Etude comparée des propriétés structurales, thermomécaniques, optiques et diélectriques de deux polymères époxydes renforcés au graphite : expérience et modélisation

Two thermosetting polymers, Bisphenol A Diglycidyl ether (DGEBA) and Triglycidyl-p-aminophenol (TGAP), cured by the same agent, diethylenetriamine (DETA), were characterized and compared from a structural (by FTIR and XRD), thermal (by DSC and TGA), thermomechanical (by DMTA), optical (by UV-VIS spectroscopy) and dielectric (by impedance spectroscopy) viewpoint. Somme differences were highlighted and allowed to correlate structures to properties. Interfacial relaxations identified only for TGAP (from impedance spectroscopy), were associated with nanostructures present within this polymer, as revealed by XRD. Another difference concerns the nature of the band gap optical transition. A new approach derived from the Tauc relation, was considered, and allowed to discriminate the two transitions, direct for DGEBA and indirect for TGAP. This approach also allowed to highlight some singularities difficult to distinguish on the initial spectra.The same studies were carried out on these two polymers, reinforced with graphite at rates lower than 1% by mass. From the thermomechanical viewpoint, no significant variation was observed on the TGAP/graphite samples, whereas a stiffness improvement was observed for the DGEBA/graphite samples, for which the storage modulus increases by nearly 50% for 0.1%-0.3% graphite. This increase due to the densification of the cross-linked network, was accompanied by a transfer between the relaxations associated with short and long chains. Concerning the dielectric properties, an increase in the activation energy (of the order of 30%) related to the chains movement was observed on the DGEBA/graphite samples only, in perfect agreement with the thermomechanical results. The two composites also showed dissimilarities in terms of relaxation time distributions, activation temperature range and type of behavior Arrhenius or VFT.