Investigation of optical, dielectric and thermal properties of organic dye additive composites

In this thesis, it was aimed to investigate the effect of Congo red dyestuff (CR) used as an additive on the optical, dielectric and thermal behavior of PMMA and PVC polymers showing insulating behavior. For this purpose, optical properties such as reflectance, refractive index and optical energy band gap of Congo red doped PMMA and PVC composites were determined. Optical transmittance spectrum measurements of CR-doped PMMA and PVC films showed high absorption in the ultraviolet-visible region (UV-Vis) (at 353 nm and 518 nm) and significantly blocked broad visible region light (190 nm-640 nm). PMMA/CR and PVC/CR composite films containing 1 wt% CR showed maximum absorption bands at 290 nm and 416 nm, but their transmittance percentages were found to be reasonably reduced compared to those of pure PMMA and PVC. It was determined that both composites showed high transmittance in the range of 640 nm to 800 nm. Optical constants such as optical band energy gaps (Eg), refractive index and % reflectance of PMMA/CR and PVC/CR composite films were calculated. From the dielectric graphs, it was observed that the dielectric constant increased when Congo red was added to the polymer matrices up to 70% weight ratio. It has been determined that the dielectric constant decreases as the frequency increases for all samples. While the ac (alternating current) conductivity values of PMMA and PVC increase with increasing CR addition in the polymer composites, it was found that the ac conductivity values are between the values of pure polymers and CR. Additionally, dielectric properties and some optical studies were carried out by doping CuPc dye into PMMA and PVC polymer matrices. UV-Vis, Fourier transform infrared spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA) measurements revealed that the azo group (‒N=N‒) bonds attached to the aromatic ring were broken as a result of the thermal decomposition of Congo red at 500 °C, and it was determined that N2 gas was removed from the CC above 360 °C. In the studies investigating the thermal behavior of PMMA/CR and PVC/CR composites, the effect of CR addition on the removal of HCl from PVC was also investigated.