Thesis Abstracts 2005
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Radiation Effects on the Properties of a Polyurethane/Epoxy Graft Interpenetrating Polymer Network: An Investigation into the Application of Polymers in the Fabrication of Containers to Store Radioactive Waste
By: Aba N. Mortley, MSc (Chem Eng.) Candidate
Supervisors: Dr. H.W. Bonin and Dr. V.T. Bui
Abstract
The purpose of the present work was to investigate the toughening effects of a castor oil based polyurethane on an epoxy matrix, by means of an interpenetrating network. In addition, the radiation effects of two PU/EP graft-IPNs, 19/81 and 27/73 PU/EP graft-IPNs, were examined so that possible application of these materials in the fabrication of containers to store radioactive waste over long periods of time could be considered.
The end-product quality of the PU/EP graft-IPN was dependant on the individual polymer starting materials. Therefore, varying the curing conditions optimized the quality of the castor oil based polyurethane. These conditions, curing temperature and a corresponding curing time were varied until samples with good chemical and mechanical properties were produced. The chosen curing condition occurred at a temperature of 100ºC for 9.5 hours. The polyurethane/epoxy graft-IPN was then made by a sequential method of synthesis, in which the polyurethane prepolymer was prepared before the addition of the epoxy resin and crosslinker. The 19/81 and 27/73 PU/EP graft-IPN specimens were subjected to several degrees of radiation that ranged from 0.11 MGy to 3.0 MGy, using the SLOWPOKE-2 nuclear reactor at Royal Military College of Canada. The irradiated and unirradiated IPN samples were then subjected to a battery of chemical and mechanical tests to determine the effects of radiation. These tests included tensile tests, swelling tests, attenuated total reflectance Fourier infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy.
Based on the observations from the chemical and mechanical tests, it has been established that the 19/81 PU/EP graft-IPN is suitable for applications in radiation environments below a dose of 1.5 MGy. At doses above 1.5MGy, the 19/81 PU/EP graft-IPN shows a slight decrease in its chemical and mechanical properties. The 27/73 PU/EP graft-IPN is unsuitable for radiation applications at low doses, however it shows a noticeable increase in chemical and mechanical properties with increasing accumulated dose. Therefore, to compensate for the slight decrease in chemical and mechanical properties of the 19/81 PU/EP graft-IPN at doses above 1.5MGy and for the poor behaviour of the 27/73 PU/EP graft-IPN at low doses, past work has shown that beneficial properties of a ThO2 filler within the radioactive waste container. With regard to the design of the disposal containers, with the aid of aThO2 filler, it is the opinion from the present work that the graft-IPNs could potentially be used in the fabrication of containers to store low and intermediate level radioactive waste, as well as spent nuclear fuel and high level radioactive waste.
