Preparation of new chitosan-polystyrene based nanocomposites containing TiO2 nanowires and investigation of their thermal and biological properties

In this thesis, emphasis is placed on addressing the persistent environmental and health issues caused by waste originating from synthetic raw materials in recent years, with a particular focus on synthesizing and characterizing nanocomposites derived from chitosan (CS), an ecologically sustainable biopolymer. In the first phase of this research, a synthetic polystyrene derivative (PFST) containing fluorine atoms in its side chains was synthesized and subsequently blended with CS via a hydrothermal process. Following this, PFST-CS/TiO2 nanocomposites were produced by incorporating TiO2 nanotubes (NWs) at varying weight ratios into the PFST-CS mixture, using the same methodological framework. The structural and morphological properties of the resulting composites were meticulously analyzed using advanced characterization techniques, including Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and Transmission Electron Microscopy (TEM). SEM analyses revealed that the inclusion of PFST and TiO2 NWs led to a significant morphological change in the CS matrix, thereby enhancing surface interactions. FTIR evaluations indicated the formation of hydrogen bonds between the PFST and CS polymer chains, resulting in stronger interfacial interactions with the TiO2 NWs. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were employed to determine the thermal properties, demonstrating that the PFST-CS blend exhibits superior thermal stability and a higher glass transition temperature (Tg) compared to pure CS. In particular, the fluorine-containing side chains of PFST is assumed to enhance thermal stability through strong interactions with the hydroxyl (OH) and amine (NH2) functional groups in the CS chains. Moreover, the addition of TiO2 NWs shifted the thermal degradation profile of the composites to higher temperature thresholds. Examination of the water contact angle (hydrophilic/hydrophobic properties) showed that incorporating PFST and TiO2 NWs enhanced the hydrophilic nature of the CS surface. This observation may be viewed as evidence of the high surface energy associated with TiO2 NWs, combined with the synergistic interactions introduced by PFST in the CS matrix. Conversely, impedance spectroscopy analyses of dielectric behaviour revealed that adding TiO2 NWs decreased both the dielectric constant and AC conductivity values in PFST-CS composites, indicating that TiO2 NWs impart an insulating character within the composite architecture. From a biological perspective, the synthesized nanocomposites displayed significantly higher antimicrobial activity against E. coli and C. albicans strains than pure CS. It has been suggested that this antimicrobial efficacy could be attributed both to the fluorine-rich structure of PFST and to the reactive oxygen species generated as a result of surface interactions and the photochemical properties of TiO2 NWs. Additionally, DPPH radical scavenging experiments indicated a reduction in the radical inhibition percentage of CS following blending with PFST; nevertheless, the newly formed nanocomposites exhibited a marked increase in antimicrobial activity. In summary, within the parameters of this thesis, the PFST-CS/TiO2 nanocomposites developed were found to offer enhanced surface interactions and high thermal stability, as well as commendable antimicrobial performance and advantageous dielectric properties. After evaluating all findings, it can be concluded that this new generation of bio-based nanocomposites holds the potential to serve as a sustainable alternative to conventional, non-biodegradable packaging materials.