Effects of mixed carbon filler composition on electric heating behavior of thermally-cured epoxy-based composite films

Preparation and property investigation of multi-walled carbon nanotube (MWCNT)/epoxy composite films as high-performance electric heating (resistive heating) element

“…Unlike the graphene/epoxy composite films [8], the τ g values of the MWCNT/epoxy composite films were not strongly dependent on the MWCNT content within the experimental error. The average τ g value of 8.05±0.65 s for all the composite films was slightly higher than that of the graphene/epoxy [8] and graphene/ MWCNT/epoxy [9] composite films, while it was found to be lower than that of the MWCNT/ polyethylene composite reported in the literature [14]. This result demonstrates that the MWCNT/epoxy composite films in this paper exhibited a significantly rapid temperature response to the applied voltage.…”

“…The h r+c value was found to increase slightly with the MWCNT content because of the higher equilibrium temperatures at an identical voltage, which intensifies the heat exchange with the composite films and its surroundings. In addition, compared with the h r+c values for other carbon nanofiller/epoxy [8,9] and MWCNT/polyethylene [14] composites, the average h r+c value of 4.88±0.68 mW/°C for the composite films in this paper is excellent, which indicates that MWCNT/epoxy composite films exhibited excellent electric heating efficiency by applying a comparatively low electric power to reach a high equilibrium temperature. When the applied voltage was turned off at 120 s, the electric heating behaviour disappeared, and the surface temperature gradually cooled down to the ambient temperature in accordance with Newton's law of cooling.…”

“…The variations in the equilibrium temperatures (T e ) of the composite films as a function of the applied voltage (V) were nonlinear, as seen in Figure 7a. The electric power (P) computational formula can be express by Equation (8) [9]: Combining the Equation (8) with the Equation (1), we obtain the Equation (9) [9]: (9) Hence, we can find that the electric power (P) is proportional to the square of the voltage (V). For composite films with 0.01-2.0 wt% MWCNTs, the electric power values calculated from the Equation (8) are presented in Figure 7b.…”

“…It should be noted that, the I-V curves showed non-linear behaviour in the high applied voltage range with regard to the CNT/EP_1.0 and 2.0. This non-linear behaviour can be explained by the electron transition activated by the Joule heating effect [9,11]. The quantum tunneling mechanism reveals that electrons can hop from a CNT to another disconnected CNT to realize electric conduction when they are close enough.…”

“…In the case of CNT/ EP_0.05, the surface temperature remained at ambient temperature without any obvious change under a relatively low voltage of 10 V, which indicates that the electric current throughout the composite film was not enough to cause a surface temperature change. However, when applied voltages above 20 V were applied at 5 s, the surface temperature increased rapidly, reached an equilibrium temperature within ~30 s, remained at the equilibrium temperature up to 120 s, and then cooled down to ambient temperature within a brief period as the applied voltage was turned off at 120 s. Compared with the graphene/epoxy [8] and graphene/MWCNT/epoxy [9] composite films, the electric heating behaviour of the MWCNT/epoxy composite films was observed at a lower filler content, and this observation was associated with the nanostructure and dispersion state of the CNTs. For the other composite films with higher MWCNT contents of 0.07-2.0 wt%, similar electric heating behaviour was observed, and the noticeable difference was that the equilibrium temperature at an identical applied voltage was even higher with the increasing MWCNT content.…”