Kendi Kendini Onarabilen Polibenzoksazin Esaslı Nanokompozit Malzemelerin Geliştirilmesi

Abstract

This study was financially supported by Hacettepe University Scientific Research Projects Coordination Unit with a graduate project entitled "The Development of Self Healing Polybenzoxazine Based Nanocomposite Materials" (FYL-2018-17251). The aim of this thesis is to develop composite materials which have good mechanical strength and self healing ability to be used in fields such as aerospace and automotive.

Core/shell structure nanofibers were produced by coaxial electrospinning method. The core and shell consist of dicyclopentadiene (DCPD) and polyacrylonitrile (PAN), respectively. DCPD was used as healing agent and PAN was used to keep DCPD. PAN plays a role to diffusion of DCPD in the composite when the crack is arised. The crack area is filled by the ring opening metathesis polymerization (ROMP) reaction between the DCPD and Grubbs' catalyst. The Grubbs' catalyst was dispersed into the benzoxazine resin and the resin was impregnated into the nanofiber coated carbon fibers to produce the composite structure with self-healing ability. In the first part of the thesis, the thermal characterization of the benzoxazine resin was studied. The activation energy (Ea) and the pre-exponential factor (A) of the benzoxazine were found 85.72 kj/mole and 1.7x107, respectively by the Differential Scanning Calorimetry (DSC). The resin was applied to the each layer of the carbon fiber by hand lay-up method and put into the metal mold to curing. In this method, three different composite laminate were produced which have different fiber configuration. These were 0°/0°/0°/0°/0°, 0°/90°/0°/90°/0°, 0°/+45°/0°/+45°/0°, respectively. The tensile tests were performed both 0° and 90° direction to determine the composite which has best fiber configuration. Therefore, the best tensile strength values in 0° and 90° direction were obtained as 860.0±49.6 MPa and 568.0±18.7 MPa, respectively in the fiber direction of 0°/90°/0°/90°/0°.

In the second part of the thesis, nanofibers were produced on the carbon fiber by coaxial electrospinning. First of all, the nanofibers were observed by optical microscope. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy were used to detect the core/shell structure of the nanofibers. In addition, the Fourier Transform Infrared Spectroscopy (FTIR) and the thermal gravimetric analysis (TGA) of the nanofiber were performed to ensure that the DCPD was within the nanofiber structure. After that, the composite laminate with the Grubbs' catalyst was produced and the damage was generated. The self-healing ability of the composite laminate was studied by short beam strength test.

As a result, the tensile strength of the nanofiber reinforced composite laminate is found higher than that of the virgin laminate. Besides, the self-healing ability was gained to the composite laminate by the ROMP between the DCPD and the Grubbs' catalyst.

Keywords: Benzoxazine, carbon fiber, composite, coaxial electrospinning, nanofiber, self-healing, Grubbs' catalyst, dicyclopentadiene.