**2. Some considerations concerning the processing graphene-based/ elastomer nanocomposites**

#### **2.1 Filler dispersion**

The efficient preparation of an elastomeric nanocomposite requires appropriate dispersion of the filler in the elastomeric matrix. Whence, there is a need for the filler and matrix to be compatible, physically and/or chemically. Most properties of nanocomposites depend on the nanofillers structure in the matrix. Therefore, such intimate nanofiller/elastomeric matrix interactions are dependent on the filler size, morphology, surface treatment, and activity. Undoubtedly, the fine dispersion of nanosized particles would lead to a very large interfacial area. Undoubtedly, the reinforcement changes with the specific interfacial area, for fillers with the same chemical nature [38–40]. As a result, the filler-matrix interactions and bonding will increase, in the meantime, the filler-filler interactions will decrease, and/or the platelet interlayer distance will increase [41–45]. They permit lower loadings, weight reduction of the fillers, and allow for the nanoparticles of ≤1 μm size the formation of a sort of colloidal suspensions. In the specific case of graphite-based fillers, because of the positive effect of aromatic rings, they would allow for the establishment of an intimate interaction between the nanofiller and the rubber matrix [40, 46–48]. One should note that elastomeric polymers possess high viscosity and thus necessitate intensive mixing and blending to achieve an even dispersion and distribution.

During the dispersive step, in the mixing process, large components undergo size reduction through erosion and rupture into smaller fragments that are then separated into the matrix [49–51]. These two last phases most likely happen rather simultaneously [49, 52]. Ideal dispersion of platelets-like (lamellar) nanofillers requires that all layers should be separated from each other, i.e., complete exfoliation. However, the strong interlayer interactions need to be circumvented, more often through intercalations to facilitate exfoliation [53–55].

Graphite is like montmorillonite clay (MMT), and researchers applied similar procedures for the dispersion of graphene-based fillers [56–58]. Intercalated and exfoliated compounds are in common usage. To reduce the strong p-p interactions between graphene platelets, graphene sheets are customarily surface-modified [56–58]. For the classification of graphene-based fillers, for example, a stack of few-layer graphene is called graphene nanoplatelets (GNP) [27, 59, 60].

**Figure 2b** is a representation of stacked, expanded, and exfoliated graphite platelets in an elastomeric matrix. Exfoliation of GNPs into an elastomer is desired to enhance the properties of the final material. Most exfoliation processes are performed in suspension rather than during bulk processing, during which, high shear is reported to break the platelets rather than exfoliate them [27, 59, 60].

#### **2.2 Surface functionalization**

For surface functionalization of graphene sheets, there is firstly a *non-covalent* and secondly a *covalent* approach. Non-covalent functionalization is primarily based on hydrophobic, van der Waals, and electrostatic interactions [61–65]. Covalent functionalization is dependent on the oxygen functional groups on the graphene surface. They can be utilized to change the surface functionality of graphene. The main functional groups are the carboxylic acid at the edges and epoxy and hydroxyl groups on the basal plane [66–69].

A comprehensive summary of the functionalization of graphene has been reviewed in the literature [70–74].

#### **2.3 Graphene-based fillers in the reinforcement of elastomer nanocomposites**

Fillers have been employed as reinforcing agents for ages. Fillers, depending on their activity, can be categorized as extenders, which increase the volume of materials. On the one hand, reinforcing fillers leads to improve certain physical and mechanical properties. The reinforcing ability of fillers is dependent on the particle shape, size, agglomeration (dispersion), surface properties, and most importantly, the degree of interaction between the filler and the matrix.

#### *2.3.1 Graphene oxide (GO) as a reinforcing filler*

The research community focused attention on the field of polymer nanocomposites on graphene oxide (GO). This could be attributed to the variety of chemical functional groups available on the surface of GO that make it tunable, hydrophilic, and relatively low-cost as compared with pristine graphene. Its interaction with polar polymeric matrices is improved by the presence of such hydrophilic functional groups.

Improving the interfacial adhesion of GO and the host polymers through covalent bonding has been the subject of several studies [75–77]. Thus, GO becomes intertwined as a single phase with the host chains. In consequence, the superior properties of GO are transferred to the matrix, and thus improvements in the final properties of the composites will ensue. Various approaches have been explored for producing GO-polymer nanocomposites through covalent bonding [78–83]. These methods normally involve the incorporation of thermally reduced GO (TrGO) [84, 85] or in situ chemically reduced GO (CrGO) in the rubber matrix [86, 87]. Homogeneity of TOGO in the rubber matrix is assisted by ultrasonication or high shear mixing. A strong polymer-filler interaction is critical for GO to act as a successful reinforcement agent [88–92]. For GO, the change in the degree of oxidation may significantly impact the physicochemical structure of the GO surface.

#### *2.3.2 Other reinforcing fillers*

Conventionally, the most widely used and effective conventional reinforcing filler for rubber is carbon black (CB). It provides a notable improvement in the properties of elastomers, in general. The drawback, in some cases, is when colored rubber compositions are needed. Due to its high specific surface area, silicon dioxide (SiO2) is

#### *Processing of Graphene/Elastomer Nanocomposites: A Minireview DOI: http://dx.doi.org/10.5772/intechopen.104849*

known to be the most effective reinforcing non-black fillers. it is reported that about 90% of the worldwide production of CB is employed and applied in the tire industry, enhancing tear strength, modulus, and wear characteristics of the tires [93]. Recently, nanofillers have gained momentum both in fundamental and industrial fields. This is mainly due to the high specific surface area and quite often to their high aspect ratio that can be dispersed in the elastomeric matrix. There exist interactions at the molecular level between the elastomeric matrix and the nanofiller. As a result, extraordinary properties are achieved compared with conventional filler materials. Based on their dimensions in host matrices, nanofillers are classified into three categories: spherical nanoparticle fillers, elongated structure with only two dimensions is in the nanometer scale, and the third is larger, e.g., nanotubes and whiskers, and layered structures with only one dimension of the filler is in the nanometer scale, such as graphene that is the subject of our study. One notes that these nanofillers have a strong tendency to form aggregates and agglomerates, owing to their high surface energies.
