Nano-engineered prepreg manufacturing: control of capillary rise of resin into VACNTs’ forests

Abstract

The incorporation of vertically aligned carbon nanotubes (VACNTs) between composites plies has been said to enhance the through-thickness strength, and it can also decrease the risk of interply delamination and reduce crack initiation. Thanks to these high mechanical performances, nano-engineered hybrid composites are seen as promising for highly demanding structural reinforcement applications. This paper is part of a study that focuses specifically on the methodology for trans-ferring VACNTs onto a prepreg surface while maintaining their initial vertically aligned morphology. The chosen method involved bonding the VACNTs' forest through capillary impregnation of the forest by the prepreg's resin. Key parameters for an effective transfer and to achieve a partial capillary rise of the resin into the VACNTs will be discussed here.

Composite laminates reinforced by vertically aligned carbon nanotubes: Detailed manufacturing process, from nanotubes transfer to composite consolidation

“…b) Yellow dotted line indicates the boundary between the VACNTs dry zone and the impregnated one. shows that the VACNTs forest transferred onto prepreg surface maintain their initial morphology. The method to determine the level of capillary rise of the resin is detailed in a previous study 49 , the yellow dotted line separates the wet and dry areas, indicating the limit between the resin-impregnated zones and the dry zones. The partial impregnation of resin into VACNTs forest is demonstrated under the impregnation process combination of 1 bar – 60°C – 10 min.…”

“…The feasibility of impregnating VACNTs forest with epoxy resin through capillary rise has been previously reported by the authors. 49 By changing the temperature and therefore the resin’s viscosity, the impregnation of the VACNTs by the epoxy resin from the prepreg can be controlled. The resin viscosity and therefore the impregnation speed can be adjusted by changing the temperature during the process, as long as the resin crosslinking is kept to a minimum.…”

“…High pressure can cause buckling of VACNTs during impregnation, resulting in non-aligned nanotubes after impregnation. 49 On the other hand, low pressure can reduce the contact between the VACNTs and the prepreg leading to local lack of transfer. Therefore, a vacuum pressure of 1 bar is selected for the impregnation process, as buckling was not observed at this pressure (see Figure 9).…”