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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3. Results and discussion 3.1. Epoxy resin suspension viscosity

All materials (neat resin and resin enhanced with small percentages of grapheme) exhibit a Newtonian behaviour, and the values obtained from the viscosity measurements are shown in Table 1. It is possible to conclude that, for the neat resin, the values obtained are in accordance with the supplier’s datasheet and, when the graphene is added to the resin, it promotes an increase in the suspension’s viscosity. This increase, compared to the neat resin, is about 16.3% when the resin is nano-enhanced with 1 wt.% of graphene, which agrees with the literature. For example, a similar trend was observed by Ceccia et al. (2008), Koziol et al. (2017) and Rathinasabapathi and Krishnamoorthy (2019) for similar amounts of graphene.

Table 1. Resin suspension viscosity. Wt. Graphene (%)

Viscosity (Pa.s)

0,86 ± 0.01 0,87 ± 0.01 0,90 ± 0.01 1.00 ± 0.01

0

0.25 0.50

1.0

3.2. Contact angle between resin and graphene

Figure 1 shows the evolution of the contact angle with time between resin and graphene wafers. The initial contact angle is around 69º, and this value substantially decreases reaching, for example, values around 37º after 1.5 seconds. Therefore, the values and the time profile clearly indicate that the resin has the ability to wet the graphene particles, suggesting that cohesive forces occur between resin and grapheme particles in the composite.

Figure 1 Evolution of the contact angle with time between resin and graphene wafers.

3.3. Effect of mixture condition on polymerization rate Figure 2 shows the effect of the mixing condition on the polymerization rate, which is expressed by the increase in the temperature of the reaction system. It is noted that the addition of graphene promotes a decrease in the maximum temperature reached during polymerization, but without changing the time needed to reach this temperature. Similar behaviour was found by Koziol et al. (2017) in which the presence of graphene decreased the peak temperature during polymerization. However, contrary to what was observed in this study, authors noted that the time to reach the peak