Evidence of thermo-oxidation phenomena occurring during hygrothermal aging of thermosetting resins for RTM composite applications

This paper focuses on the humid aging of a high temperature thermosetting resin employed for the realization of aircraft parts manufactured by the RTM process. Accelerated humid aging at several different temperatures (40–90 °C) and relative humidity values (50–100%) has been carried out by means of gravimetric tests. Anomalous behavior with respect to Fick’s diffusion law and a color gradient from the edge to the center of the samples has been observed. Drying of samples after aging and mechanical tests on aged and dried samples have shown the existence of irreversible phenomena taking place during humid ageing: uniform tensile tests revealed resin embrittlement, Ultra Micro Indentation tests allowed measuring a gradient of properties from the surface to the centre of the samples. This behavior – associated to the color changes observed on aged samples – indicates that oxidation phenomena take place during hygrothermal aging.