Development of Laminated Carbon Nanofiber Reinforced Polyurethane Composites

Open Access
Author:
Mangiagli, Patrick Michael
Graduate Program:
Engineering Science and Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 09, 2013
Committee Members:
  • Charles E Bakis, Thesis Advisor
  • Christopher Rahn, Thesis Advisor
  • James Hansell Adair, Thesis Advisor
  • Judith Todd Copley, Thesis Advisor
Keywords:
  • aligned carbon nanofiber
  • CNF
  • nanocomposite
  • Halpin-Tsai
  • flexible laminates
  • bio-inspired
  • silane coupling agents
Abstract:
Fiber reinforced elastomers are of wide interest for adaptive structures that can change shape or stiffness with external stimuli. In order to manufacture such flexible matrix composites of reduced size and thickness (sub-millimeter), traditional continuous fiber composite manufacturing methods are not suitable. Therefore, the objective of the current investigation is to develop a manufacturing method for laminated carbon nanofiber (CNF) reinforced elastomer composites that demonstrate stress-strain behavior similar to laminated continuous fiber composites. The scope of the work includes: (i) the development and refinement of an extrusion-based CNF alignment procedure for sub-millimeter films that is compatible with the short pot life and high viscosity of polyurethane (PU) matrices; (ii) development of a lamination procedure for thin CNF/PU composites; and (iii) testing and analysis of the CNF/PU laminates to demonstrate that the material follows classical laminated plate theory. To-date, there is no published literature on laminated CNF reinforced flexible composites, making the current investigation the first of its kind. Theoretical predictions suggest that the ratio of longitudinal to transverse modulus of elasticity of the aligned CNF/PU composite with 10.5% CNFs by volume should be 22. However, the experimental modulus ratio was only in the range of 2.5 to 3.5. The greatest increase in the elastic modulus of the material in the alignment direction was a factor of 19 versus the unreinforced matrix for the case of functionalized CNFs, which is less than the ideal factor of 28 predicted by theory. Both of these results indicate imperfect alignment or bonding of the CNFs in the PU matrix. Once the elastic properties of the as-extruded material were characterized, good agreement with classical lamination theory was obtained for a variety of laminates with different CNF orientations. Recommendations are made for enhancing the alignment and/or straightening of the CNFs within the matrix.