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°C/1 h followed by 180°C/2 h. Two different post‐cure procedures, (PCPs), PCP‐I (210°C/2 h + 250°C/1 h) and PCP‐II (280°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 (Tg), by about 35°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 Tg 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‐I 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 tanδ max values observed in these resin casts by DMA. The DMA and differential scanning calorimetry gave comparable Tg values for both the PCP‐I and PCP‐II resin casts.