological, mechanical and thermal properties were characterized to illustrate the processing-structure-property relationship during ultrasonic extrusion and film casing. Generally, the torque of the extruder decreased with the increasing ultrasonic amplitude, which is favorable in industrial practice to increase the throughput. Ultrasonic treatment showed significant effect on improving the dispersion of CNT in PC composites and cast films and decreasing the electrical and rheological percolation threshold. Also, the application of ultrasound caused some degradation of PC matrix. The Young’s modulus and yield stress of PC/CNT composites and films generally increased, while the elongation at break and tensile strength decreased with increasing CNT concentration. The mechanical properties were slightly improved by ultrasonic treatment. The storage and loss moduli and complex viscosity of composites was increased and loss tangent was decreased by the incorporation of CNT and ultrasonic treatment, especially in low frequency region. The comparison of PC composites with different CNT indicated that the aspect ratio, surface area, dispersability and entanglement structure of CNT had significant influence on the dispersion and performance of the polymer composites and cast films. For PC/MWNT composites with PC of two different molecular weights, the effect of ultrasound on improving MWNT dispersion was more pronounced in the composites with PC of lower molecular weight. During extrusion at a high flow rate, the dispersion of MWNT in PC was poor, due to short residence time and less shearing energy. Ultrasonic treatment improved the dispersion of MWNT with increasing ultrasonic amplitude leading to decreasing electrical percolation threshold. The effect of screw configuration on dispersion and distribution of SWNT was explored in the online film casting of PC/SWNT composite films. The screw design containing more kneading blocks led to better SWNT dispersion and distribution, while the effect of ultrasound was more prominent in screw design with less kneading blocks. Moreover, the necking phenomenon during online ultrasonic film casting of PC/MWNT composite films was investigated. The incorporation of CNT reduced the necking of films, resulting in larger film width. Numerical simulations of film casting process under isothermal and non-isothermal conditions were performed to predict film profile along casting direction. Velocity in stretching direction, temperature, thickness and width of film in stretching direction and stretching force were calculated. It was found that the predicted film profile obtained from non-isothermal simulation were in better agreement with the film profile obtained in experiment.
Avraam Isayev (Advisor)
Erol Sancaktar (Advisor)
Younjin Min (Committee Chair)
Yu Zhu (Committee Member)
Jiahua Zhu (Committee Member)
370 p.

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Citations

  • Gao, X. (2017). Ultrasound Assisted Extrusion and Properties of Polycarbonate/Carbon Nanotubes Composites and Cast Films [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493394163570255

    APA Style (7th edition)

  • Gao, Xiang. Ultrasound Assisted Extrusion and Properties of Polycarbonate/Carbon Nanotubes Composites and Cast Films. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1493394163570255.

    MLA Style (8th edition)

  • Gao, Xiang. "Ultrasound Assisted Extrusion and Properties of Polycarbonate/Carbon Nanotubes Composites and Cast Films." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493394163570255

    Chicago Manual of Style (17th edition)