**3.2 CFRP characterization**

CFRPs were fabricated with Fibre Glast CF fabrics and Fibre Glast 2000/2060 resin base with different weight loadings of ERFG according to the procedure

**Figure 3.** *FT-IR spectra of ERFG and its synthetic precursors (a), and TEM image of an ERFG particle (b).*

**Figure 4.**

*Fabrication of CFRP using wet layup method.*


#### **Table 1.**

*Mechanical properties, through-plane thermal conductivity, and hydrogen permeability of CFRP made by Fibre Glast CF fabrics and Fibre Glast 2000/2060 resin with different wt% of ERFG (standard deviation).*

shown in **Figure 4**. The mechanical, thermal, and gas barrier properties of these samples were investigated and are summarized in **Table 1**.

Unlike the carbon fiber surface particle coating from previous reports, adding particles to the polymer matrix increased both the elastic modulus and the tensile strength. The increase of the elastic modulus of the CFRP made by ERFG resin correlated well with the increase of the ERFG loading below 15 wt%. However, the tensile strength decreased for CFRP with 15 wt% ERFG. There are two possible explanation for this phenomenon. First, the viscosity of resin with ERFG particles increased when adding more particles. For highly viscous resin, higher vacuum pressure and elevated temperature are required for uniform wetting. Second, 15 wt% of particles in the resin can form aggregates or liquid crystal domains. Both these structures prevent the uniform distribution of the particles through the CF fabric. Since the enhanced interfacial interaction between CFs and polymer matrix is based on the premise of attachment of the ERFG present in the polymer matrix to the surface of CF to form a physical interlock. The formation of aggregates or liquid crystal domains decreases the density of ERFG coated onto the CF surface and causes less effective stress transfer and results in decrease of CFRP's overall tensile strength. Further investigations are underway to reveal which mechanism dominates at higher particle loading CFRPs.

The in-plane thermal conductivity of C FRP can reach ~1000 W/(m × K) due to the continuous nature of the carbon fibers [39]. In contrast, the through-plane thermal conductivity of CFRP is in the 0.2–0.5 W/(m × K) range [40] because the polymer matrix separates the carbon fiber tows. Historically reported approaches

*Mechanically Improved and Multifunctional CFRP Enabled by Resins with High Concentrations… DOI: http://dx.doi.org/10.5772/intechopen.100141*


**Table 2.**

*Hydrogen permeability of conventional polymer liner for COPV tanks [43].*

added highly thermally conductive particles like graphene [40] or diamond [41] into the polymer matrix to increase the through-plane conductivity, but this compromises the other properties of CFRP, mainly mechanical properties. In this work, a significant improvement in the through-plane conductivity is achieved. The ERFG particles serve as bridges to facilitate the conduction of heat between individual carbon fibers. A 60% improvement in the through-plane thermal conductivity was realized in this way (**Table 1**). This significant improvement on the through-plane thermal conductivity can improve the CFRP's stability under thermal cycling and will enable the replacement of metal built electronic box in weight essential applications [42].

The 2D structure and high aspect ratio of the ERFG particles dispersed within the cured epoxy matrix were efficient in blocking the through-plane permeation of hydrogen gas. The hydrogen permeability of CFRP made with 10 wt% ERFG was 81 times lower than that of CFRP made with pure, unfilled epoxy resin (**Table 2**). These results make ERFG-enhanced CFRPs as state-of-the-art hydrogen barrier materials, far exceeding the properties of conventional polymer liner used in COPV (Composite Overwrapped Pressure Vessels) tanks [43, 47, 48]. The decreased hydrogen permeation is a huge benefit for building COPV tanks for hydrogen or natural gas storage. Additionally, use of ERFG-enhanced CFRPs eliminates one manufacturing step – polymer liner pre-molding – required to manufacture the current Type IV COPV tanks. This multifunctional CFRP is very promising for direct manufacturing of liner-less Type V COPV tanks.
