Electrically conductive GNP/epoxy composites for out-of-autoclave thermoset curing through Joule heating

Abstract

The development of scalable Out-of-Autoclave (OoA) in-situ thermoset curing methods are required to overcome important drawbacks related to the autoclave-based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heating, emerges as a promising route to replace the conventional processing methods. In this work the electrical behaviour of both uncured and oven cured GNPs/epoxy composites with loadings of up to 10 wt.% were evaluated and electrical percolation thresholds were established for both. Above the critical loading found for oven cured materials (~ 8.5 wt.%) the electrically conducting networks of GNPs formed in the matrix showed the ability to act as integrated nanoheaters when an electric current was passed through them, successfully curing the composites by Joule heating. Composites prepared by this OoA curing method (as an alternative to the traditional oven based one) at 10 wt.% loading of GNPs were also prepared and compared to the oven cured ones. They showed more compact composite 2 structures, with less microvoids and a preferred orientation of the GNPs in the matrix relative to the oven cured material at identical loading, as revealed by electron microscopy and polarized Raman spectroscopy, respectively. This microstructure and anisotropy induced by the electrically-induced (i.e. OoA) cure led to GNPs/epoxy composites with superior electrical and mechanical properties (revealed by tensile testing). The well-distributed GNP nanoparticles acting as nanoheaters integrated in a thermosetting matrix, in combination with excellent mechanical and electrical performances achieved for the overall graphene/epoxy composites and the simplicity associated to the method, should open the door to novel industrial applications.

Enhanced Thermal and Dynamic Mechanical Properties of Synthetic/Natural Hybrid Composites with Graphene Nanoplateletes

“…However, at higher GNP wt.% (0.75) there was no change in decomposition temperature. A similar trend was observed by Xia et al [51] when using GNP filler in epoxy. DSC results were similar to TGA results and revealed that the composite samples (S1, S2, S3, S4, and S5) after adding GNP exhibited virtuous resistance or stability towards heat in the epoxy composites.…”

“…However, at higher GNP wt.% (0.75) there was not much improvement in T g due to the agglomeration at the interface of the polymer and reinforcement which hinders the polymer cross linking [49,50]. No exothermic peak was observed in any case which corroborated the compete cure of all the composites [51]. The next endothermic region found around 350–380 °C was the decomposition of aromatic epoxy and aliphatic amine hardener [41].…”

Smart Coatings with Carbon Nanoparticles

“…Nevertheless, they found preferential orientation of the GNPs which was associated to the presence of an electric field during curing stage as it was not observed in oven-cured samples. This fact is very important as they found improved electrical and mechanical performance in this direction, but this anisotropic behavior must be taken into account when designing elements with these materials [63].…”

Sustainable and self-regulating out-of-oven manufacturing of FRPs with integrated multifunctional capabilities

“…The recent interest in nanomaterials, especially carbon based nanofillers like carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) with good thermal and electrical properties have enabled the development of many high performance multifunctional composites [4][5][6][7][8]. The use of CNTs and/or GNPs has not only introduced multifunctionalities like electrical or thermal conductivities and strain or damage sensing capabilities [9][10][11][12][13], but has also demonstrated its potential as a Joule heating source to efficiently heat up composite laminates and cure thermoset resins [14][15][16][17][18][19]. For example, Lee et al reported an out-of-oven curing technique via resistive heating of an aligned carbon nanotube film, which could be detached after curing.…”