Thermooxidative and thermohydrolytic aging of composite organic matrices

Abstract

This chapter deals with the main causes of chemical ageing in organic matrix composites: hydrolysis, essentially in polyesters and polyamides, and oxidation in all kinds of polymer matrices. The first section is devoted to common aspects of chemical degradation of organic matrices. It is shown that chain scission and, at a lesser extent, crosslinking are especially important because they induce embrittlement at low conversions. Quantitative relationships between structural parameters and mechanical properties are briefly examined. The second section deals with diffusion-reaction coupling. In the cases of hydrolysis and oxidation, kinetics can be limited by respectively water and oxygen diffusion. Then, degradation is confined in a superficial layer, that can carry important consequences on use properties. The third section is devoted to hydrolysis. The kinetic equations are presented in both cases of non equilibrated and equilibrated hydrolysis. Structure-stability relationships are briefly examined. Osmotic cracking process, very important in the case of glass fiber/unsaturated polyester composites, is described. The last section is devoted to thermal oxidation. The simplest kinetic models are presented. The main gravimetric behaviours are explained. A mechanism is proposed for the "spontaneous cracking" in the superficial layer of oxidized samples.