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Polystyrene Based Layered Silicate Nanocomposite Foam Using Carbon Dioxide as Blowing Agent and Shear Rheology Study

Zhu, Bin
http://rave.ohiolink.edu/etdc/view?acc_num=osu1338226070

Abstract Details

2012, Doctor of Philosophy, Ohio State University, Chemical and Biomolecular Engineering.
Exfoliated layered silicate in the polystyrene (PS) block copolymer with different molecular weights was employed as a model material to investigate the PS nanocomposite foam expanded by the carbon dioxide. Using a well-controlled foaming procedure, we investigated the influence of molecular weight of PS and PS block copolymer, dispersion and loading of layered silicate and pressure drop rate of the blowing agent on the cell size and cell density. Our experimental results indicate that only exfoliated layered silicate can inhibit the cell expansion and has high nucleation efficiency during foaming. On the contrary, aggregated layered silicate in PS did not show any effect on the cell morphology of PS foam. In this dissertation, a hypothesis, which is different from the theory of heterogeneous nucleation, is proposed to explain the mechanism of the exfoliated layered silicate affecting PS foam cell size. The hypothesis is a continuous structure formed by the layered silicate substantially inhibits any deformation in the polymer phase including cell expansion. The dynamic frequency small amplitude oscillatory shear measurement was performed on all PS-70k/LS and Block-70k/LS samples to investigate the development and formation of percolation network formed by layered silicate in polymer matrix. Only in Block-70k/5-LS, the exfoliated layered silicate formed the percolation network which exhibited large reinforcement in G’, G” and |η*| and made the hybrid material to show solid-like properties in the whole tested frequency region. Due to a good dispersion of layered silicate, the threshold value of Block-70k/LS is 4.5wt.% which is much lower than that of PS-70k/LS. The dynamic strain amplitude sweep shear measurement was performed on the same samples to investigate the strain amplitude dependence of PS-70k/LS and Block-70k/LS. The tactoids of layered silicate, which could not form percolation network in PS-70k, were orientated and aligned under shearing with large strain amplitude. In that case, the viscoelastic properties of PS-70k/5-LS were very close to those of unfilled PS-70k. For Block-70k/5-LS, the percolation network formed by exfoliated layered silicate still existed under large strain amplitude shearing and exhibit significant reinforcement on viscoelastic properties of the hybrid material. The high pressure steady shear rheology was performed on PS-70k/LS and Block-70k/LS. All samples were tested at different temperatures and under different pressures of carbon dioxide. Magnitudes of shear viscosity exhibit obvious dependence on the testing temperature and pressure of carbon dioxide. Results of rheological measurements indicate that tactoids of layered silicate in PS-70k/LS were completely aligned under shearing. In that case, the viscosity curve of PS-70k/5-LS was merged to that of unfilled PS-70k that means the reinforcement effect from tactoids of layered silicate could be neglected. Since 5 wt% of exfoliated layered silicate could form percolation network in Block-70k/5-LS, the hybrid material exhibits obvious solid-like properties during the test of high pressure shear rheology. The shear viscosity was significantly reinforced by the percolated layered silicate and exhibited independence on testing temperature and pressure of carbon dioxide. In high shear rate region, since the structure of percolation network was deformed under shearing, the shear viscosity gradually decreases with the shear rate.
L. James Lee, PhD (Advisor)
Kurt Koelling, PhD (Committee Member)
Jose Castro, PhD (Committee Member)
191 p.
Chemical Engineering; Polymers
Layered Silicate; Polystyrene; Foam; Shear Rheology; Carbon Dioxide; High Pressure

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Citations

  • Zhu, B. (2012). Polystyrene Based Layered Silicate Nanocomposite Foam Using Carbon Dioxide as Blowing Agent and Shear Rheology Study [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338226070

    APA Style (7th edition)

  • Zhu, Bin. Polystyrene Based Layered Silicate Nanocomposite Foam Using Carbon Dioxide as Blowing Agent and Shear Rheology Study. 2012. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1338226070.

    MLA Style (8th edition)

  • Zhu, Bin. "Polystyrene Based Layered Silicate Nanocomposite Foam Using Carbon Dioxide as Blowing Agent and Shear Rheology Study." Doctoral dissertation, Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338226070

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.