Rheological study of gel phenomena during epoxide network formation in the presence of sepiolite

The dynamic behaviour during the crosslinking of an epoxy polymer near the gel point was monitored using rheological multiple frequency experiments. The influence of a needle-shaped inorganic nanofiller, sepiolite, either non-modified or organically surface modified during the cure process in the presence of an aliphatic and an aromatic hardener was investigated. The validity of various criteria for determining the gel point was examined for the crosslinking of these filled thermosets. The WinterChambon criterion at the gel point is obeyed by the unfilled and by the non-modified sepiolite-filled epoxy matrix with either of the two hardeners. However, physical gels are formed in the presence of the organically modified sepiolite and the WinterChambon criterion is not valid. For all the systems investigated, the nanofiller reduces the time to reach gelation. Critical relaxation exponents and gel strength have been determined indicating a more elastic and stronger gel in the presence of the aliphatic hardener. (c) 2012 Society of Chemical Industry