Synergetic effects of hybrid nanoparticles on the mechanical properties of carbon fiber reinforced epoxy nanocomposites

Abstract

Graphene and carbon nanotubes have a wide range of applications because of their superior mechanical, electrical, and thermal properties. Even a very small amount of nanofiller addition to the polymer matrix provides a significant improvement of such properties of the composite. However, the nanoparticles have some features that need to develop, like aggregations in the matrix. The strong van der Waals forces and π- π interactions between the nanofillers cause dispersion problems in the polymer. This problem can be solved by hybrid applications of the nanoparticles. In the first part of this thesis, the various hybrid nanocomposite studies in the literature were given. Nanofiller addition provides the improvement of the properties to a certain point. Then, the properties deteriorate with the increase in nanofiller content. It is important to find the optimum nanofiller content. In this study, combinations of different amounts of nanoparticles were investigated for this purpose. In the second part of the thesis, the materials and production methods were explained in detail. Graphene nanoplatelets and multi-walled carbon nanotubes were combined in the ratios of 1:1, 1:3, and 3:1. The epoxy resin was modified with the nanoparticles at weight percentages of 0.1%, 0.2%, 0.3%, and 0.4%. In addition to the mechanical test, characterization tests were performed, such as Thermogravimetric analysis (TGA), Differential scanning Calorimetry (DSC), X-ray diffraction (XRD), and Scanning electron microscopy (SEM). In the third part, the results of the analysis were discussed. According to the tensile test results, the improvement of the mechanical properties was observed in the nanofiller weight percentage of 0.3%. After that point, a sharp decline was observed in the mechanical properties of the hybrid nanocomposites. All specimens with a nanoparticle content of 0.4% by weight showed a decrease compared to the neat epoxy. It is caused by the increased aggregation of the nanoparticles. The best configuration of the hybrids was determined to be an MWCNT:GNP ratio of 1:3 (0.3%) with a tensile strength of 75.1 MPa, and the MWCNT/GNP/epoxy/carbon fiber laminates were fabricated on this basis. The mechanical test was performed for nanocomposite laminate and compared with the neat composite laminate. The nanoparticle-added composite laminate outperformed the other with a tensile strength of 728.5 MPa. Also, the strain percentages of the specimens were evaluated. MWCNT:GNP ratio of 1:1 (0.1%) and MWCNT:GNP ratio of 1:3 (0.3%) specimens have the highest values of elongation at break with 4.72% and 4.07%, respectively. The nanoparticle-added composite laminate showed an increase in the fracture strain percentage of 1.3%. Elastic modulus showed an increase of 7% comparing to the neat epoxy specimen. However, 11% decrease was seen in elastic modulus comparing to the neat epoxy laminate. The glass transition temperatures (Tg) of all specimens were determined with the analysis of differential scanning calorimetry (DSC). It is observed that this temperature increased up to a nanofiller weight percentage of 0.2% and 0.3% with the increasing nanoparticle content and decreased after that point. The glass transition temperature was determined at 87.25 °C, while MWCNT:GNP ratio of 1:1 (0.3 wt.%) has the highest glass transition temperature at 114.67 °C. The investigation into the thermal decomposition behavior of the specimens was carried out through the use of thermogravimetric analysis (TGA). The initial decomposition temperature of the neat epoxy was determined at 331.15 °C. MWCNT:GNP ratio of 1:3 (0.4 wt.%) showed a little increase compared to the neat epoxy, and its initial decomposition temperature was determined at 333.26 °C. Also, the weight percentages of the residue were determined with TGA. The residual weight percentage of neat epoxy is 9.52%. MG13-0.3 has the lowest weight loss value with 14.12%. Fracture can be initiated by surface defects, agglomerates, and particles with weak bonds. According to the SEM images, GNPs are non-uniformly dispersed and aggregated, while MG13/Epoxy has morphologies without any aggregations and is difficult to be distinguished. This suggests good dispersion and compatibility of MG13 in epoxy matrix. In the last part, all results were concluded. This study investigated the synergetic effect of nanoparticles on the mechanical properties of carbon fiber-reinforced epoxy nanocomposites. Graphene nanoplatelets and multi-walled carbon nanotubes were combined in various ratios and added to the epoxy matrix, resulting in improved mechanical and thermal properties.