## 3 Results and Discussion
### Microwave Cure in the Presence of CNTs
When considering materials cured solely in a convection oven, no significant difference in the thermal behavior between resins with and without CNTs is observed, as can be seen in Figure 6. In Figure 6A, the DSC curves of samples with and without CNTs exhibit a very similar trace, with only discrete transitions, indicating that both materials are completely cured after being heated at 140 \({}^{\circ}\)C in a convection oven for 6 h. Likewise, the TG curves of samples with and without CNTs (Figure 6B) are very similar up until 498 \({}^{\circ}\)C, when most of the materials have been completely degraded. One possible reason for the lower residue content of the resin cured in the presence of CNTs may be the catalytic action of metals present in the CNTs during the final stages of the thermal decomposition (\(>\)470 \({}^{\circ}\)C), when high molecular weight and carbonized fragments experience further degradation in comparison to samples devoid of CNTs. Indeed, the CNTs have not been purified before being incorporated in the resin. They have a nominal ash content of 1.5 wt %, rich in Fe and Al. As will be discussed later in the text, before reaching temperatures \(>\)470 \({}^{\circ}\)C, the effects imparted by the use of CNTs are negligible in the thermal behavior of the system. Therefore it can be concluded that CNTs had little effect on the polymerization reaction carried out in a convection oven. The situation is completely different when the cure is carried out under microwaves. With the goal of finding the appropriate microwave conditions that result in a fully cured sample in the shortest possible time, it was hypothesized that due to the rapid and uniform heating obtained by microwave irradiation of well dispersed CNTs in the tung oil-based resin, the cure time can be drastically reduced in comparison to the regular cure carried out in a convection oven. After preliminary tests, an ideal microwave step was established with irradiation at 100 W for 10 min, followed by irradiation at 200 W for 10 min. When heating the crude monomer mixture under microwaves, a fine control over the microwave power utilized is necessary. If excessive heat is applied over a short time interval, the  
Figure 6: **(A)** DSC curves of: (a) unreinforced tung oil-based resin cured for 6 h at 140 \({}^{\circ}\)C in a convection oven, (b) tung oil-based resin reinforced with 0.2 wt % of CNTs and cured for 6 h at 140 \({}^{\circ}\)C in a convection oven, (c) a tung oil-based resin reinforced with 0.25 wt % CNTs microwaved at 100 W for 10 min, followed by 200 W for 10 min, and (d) a tung oil-based resin reinforced with 0.25 wt % CNTs microwaved at 100 W for 10 min, followed by 200 W for 10 min, and a 2 h 10 min post-cure step at 140 \({}^{\circ}\)C in a convection oven; **(B)** TG curves of tung oil-based resins cured for 6 h at 140 \({}^{\circ}\)C in a convection oven with and without CNTs. monomers boil before the polymerization is completed, resulting in an undesirable rigid foam structure. If excessive time is applied during the microwave cure, signs of thermal degradation are observed in the samples. The ideal microwave schedule obtained allowed for full consolidation of the thermoset, without formation of bubbles or cracks. Samples submitted to that schedule, however, still exhibit a residual cure peak when analyzed by DSC. In the DSC curve of a microwaved CNT/tung oil-based sample, the prominent exothermic peak at 190 \({}^{\circ}\)C reveals that the microwave cure step alone did not result in a completely cured material (Figure 6A). When testing alternative post-cure times, it has been found that after a post-cure step of 1 h 30 min, the resin is still not completely cured (Figure S2). However, a completely cured sample is obtained when the material undergoes a 2 h 10 min post-cure at 140 \({}^{\circ}\)C in a convection oven after the microwave step (Figure 6A). The absence of exothermic peaks in Figure 6A (curve d) is indicative that the sample is fully cured.