טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAvram Ya'akobovich
SubjectStructure and Other Characteristics of Epoxy/CNT Mats
and Fibers
DepartmentDepartment of Chemical Engineering
Supervisors Full Professor Cohen Yachin
Full Professor Allen Wiendel
Full Thesis textFull thesis text - English Version


Abstract

Carbon Nano Tubes (CNT) form a unique material, which has been widely investigated. The physical properties of CNTs are unique and considered superior to most commonly used materials. Throughout the research done on the characteristics of CNTs, the goal remains to exploit their properties as an engineering material capable of being used in 'industrial scale' production processes. The route towards this engineering material suggested here is production of a fiber like material, which consists only of CNTs and harnessing its properties from the micrometer or nanometer scale into the macro scale.

The CNT fiber used in this research was produced through a floating CVD process. In this process a 'cloud' of CNTs is created, pulled, and condensed while being wound onto a spindle. Investigation of its inner structure reveals that the production of this CNT fiber cannot be without defects and diversion from stoichiometry in order to achieve the necessary winding ability of the CNT fiber. In addition, the alignment of the CNTs within the CNT fiber is closely related to its winding speed. The same applies if its left uncondensed and in the shape of a non-woven mat (CNT mat).

Both the CNT mat and CNT fiber were investigated in terms of their inner structure and the effect of production parameters on their composition and alignment. CNT mats were infiltrated with epoxy and underwent tensile testing which showed significant differences between longitudinal and transverse loading in conjunction with the winding direction. Furthermore, the overall loading of CNT reached 17% by weight, which is considered very high. The resulting improvement in strength was only 2.5 times for the best case of longitudinal tension, not as high as one would expect at such high loadings. The reasons for this are explained through imaging of the mode of failure which shows poor adhesion of the CNTs to the epoxy matrix in some cases.

Samples of CNT fibers were prepared for TEM imaging by ultramicrotomy process. It is shown here that this process could be referred as a mechanical properties experimental set up while changes in the width of the microtomed slices was explained based on existing theory where correlation is drawn between experimental set up and mechanical characteristics of the microtomed polymer and the resulting slice characteristics. It is also shown that this method could assist in local analysis of mechanical properties at the nano-scale.

Tensile testing of a CNT fiber, was performed inside the chamber of the SEM. The main goal of this test was to view, in real time mechanical behavior of the CNTF that could be explained and analyzed by imaging at the nano-scale together with force and elongation recorded during the tensile test. This experiment resulted in a clear strain stress curve which demonstrated two different stiffness moduli at different stages of the tensile test. The mode of failure was also observed, and an explanation is given for both the mechanical behavior and the mode of failure. Both are related to the nano-structure of the CNTF.