The Effect Of Halloysite Nanotubes On The Processing, Thermal, Mechanical, And Electrical Properties Of Polymeric Composite Materials

Official URL: https://risc01.sabanciuniv.edu/record=b3210368

This thesis focuses on achieving a broad understanding of one polymeric system, which is epoxy reinforced with Halloysite nanotubes (HNTs) (epoxy/HNT). The curing kinetics of this system is analyzed, and some of its properties are scanned, whether they are mechanical, thermal, or electrical ones. Comprehensive characterization of epoxy/HNT is conducted to facilitate its practical implementation as a matrix component for Carbon Fiber Reinforced Polymer (CFRP) composites to produce CFRP composites reinforced with HNTs (CFRP/HNT) for aerospace, and automobile applications. The first part of this thesis seeks to detect the most beneficial epoxy/HNT nanocomposites. A series of epoxy/HNT nanocomposites were prepared with various concentrations of HNTs and then tested under flexural stress. To understand the effect of HNTs concentration on the curing process, the curing kinetics of the epoxy and epoxy/HNT nanocomposites were explored by Differential Scanning Calorimetry (DSC) and rheological studies. Model-free (i.e., Friedman method) and model-based kinetic analysis (i.e., Kamel and Sourour (KS) model-based analysis) were used to analyze the DSC experimental data. Each concentration of HNTs produced a combination of both acceleration and inhibition mechanisms during The polymerization process, which led to different local topologies in the polymeric network. The effect of different polymeric networks, in these epoxy/HNT systems with different concentrations of HNTs, on the thermal, mechanical, and thermomechanical performances of nanocomposites was evaluated in detail. Additionally, the feasibility of epoxy/HNT, for usage as materials for structural capacitor applications, was examined by manufacturing epoxy/HNT composites with ionic liquid and lithium perchlorate as additives. The electrical properties of modified epoxy/HNT nanocomposite were tested by Electrochemical Impedance Spectroscopy (EIS), and the analysis of conductivity spectra showed that 5 wt.% and 10 wt.% of HNTs provide ionic conductivity with values close to what was provided by incorporating 1 wt.% on ionic liquid and lithium perchlorate. The results of EIS prove that epoxy/HNT are viable systems for further tuning of ionic conductivity. The second part of this thesis investigates the effect of HNTs on the properties of CFRP composites, which were prepared by Resin Transfer Molding (RTM) method. The manufactured CFRP and CFRP/HNT plates were subject to flexural and in-plane shear load tests. It was found that HNTs highly affect the deformation mechanisms of CFRP. This result was further corroborated by health monitoring techniques (i.e., Acoustic Emission (AE), Digital Image Correlation (DIC), and thermal imaging system (IRT)), which were simultaneously employed during the mentioned tests. HNTs improved the flexural- and inplane shear moduli by ~18% and ~ 27%, respectively. Deformation mechanisms were identified, then the experimental data were further supported by non-local meshless numerical analysis, Peridynamics. Furthermore, the RTM mold’s design creates a certain flow path for the resin during the wetting process. Therefore, the effect of the flow path on the infiltration of HNTs and the properties of CFRP/HNT composite plates was analyzed by using two different RTM molds. The design of the RTM, and the placement of the inlet and outlet port creates a characteristic front flow path for each type of preform-resin system. The inlet port in the first RTM (RTM(I)) is in the middle of one side of the rectangular mold, and the outlet ports are on the opposite side. The design of RTM(I) creates a linear front flow path. In the second RTM (RTM(II)), the inlet port is in the middle of one side of the mold, and the outlet port is in the center of the plate. This placement in RTM(II) creates a curved front flow path for the resin. In both RTMs, 10 wt.% of HNTs were added to the resin, ~4.5 wt.% of HNTs were impregnated within the fibers and ~5.5 wt.% of HNTs were washed away. In RTM(I) the precipitation of HNTs increased gradually from the inlet toward the outlet, however, in RTM(II), the filtration of the nanotubes occurred with variant levels throughout the composite plate and CFRP/HNT plates were inhomogeneous in Vv and HNT wt.% , therefore the average flexural and in-plane shear modulus were negatively affected.