Development of de-icing/self-sensing structural composites via controlled Joule heating curing

Joule heating curing is among the most promising strategies for obtaining cured structural components. This polymerization methodology consumes less than 1 % of the energy required by traditional oven/autoclave processes. In light of the relevant impact on the environmental sustainability of manufacturing processes, several aspects related to this curing methodology have been thoroughly investigated. Structural thermoset resins filled with a percentage of 3 % wt./wt. carbon nanotubes (CNTs) were produced by comparing two hardening processes: the classical thermal curing in the oven and the more recent Joule heating curing. The electrical resistance change ratio was monitored during the two curing processes to understand how the hardening reactions and the type of curing process affect the electrically conductive network in the composite. It was found that the alignment of CNTs, also previously detected for traditional curing performed under applied high electric field, mainly occurs in the fluid epoxy mixture's initial curing stage and is maintained thanks to the stiffening caused by the polymerization reactions. CNT alignment was verified through tunneling atomic force microscopy (AFM-TUNA). Furthermore, when the heating occurs in the oven, the resistance (R) of the sample increases sensitively, showing a typical positive temperature coefficient behavior. An opposite behavior (negative temperature coefficient) is manifested when the temperature increases via Joule heating by applying an electrical field, obtaining a strong reduction of the sample resistance. Joule heating cured glass fiber reinforced composites manifest the intrinsic coexistence of smart properties (self-heating, de-icing, and self-sensing). The peculiar anisotropic electrical properties conferred by the Joule heating to the glass fiber reinforced composites can be exploited to enhance the efficacy of the self-sensing function in the direction normal to CNTs alignment. The high gauge factor of 39 ± 4 (in the linear region between 0 % and 0.33 % of strain) was detected. These composites exhibit enhanced smart functions compared to traditionally hardened ones, opening up new possibilities for safety and efficient industrial applications.