Biyo-Esinlenmiş Hiyerarşik Polimer Nanokompozitlerin Tasarımı, Hazırlanması ve Karakterizasyonu

Abstract

Synthetic routes in the polymer composite production induce strength by compromising toughness and ductility. This results in premature failure leading to reduced life-time. It is crucial to enhance the lifetime of contemporary composite materials by implementing new reinforcing approaches since they are utilized vastly in many aspects of modern life. For instance, in macro-scale polymer composites are utilized in aviation (as components of rockets and aircrafts) and prosthetic (as artificial bone, leg and arm) industries. In addition to it, in micro-scale; they are used in many applications such as in micro-electronics and thin film protections. In this thesis, it is aimed to design, synthesis, characterization of hierarchical graded polymer nano/micro composite materials and investigation of the mechanical properties of the produced materials, inspired by biological structures with high mechanical properties such as human bones and oysters. There are two benefits to replace hierarchical graded composites with their conventional counterparts. First, graded composited are crucial to join mechanically different materials in continuous manner. For instance, biological systems such as bone, cartilage and mussel are connected via graded particle distribution preventing interface damage and failure. Second, composites could become both strong and tough by inducing hierarchical distribution of particles which have diverse length scales (nano-, micro and macro-scaled). In fact, living organisms utilizing hierarchic distribution of reinforcements are able to preserve both strength and toughness which could not be attained by reinforcing in only one particular length-scale. Artificial hierarchical composites with polymer matrix could mimic nature in the means of elasticity and low density thanks to their organic nature. Eco-friendly route has been developed in this study focusing on the production of the biocompatible polymer nanocomposites. Two different types of nanoclay (halloysite nanotube and bentonite) and silica were utilized in this study. As the polymer matrix, Polyvinylpyrrolidone (PVP) was chosen. All nanocomposites were produced via solution mixing production method. Nanocomposite structures were characterized by FTIR, XRD and TGA analyses. Distribution of HNT and BNT within PVP matrix was investigated by high resolution Transmission Electron Microscopy (TEM). Both PVP and the synthesized nanocomposites were blended with low density polyethylene (LDPE). Mechanical test specimens were produced by injection molding machine. The three-point bending tests and notched impact tests of the specimens were carried out. The fracture surface of the specimens (after 3-point bending test) were examined via Scanning Electron Microscopes (SEM). Gradient PVP-HNT nanocomposite films were fabricated by spin coater. The morphology and roughness analysis of the films were analyzed via Atomic Force Microscopy (AFM). Instrumented-micro indentation test was conducted to unveil mechanical improvements achieved by halloysite nanotube clay mineral addition. The proposed nanocomposites at the end of this study would serve as an environmentally-friendly alternative to commercial engineering polymers/composites which could be utilized in bone implants, dental implants, biofilms and as substrates of flexible electronics for biosensors.