Enhancing the fracture toughness of hierarchical composites through amino‒functionalised carbon nanotube webs

Abstract

The introduction of carbon nanotubes (CNTs) in structural fibre-reinforced polymers, to imbue the composite with multifunctional properties (e.g. enhancing electrical/thermal conductivity, structural health monitoring), has received much attention in recent years. Maintaining, and preferably enhancing, the structural integrity of the composite is imperative. Consequently, strong interfacial bonding between the CNTs and the polymer matrix is sought. If the sought multifunctionality is dependent on specific CNT alignment or orientation, achieved through fragile CNT assemblies, gas-phase chemical functionalisation of the CNT assembly is a viable approach in order to chemically modify the CNT surface without damaging the CNT assembly. This study reports on the gas-phase amino-functionalisation of CNT webs (CNTw) and further explores its influence on the in situ electrical conductivity. The placement of an ethylenediamine-functionalised multilayer CNTw (0.2 g•m-2) between CF plies resulted in a 13 % enhancement in the interlaminar Mode I fracture toughness, while providing an electrical conductivity of 10 3 S•m-1 in the direction of the CNTs within the interleaved CNTw. The effectiveness of the aminofunctionalised CNTw in enhancing the mechanical properties of an epoxy composite is related to an epoxy opening reaction, as demonstrated by Differential Scanning Calorimetry (DSC). Raman and X-ray photoelectron spectroscopies are used to confirm that gas-phase amino-functionalisation does not damage the graphene-based structure and its structural dependent properties.

Interlaminar toughening in structural carbon fiber/epoxy composites interleaved with carbon nanotube veils

“…CNT sizing) [40,69,70], (iii) physical transfer of the CNT particles (i.e. spray coating) [42,[71][72][73][74][75] and (iv) CNT interleaving technique [13,24,48,76]. The first method often leads to large improvements in matrix properties at low mass fractions, however, due to issues such as agglomeration and filtering effects of nanofillers, improvements in mechanical properties under higher mass fractions were rarely reported.…”

Mode I interlaminar fracture toughness of thin-ply laminates with CNT webs at the crack interface

“…Previous investigations have shown good compatibility between CNT web and the SE84LV resin from Gurit [7], so this was chosen in combination with the dry thin plies provided by TexTreme in order to assess the thin-ply effect, in comparison to conventional laminates [7][8][9]. Control samples (TRC, i.e.…”

“…Nistal et al [8,9] demonstrated a way of improving the interaction between the resin and CNT web without affecting the orientation or the microstructure of the CNTs, important in underpinning the development of CNT web-based multifunctionality. This was achieved through a single step gas-phase amino functionalisation which enhanced ILFT of conventional SE84LV CFRP by 24% with respect to pristine CNT webs.…”

Hybrid FRP/CNT veil hierarchical composites with enhanced interlaminar properties and integrated multifunctionalities

“…CNT interleaving technique [88,89,147,148] (Figure 2-13c). The first method often leads to large improvements in matrix properties at low volume fractions, but reaching saturation around 5 wt.%, after which mechanical enhancements become less significant.…”

“…Recently, much attention has been paid to the use of thin veils of carbon nanotubes (CNT) as interleaves in laminated composites [147,148,[156][157][158]. These veils can be intercalated between the primary reinforcing fiber layers before infusion, so there is no need to disperse them into the resin.…”