The Degradation and Stabilisation of Epoxide Resins to Ultraviolet Radiation

Abstract

This thesis was an investigation of the chemical and physical changes which occurred on exposure of two epoxide resins, one amine and the other anhydride cured, to ultraviolet light. The method of study was by investigation of the changes in both cured resins and the monomers from which they were synthesised. Also, because of the intractable nature of the cured structures, the degradation of a number of model compounds which were structurally similar to the cured systems were investigated. The results showed that the monomer itself was susceptible to the radiation used. Monomer purity decreased the rate but it did not eliminate the degradation process. From quantum yields studied, the initiation was found to result in a non-chain reaction. The extent of degradation was proportional to the intensity of the light used. No "dark" chemical reactions were observed to occur with any of the compounds studied, although "dark" physical reactions by diffusion of degradation products did occur in the cured structures. The wavelengths of light causing maximum degradation were contained in the short wavelength region of the lamp. In the anhydride cured resins the 365 nm band was also found to contribute to the overall degradation process. The photo-oxidative degradation resulted in the formation of an oxidised surface layer of material from crosslinking reactions involving atmospheric oxygen. Volatile compounds were evolved during irradiation and their rate of concentration change confirmed the surface layer theory, as did measurement of the torsion modulus of the cured systems. Complete stabilisation of the materials with existing stabilisers, and new synergistic mixtures failed. However it was possible to decrease the rate of degradation in both the amine and anhydride cured polymers.