Glass and sub-glass relaxation changes induced by thermal ageing of epoxy-amine polymer networks-A DMA study

Four epoxy-amine networks were characterized by Dynamical Mechanical Analysis (DMA) and by Dielectric Relaxation Spectroscopy (DRS). The epoxy-amine networks were cured with DGEBA and four aliphatic amine hardeners: three ethylamine hardeners of increasing complexity: ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA), and 4,7,10-Trioxa-1,13-tridecanediamine (TTDA). DGEBA-DETA was aged at 160 degrees C. Its a relaxation temperature was shown to decrease with time, implying a predominant chain scissions mechanism through the thermal oxidation. DGEBA-DETA and DGEBA-TETA were also shown to display a sub-glassy relaxation made of two components. After ageing at 160 degrees C, the lowest one around 50 degrees C, associated to the local motions of hydroxypropyl ether segments, increases in intensity. The second one around 30 degrees C, with unknown origin but probably from motions in more densely crosslinked areas within the network, disappears with ageing. Those results are discussed regarding the molecular aspects of oxidation.