Polymer/graphene nanocomposites have shown promising potentials in energy storage applications due to their high permittivity, enhanced energy storage density, flexibility, and improved thermal and mechanical properties. The addition of graphene nanosheets to polymer matrix improves existing and incorporate new properties on such nanocomposites for various engineering applications. For instance, graphene nanosheets in polymer matrix are believed to form microcapacitors. Each microcapacitor contributes to the effective capacitance and dielectric constant of the composite. Although research has proved polymer/graphene composites as high dielectric constant materials, the major challenges facing their practical applications are high energy dissipation, high dielectric loss, and low electric field strength. In view of this, many researchers have shown efforts to minimize energy losses associated with polymer/graphene composites by insulating graphene nanosheets with different organic and inorganic substances. This is believed to prevent direct contact of graphene nanosheets and reduce the high mobility of π‐orbital or free electrons in the polymer matrix. However, maintaining high dielectric constant at low dielectric loss in polymer/graphene composites has not been achieved. If this challenge can be addressed in the future, polymer/graphene composites can yield energy storage capacity comparable with those of electrochemical capacitors. Therefore, this review considered energy storage and loss capacity of poly(vinylidene fluoride)/graphene nanocomposites from the perspective of electrical and dielectric properties. This article to the best of our ability reviewed various research results on dielectric constants/losses, breakdown strengths, energy densities, and electrical and thermal conductivities of poly(vinylidene fluoride)/graphene nanocomposites. Results extracted from the different published literature were tabulated and discussed at length to outline the reasons for the high dielectric loss in the neighborhood of percolation thresholds and the way forward.

Polymer/graphene nanocomposites (PGNs) have shown great potential as dielectric and energy storage materials. However, insolubility of graphene in most solvents, hydrophobic behaviour and poor dispersion in polymer matrix restrict wider fabrications and applications of PGNs. In this study, we present co-fabricated PGNs engineered by solution blending and melt compounding methods with improved dielectric performance. Further processing of PGNs by melt mixing after solution blending not only improved dispersion of graphene in the matrix but also ensured good interfacial interaction of the composites’ constituents and reduction of oxygen content in PGNs. Graphene nanoplatelets used in this study was slightly functionalized (fGNPs) to enhance dispersion in the polymer matrix. It was later characterized using Fourier transform infrared (FTIR) and Raman spectrometer. Scanning electron microscope (SEM) was used in morphological study of the fabricated composites. Dielectric properties, electrical conductivity, breakdown strength and energy storage capacity of the fabricated composites were investigated. The results obtained showed well-dispersed fGNPs in poly (vinylidene fluoride) (PVDF) matrix and improved dielectric performance. For instance, with 3.34 wt% and 6.67 wt% fGNPs co-fabricated composites, dielectric constant increased from about 9 for neat PVDF to 9930 and 38,418 at 100 Hz, respectively. While 7588 and 12,046 were respectively measured for solution blended-only composites at similar fGNPs content. These resulted to about 176.9% and 376.4% increase in energy storage density with 3.34 wt% and 6.67 wt% fGNPs co-fabricated composites when compared to their counterparts. These results were also credited to strong bonding, reduction of oxygen and recovered graphene structure by melt-mixing approach.

In most engineering applications where fluid lubrication is practically impossible such as high temperature environment, solid lubrication becomes an alternative option. Polymers such as polytetrafluoroethylene are often used for solid lubrication due to their ability to provide low friction on interfacial sliding conditions. However, polymeric materials often show low wear resistance, which limits their applications. Therefore, there is need for high wear resistance polymers or polymer composites for such application. In this study, wear resistance of poly (vinylidene fluoride) (PVDF) was improved by incorporating hydroxylated titanium dioxide (TD-OH) and functionalized graphene nanoplatelets (fGNPs). The composites were fabricated by solution blending and further processed by melt compounding. Raman and X-ray diffractometer were used to characterize the particles, while morphological study and wear scars on the composite samples were examined using scanning electron microscope. From the results obtained, wear volume (WV) reduced from about 0.6255 mm3 for pure PVDF to 0.2439 mm3 for 3.34 wt% fGNPs composite and further reduced to 0.1473 mm3 with the addition of 10 wt% TD-OH to 3.34 wt% fGNPs composite. These are about 61% and 76% reduction respectively, compared to pure PVDF. It was noted that increase in TD-OH content up to 20 wt% in fGNPs binary composites increased the WV of the ternary composites. This indicates that ceramic nano-fillers at appropriate proportions in polymer/graphene composites can enhance the wear resistance of such composites. On the other hand, the ternary composites showed lower thermal stability compared to the binary composites, which was attributed to low thermal stability product(s) of chemical reaction between fGNPs and TD-OH in the PVDF matrix.

Slightly oxidized graphene nanoplatelets (GNPs) were functionalized using 3-hydroxytyramine hydrobromide. The functionalized GNPs, denoted as fGNPs, were examined using Fourier transform infrared and a Raman spectrometer, which revealed a slight reduction in the sp2 network domain compared with unmodified GNPs. Compared with previous reports on functionalized highly oxidized graphene, the degree of the sp2 structural destruction was less, as revealed by Raman analysis. The aim was to address the challenges of high agglomeration of graphene in polymer matrix and high destruction of graphene’s conjugal structure during functionalization, which deteriorates graphene’s excellent properties and makes it less effective in improving the polymer’s properties. This was achieved by slight functionalization of GNPs because they contained little oxygen functional groups. In this study, a thermal conductivity increase of about 295 % was recorded when 6.67 wt. % fGNPs were incorporated into the poly(vinylidene fluoride) (PVDF) matrix. Also, with 3.34 wt. % of the GNPs composite, the tensile strength and Young’s modulus were measured with an increase of about 64 % and 100 %, respectively. The enhanced properties of the polymer nanocomposites were due to better dispersion of fGNPs and interaction with the polymer matrix compared to unfunctionalized GNPs composites as was indicated by a scanning electron microscope. The composites were prepared by solution blending and melt compounding process. Such composites can find application in automobile and aerospace industries in which good mechanical and thermal properties are required.

Polypropylene (PP) has a wide range of engineering applications in automobile, biomedical, energy, machine parts, electronic packaging etc. However, PP lacks some desired engineering properties such as good thermal properties and mechanical strength. For instance, PP is known for its low melting temperature, high flammability and low heat resistance. This has resulted in continuous improvement in various properties of PP via modification of its matrix. One of the ways this has been achieved is by incorporation of foreign bodies in form of reinforcements in the PP matrix. The recent discovery of carbon nanotubes (CNTs) has further paved the ways for advancing the properties of PP via the development of PP-CNTs composites. Such composites have not only shown improved engineering properties but retain the lightweight and flexibility of PP. The advanced engineering properties recorded by various studies using PP-CNTs composites are due to the good properties of PP in conjunction with the excellent properties of CNTs such as high thermal conductivity, strength, electron mobility and formation of conductivity networks in the PP matrix. Although the development of PP-CNTs composites faces challenges of high agglomeration and incompatibility of CNTs in the matrix, the moves towards addressing the hurdles and achievements recorded so far are encouraging. Therefore, this review investigated the contribution of CNTs on various advanced engineering properties of PP-CNTs composites. Various results drawn from previously published literature within the decade were tabulated for future academic references and industrial purposes. Current hurdles faced by PP-CNTs composites, future prospect and their advanced engineering applications were discussed.