Cure behavior of epoxy-cyanate ester blend in composite systems: Evaluation studies in neat resin cast by thermal and FTIR techniques

The post-cure behavior of a commercially available DGEBA-based epoxy modified cyanate ester resin (1,1-bis (4-cyanato phenyl) ethane) was investigated by thermo analytical techniques and Fourier Transform Infrared (FTIR) spectroscopy. Thermally initiated resin cure was carried out at 170 degrees C/1 h followed by 180 degrees C/2 h. Two different post-cure procedures, (PCPs), PCP-1 (210 degrees C/2 h + 250 degrees C/1 h) and PCP-II (280 degrees C/3 h), were independently followed for the cured resin material. Dynamic mechanical analysis (DMA) characterization of the resin casts indicated significant lowering of glass transition temperature (T-g), by about 35 degrees C in PCP-II casts in comparison with PCP-I, though the former was post cured at higher temperature. However, the PCP-II specimens recorded considerable enhancement in storage modulus values at room temperature and above till about the T-g region. FTIR spectroscopic studies of the resin cast support the formation of both cyanurate triazine ring (1563 cm(-1), 1368 cm(-1)) and oxazolidinone ring (1736 cm(-1)) for the PCP-1 resin cast while in the PCP-II specimens the former, namely the cyanurate formation was found to be absent. The absence of rigid cyanurate triazine rings in PCP-II was further strengthened by the tan delta(max) values observed in these resin casts by DMA. The DMA and differential scanning calorimetry gave comparable Tg values for both the PCP-1 and PCP-II resin casts. (c) 2008 Wiley Periodicals, Inc.