Parçalanabilen polilaktik asit termoplastiklere nano katki maddelerinin ilavesinin termo-mekanik özellikleri̇ ve kırılma tokluğu üzerindeki etkilernin moleküler dinamik analizleri ve deneysel olarak incelenmesi

Nowadays, Additive Manufacturing (AM) has become a modern manufacturing technique with the spread of other related technologies. Fused deposition modeling (FDM) is one of the well-known and widely used AM methods that emerges some advantages, such as low cost and high speed, and has been used in the production of polymer composite parts. However, FDM 3D printing has some limitations due to shortcomings in the thermo-mechanical properties of its building materials, known as polymeric filaments, although they have advantages such as easy processability, low cost, and good chemical resistance. Therefore, the FDM technique may be able to extend its application areas with the reinforcement of nanoparticles in building materials. The aims of this study are to (i) expand the use of polymer-based nanocomposite parts with superior thermo-mechanical properties and fracture behaviors by using a rapid and cost-effective FDM technology and (ii) produce polymer-based nanocomposite parts by utilizing the injection molding process to investigate the effectiveness of molecular dynamics (MD) simulations in forecasting the mechanical performance of parts through the comparison of mechanical properties of produced parts with the results of MD simulations. In order to accomplish the first objective, polylactic acid (PLA), one of the foremost biodegradable polymers, was chosen as the matrix material, while calcium carbonate (CaCO3) nanoparticles were used as reinforcement materials. For this purpose, the PLA/CaCO3 nanocomposite filaments, containing different weight ratios (0, 0.5, and 1 wt%) of nanoparticles in the matrix, have been synthesized by melt-blending technique using a twin-screw extruder system. These filaments were used to produce samples by FDM technique with different printing parameters to study the effects of nanoparticles and printing parameters on the mechanical properties and fracture behavior of the PLA nanocomposites under mixed-mode fracture loadings. In this regard, this study investigates the effects and significance of these different parameters, which are called printing speed, weight fractions of nanoparticle addition, layer thickness, filling ratio, and internal architecture, on the fracture characteristics and mechanical behavior of FDM 3D printed PLA and PLA/CaCO3 nanocomposites. To this end, the analysis of the Taguchi L27 design has been conducted based on the experimental results to determine the optimized levels of factors by which the maximum level of material properties could be obtained. Thus, it has been determined which combination can be used in further FDM 3D printing of PLA-based materials, or which factor level will be appropriate. A response surface methodology (RSM) was employed to model and predict the mechanical and mixed-mode fracture properties of the PLA-based nanocomposites produced in different weight ratios and different FDM printing parameters. The produced samples were subjected to uniaxial tensile tests for mechanical characterization. Mixed-mode fracture behavior of the synthesized samples were studied by applying mixed-mode loadings on the pre-cracked samples using an in-lab developed fixture mounted on the uniaxial tensile test machine. Finite element simulations are employed to simulate the crack opening on such specimens and calculate the geometry shape functions of the fracture samples at different loading angles. Finally, after the experimental procedures, scanning electron microscopy (SEM) examinations have been conducted on the fractured surfaces of the test samples to reveal the fracture morphology of parts and validate the presence of nanoparticles. In addition, differential scanning calorimetry (DSC) analyses are conducted to determine the variations in the glass transition and heat capacity of the PLA polymer by the incorporation of CaCO3 nanoparticles in the PLA matrix. Secondly, uniaxial tensile test specimens of PLA and PLA/CaCO3 nanocomposites have been produced with the injection molding process to verify the MD simulations. Material Studio software is employed to investigate the physical behavior of injection molded PLA/CaCO3 nanocomposites in different weight ratios (1, 3, and 5 wt%) and to research the details of interactions between the molecules and nanoparticles on an atomic scale. For the reason that the molecular dynamics simulations verify the experimental results, graphene (GR) reinforced PLA nanocomposites were simulated to predict the mechanical properties of injection molded PLA/GR in different weight fractions. It has been observed that Materials Studio software provides accurate results in estimating the mechanical properties of materials.