Contribution to Photodegradation Study, Chemical Behaviour of Unsaturated Polyester Resin Under Irradiation

Abstract

This survey reports the effect of thermosetting polymer degradation (unsaturated polyester): chemical degradation, under ultraviolet exposure and damage by neutrons irradiation. In order to evaluate the deterioration of present material, some comparative characterizations have been done between standard samples (blank) and damaged ones. Gel permeation chromatography, differential scanning calorimetry, scanning electron microscopy, FTIR spectroscopy are the techniques which have been used. Photomicrography shows the sample surface attack after few minutes in hot water in addition to an immersion of 2 d within a solvent. For this last test, a loss of mass higher than 25 % has been recorded. The FT-IR spectrum of the deteriorated sample surface confirms the damage. A similar phenomenon is observed with UV degradation (the radiance being fixed at 750 w/m²) the weight loss was 2.25 %. Three identical samples were exposed to a neutron flux 10¹² n/cm².s during 0.5, 1.0 and 1.5 h. Photomicrography obtained by SEM show the polymer damage degree, several reactions seem to be in competition: crosslinking, the chain breaking and oxidation by radicals. In order to assess the rigidity of present thermosetting polymer, the elastic modulus using the ultrasonic methods was determined. A hardness test (Shore D) has also been carried out. The obtained values of the Young's modulus can be interpreted in terms of crosslinking considering the used irradiation level.