PSI - Issue 37

J.M. Parente et al. / Procedia Structural Integrity 37 (2022) 820–825 J.M. Parente/ Structural Integrity Procedia 00 (2019) 000 – 000

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temperature increased with the presence of grapheme due to the decrease in the epoxy vitrification caused by the presence of graphene.

Figure 2 Polymerization effect results

3.4. Shrinkage Table 2 shows the results obtained from the shrinkage tests. results can be seen in table 2. It is possible to observe that the graphene content has an expressive effect on the shrinkage behaviour. Compared to the neat resin, where the shrinkage value is 3.2%, an increase of about 78.1% and 84.4% was found when the matrix is nano-enhanced with 0.5% and 1% of graphene, respectively. Using a similar method, Koziol et al. (2017) observed a reduction in shrinkage with the addition of 1.0 wt.% of graphene, which can be due to the change in the epoxy structure, creating, in this case, a more compact material. However, more detailed studies are needed to assess this behaviour.

Table 2. Shrinkage results. Graphene content (wt.%)

Shrinkage (%)

0

3.2 5.7 5.9

0.5 1.0

3.5. Hardener mixing time Table 3 shows the effect of the hardener mixing time on the mechanical properties for a neat nanocomposite. Compared to the properties obtained for a mixing time of 0.5 minutes, the bending stress increased around 14.9% for a mixing time of 2.5 min, while this value was only 11.1% for 5 min. The same comparison for the bending stiffness promoted increases of 10.5% and 61.9%, respectively. Finally, the bending strain decreased 28.3% for a mixing time of 2.5 min, while for 5 min of mixture the value was similar to that obtained for 0.5 min. Therefore, considering the overall performance, a hardener mixing time of 2.5 min was selected for the other tests.

Table 3. Effect of hardener mixing time on the bending properties. Hardener mixing time (min) Bending stress (MPa) Bending stiffness (GPa) Bending strain (%) 0.5 98.31 (2.0) 2.94 (0.06) 4.6 (0.04) 2.5 112.9 (2.5) 3.25 (0.09) 3.3 (0.04) 5.0 109.2 (3.4) 4.76 (0.15) 4.6 (0.07) () =standard deviation