Relationship between viscoelastic properties and gelation in the epoxy/phenol-novolac blend system with N-benzylpyrazinium salt as a latent thermal catalyst

A study of viscoelastic properties and gelation in epoxy/phenol-novolac blend system initiated with 1 wt % of N-benzylpyrazinium hexafluoroantimonate (BPH) as a latent cationic thermal initiator was performed by analysis of rheological properties using a rheometer. Latent behavior was investigated by measuring the conversion as a function of curing temperature using traditional curing agents, such as ethylene diamine (EDA) and nadic methyl anhydride (NMA) in comparison to BPH. In the relationship between viscoelastic properties and gelation of epoxy/phenol-novolac blend system, the time of modulus crossover was dependent on high frequency and cure temperature. The activation energy (E_c) for crosslinking from rheometric analysis increased within the composition range of 20-40 wt % phenol-novolac resin. The 40 wt % phenol-novolac (N40) to epoxy resin showed the highest value in the blend system, due to the three-dimensional crosslinking that can take place between hydroxyl groups within the phenol resin or epoxides within the epoxy resin involving polyaddition of the initiator with BPH.