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Study the Toughening Mechanisms in Hybrid Epoxy/Rubber/CNT Nanocomposites

Jafari, Mohadeseh | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49681 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza; Pircheraghi, Gholamreza
  7. Abstract:
  8. Epoxy resins are used for a wide number of application due to good stiffness, chemical resistant and dimensional stability. This is the reason of their use as matrix in composite material. The incorporation of a small amount of carbon nanotubes (CNTs) in epoxy increases mechanical properties if nanocomposite have strong interfacial interaction between epoxy and CNTs, fine dispersion of CNTs and high final aspect ratio CNTs. In Noncovalent functionalization by polymer surfactant, CNTs are dispersed in a solvent/surfactant solution by ultra-sonication and then added to epoxy. In this thesis a novel study of toughening and mechanical properties of epoxy/ rubber/ CNT nanocomposite is presented. Carbon nanotube/epoxy nanocomposites were prepared via re-dispersion of ultrasonically dispersed CNTs in ethanol/ pluronic F127 solution. The ethanol solvent was evacuated from the epoxy nanocomposite during its re-dispersion in epoxy matrix and further using a vacuum oven at high temperature. The dispersion state of CNT in different solvents and epoxy matrix is assessed using different rheological measurements as well as UV-vis spectroscopy. The UV-vis and rheological measurements demonstrate that by using tetrahydrofuran and ethanol as solvent, the dispersion will be qualified. Afterward the effect of residual solvent, surfactant, CNTs and rubber on cured epoxy is evaluated. The outcome asserts that residual ethanol and surfactant result in decreasing fracture toughness and increasing glass transition temperature.Further, adding 0.15wt% CNT to epoxy leads to reducing Tg ( ̴ 4ᵒC) and UTS ( ̴ 44%), without changing in fracture toughness. Although SEM images of fractured surface of nanocomposite show good dispersion of CNT in cured epoxy, distribution of CNT is not uniform and stress concentration in CNT-rich area prevented from increasing fracture toughness. Eventually, it is illustrated addition of 5phr rubber to epoxy/ CNT nanocomposite increase fracture toughness significantly. In this line of thought rubber cavitation, shear yielding and pull-out of CNT are the main toughening mechanisms
  9. Keywords:
  10. Hybrid Nanocomposite ; Carbon Nanotubes ; Fracture Toughness ; Epoxy Resin

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