**1. Introduction**

Carbon Fiber Reinforced Plastics (CFRP) have been widely used as lightweight materials replacing metals because of their superior specific strength, stiffness, and corrosion resistance [1]. In recent years, their application has been extended from high-end industries, like aerospace, aircraft, sports, and military to cost-sensitive industries, like automotive and energy [2]. This new trend requires reducing the cost of parts made from CFRP. This price reduction can be achieved through two approaches: 1) enhancing mechanical properties of CFRPs resulting in lower usage for same function and 2) eliminating functional parts by enabling CFRPs with these functions.

Improving the stress transfer between the carbon fibers (CF) and improvement of stiffness of polymer matrix are most popular research topics. Besides development of highly efficient CFRP fabrication techniques, low price CF manufacturing and material-saving structure designs, these studies also aim at cost reduction via decrease in CFRP usage. Due to the weak interfacial interaction between the load bearing CFs and the polymer matrix that integrate the structure, delamination is one of the major failure modes for CFRP. One of the key reasons for this failure is that CF has relatively low density of surface functional groups, which result in lesser surface interactions. To address this problem, increasing the interface interaction through sizing, a polymer coating that improves stress transfer through chemical bond and physical interlock, is required as part of the CF manufacturing process [3]. Inspired by the sizing mechanism, rigid particles have been added either into polymer sizing or by spraying on the CFs, to encourage strong physical interlock.

New approach to lower the cost and weight of systems containing CFRPs is to make CFRP a functional part in the system. For example, Type V storage vessels used for hydrogen storage are designed with only a single layer of CFRP which endures the compressed gas pressure and simultaneously acts as an efficient hydrogen barrier. Compared with other tank designs (e.g. Type IV), Type V tank is more cost competitive via process, material, and weight saving through limiting the hydrogen barrier liner. However, to realize this design, a large amount of fillers with good gas barrier properties need to be present into the CFRP to form an effective gas barrier layer.

Carbon-based materials use in polymer sizing have drawn a lot of attention to this approach because of their superior mechanical properties, chemical structure like that of CFs, and most importantly due to their high aspect ratio. Methods including electrophoretic deposition [4, 5], spray [6, 7], and dip coating [8–12] have been employed to deposit graphene and carbon nanotubes onto CFs surfaces. CFRPs made with these coated CFs show ~20–70% improvement on interlaminar shear strength. Up to 10 wt% of particles laden sizing coated onto CF by such approaches have been demonstrated [8]. However, this approach generally does not improve the tensile or flexural modulus [5, 8, 13]. This is because the polymer matrix is much weaker compared to CF, and as a result, the polymer matrix deforms under stress. To reinforce both the modulus and strength of CFRP, researchers have tried to add carbon-based particulate materials directly into the resin matrix as well, [14–19] but this approach achieved only limited improvement in mechanical properties. The primary limitation is particle aggregation, which prevents high particle loading resins [16, 20]. Typically, CFRP with ~1 wt% of carbon-based fillers in the polymer matrix have shown the best properties. A polymer matrix containing a high loading of dispersed carbon-based materials would therefore be likely to radically increase both, strength and modulus, of CFRPs. Meanwhile, carbon-based materials have been appraised for their excellent properties as electrical and thermal conductors, gas barrier, fire retardant et al. [21, 22]. The advantages of their multifunction can introduce CFRP with special properties to replace other functional part and reduce the device price, when the particle concentrations are high enough.

Fluorographene (FG) is a unique carbon-based material which maintains the excellent mechanical properties of graphene but with excellent chemical, electronic, *Mechanically Improved and Multifunctional CFRP Enabled by Resins with High Concentrations… DOI: http://dx.doi.org/10.5772/intechopen.100141*

#### **Figure 1.**

*Illustration of CFRP containing a high loading of epoxy-reacted fluorographene (ERFG, orange ovals) in the polymer matrix.*

tribological, and hydrophobic properties, due to the presence of fluorine atoms [23]. One distinctive advantage of FG is that it is easily forms dispersion and exfoliates because fluorination disrupts the van der Waals forces between FG sheets [24]. Other researchers have studied the electrical, thermal and mechanical properties of FG-reinforced polyimide [25–27]. We have previously reported on dispersing epoxymonomer–functionalized FG in epoxy with 30 wt% loading, which achieved ~90%, ~60%, and ~ 170% improvement in the tensile strength, modulus, and toughness respectively [28]. In this work, resin containing ERFG was used to make CFRP by wet lay-up method. The high particle loading in the polymer matrix improves stress transfer between the CF, both by physically interlocking with the CFs to improve strength, and by chemical linkage within the polymer matrix to improve modulus (**Figure 1**). Additionally, the high particle loading also enables the CFRP to exhibit properties of FG present within the CFRP, such as low gas permeability, high thermal conductivity, et al. This mechanically improved and multifunctional CFRP is a very competitive composite for cost sensitive CFRP applications.

## **2. Experimentation**

#### **2.1 Materials**

Graphite fluoride (FG, also called fluorographite), triethylenetetramine (TETA), and acetone were bought from Sigma Aldrich. Bisphenol A based epoxy resins (EPON 826) with 178 g/mol EEQ (Epoxy Equivalent Weight [29]) was purchased from Miller-Stephenson Chemical Co., Inc. Fibre Glast 2000 (Epoxy), Fibre Glast 2060 (Hardener), 2 K 2 × 2 twill weave carbon fiber fabrics and all the materials for wet layup were from Fibre Glast. Toray T700 12 K 2 × 2 plain weave fabrics and T300 3 K 2 × 2 plain weave fabrics were purchased from Composite Envisions. T800S 12 K 2 × 2 twill weave fabrics and M55JB 6 K 2 × 2 plain weave fabrics were supplied by Rock West Composites. MGS L285 (epoxy) and H287 (hardener) were purchased from Aircraft Spruce & Specialty Co.

**Figure 2.** *Synthesis of ARFG and ERFG from fluorographite.*
