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SOC Thesis ETD 06142016.pdf (2.69 MB)

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EXTENSIONAL FLOWS IN POLYMER PROCESSING: EFFECTS ON MIXING AND MATERIAL PERFORMANCE

Carson, Sidney O
http://rave.ohiolink.edu/etdc/view?acc_num=case1466073482

Abstract Details

2016, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering.
This dissertation focuses on the study of the presence of extensional flows in common plastics processing operations, mainly in twin-screw extrusion. Twin-screw extruders are one of the most commonly used pieces when a mixing task for polymer processing is presented, and as such there is much interest in the investigation of its overall mixing capabilities. Shear flows have been proven time and again to be inferior in mixing efficiency when compared to extensional flows. Kneading blocks (KB) make up the majority of the mixing profile of a typical twin-screw extruder screw, and while there are extensional flow component present in their mixing operations, the main mixing mechanism in these elements is still shear dominated. Considering this, the Extensional Mixing Elements (EME) for twin-screw extrusion were developed for the purposes of imposing extension dominated flow during twin-screw extrusion and therefore increase the mixing capabilities of current mixing and processing equipment. The EME was designed as a static element that interfaces directly with the screw shaft of a twin-screw extruder, being built in a screw configuration like a standard element. It achieves mixing by forcing flowing material through channels around the diameter of each element that are designed as hyperbolic contractions, which impart extension dominated flow along their centerline. Computational investigations of the velocity profiles through each of the contractions at typical operating conditions suggest the presence of these extensional flows with measurable and predictable strain rates. The first experimental validation of the EME was performed by compounding incompatible polypropylene/polystyrene blends (PP/PS) and comparing with the same blends produced through a standard KB configuration. Four viscosity ratios were investigated (0.3, 1, 3, and 10) and the resulting morphologies were characterized using SEM and image analysis. Statistically, the EME proved to be the superior dispersive mixing device when considering the measured droplet sizes over all viscosity ratios. This was extended further to the compounding of polymer-solid filler composites using carbon black, carbon nanotubes, and graphene nanosheets. These composites were characterized using optical microscopy to probe micro-level dispersion followed by rheology and electrical resistivity measures to probe nano-level dispersion. At the micro-level (investigating agglomerate sizes), the EME outperformed the chosen KB configuration by a large margin; however, at the nano-level, there does not seem to be any improvements in property enhancement or individualization of filler particles with the two geometries. More computational investigations of more extreme contraction geometries were undertaken to determine the limits of design flexibility for the EME. The mixing profiles (degree of shear vs. extensional flow, overall stress level) of these geometries were also compared with a KB configuration. All contractions showed more extension dominated flow patterns when compared to the KB, with more extreme contractions also matching the average stress level seen in operation. Increasing the contraction intensity predictably increased the extensional profile of the contractions, but balance with the required pressure in operation had to be considered as well. Finally, the presence of extensional flows in injection molding and their influence on final part properties was investigated as an extension of the consideration of flow type in practical processing operations. Polycarbonate/carbon nanotube composites were molded into shear dominated parts (plaques) and two different hyperbolic contractions and their electrical resistivity was measured. Highly extension dominated flow decreased the resistivity of the resulting composites, indicating that part design and flow type in injection molding play a role in the development of important composite properties.
João Maia (Advisor)
Ica Manas-Zloczower (Committee Member)
Alexander Jamieson (Committee Member)
James McGuffin-Cawley (Committee Member)
176 p.
Engineering; Polymers

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Citations

  • Carson, S. O. (2016). EXTENSIONAL FLOWS IN POLYMER PROCESSING: EFFECTS ON MIXING AND MATERIAL PERFORMANCE [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1466073482

    APA Style (7th edition)

  • Carson, Sidney. EXTENSIONAL FLOWS IN POLYMER PROCESSING: EFFECTS ON MIXING AND MATERIAL PERFORMANCE. 2016. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1466073482.

    MLA Style (8th edition)

  • Carson, Sidney. "EXTENSIONAL FLOWS IN POLYMER PROCESSING: EFFECTS ON MIXING AND MATERIAL PERFORMANCE." Doctoral dissertation, Case Western Reserve University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1466073482

    Chicago Manual of Style (17th edition)

case1466073482
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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.