Effect of ZnO nanoparticles on the thermal stability of a T-DDM benzoxazine resin

In this work, nanocomposites with a high thermal stability were developed using T-DDM, a benzoxazine resin based on 4,4’-diaminodiphenylmethane (DDM) and Tyrosol, and zinc oxide nanoparticles. The neat T-DDM resin was investigated for its curing kinetics and its cure cycle was improved. Data from DSC experiments allowed to determine an activation energy of 90 kJ/mol and an overall order of reaction in the range of 2.2 to 2.5 for the autocatalytic curing reaction. A cure cycle was devised based on the criteria of a complete cure and a minimal cycle time. The resulting cycle is composed of three steps: (i) 60 minutes at 165°C, (ii) 90 minutes at 200°C, and (iii) 30 minutes at 220°C to achieve a complete cure. While this cycle worked well in DSC, it should be improved for curing of larger samples in a furnace. Nanocomposite blends were produced at various concentrations of ZnO and with different sonication times. The dispersion of the nanoparticles within the blends was evaluated with SEM and TEM. Blends up to 5wt% ZnO were found to have an adequate dispersion for 90 seconds of sonication. In blends at 10wt% ZnO sonicated for 90 seconds, the particles formed some large aggregates. DSC experiments showed a synergic increase of the heat of reaction due to the addition of the nanoparticles with a maximum at 17wt% ZnO, associated with an increase of the expected value by 16%. TGA measurements showed an improved thermal stability for the blends compared to the neat T-DDM resin. A significant raise of the degradation temperatures was observed for only a small fraction of ZnO nanoparticles in the blends. Moreover, a synergy was observed for the char yield. At 11wt% ZnO, 27% of char yield is added, due to the ZnO and the synergy, to the char yield of the neat resin. Finally, the interactions between the T-DDM resin and ZnO were studied by FTIR. In cured nanocomposites, a peak at 1678 cm-1 was observed and attributed to hydroxyl groups, originating from the water of a condensation reaction in T-DDM chemisorpted on the ZnO nanoparticles