2. Synthesis approach of graphene-like nanomaterials

2D nanosheets are synthesized using a variety of methods based on two topdown and bottom-up approaches. In top-down approach, the bulk of the parent material is used and the final 2D nanosheets are produced during the processes. This approach can be cost-effective depending on the material used. In this view, 2D nanomaterials are produced by methods such as separation, peeling, cleavage and exfoliation. Micromechanical cleavage, ball milling, liquid/chemical exfoliation and functionalization (covalent and non-covalent) are common methods in this category [17–25].

In the bottom-up, the precursor materials are used for producing of GLNs, with methods such as chemical synthesis, chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD). However, there are the main challenges facing researchers in this field. One of them is the need for high amounts of nanomaterials and low yield synthesis methods of these nanomaterials. A great effort is being made for improvement the efficiency of the synthesis of these nanosheets [26–28].

In general, interfacial interaction is believed to play an important role in determining the final properties of polymer nanocomposites. Interfacial interaction between the polymer matrix and the filler materials includes van der Waals interactions, hydrous bonds, covalent bonds, and ionic bonds [29]. Hence, many efforts have been made to develop and improve interfacial interactions of nanocomposites including filler or matrix. The functionalization of the filler surface and the use of compatibilizer are common to be modified the surface of filler in terms of polar/nonpolar nature and to be able to interact with the polymeric matrix due to the hydrophobic/hydrophilic nature of polymers used in the composite and coating industry.

nanocomposites, polymer chains are intercalated between 2D layers, which partially open the layers. The characteristic peak displacement of these nanosheets to lower angles represents intercalating. In the third group, the suitable interaction between filler and the polymer matrix leads to the complete exfoliation of the layers by the polymer chains. The characteristic peak related to these nanosheets disappears in the diffraction pattern of these nanocomposites. In practice, however, it is rarely

Schematic view of different groups of composites; conventional, intercalated and exfoliated nanocomposites.

The final properties of nanocomposites depend on the method and processing conditions. Most polymer composites are processed using the following methods: (i) melt processing (ii) solvent processing (iii) In-situ polymerization; (iv)

The melt mixing method is one of the most economical and environmentally friendly methods used to make nanocomposites. In fact, this process is the choice of most industries. The mixing of materials is often done through a single or double extruder, in such a way that the reinforcement is mixed with the molten polymer. The mixer uses shear force to separate the filler agglomerates and disperse them throughout the polymeric matrix (Figure 3(a)). Another point of this method is the lack of any solvent for processing. Most polymers used in this method include lowdensity polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), poly(methyl methacrylate) (PMMA), polyamide polyester

Solution mixing is another way of producing nanocomposites containing GLNs. In

this method, the nanomaterials and polymers are dissolved in the solvent before being molded and then the solvent is evaporated (Figure 3(b)). In this method, both thermoset and thermoplastic polymers can be used. Polymers such as PMMA,

electrospinning and (v) layer by layer (LBL) assembly (Figure 3).

possible to achieve complete exfoliation [31, 32].

4. Processing

Figure 2.

Graphene-Like Nanocomposites

DOI: http://dx.doi.org/10.5772/intechopen.85513

and polycarbonate [30, 33–37].

145

#### 3. Graphene-like nanocomposites and their importance

Due to inherent and impressive properties of mechanical, electronic and thermal conductivity of GLNs, these compounds are considered as a promising candidate for using in polymer nanocomposites as fillers. Compared to conventional composites, these nanocomposites show a dramatic increase in properties, even in a low content of filler. Hence, the 2D nanomaterials and GLNs based-nanocomposites are not only lighter, but also have more and stronger multi-functional properties. As mentioned in the previous section, due to the high surface area of GLNs, the physicochemical interaction of the filler with the polymeric matrix enhances. This helps strengthen and enhancement of interfacial bonding between layers of GLNs and polymer matrix [30].

According to the interaction between filler and polymer matrix, polymer composites are divided into three groups; conventional or immiscible composites, intercalated composites, and exfoliated or miscible composites (Figure 2). In conventional composites, 2D nanosheets remain as agglomerates in the polymer matrix and retain their original structure. The diffraction pattern of conventional composites is the same as that for the first powder of these nanosheets. In intercalated

Graphene-Like Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.85513

reviewed the synthesis methods of GLNs and the processing polymer-based nanocomposites. Some applications of these nanomaterials have been investigated. Ultimately, we have studied the problems and limitations facing this category of

2D nanosheets are synthesized using a variety of methods based on two topdown and bottom-up approaches. In top-down approach, the bulk of the parent material is used and the final 2D nanosheets are produced during the processes. This approach can be cost-effective depending on the material used. In this view, 2D nanomaterials are produced by methods such as separation, peeling, cleavage and exfoliation. Micromechanical cleavage, ball milling, liquid/chemical exfoliation and functionalization (covalent and non-covalent) are common methods in

In the bottom-up, the precursor materials are used for producing of GLNs, with methods such as chemical synthesis, chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD). However, there are the main challenges facing researchers in this field. One of them is the need for high amounts of nanomaterials and low yield synthesis methods of these nanomaterials. A great effort is being made for improvement the efficiency of the synthesis of

In general, interfacial interaction is believed to play an important role in determining the final properties of polymer nanocomposites. Interfacial interaction between the polymer matrix and the filler materials includes van der Waals interactions, hydrous bonds, covalent bonds, and ionic bonds [29]. Hence, many efforts have been made to develop and improve interfacial interactions of nanocomposites including filler or matrix. The functionalization of the filler surface and the use of compatibilizer are common to be modified the surface of filler in terms of polar/nonpolar nature and to be able to interact with the polymeric matrix due to the hydrophobic/hydrophilic nature of polymers used in the composite and

Due to inherent and impressive properties of mechanical, electronic and thermal conductivity of GLNs, these compounds are considered as a promising candidate for using in polymer nanocomposites as fillers. Compared to conventional composites, these nanocomposites show a dramatic increase in properties, even in a low content of filler. Hence, the 2D nanomaterials and GLNs based-nanocomposites are not only lighter, but also have more and stronger multi-functional properties. As mentioned in the previous section, due to the high surface area of GLNs, the physicochemical interaction of the filler with the polymeric matrix enhances. This helps strengthen and enhancement of interfacial bonding between layers of GLNs

According to the interaction between filler and polymer matrix, polymer com-

posites are divided into three groups; conventional or immiscible composites, intercalated composites, and exfoliated or miscible composites (Figure 2). In conventional composites, 2D nanosheets remain as agglomerates in the polymer matrix and retain their original structure. The diffraction pattern of conventional composites is the same as that for the first powder of these nanosheets. In intercalated

2. Synthesis approach of graphene-like nanomaterials

3. Graphene-like nanocomposites and their importance

nanocomposites.

Nanorods and Nanocomposites

this category [17–25].

these nanosheets [26–28].

coating industry.

and polymer matrix [30].

144

Figure 2. Schematic view of different groups of composites; conventional, intercalated and exfoliated nanocomposites.

nanocomposites, polymer chains are intercalated between 2D layers, which partially open the layers. The characteristic peak displacement of these nanosheets to lower angles represents intercalating. In the third group, the suitable interaction between filler and the polymer matrix leads to the complete exfoliation of the layers by the polymer chains. The characteristic peak related to these nanosheets disappears in the diffraction pattern of these nanocomposites. In practice, however, it is rarely possible to achieve complete exfoliation [31, 32].

#### 4. Processing

The final properties of nanocomposites depend on the method and processing conditions. Most polymer composites are processed using the following methods: (i) melt processing (ii) solvent processing (iii) In-situ polymerization; (iv) electrospinning and (v) layer by layer (LBL) assembly (Figure 3).

The melt mixing method is one of the most economical and environmentally friendly methods used to make nanocomposites. In fact, this process is the choice of most industries. The mixing of materials is often done through a single or double extruder, in such a way that the reinforcement is mixed with the molten polymer. The mixer uses shear force to separate the filler agglomerates and disperse them throughout the polymeric matrix (Figure 3(a)). Another point of this method is the lack of any solvent for processing. Most polymers used in this method include lowdensity polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), poly(methyl methacrylate) (PMMA), polyamide polyester and polycarbonate [30, 33–37].

Solution mixing is another way of producing nanocomposites containing GLNs. In this method, the nanomaterials and polymers are dissolved in the solvent before being molded and then the solvent is evaporated (Figure 3(b)). In this method, both thermoset and thermoplastic polymers can be used. Polymers such as PMMA,

better dispersity of nanosheets in the polymeric matrix [16]. Different solvents can be

Another technique is in situ polymerization that both thermoset and thermoplastic polymers can be used. The filler should be dispersed in the monomer that is supposed to polymerize (Figure 3(c)). Polymerization begins with the use of a chemical that initiates the reaction or the mixing of the two monomers or with the help of temperature. One of the advantages of this method is the ability to graft polymer molecules to the filler surface and better dispersion of nanosheets. This technique can be used to make polymer composites that are not soluble in common solvents or are thermally unstable (for melt mixing). This method has been used in the development of PE [41], PP [42], PMMA [43], nylon 6 [44], PU [45],

Another method used to make this type of nanocomposite is electrospinning, which has been reported with the use of polymers such as polyimide, polyurethane (PU) [47], poly(vinyl alcohol) (PVA) [48], gelatin [49], nylon 6 [50], polyaniline (PANI) [51]. In this method, nanosheets orientation is possible along the axis of the fibers (Figure 3(d)). Electrospun diameter of polymer fibers can be controlled

Another possible way to achieve the proper dispersion of GL nanosheets in the polymeric matrix is layer by layer (LBL) assembly while to maintain the unique properties of the components (Figure 3(e)). This technique is obtained by

sequential absorption of the charged components in opposite direction by attractive forces such as electrostatic, hydrogen bonding, etc. Therefore, multi-layer structures using the LBL assembly can be manufactured reproducibly, so that it is possible to control the thickness and composition of hybrid nanocomposite at the

Depending on the type of GLNs and its inherent properties, the designed properties of nanocomposite can be received. Extraordinary properties of GLNs, such as BNNSs, including high thermal properties, structural stability, good mechanical properties, and antioxidant ability, have attracted the attention of researchers to use as a filler [53, 54]. A summary of the application of GLNs nanocomposites is shown

Fillers with a high aspect ratio and crystallinity can improve thermal conductivity and reduce Kapitza resistance [55, 56]. For example, most thermoplastic polymers, such as polyethylene, polypropylene, polyamide and thermosets such as epoxy, are insulating and have very low thermal conductivity, but these properties can be improved by adding fillers such as boron nitride. The use of BN in insulating polymer matrix is the solution if both of electrical properties and thermal conductivity are needed in an electronic device [57]. So far, few studies have been carried out on the thermal conductivity of thermoplastics filled with 2D boron nitride [58–65]. Therefore, researchers focus the investigation on the effect of filler (chemical composition, morphology, surface characteristics, shape and size) on

Despite the successful use of various methods in the synthesis of these nanocomposites, there is still a lack of information about: (1) the use of a suitable method for a particular compound of a matrix and reinforcement; (2) the maximum reinforcement content for achieving an optimal combination of properties and the low costs [16]. Therefore, it is still necessary to use the simulation and

in the range of tens of nanometers to several micrometers [16].

modeling method to achieve the answer to these unbeknownst.

5. Application of graphene-like nanocomposite

put in this category such as chloroform, acetonitrile and toluene [38–40].

polylactic acid (PLA) [46], etc. composites.

Graphene-Like Nanocomposites

DOI: http://dx.doi.org/10.5772/intechopen.85513

nanoscale level [52].

in Figure 4.

electrical conductivity.

147

#### Figure 3.

Schematic image of basic set-up of processing methods of composites (a) melt processing, (b) solvent processing, (c) in-situ polymerization, (d) electrospinning and (e) layer by layer (LBL) assembly.

polyvinyl alcohol, poly(hydroxy amino ether), PS, polyethylene (PE), polyethylene oxide (PEO) and epoxy can be used. Low viscosity of polymer in the solution (contrary to the molten method) with mechanical stirring or ultrasonic waves can help the

#### Graphene-Like Nanocomposites DOI: http://dx.doi.org/10.5772/intechopen.85513

better dispersity of nanosheets in the polymeric matrix [16]. Different solvents can be put in this category such as chloroform, acetonitrile and toluene [38–40].

Another technique is in situ polymerization that both thermoset and thermoplastic polymers can be used. The filler should be dispersed in the monomer that is supposed to polymerize (Figure 3(c)). Polymerization begins with the use of a chemical that initiates the reaction or the mixing of the two monomers or with the help of temperature. One of the advantages of this method is the ability to graft polymer molecules to the filler surface and better dispersion of nanosheets. This technique can be used to make polymer composites that are not soluble in common solvents or are thermally unstable (for melt mixing). This method has been used in the development of PE [41], PP [42], PMMA [43], nylon 6 [44], PU [45], polylactic acid (PLA) [46], etc. composites.

Another method used to make this type of nanocomposite is electrospinning, which has been reported with the use of polymers such as polyimide, polyurethane (PU) [47], poly(vinyl alcohol) (PVA) [48], gelatin [49], nylon 6 [50], polyaniline (PANI) [51]. In this method, nanosheets orientation is possible along the axis of the fibers (Figure 3(d)). Electrospun diameter of polymer fibers can be controlled in the range of tens of nanometers to several micrometers [16].

Another possible way to achieve the proper dispersion of GL nanosheets in the polymeric matrix is layer by layer (LBL) assembly while to maintain the unique properties of the components (Figure 3(e)). This technique is obtained by sequential absorption of the charged components in opposite direction by attractive forces such as electrostatic, hydrogen bonding, etc. Therefore, multi-layer structures using the LBL assembly can be manufactured reproducibly, so that it is possible to control the thickness and composition of hybrid nanocomposite at the nanoscale level [52].

Despite the successful use of various methods in the synthesis of these nanocomposites, there is still a lack of information about: (1) the use of a suitable method for a particular compound of a matrix and reinforcement; (2) the maximum reinforcement content for achieving an optimal combination of properties and the low costs [16]. Therefore, it is still necessary to use the simulation and modeling method to achieve the answer to these unbeknownst.
