Environmental degradation of fiber reinforced plastic materials in neutral, acidic, and basic aqueous solutions

Kinetic measurements on the dissolution of oxide components of fiber-reinforced plastics show that the dissolution in aqueous media is a complex phenomenon and that changes in the nature of the controlling mechanism during the time of exposure can lead to an increase in rate. As a result, thorough understanding of the mechanisms is imperative in developing models for prediction of the long-term degradation of these composites. Thermogravimetric analysis has been found to be a promising indicator of the structural changes associated with the degradation process. Results obtained on specimens of concrete reinforcement rods made out of a E-glass/vinylester FRP material show that weight loss between 150 and 300 C is sensitively dependent on the nature of the corroding medium, the duration of exposure, and, in particular, the temperature at which the material was previously exposed. This weight loss correlates with the extent of moisture absorption. The enhanced weight loss between 150 and 300 C observed in the cases of samples previously exposed to attack by an aqueous media apparently reflects the increase in number of monomeric species as a result of the exposure. Increase in the effective area out of which monomers may volatilize as a result of the formationmore » or propagation of microcracks, pores, or fiber-matrix interfacial gaps in the course of exposure may also contribute to enhanced weight loss. The conclusion that the extent of weight loss is indicative of the extent of degradation is supported by chemical, infrared and NMR analysis of the evolved vapors and by determination of their molecular weight. Both the weight loss at elevated temperatures and the tensile strength show a strong dependence on temperature and a parabolic time dependence. Raman spectroscopy is a highly sensitive and convenient technique of following structural changes. The techniques explored here can provide important data for modeling of the environmental degradation process.« less