Gelling and curing behaviors of benzoxazine/epoxy formulations containing 4,4′-thiodiphenol accelerator

Benzoxazine (BOX)/diglycidyl ether of bisphenol A (DGEBA) based epoxy resins (BOX/DGEBA = 100/0, 75/25 and 50/50 wt.%) with and without 4,4′-thiodiphenol accelerator (DT300) were prepared. The gelling and curing behaviors of the BOX and BOX/DGEBA mixtures in presence and absence of DT300 (10 parts per hundred resin, phr) were investigated using plate–plate rheometry and differential scanning calorimetry (DSC). The gel time was determined in isothermal scans at three different temperatures (T = 180, 200, and 220 °C). Dynamic DSC scans were registered at four heating rates (β = 5, 10, 15, and 20 °C min−1, respectively). The activation energy of gelling was assessed by an Arrhenius, whereas that of the curing by the Kissinger and Ozawa methods. Combination of BOX with DGEBA delayed the gel formation and increased the activation energy of both gelling and curing processes compared to neat BOX resin. By contrast, addition of 4,4′-thiodiphenol as co-reactive accelerator markedly reduced the gel time and the activation energy of both gelling and curing of BOX and BOX/DGEBA formulations.