Gamma-irradiated Polycarbonate Research Articles

Thermally Stimulated Luminescence and Electron Spin Resonance Study of Gamma Irradiated Poly Carbonate

Polycarbonate (PC) is an industrially important polymer. Gamma irradiation effects of PC are investigated by thermally stimulated luminescence (TSL) and electron spin resonance (ESR) techniques. The TSL spectra of irradiated PC have shown two glow peaks, around 149oC (422 K) and 165oC (438 K). The observed glow peaks are analysed by initial rise methods, Chen’s method and modified initial rise method. The trap parameters corresponding to the two glow peaks and their activation energies are evaluated. A correlation of results between the three methods was observed. The glow peaks are assigned to be due to the release of trap centres facilitated by molecular motion of PC chains around the glass transition region. The trap centres are thought to be created due to the chain cleavages and subsequent reactions occurred due to irradiation of PC. The results are further confirmed by recording ESR spectra of irradiated PC under different conditions. Cite this ArticleB. Sanjeeva Rao, M. Papi Reddy, A. Raju et al. Thermally Stimulated Luminescence and Electron Spin Resonance Study of Gamma Irradiated Poly Carbonate. Emerging Trends in Chemical Engineering. 2017; 4(2): 23–39p.

Recycled polycarbonate from electronic waste and its use in concrete: Effect of irradiation

Attending the environmental problems caused by polycarbonate, generated by electronic waste, in this work physical and chemical characterization of gamma-irradiated particles of recycled polycarbonate from electronic waste was made by: X-ray diffraction, energy dispersive spectroscopy (EDS), scanning electron microscope (SEM) and digital photography. Cement concrete was elaborated with Portland cement, aggregates, water and gamma-irradiated polycarbonate. The effects of size, concentration and gamma irradiation doses of polycarbonate particles, on the mechanical properties of concrete, were studied. Results show improvement on the compressive strength (up to 12%). The increments in irradiated recycled polycarbonate concentrations provoke diminution of densities and due to irradiation process, polycarbonate particles become textured and brittles.

Fracture toughness of gamma irradiated polycarbonate sheet using the essential work of fracture

Polycarbonate (PC), a ductile polymer, has been found by both linear elastic fracture mechanics and impact tests to present a ductile-brittle transition, which depends on notched specimen thickness, test speed and gamma irradiation. Owing to large amounts of plastic deformation, fracture toughness measurements by these test methods are not precise. In the present communication, a better method, the Essential Work of Fracture (EWF), to assess the fracture characteristics in plane state of stress was for the first time used to evaluate the fracture toughness of PC sheets subjected to gamma irradiation dose. Three-points bend tests of sharp pre-cracked specimens with different ligament lengths were 340 kGy gamma irradiated. EWF results showed that the total fracture work increased linearly with length for both non-irradiated and gamma irradiated conditions. A significant decrease in EWF fracture toughness was associated with brittleness promoted by gamma irradiation. This brittleness was also confirmed by macro and microscopy (SEM) evidence.

Environmental stress cracking in gamma-irradiated polycarbonate – A diffusion approach

Polycarbonate (PC) is an engineering polymer which presents interesting properties. This material has been also used in medical devices, which is frequently exposed to gamma radiosterilization and to chemical agents. This may produce significant changes in polymer structure, leading to failure in service. The present work brings about a new approach on environmental stress cracking (ESC) processes elucidation in 100kGy gamma-irradiated PC, by evaluating the diffusion process of methanol or 2-propanol in test specimens and determining the diffusion parameters on solvent-irradiated polymer systems. A comparison of diffusion parameters for both solvents indicated that methanol has a considerable ESC action on PC, with diffusion parameter of 7.5×10−14±1%m2s−1 for non-irradiated PC and 7.8×10−14±2.8%m2s−1 for PC irradiated at 100kGy. In contrast, 2-propanol did not act as an ESC agent, as it did promote neither swelling nor cracks in the test specimens. These results were confirmed by visual analysis and optical microscopy. Unexpectedly, structural damages evidenced in tensile strength tests suggested that 2-propanol is as aggressive as methanol chemical for PC. Moreover, although some manufacturers indicate the use of 2-propanol as a cleaning product for PC artifacts, such use should be avoided in parts under mechanical stress.

Kinetics of hardness evolution during annealing of gamma-irradiated polycarbonate

This study focuses on the evolution in microhardness values that accompany isothermal annealing in gamma-irradiated polycarbonate (PC). Hardness increases with increasing annealing time, temperature, and gamma radiation dose. A model composed of a mixture of first and zero order structure relaxation is proposed to interpret the hardness data. The rate constant data fit the Arrhenius equation, and the corresponding activation energy decreases with increasing dose. The extent of structural relaxation that controls the hardness in post-annealed PC increases with increasing annealing temperature and dose. The model demonstrates that hardness evolution in PC is an endothermic process. By contrast, when the model is applied to irradiated poly(methyl methacrylate) and hydroxyethyl methacrylate copolymer, hardness evolution is an exothermic process.

Dynamic behavior of gamma-irradiated polycarbonate

The aim of the present work was to establish the relationship between dynamic behavior of Bisphenol A polycarbonate (BAPC) and degradation by gamma irradiation. The BAPC was exposed to 340 kGy dose and the molecular weight was evaluated by Size Exclusion Chromatography (SEC). A modified split Hopkinson pressure bar was used to measure stress-strain dynamic relations. The results showed little change in the dynamic behavior of irradiated BAPC in the highest strain rate used in this work, in spite of the high decrease in the molecular weight of irradiated BAPC. The lowest strain rate used in this work produced the highest change in the dynamic behavior of irradiated BAPC.

Modification of optical properties of polycarbonate by gamma irradiation

A detailed analysis of absorption, transmission, and reflection spectra of virgin and gamma-irradiated (50–800 kGy) polycarbonate polymer reveals that both indirect as well as direct band gap coexist in virgin and gamma-irradiated samples. The indirect band gap has been found to decrease from 3.00 eV (virgin sample) to 2.78 eV at a dose of 800 kGy. The emission behaviour of gamma-irradiated polycarbonate indicates a clear-cut emission peak in the visible region at –466 nm in the samples with a gamma dose of 400 kGy and above. The refractive index has a decreasing tendency as a result of the increasing gamma dose.

Toughness behavior of gamma-irradiated polycarbonate

The toughness behavior of polycarbonate sheets was investigated, before and after gamma irradiation in air, using physicochemical (determination of viscosity-average molecular weight and Fourier transform infrared spectroscopy) and mechanical (tensile and fracture toughness) tests. The failure mechanisms were analyzed by microscopy and related to the test results. It was found that, as the gamma irradiation dose is increased, there is a decrease in the molecular weight and an increase in the chain scission on carbonyl groups, as detected by infrared spectroscopy analysis. The mechanical properties of polycarbonate were affected by gamma irradiation, showing that polycarbonate presents a ductile-to-brittle transition as radiation dose increases, as confirmed by fractographic analysis. These results are presented and discussed.

Structural modifications and track registration response of some gamma irradiated polycarbonate detectors

Makrofol-E, Lexan and Polycarbonate detectors exposed to gamma irradiation in the dose range of 101-106 Gy have been characterized by track methods and UV-Vis, IR and ESR spectroscopy. The track registration response is studied through variation of etching characteristics and the activation energy for bulk-etching at different doses of gamma rays was determined. Thermal stability studies were also carried out for understanding the effects of gamma irradiation on the thermal resistance of these irradiated polymers. The experimental results show that up to 106 Gy gamma exposure the examined materials are rather gamma insensitive radiation hard detectors.

An ESR study of the influence of fatigue on the decay of free radicals in gamma irradiated polycarbonate

Polycarbonate was subjected to long-term stress by transverse bending. Stressed, as well as non-fatigued, samples were irradiated by gamma radiation in evacuated ampoules. The concentration of free radicals was measured by ESR in the course of gradual heating of the samples. It appeared that the free radicals in the samples subjected to long-term stress were more stable than the free radicals in the non-fatigued samples. This suggests that the arrangement of polymer chains changes during fatigue and the free volume in the proximity of radical centres decreases so that the transfer of these centres to adjoining chains is retarded.