Curing FTIR study and mechanical characterization of glass bead filled trifunctional epoxy composites

The cure process of a composite formed by a trifunctional epoxy resin filled with glass beads has been analyzed using Fourier transform infrared spectroscopy (FTIR). With this technique it was possible to follow the curing reactions, studying and quantifying the conversion of different representative functional groups. The evolution of concentration of primary and secondary amines as well as epoxide groups has been followed as a function of the applied curing process. The primary amines were found to be the most useful band in the monitoring process due to the absence of overlapping. The introduction of the rigid phase had a remarkable influence on the curing process, especially when the glass beads where treated with a silane coupling agent. In this latter case the rate of amine conversion was faster than that observed in the unfilled matrix or for the untreated glass-filled composite. However, the filler treatment with a coupling agent was revealed to be inefficient in terms of mechanical properties, probably due to the high temperatures involved during the epoxy curing process. The mechanical properties like Young’s modulus and composite stress at break where found to largely increase and hold its original value, respectively, on the contrary, the strain at break decreased at a value near 50% of the neat matrix. The mechanical composite properties were also evaluated in terms of the stress intensity factor (KI) and the energy release rate (GI). Both values achieved a maximum around the 20%v of glass-beads and were found to decrease slightly with higher volumes of filler. Scanning electron microscopy (SEM) was carried out in order to assess the toughening mechanism associated with the presence of glass beads.