Avant-Garde Polymer and Nano-Graphite-Derived Nanocomposites—Versatility and Implications

: Graphite (stacked graphene layers) has been modiﬁed in several ways to enhance its potential properties/utilities. One approach is to convert graphite into a unique ‘nano-graphite’ form. Nano-graphite consists of few-layered graphene, multi-layered graphene, graphite nanoplatelets, and other graphene aggregates. Graphite can be converted to nano-graphite using physical and chemical methods. Nano-graphite, similar to graphite, has been reinforced in conducting polymers/thermoplastics/rubbery matrices to develop high-performance nanocomposites. Nano-graphite and polymer/nano-graphite nanomaterials have characteristics that are advantageous over those of pristine graphitic materials. This review basically highlights the essential features, design versatilities, and applications of polymer/


Introduction
Natural graphite has stimulated dynamic research interest towards hybrid polymeric materials [1].Various polymeric matrices have been characteristically reinforced by graphite filler: polyaniline/graphite, epoxy/graphite, polystyrene graphite, PMMA/graphite, and many others [2].The inclusion of graphite in polymers has remarkably improved their electrical, thermal, mechanical, and other essential physical properties [3][4][5].Pristine graphite-and polymer-based materials have been applied in electronics and energy devices, packaging, anticorrosion coatings, membranes, etc. [6].However, the stacked layered structure of graphite has limited dispersion in polymers and ensuing final high performance.In this regard, various research attempts have focused on the altered forms of compact graphite structures.
Nano-graphite is an exceptional modified form of graphite, having a mixture of layered graphene, nanosheets, and nanoplatelet components [7].Nano-graphite has been obtained from pristine graphite by using simple techniques, ranging from physical grinding and sonication to chemical conversion techniques.Similar to graphite, it has been reinforced in polymeric matrices in order to form polymer/nano-graphite nanocomposites [8,9].However, the properties of the resulting nanocomposites have been found to be better than those of pristine-derived polymeric composites.In particular, nano-graphite has been suggested to possess enhanced dispersion in various polymeric matrices, matrixnanofiller interactions, and end properties.The recent literature has shown the upgraded utility of nano-graphite-derived nanocomposites in technical application areas, including electronics, EMI, and solar cells [10].However, no review article has been published in the literature to date regarding high-performance polymer/nano-graphite nanocomposites.Hence, this state-of-the-art review definitely contributes important knowledge towards the the literature to date regarding high-performance polymer/nano-graphite nanocomposites.Hence, this state-of-the-art review definitely contributes important knowledge towards the future design possibilities and methodological potential of novel polymer/nano-graphite nanocomposites.

Nano-Graphite
Graphite is a naturally abundant carbon allotrope [11].It is made up of stacked layers of sp 2 -hybridized carbon atoms, also known as graphene [12].The graphene layers are usually held together through weak van der Waals forces.The parallel stacking of carbon layers may form a three-dimensional lattice structure.
Nano-graphite is a simply modified form of graphite.The structure of nano-graphite is actually a mixture of nanocarbon nanomaterials with graphitic nanoplatelets or nanosheets and layered graphene [13].In nano-graphite, the few-layered graphene may consist of two to ten layers or nanosheets.Moreover, graphene nanoplatelets and fewlayered graphite oxides also exist.The nanoplatelets may have a thickness of 30-50 graphene layers.Figure 1 displays a simple illustration of the nano-graphite structure.Nanographite has fascinating physicochemical characteristics.The electrical, thermal, and mechanical properties of nano-graphite have been found in between the graphite and graphene layers [14].The preparation of nano-graphite from graphite has been performed through numerous straightforward approaches, such as mechanical exfoliation (cavitation [15], shear mixing [16], grinding [17], high-pressure homogenization [18], and microfluidization [19]) and sonication, as well as various thermal and chemical reduction methods.The mechanical exfoliation methods are preferred for the conversion of graphite to nano-graphite due to their low-cost, no use of toxic chemicals, and environmental friendliness [20].Blomquist and co-workers [21] applied a metal-free aqueous method to obtain nano-graphite.The detonation technique, involving the use of oxygen-deficient explosives, has also been adopted to form nano-graphite [22].Ioni et al. [23] applied high-power sonication as a single-step method to attain nano-graphite dispersion in various solvents.In another study, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, and Raman spectroscopy were used to examine the nano-graphite nanostructure.The nano-graphite had 30-50 graphene layers in its structure [24].The lateral sizes of the nano-graphite platelets were found to be in the range of 300-500 nm.The thicknesses of the nano-graphite platelets were ~20-40 nm.Due to its unique nanostructure, the charge transference properties of nano-graphite have been found to be remarkably high, so it is useful for various related technical applications [25].The applications of nano-graphite have been observed in thermal/electrical conductors, microwave absorbents, lubricants, coatings, absorbents, electromagnetic shields, C 2023, 9, 13 3 of 20 gaskets, etc.In polymers, graphite has been applied as an electrically conducting and strengthening filler.

Polymer and Nano-Graphite-Derived Nanocomposites: Variations and Features
In bulk form, graphite is a layered material with a high electrical conductivity of ~10 6 S/m [26].Graphite has been widely used as a filler in polymeric composites to improve their electrical, thermal, mechanical, and other physical properties.Polymer/graphite nanocomposites have been fabricated using facile approaches, such as in situ polymerization, solution blending, and melt processing [27].The graphite dispersion in polymers depends on the choice of the processing technique [28].It has been observed that graphite particles may develop an interconnecting network to support the percolation threshold of conductivity in the matrix.Nylon 6, polyamides, polystyrene, and other thermoplastics have been effectively filled with graphite using solution mixing in situ and melt routes.The fine graphite content and dispersion have led to the application of polymer/graphite composites in wide a range of applications, from automobile parts to electronics [29].
The performance of polymer/nano-graphite nanocomposites depends on the manufacturing techniques used and the related processing parameters [30].Polymer/nano-graphite nanocomposites have been mostly processed using solution, melt, in situ, and other facile manufacturing techniques.The choice of technique determines the nanofiller dispersion, matrix-nanofiller interactions, and interface formation, affecting the enhancements in the final material properties [31].Most importantly, the preparation method and the parameters determine the extent of nanofiller scattering in the polymers.Solution blending has the advantages of fine nanofiller dispersion and the homogeneous morphology of the nanocomposites; however, its major disadvantage is the use of toxic organic solvents [32].The melt processing system can be considered ecofriendly; however, it may have a nanofiller aggregation problem [33].The in situ technique has also been successfully used to form polymer/nano-graphite nanocomposites, and it can use eco-friendly solvents [34].Therefore, the processing of polymer/nano-graphite nanocomposites by using an appropriate manufacturing strategy may form homogeneous microstructures with enhanced electrical, mechanical, thermal, and other physical properties [35].

Conducting Polymer/Nano-Graphite
Similar to graphite, the reinforcement behavior and features of nano-graphite have been investigated in nanocomposites.Consequently, nano-graphite has been filled in various polymers using suitable processing techniques, such as solution mixing, melt blending, and in situ polymerization [36].Conducting polymers and graphite-based nanocomposites have been reported [37].Most importantly, graphite has been frequently used to enhance the electrical conductivity of conjugated polymers [38].Singhal et al. [39] designed a poly (3,4ethylenedioxythiophene): poly(styrenesulfonate)-and nano-graphite-based nanocomposite using the solution method.To consistently disperse the nano-graphite, the swift heavy ion method was used with a Ni ion beam of 80 MeV.The swift heavy ion method actually breaks the nano-graphite accumulation due to van der Waals interactions.Figure 2 depicts the solution processing of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/nanographite nanocomposite.After solution processing, the nanocomposite films were cast on a glass substrate through solution evaporation.Figure 3 displays the transmission electron microscopy images of the pristine nano-graphite and the nanocomposite.A cross-section image of the poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate)/nano-graphite nanocomposite after irradiation showed that the nano-graphite stack had 7-8 graphene layers with a 2.6 nm thickness.Moreover, the nano-graphite had an inter-layer distance of 0.335 nm.Shinde and co-workers [40] prepared nano-graphite via planetary ball milling.Then, the polyaniline/nano-graphite nanocomposites were shaped in the form of pellets via cold pressing.The nanocomposites were characterized for their electrical conductivity and hardness.Mo et al. [41] sonicated expanded graphite in a 95% alcohol solution to obtain nano-graphite.Polypyrrole/nano-graphite nanocomposites were developed through in situ polymerization.The electrical conductivity of the polypyrrole/nano-graphite nanocomposites was enhanced with the nanofiller loading.The maximum electrical conductivity of 80.0 Scm −1 was achieved with a 3 wt.%nanofiller.Accordingly, the electrical conductivity of the conducting polymers was further boosted with graphite filler loading.
graphite had an inter-layer distance of 0.335 nm.Shinde and co-workers [40] prepared nano-graphite via planetary ball milling.Then, the polyaniline/nano-graphite nanocomposites were shaped in the form of pellets via cold pressing.The nanocomposites were characterized for their electrical conductivity and hardness.Mo et al. [41] sonicated expanded graphite in a 95% alcohol solution to obtain nano-graphite.Polypyrrole/nanographite nanocomposites were developed through in situ polymerization.The electrical conductivity of the polypyrrole/nano-graphite nanocomposites was enhanced with the nanofiller loading.The maximum electrical conductivity of 80.0 Scm −1 was achieved with a 3 wt.%nanofiller.Accordingly, the electrical conductivity of the conducting polymers was further boosted with graphite filler loading.

Polystyrene/Nano-Graphite
Polystyrene has been widely used as an important matrix for pristine graphite, similarly used with nano-graphite [42][43][44].Xuemei et al. [45] adopted the detonation method graphite had an inter-layer distance of 0.335 nm.Shinde and co-workers [40] prepared nano-graphite via planetary ball milling.Then, the polyaniline/nano-graphite nanocomposites were shaped in the form of pellets via cold pressing.The nanocomposites were characterized for their electrical conductivity and hardness.Mo et al. [41] sonicated expanded graphite in a 95% alcohol solution to obtain nano-graphite.Polypyrrole/nanographite nanocomposites were developed through in situ polymerization.The electrical conductivity of the polypyrrole/nano-graphite nanocomposites was enhanced with the nanofiller loading.The maximum electrical conductivity of 80.0 Scm −1 was achieved with a 3 wt.%nanofiller.Accordingly, the electrical conductivity of the conducting polymers was further boosted with graphite filler loading.

Polystyrene/Nano-Graphite
Polystyrene has been widely used as an important matrix for pristine graphite, similarly used with nano-graphite [42][43][44].Xuemei et al. [45] adopted the detonation method to form nano-graphite.A nanoparticle size of 16 nm and a specific surface area of 583.6 m 2 •g −1 were attained by using the Brunauer-Emmett-Teller (BET) equation.The polystyrene/nano-C 2023, 9, 13 5 of 20 graphite nanocomposite was prepared via Pickering emulsion polymerization, with azobisisobutylonitrile as the initiator in an aqueous solution.Figure 4 displays the optical micrographs of the polystyrene/nano-graphite Pickering emulsion microspheres.The micrographs clearly indicate that the polystyrene microspheres were homogeneously surrounded with a layer of detonation nano-graphite particles.The resulting polystyrene microspheres had a fine dispersity, spherical shape, and uniform size of up to 100 µm.The nanocomposite-encapsulated polystyrene microspheres were polydispersive due to the sonication emulsification method used.A large number of nano-graphite particles densely anchored to form shells around the polystyrene droplets.The use of nano-graphite instead of graphite led to the recompences of better interactions between the nanofiller particles and the polymeric microspheres.The better matrix-nanofiller association and interface formation directly influenced the nano-graphite dispersion and final physical property improvement of the nanocomposite.
to form nano-graphite.A nanoparticle size of 16 nm and a specific surface area of 583.6 m 2 ⋅g −1 were attained by using the Brunauer-Emmett-Teller (BET) equation.The polystyrene/nano-graphite nanocomposite was prepared via Pickering emulsion polymerization, with azobisisobutylonitrile as the initiator in an aqueous solution.Figure 4 displays the optical micrographs of the polystyrene/nano-graphite Pickering emulsion microspheres.The micrographs clearly indicate that the polystyrene microspheres were homogeneously surrounded with a layer of detonation nano-graphite particles.The resulting polystyrene microspheres had a fine dispersity, spherical shape, and uniform size of up to 100 µ m.The nanocomposite-encapsulated polystyrene microspheres were polydispersive due to the sonication emulsification method used.A large number of nano-graphite particles densely anchored to form shells around the polystyrene droplets.The use of nano-graphite instead of graphite led to the recompences of better interactions between the nanofiller particles and the polymeric microspheres.The better matrix-nanofiller association and interface formation directly influenced the nano-graphite dispersion and final physical property improvement of the nanocomposite.

Poly(Methyl Methacrylate)/Nano-Graphite
Poly(methyl methacrylate) has been applied as a vital thermoplastic matrix to form nanocomposites with neat graphite [46][47][48].Likewise, nano-graphite nanofiller has also been reinforced in poly(methyl methacrylate) matrices.Singhi et al. [49] used commercially obtained nano-graphite of ~400 nm.A poly(methyl methacrylate)/nano-graphite nanocomposite was formed using the in situ polymerization of methylmethacrylate monomer and nano-graphite along with sonication.The nano-graphite was loaded in the range of 0.25-1.5 wt.%.The thermal stability of the neat poly(methyl methacrylate) and poly(methyl methacrylate)/nano-graphite nanocomposites was determined by conducting a thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).The results of the thermal studies are given in Table 1.According to TGA, the initial decomposition temperature of the poly(methyl methacrylate)/nano-graphite nanocomposites increased with the nanofiller loading up to 154 °C relative to that of the neat polymer (114 °C).The DSC thermograms also revealed improvements in the glass transition temperature of up to 114 °C compared with that of the neat polymer (110 °C).The increase in the thermal constancy and glass transition of the nanocomposite can be attributed to the polymer chain stiffness and stability due to the addition of the nano-graphite nanofiller.Soni et al. [50] produced a poly(methyl methacrylate)/nano-graphite nanocomposite by using the solution casting technique.The nano-graphite nanofiller was loaded in 1-5 wt.% contents.The nanocomposite was studied for its optical properties.The optical properties of

Poly(Methyl Methacrylate)/Nano-Graphite
Poly(methyl methacrylate) has been applied as a vital thermoplastic matrix to form nanocomposites with neat graphite [46][47][48].Likewise, nano-graphite nanofiller has also been reinforced in poly(methyl methacrylate) matrices.Singhi et al. [49] used commercially obtained nano-graphite of ~400 nm.A poly(methyl methacrylate)/nano-graphite nanocomposite was formed using the in situ polymerization of methylmethacrylate monomer and nano-graphite along with sonication.The nano-graphite was loaded in the range of 0.25-1.5 wt.%.The thermal stability of the neat poly(methyl methacrylate) and poly(methyl methacrylate)/nano-graphite nanocomposites was determined by conducting a thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).The results of the thermal studies are given in Table 1.According to TGA, the initial decomposition temperature of the poly(methyl methacrylate)/nano-graphite nanocomposites increased with the nanofiller loading up to 154 • C relative to that of the neat polymer (114 • C).The DSC thermograms also revealed improvements in the glass transition temperature of up to 114 • C compared with that of the neat polymer (110 • C).The increase in the thermal constancy and glass transition of the nanocomposite can be attributed to the polymer chain stiffness and stability due to the addition of the nano-graphite nanofiller.Soni et al. [50] produced a poly(methyl methacrylate)/nano-graphite nanocomposite by using the solution casting technique.The nano-graphite nanofiller was loaded in 1-5 wt.% contents.The nanocomposite was studied for its optical properties.The optical properties of the poly(methyl methacrylate)/nano-graphite nanocomposite were not affected by the nanofiller loading; C 2023, 9, 13 6 of 20 however, the optical properties of the films decreased with an increase in the temperature.The reason for this seems to be the decrease in the transmittance and energy bandgap at higher temperatures.Poly(methyl methacrylate)/nano-graphite nanocomposites have been fabricated through in situ and solution methods.The effect of nano-graphite loading has mostly been considered for the enhancement of optical and thermal properties.[51][52][53].Poly(vinyl chloride) is another thermoplastic matrix nanocomposite with nano-graphite.Zhang et al. [54] adopted commercial nano-graphite to form a nanocomposite with a titania and poly(vinyl chloride) matrix.The photocatalytic degradation mechanism of the poly(vinyl chloride) nanocomposite with nano-graphite and titania is demonstrated in Figure 5.The nano-graphite and titania were consistently distributed in the polymeric matrix and, thus, improved the conductivity and photocatalytic activity of the nanomaterial.Figure 6 shows that the photocatalytic degradation weight loss of the nanocomposite was significantly more enhanced than that of the neat poly(vinyl chloride) and pristine nano-graphite.The inclusion of the combination of nanocarbon and titania not only upsurged the photocatalytic efficiency due to electron/photon transfer but also promoted structural stability due to interfacial interactions.Although few poly(vinyl chloride)/nano-graphite systems have been explored to date, enhancements in dispersion, thermal, and photocatalytic behaviors have been observed with nanofiller loading.
C 2023, 9, x FOR PEER REVIEW 6 of 20 nanofiller loading; however, the optical properties of the films decreased with an increase in the temperature.The reason for this seems to be the decrease in the transmittance and energy bandgap at higher temperatures.Poly(methyl methacrylate)/nano-graphite nanocomposites have been fabricated through in situ and solution methods.The effect of nanographite loading has mostly been considered for the enhancement of optical and thermal properties.[51][52][53].Poly(vinyl chloride) is another thermoplastic matrix nanocomposite with nano-graphite.Zhang et al. [54] adopted commercial nano-graphite to form a nanocomposite with a titania and poly(vinyl chloride) matrix.The photocatalytic degradation mechanism of the poly(vinyl chloride) nanocomposite with nano-graphite and titania is demonstrated in Figure 5.The nano-graphite and titania were consistently distributed in the polymeric matrix and, thus, improved the conductivity and photocatalytic activity of the nanomaterial.Figure 6 shows that the photocatalytic degradation weight loss of the nanocomposite was significantly more enhanced than that of the neat poly(vinyl chloride) and pristine nano-graphite.The inclusion of the combination of nanocarbon and titania not only upsurged the photocatalytic efficiency due to electron/photon transfer but also promoted structural stability due to interfacial interactions.Although few poly(vinyl chloride)/nano-graphite systems have been explored to date, enhancements in dispersion, thermal, and photocatalytic behaviors have been observed with nanofiller loading.

Poly(Vinylidene Fluoride)/Nano-Graphite
Into the bargain, the literature reports on poly(vinylidene fluoride)-and graphitebased materials were examined [55][56][57].Poly(vinylidene fluoride) has also been adopted to form a nanocomposite with a nano-graphite nanofiller.Li et al. [58] developed nanocomposites of poly(vinylidene fluoride) and nano-graphite via solution casting and compression molding.The nanofiller contents at the percolation threshold were efficient in improving the dielectric permittivity of the nanocomposite.Abdelaziz et al. [59] reported the development of a poly(vinylidene fluoride)-, hydroxypropyl cellulose-, and nanographite-based nanocomposite via the solution method.The addition of nano-graphite generated the β-phase polymorph in the poly(vinylidene fluoride) and matrix-nanofiller interface.Due to the β-phase and interface effects, the dielectric and thermal properties of the nanocomposite were positively affected.Again, in the case of the poly(vinylidene fluoride)/nano-graphite nanocomposite, the literature is limited.Further efforts are required in order to uncover the features and technical potential of poly(vinylidene fluoride)/nanographite nanocomposites.

Poly(Lactic Acid)/Nano-Graphite
The literature also reports poly(lactic acid)-and graphite-derived composites [60][61][62].Correspondingly, research has led to the inclusion of nano-graphite in poly(lactic acid) nanocomposites.Gardella et al. [63] produced nano-graphite through the sonication of graphite in an ionic liquid, 1-butyl-3-methylimidazoliumhexa-fluorophosphate (80 °C).The ionic liquid was also used as a medium to disperse the nano-graphite in order to form a nanocomposite with poly(lactic acid).The poly(lactic acid)/nano-graphite nanocomposite was processed via melt blending.The ionic liquid solvent was stable and did not decompose during the nanocomposite processing.According to a scanning electron microscopy analysis, nano-graphite aggregates of 300 nm were observed in the matrix.Guo et al. [64] used a commercial nano-graphite with a diameter of 1.5-2.0µ m.Poly(lactic acid)/nano-graphite nanocomposites were designed via Fused Deposition Modeling.Figure 7 shows the thermal conductivity of the poly(lactic acid)/nano-graphite nanocomposites with varying nanofiller contents.The thermal conductivity increased with an increase in the nano-graphite content.The reason for this was the formation of

Poly(Vinylidene Fluoride)/Nano-Graphite
Into the bargain, the literature reports on poly(vinylidene fluoride)-and graphitebased materials were examined [55][56][57].Poly(vinylidene fluoride) has also been adopted to form a nanocomposite with a nano-graphite nanofiller.Li et al. [58] developed nanocomposites of poly(vinylidene fluoride) and nano-graphite via solution casting and compression molding.The nanofiller contents at the percolation threshold were efficient in improving the dielectric permittivity of the nanocomposite.Abdelaziz et al. [59] reported the development of a poly(vinylidene fluoride)-, hydroxypropyl cellulose-, and nano-graphite-based nanocomposite via the solution method.The addition of nano-graphite generated the βphase polymorph in the poly(vinylidene fluoride) and matrix-nanofiller interface.Due to the β-phase and interface effects, the dielectric and thermal properties of the nanocomposite were positively affected.Again, in the case of the poly(vinylidene fluoride)/nano-graphite nanocomposite, the literature is limited.Further efforts are required in order to uncover the features and technical potential of poly(vinylidene fluoride)/nano-graphite nanocomposites.

Poly(Lactic Acid)/Nano-Graphite
The literature also reports poly(lactic acid)-and graphite-derived composites [60][61][62].Correspondingly, research has led to the inclusion of nano-graphite in poly(lactic acid) nanocomposites.Gardella et al. [63] produced nano-graphite through the sonication of graphite in an ionic liquid, 1-butyl-3-methylimidazoliumhexa-fluorophosphate (80 • C).The ionic liquid was also used as a medium to disperse the nano-graphite in order to form a nanocomposite with poly(lactic acid).The poly(lactic acid)/nano-graphite nanocomposite was processed via melt blending.The ionic liquid solvent was stable and did not decompose during the nanocomposite processing.According to a scanning electron microscopy analysis, nano-graphite aggregates of 300 nm were observed in the matrix.Guo et al. [64] used a commercial nano-graphite with a diameter of 1.5-2.0µm.Poly(lactic acid)/nano-graphite nanocomposites were designed via Fused Deposition Modeling.Figure 7 shows the thermal conductivity of the poly(lactic acid)/nano-graphite nanocomposites with varying nanofiller contents.The thermal conductivity increased with an increase in the nano-graphite content.The reason for this was the formation of transportation conducting pathways due to the nanofiller linking in the polymeric matrices.Owing to the high thermal/electrical con-ductivity, the poly(lactic acid)/nano-graphite nanocomposites were printed using Fused Deposition Modeling.Figure 8 shows the printed models on paper and flexible materials.The printed models had a fine flexibility and adhesion to the substrates due to fine matrix-nanofiller interactions and interface formation.
C 2023, 9, x FOR PEER REVIEW 8 of 20 transportation conducting pathways due to the nanofiller linking in the polymeric matrices.Owing to the high thermal/electrical conductivity, the poly(lactic acid)/nano-graphite nanocomposites were printed using Fused Deposition Modeling.Figure 8 shows the printed models on paper and flexible materials.The printed models had a fine flexibility and adhesion to the substrates due to fine matrix-nanofiller interactions and interface formation.transportation conducting pathways due to the nanofiller linking in the polymeric matrices.Owing to the high thermal/electrical conductivity, the poly(lactic acid)/nano-graphite nanocomposites were printed using Fused Deposition Modeling.Figure 8 shows the printed models on paper and flexible materials.The printed models had a fine flexibility and adhesion to the substrates due to fine matrix-nanofiller interactions and interface formation.

Polyurethane/Nano-Graphite
Polyurethane has also been applied as an important nanocomposite matrix.Mishra et al. [65] developed a polyurethane/nano-graphite nanocomposite for energy devices.The electrical conductivity of the polyurethane/nano-graphite nanocomposite with varying nanofiller contents is shown in Figure 9.
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Polyurethane/Nano-Graphite
Polyurethane has also been applied as an important nanocomposite matrix.Mishra et al. [65] developed a polyurethane/nano-graphite nanocomposite for energy devices.The electrical conductivity of the polyurethane/nano-graphite nanocomposite with varying nanofiller contents is shown in Figure 9.The percolation threshold of the nano-graphite in the polyurethane matrix was analyzed.The electrical conductivity of the polyurethane/nano-graphite nanocomposite was enhanced after the addition of 3 wt.%nanofiller, and it was stabilized after 5 wt.%.The 3 wt.%nano-graphite content was used as the percolation threshold value for energy device applications.Although there have been limited attempts to develop polyurethane/nanographite nanocomposites, the effect of the nanofiller on the conductivity properties points to the important technical significance of these nanomaterials.

Rubber/Nano-Graphite
Rubber-and graphite-based composites have gained vital importance due to their thermal/mechanical properties and engineering applications [66,67].El-Nashar et al. [68] prepared nano-graphite using a poly(ethylene glycol)-based method.In acrylonitrilebutadiene rubber, the nano-graphite nanoparticles enhanced the mechanical properties (Young's modulus and hardness) and thermal stability of the matrix.According to dielectric studies, the permittivity and dielectric loss were found to increase with a rapid increase in the percolation threshold upon the addition of the nano-graphite.The acrylonitrilebutadiene rubber/nano-graphite nanocomposite was found to be useful for antistatic applications.Tiwari et al. [69] loaded nano-graphite in a chlorobutyl elastomer matrix.A nano-graphite loading of 6 phr was used as the percolation threshold in order to enhance the electrical conductivity of the nanocomposite.Scanning electron microscopy revealed some agglomerative nano-graphite nanoparticles, as well as the formation of an unremitting network in the matrix.The storage modulus and dielectric properties of the rubber/nano-graphite nanocomposite were dependent on the matrix-nanofiller interactions and were also affected by the rubber-nano-graphite network formation.Thus, rubber/nano-graphite nanocomposites have been investigated due to their advantageous dispersion, conductivity, dielectric, thermal, and mechanical features for relevant practical applications.The percolation threshold of the nano-graphite in the polyurethane matrix was analyzed.The electrical conductivity of the polyurethane/nano-graphite nanocomposite was enhanced after the addition of 3 wt.%nanofiller, and it was stabilized after 5 wt.%.The 3 wt.%nano-graphite content was used as the percolation threshold value for energy device applications.Although there have been limited attempts to develop polyurethane/nanographite nanocomposites, the effect of the nanofiller on the conductivity properties points to the important technical significance of these nanomaterials.

Rubber/Nano-Graphite
Rubber-and graphite-based composites have gained vital importance due to their thermal/mechanical properties and engineering applications [66,67].El-Nashar et al. [68] prepared nano-graphite using a poly(ethylene glycol)-based method.In acrylonitrilebutadiene rubber, the nano-graphite nanoparticles enhanced the mechanical properties (Young's modulus and hardness) and thermal stability of the matrix.According to dielectric studies, the permittivity and dielectric loss were found to increase with a rapid increase in the percolation threshold upon the addition of the nano-graphite.The acrylonitrilebutadiene rubber/nano-graphite nanocomposite was found to be useful for antistatic applications.Tiwari et al. [69] loaded nano-graphite in a chlorobutyl elastomer matrix.A nano-graphite loading of 6 phr was used as the percolation threshold in order to enhance the electrical conductivity of the nanocomposite.Scanning electron microscopy revealed some agglomerative nano-graphite nanoparticles, as well as the formation of an unremitting network in the matrix.The storage modulus and dielectric properties of the rubber/nanographite nanocomposite were dependent on the matrix-nanofiller interactions and were also affected by the rubber-nano-graphite network formation.Thus, rubber/nano-graphite nanocomposites have been investigated due to their advantageous dispersion, conductivity, dielectric, thermal, and mechanical features for relevant practical applications.
Hence, various polymers, such as poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate), polyaniline, polypyrrole, polystyrene, poly(methyl methacrylate), poly(vinyl chloride), poly(vinylidene fluoride), poly(lactic acid), polyurethane, acrylonitrilebutadiene rubber, chlorobutyl elastomer, and silicone rubber, have been employed as matrices for nanographite nanofillers.The dispersion of the nanofiller in the conducting polymer matrices formed via in situ methods have been found to be superior.Moreover, the nanofiller dispersion in thermoplastic matrices via solution methods has also been found to be homogeneous.All the conducting polymers, thermoplastics, and rubbery matrices behave differently with nano-graphite in terms of physical properties, depending on the backbone composition.Hence, advantageous properties can be obtained using various polymers and nano-graphite nanofillers, and no single polymer/nano-graphite nanocomposite category can be referred to as the best.However, nanofiller dispersion has been found to be dependent on the amount of nanofiller loaded, as well as on the processing technique used for the nanocomposite formation.The fine nanofiller dispersion attained via the facile processing technique may lead to enhanced properties for all the polymer/nano-graphite categories.
The structure of the nano-graphite affects the final properties and performance of the nanocomposites.Therefore, nano-graphite with a fine quality, the least impurities, and less structural disorders plays an essential role in the improvement of nanofiller dispersion, the provision of superior physical properties, and the production of high-performance nanocomposites.Consequently, the addition of nano-graphite influences the microstructure, surface morphology, and phase composition of nanocomposites.Subsequently, nanographite affects the compatibility of the polymer-nanofiller in a nanomaterial.In particular, the thermal stability, glass transition temperature, thermal conductivity, electrical conductivity, and mechanical behavior have been tuned with the addition of nano-graphite nanofiller.The better nano-graphite interactions with the polymer chains lead to mechanical interlocking, which enhances the mechanical properties.Moreover, the polymer chain rigidity and stability improve, leading to an upgraded heat stability and glass transition temperature.The inclusion of nanofiller in polymers through physical/covalent means also affects electron and thermal transportation through the nanocomposite systems.

In Dye-Sensitized Solar Cells
A dye-sensitized solar cell (DSSC) is usually composed of counter electrodes as crucial components [70].Platinum (Pt) has been commercially used as a counter electrode in DSSCs in addition to indium tin oxide or fluorine tin oxide electrodes [71].Pt-electrodebased DSSCs have the disadvantages of a high cost and weight.Pt electrodes have been beneficially replaced with carbon-based materials [72].For instance, graphite, carbon black, carbon nanotubes, etc., have been used as DSSC electrodes, showing high conductivity [73,74].To constructively use carbon materials in electrodes, conducting polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [75], polyaniline [76], and polypyrrole [77], have been used.Polyaniline-based nanocomposites are frequently fabricated for DSSC electrodes [78].Polyaniline/graphite nanocomposites have been used in DSSC electrodes [79].Correspondingly, Huang et al. [80] applied a polyaniline/nanographite nanocomposite in a DSSC counter electrode.The polyaniline/nano-graphite nanocomposite was prepared by using electro-polymerization.The power-conversion efficiency of the polyaniline/nano-graphite-nanocomposite-based DSSC was high at ~7.07%, i.e., comparable to the platinum electrode DSSC (7.19%).Yue et al. [81] prepared various counter electrodes for DSSCs, such as polypyrrole (PPy), platinum (Pt), nano-graphite (NG), and nano-graphite/polypyrrole (NG/PPy) counter electrodes.Figure 10 shows the comparative electrochemical impedance spectra (EIS) of the counter electrodes studied.The electrochemical performance of the NG/PPy electrode revealed a low charge-transfer resistance at the electrolyte-electrode interface, as well as excellent electrocatalyst performance.From the EIS spectra, the electrocatalytic activity of NG/PPy was determined from a semicircle diameter to be 0.1-100 kHz.The photovoltaic performance of the DSSC is given in Figure 11 and Table 2.Among all the electrodes, the DSSC with the NG/PPy electrode had a higher short-circuit current density and a power conversion efficiency of 14.83 mA•cm −2 and 7.40%, respectively.In solar cells, more novel polymer/nano-graphite combinations have been found to be desirable to attain a high power conversion efficiency of >8%.
C 2023, 9, x FOR PEER REVIEW 11 of 20 resistance at the electrolyte-electrode interface, as well as excellent electrocatalyst performance.From the EIS spectra, the electrocatalytic activity of NG/PPy was determined from a semicircle diameter to be 0.1-100 kHz.The photovoltaic performance of the DSSC is given in Figure 11 and Table 2.Among all the electrodes, the DSSC with the NG/PPy electrode had a higher short-circuit current density and a power conversion efficiency of 14.83 mA•cm −2 and 7.40%, respectively.In solar cells, more novel polymer/nano-graphite combinations have been found to be desirable to attain a high power conversion efficiency of >8 %.   resistance at the electrolyte-electrode interface, as well as excellent electrocatalyst performance.From the EIS spectra, the electrocatalytic activity of NG/PPy was determined from a semicircle diameter to be 0.1-100 kHz.The photovoltaic performance of the DSSC is given in Figure 11 and Table 2.Among all the electrodes, the DSSC with the NG/PPy electrode had a higher short-circuit current density and a power conversion efficiency of 14.83 mA•cm −2 and 7.40%, respectively.In solar cells, more novel polymer/nano-graphite combinations have been found to be desirable to attain a high power conversion efficiency of >8 %.

In Electronics
Electronic devices, such as stretchable sensors, actuators, and flexible electrical devices, have been focused on for the use of innovative nanomaterials [82,83].Polymer-and graphite-derived materials have been applied in next-generation electronic devices [84].A polytetrafluoroethylene/nano-graphite grid was prepared and compared with a commercial lead alloy (Figure 12).The polytetrafluoroethylene/nano-graphite grid had a smooth surface (Figure 12B,C), and it was more efficiently used as a negative current collector in batteries compared to the commercial lead-based grids (Figure 12A).Room-temperaturevulcanized (RTV) silicone rubber/nano-graphite-based stretchable strain sensors and actuators have been industrialized [85].Previously, carbon nanotubes have been used in RTV silicone rubber devices to augment their stiffness to some extent [86].

In Electronics
Electronic devices, such as stretchable sensors, actuators, and flexible electrical devices, have been focused on for the use of innovative nanomaterials [82,83].Polymer-and graphite-derived materials have been applied in next-generation electronic devices [84].A polytetrafluoroethylene/nano-graphite grid was prepared and compared with a commercial lead alloy (Figure 12).The polytetrafluoroethylene/nano-graphite grid had a smooth surface, and it was more efficiently used as a negative current collector in batteries compared to the commercial lead-based grids.Room-temperature-vulcanized (RTV) silicone rubber/nano-graphite-based stretchable strain sensors and actuators have been industrialized [85].Previously, carbon nanotubes have been used in RTV silicone rubber devices to augment their stiffness to some extent [86].Nevertheless, the use of new nano-graphite materials has suitably adjusted the flexibility and stretchability of RTV silicone rubber devices [87].The noteworthy piezo-resistive strain-sensing and actuation performances of RTV silicone rubber/nano-graphite devices have been experiential.Nano-graphite with a few layers of three-dimensional nanoplatelets with a diameter of 12-15 nm was filled in RTV silicone rubber devices.The addition of 5 phr of nano-graphite boosted the compressive modulus and tensile modulus of the RTV devices by 135% and 125%, respectively [88].The actuation displacement of the RTV silicone rubber/nano-graphite devices was also improved by 32% via a growing voltage supply from 2 to 8 kV.The strain sensor had a high stretchability of >100% and a durability of up to 5000 cycles [89].In this field, further design investigations into Nevertheless, the use of new nano-graphite materials has suitably adjusted the flexibility and stretchability of RTV silicone rubber devices [87].The noteworthy piezo-resistive strain-sensing and actuation performances of RTV silicone rubber/nano-graphite devices have been experiential.Nano-graphite with a few layers of three-dimensional nanoplatelets with a diameter of 12-15 nm was filled in RTV silicone rubber devices.The addition of 5 phr of nano-graphite boosted the compressive modulus and tensile modulus of the RTV devices by 135% and 125%, respectively [88].The actuation displacement of the RTV silicone rubber/nano-graphite devices was also improved by 32% via a growing voltage supply from 2 to 8 kV.The strain sensor had a high stretchability of >100% and a durability of up to 5000 cycles [89].In this field, further design investigations into polymer/nanographite nanomaterials have been considered significant to the discovery of important uses in next-generation flexible sensors, actuators, and related electronic devices.

EMI Shielding
The electromagnetic interference pollution from electronic/telecommunication instruments is continuously affecting human, biological, and environmental systems [90].Electromagnetic interference (EMI)-shielding materials have been developed to reduce adverse radiation affects [91].EMI shielding reduces incident radiation via the reflection and absorption phenomenon through a material.Consequently, EMI-shielding materials provide protection against incident radiation.Electrical conductivity has been considered to be an important property of EMI-shielding materials [92].Initially, metals were applied as EMI shields [93].However, metallic materials have the disadvantages of a high cost, a heavy weight, corrosion, and processability problems [94].In this regard, electrically conducting polymeric composites have been used to overawe the limits of metal shields [95].Carbon fillers have high aspect ratios, permittivity, permeability, and intrinsic conductivity for a high EMI-shielding performance [96].Accordingly, conducting fillers, such as graphite, carbon black, and carbon nanotubes, have been filled in polymeric matrices to potentially improve EMI shielding [97,98].Graphite-based materials have been preferably applied in EMI shields [99].Jeddi and co-researchers [100] developed silicon rubber/nano-graphite nanocomposites and studied their EMI-shielding effectiveness.The nanomaterials had a high electrical conductivity and low percolation threshold values, contributing to radiation protection.According to X-ray band frequency studies, the absorption loss was found to be a leading mechanism for the intensity attenuation of incident electromagnetic waves.In another attempt, Jeddi et al. [101] designed silicon rubber/nano-graphite/carbon black nanocomposites.The nanomaterials had a fine conducting network that promoted electrical properties and, thus, EMI shielding.The dielectric permittivity of the silicon rubber with the nano-graphite, carbon black, and nano-graphite/carbon black is shown in Figure 13.The values of the dielectric permittivity increased with an increase in filler contents.The combination of nano-graphite/carbon black in the silicon rubber was effective in enhancing the dielectric permittivity relative to that of the silicon rubber/nano-graphite nanocomposite.The effect was observed due to the attainment of the percolation threshold and the polarization of the matrix-nanofiller interface.The absorption loss was found to be a major mechanism for the attenuation of incident EMI radiation in these nanocomposites.However, to date, very limited nano-graphite-based design options have been discovered for EMI shields.The development of novel polymer/nano-graphite nanocomposites may result in practically important high-performance radiation-shielding materials.

Future Perspectives, Challenges, and Conclusions
Table 3 demonstrates the processing strategies, noteworthy features, and technical applications of polymer/nano-graphite nanocomposites.Nano-graphite nanofiller has been reinforced in polymer matrices to improve structural, morphological, electrical conductivity, thermal conductivity, dielectric characteristics, thermal stability, mechanical

Future Perspectives, Challenges, and Conclusions
Table 3 demonstrates the processing strategies, noteworthy features, and technical applications of polymer/nano-graphite nanocomposites.Nano-graphite nanofiller has been reinforced in polymer matrices to improve structural, morphological, electrical conductivity, thermal conductivity, dielectric characteristics, thermal stability, mechanical properties, photovoltaics, sensing/actuating, radiation shielding, and other physical properties.Nano-graphite nanoparticles have been prepared using various facile physical and chemical methods.The future of polymer/nano-graphite nanocomposites relies on their potential applications in various technical fields.The potential application of polymer/nano-graphite nanocomposites has been observed for DSSCs.High-performance solar cells can be achieved due to the geometric and electronic effects of the nano-graphite in the conducting polymers.A high power conversion efficiency can be achieved for these nanocomposites.In future, a higher efficiency can be attained by using functional nano-graphite nanostructures.Nano-graphite-based nanocomposites also possess potential for use in electronics, sensors, and actuator devices.However, future efforts are needed to design high-performance polymer/nano-graphite nanocomposites for commercial electronic device applications.Similarly, the potential application of polymer/nano-graphite nanocomposites has been observed for EMI nanomaterials.Future efforts may lead to a high EMI shielding efficiency of >50 dB for commercial applications.Consequently, due to the restricted research in various fields, several future technical grounds still need to be explored for polymer/nano-graphite nanocomposites.Forthcoming research on these innovative nanomaterials may lead to applications in batteries, aerospace/automobiles, construction materials, and biomedical areas.
Challenges regarding the use of polymer/nano-graphite nanocomposites have been found related to their properties, performance, and structure-property relationship.The nanofiller dispersion has been pointed out as the main challenge in the application of polymer/nano-graphite nanocomposites.The dispersion issues can be overcome by using the appropriate processing technique and controlled processing parameters.Moreover, the use of optimum nanofiller contents and functional nano-graphite may result in better matrix-nanofiller interactions, interface formation, and a homogeneous dispersion in the polymers.In polymer/nano-graphite nanocomposites, the augmentation of the physical property in fact relies on the nano-graphite dispersion in the polymers.Additionally, it is important to understand the mechanisms of physical and chemical interactions and interface formation in polymer/nano-graphite nanocomposites in order to develop highperformance nanomaterials.Succinctly, this appraisal provides a novel insight into polymer/nano-graphite nanocomposites.Nano-graphite has been found to be practical as a unique nanofiller for polymeric nanocomposites.Numerous facile strategies have been used to design nano-graphite nanoparticles and polymer/nano-graphite nanocomposites.Polymer/nano-graphite nanocomposites have uncovered important structural, morphological, electrical, thermal, mechanical, and other essential properties.The applications of polymer/nano-graphite nanocomposites have been extended to DSSCs, electronics, and EMI-shielding devices.Future research on functional nano-graphite and polymer/nano-graphite nanocomposites may lead to enormous progressions in the related technical fields.

Figure 4 .
Figure 4. Optical picture of droplet of styrene-in-water Pickering emulsion stabilized by detonation nano-graphite particles [45].Reproduced with permission from Hindawi.

Figure 4 .
Figure 4. Optical picture of droplet of styrene-in-water Pickering emulsion stabilized by detonation nano-graphite particles [45].Reproduced with permission from Hindawi.

Figure 8 .
Figure 8. Models printed via Fused Deposition Modeling on different baseplates: (a,c) different shapes printed on paper; (b,d) the bend parts; (e) models printed on flexible materials; and (f) the bend parts [64].Reproduced with permission from MDPI.

Figure 8 .
Figure 8. Models printed via Fused Deposition Modeling on different baseplates: (a,c) different shapes printed on paper; (b,d) the bend parts; (e) models printed on flexible materials; and (f) the bend parts [64].Reproduced with permission from MDPI.

Figure 8 .
Figure 8. Models printed via Fused Deposition Modeling on different baseplates: (a,c) different shapes printed on paper; (b,d) the bend parts; (e) models printed on flexible materials; and (f) the bend parts [64].Reproduced with permission from MDPI.

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Figure 12 .
Figure 12.Photographs of lead alloy grid and nano-graphite grid [84].Reproduced with permission from Wiley.

Figure 12 .
Figure 12.Photographs of (A) lead alloy grid and (B,C) nano-graphite grids with different alignments [84].Reproduced with permission from Wiley.