Degradation of polycarbonate, bentonite, barite, carbon fiber and glass fiber filled polycarbonate via gamma irradiation and possible use of polycarbonate in radioactive waste management

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Chemistry, Turkey

Approval Date: 2017




Frequent use of bisphenol-a polycarbonate in daily life results with a huge amount of polycarbonate waste. The proper utilization of this waste would be an environmental friendly solution. As polymeric materials are used materials for radioactive waste embedding, having an aromatic structure within the main chain, the bisphenol-a polycarbonate is a candidate material to be used as an embedding matrix for the confinement of radioactive waste. This possibility would also solve the problem of huge amount of waste generated due to the use of polycarbonate. Bentonite and barite minerals have been used extensively in the radioactive waste management. On the other hand, glass and carbon fiber have been used as reinforcing agent for polymers. Incorporation of bentonite, barite, carbon fiber and glass fiber would enhance the resistance to radiation and load bearing property of polycarbonate. They would also enable to increase the initial dose rate of radioactive wastes which are intended to be embedded in to polycarbonate.In this study, changes in the properties of neat, bentonite, barite, carbon fiber and glass fiber filled polycarbonate (Lexan® LS2) samples via high dose rate gamma irradiation and possible use of them in radioactive waste management were investigated. High dose rate irradiations were carried out in the irradiation facility (60Co source) of Turkish Atomic Energy Authority located in Sarayköy. There were two dose options selected for neat and filled polycarbonates. Neat polycarbonate samples were irradiated with 10, 25, 50, 75, 684, 1291, 3280 and 4341 kGy. On the other hand, filled polycarbonate samples were irradiated up to four different doses which were 10, 25, 50, 75 kGy. To estimate the radiation stability of irradiated polymers, total irradiation doses, additives types (bentonite, barite, carbon fiber and glass fiber), and additives’ content (%1, %2, %5, %10) used in formulation were parameters which were analyzed. Characterization of irradiated polycarbonate (neat and filled) samples were performed by tensile, Dynamic Mechanical Analysis (DMA), Thermogravimetric analysis (TGA), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), spectrophotometric (for yellowness index) and Scanning Electron Microscopy (SEM) tests. The dominant reaction mechanism generated via irradiation was the chain scission resulting with deterioration in tensile, thermal and morphological properties of polycarbonates at the doses of starting with 684 kGy. High doses with 684, 1291, 3280 and 4341 kGy diminished both tensile strength and elongations at break of polycarbonates significantly that end point criteria were exceeded at each doses. Carbon and glass fiber inclusion enhanced the mechanical properties of composites significantly. 10 wt. % carbon and glass fiber reinforced composites exhibited highest load-bearing property. Barite and carbon fiber reinforced polycarbonate gave more stable results upon irradiation and this was attributed to radiation attenuation property of barite and carbon fiber. 10 wt. % carbon fiber based composite had superior mechanical and thermal properties upon irradiation. 75 kGy did not compromise the mechanical, thermal and morphological properties of composites. 10 wt. % carbon fiber reinforced composite was found as the most radiation stable material among all irradiated samples in terms of mechanical and thermal properties. End point criterion were not reached at the dose of 75 kGy. End-point criteria and radiation index for neat and filled polycarbonate samples could be achieved in between 75 and 684 kGy doses. 75 kGy could be easily stated as the eventual dose that radioactive waste could be sustained for 300 years in polycarbonate. Therefore, it could be inferred that radioactive waste having initial contact dose rate of 1.126 Gy/h with the half-life of 5.27 years could be theoretically embedded into neat and filled (bentonite, barite, carbon fiber and glass fiber) polycarbonate with remote handling procedures for 300 years.