Fabrication and mechanical properties of carbon fiber/carbon nanotube/epoxy nanocomposites

Abstract

Carbon fiber/polymer (CF/polymer) composites have been received much attentions as light-weight structural materials with high mechanical properties by replacing the conventional structural materials based on heavy metals and ceramics. However, in the current technological level, anisotropic properties of CF/polymer composites between strong carbon fibers and weak polymer matrix and weak interfaces between them limit their mechanical properties for successful replacement of conventional structural materials. In the CF/polymer composites, cracks easily initiate and propagate along the laminar interfaces in various failure modes. It causes the decrease of mechanical properties such as interlaminar shear strength and fracture toughness.

Carbon nanotubes (CNTs) are the one-dimensional (1D) nanomaterials, which have superior mechanical properties compared to other conventional fillers. CNTs can improve the mechanical properties of polymer matrix and effectively enhance the delamination resistance in CF/polymer composites due to their outstanding strength and modulus with nanoscale dimension. However, CNTs are easily agglomerated in polymer matrix due to large van der Walls force between each rope of CNTs, and interfacial bonding between CNTs and polymer matrix is poor due to lack of functional groups on the surfaces of CNTs. These problems of CNTs and their composites must be solved prior to apply the CNTs into CF/polymer composites for successful enhancement of mechanical properties of CF/polymer composites.

In this study, new functionalization methods for CF/CNT/polymer nanocomposites were suggested. The functionalized CNTs were fabricated by simple ball milling process with poly(4-aminostryene) (PAS) as functional molecules. During the ball milling process, PAS were successfully attached on the surface of CNTs by non-covalent interaction between CNTs and PAS. The 1wt% CNT/epoxy nanocomposites fabricated by using PAS functionalized CNTs (PAS-CNT) showed 41 % enhancement of Young’s modulus and 34 % enhancement of tensile strength than pure epoxy. It is mainly due to homogeneous dispersion of CNTs and strong interfacial bonding between CNTs and epoxy matrix.

The CF/CNT/epoxy nanocomposites by using PAS-CNT/epoxy showed enhancement of Young’s modulus (~ 4%), tensile strength (~ 17%), interlaminar shear strength (~ 24%) and fracture toughness (~ 26%). It showed that addition of PAS-CNT can effectively enhance the mechanical properties of CF/CNT/polymer nanocomposites.