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Effect of Microstructure Factors on Fracture Behavior of Clay-Rubber-Epoxy Hybrid Nanocomposites

Tekyeh Marouf, Bahereh | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39237 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Sceicne and Engineering
  6. Advisor(s): Bagheri, Reza
  7. Abstract:
  8. The aim of this study is to investigate the effects of nanoclay and rubber particles morphologies on fracture behavior of a lightly cross-linked epoxy. In addition, the role of cavitation resistance of rubber particles on fracture behavior of the nanoclay-rubber-epoxy hybrids was studied. Two types of organoclay and three kinds of rubber modifiers (in micron and nano-size) were incorporated into the epoxy. The results obtained indicate that addition of either intercalated or exfoliated clay increases fracture toughness of the epoxy resin, although the increases in toughness are modest (a 50% increase). The microscopy examinations and the micromechanical models revealed that the improvements in fracture toughness can be attributed to crack bifurcation and microcracking mechanisms in clay-filled epoxy nanocomposites. The results of rubber-modified systems indicate that nano-rubbers are effective toughening agents for epoxy resins (a 150-250% increase in fracture toughness). Nano-size rubber modifiers cavitated. Interestingly in the hybrid materials, addition of small amount of organoclay to a nano-size rubber toughened epoxy decrease (40-60%) the fracture resistance of the compounds as a function of organoclay content, while expected improvement of fracture toughness in the hybrid epoxies in relative to the rubber modified blends. Based on the microscopy studies, competition between micro-mechanisms is responsible for the anomalous fracture behavior of these hybrid epoxies. Furthermore, the results of this study show the importance of rubber particle cavitation resistance. In addition, X-ray ultra-microscopy (XuM) was used as a novel technique to study the fracture behavior and elucidate the toughening mechanisms in epoxy-based compounds as well. Noteworthy, XuM offers a good opportunity to look at the crack tip in epoxy compounds and suggests finger-like crack propagation in epoxy-based compounds either rubber-modified or nanoclay-filled systems.
  9. Keywords:
  10. Rubber ; Deformation ; Epoxy Compounds ; Hybrid Nanocomposite ; Nanoclay ; Toughening Mechanism

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