**8. Properties of VGCFs**

## **8.1 Mechanical properties**

The modulus and the elasticity of VGCFs can be found easily [34]. The calculated modulus value varies from 100 to over 1000 GPa. The stiffness of VGCF depends upon their diameters. Even though the fibers are produced in the same experiment the diameters increased from 6 to 32 nm, the modulus decreases 300–1200GPa [33, 34].

The degree of favored orientation of graphitic basal planes is related to the stiffness of pyrolytic carbon. The stiffness of a graphite fiber is connected as a component of the orientation point of the graphitic plane. This model was fitted to the stiffnessdata of VGCFs by measuring their orientation parameter. This model was fitted to the solidness information of VGCFs by estimating their direction parameter. As the main fitting parameter utilized in the model is free of fiber diameter, the dwindle in the solidness of thicker fibers was assigned to the decrease in their graphitic requesting.

This again is because of a swifter deposition of pyrolytic carbon during the thickening period. This is as per the finding that that increasing the graphitization of VGCF by heat-treatment also additionally increases their modulus considerably. In one example, the modulus of vapor grown fibers more than doubled to about 500 GPa when they were heated at 2200°C [30].

Heat-treated fibers are unsuccessful more commonly in the "sword-in-sheath" mode and in this mode; grouping of circumferential breaks along the internal rings permits continuous cylinders to slide telescopically inside one another, slowly diminishing the load bearing limit of the fiber. It is obvious from these outcomes that the modulus and the disappointment method of vapor grown carbon fibers are connected to their structure.

The values of the tensile strength of VGCF are progressively reliable, changing from 2.5 to 3.5 GPa for fibers with diameters across just beneath 10 μm. The reliance on the diameter however is strong [33, 34, 41]. This was clarified by accepting that thicker fibers have a larger flaws population, and a more prominent likelihood of failure, than thinner ones.

#### **8.2 Electrical properties**

The carbon structure and potential graphitization of VGCFs by heat-treatment makes them a fascinating possibility for thermal and electrical applications. VGCFs are known to have the most noteworthy electrical and thermal conductivities among carbon fibers because of their conceivable high structural perfection [42].

It was verified that VGCFs heat-treated at lower temperature have a resistivity that is practically constant with temperature. The resistivity of fibers heat-treated at higher temperatures decreases with the operating temperature. At the most elevated temperatures, the resistivity of the VGCFs approaches that of single crystal graphite, with a resistivity of about 5 × 10<sup>−</sup><sup>7</sup> ohm cm at 300 K. Besides, the decrease in resistivity with fiber diameter across is ascribed to the expanded arranged graphite regions as the diameter increases.

#### **8.3 Thermal properties**

The thermal conductivity of VGCFs is astoundingly high [31]. The thermal conductivity of both s-grown VGCFs and the other VGCFs heat-treated to 3000°C were evaluated through a temperature range of 10–300 K. It was demonstrated that

**57**

*Vapor-Grown Carbon Fiber Synthesis, Properties, and Applications*

injection molding was utilized to stimulate fiber alignment.

tiveness ever achieved for a cement-matrix composite.

ascribed to the greatly graphitic nature of the VGCF mats.

polymer before extrusion may bring better result in better dispersion.

The utilization of submicron VGCFs as arbitrary layers between layers of ceaseless carbon fibers in an epoxy matrix was studied [43] and it was found that the VGCFs improve appreciably the damping capacity of the composites at fiber

The utilization of VGCFs for fabricating thin paper was made effectively by supplanting the generally utilized commercial chopped ex-PAN and ex-pitch fibers

Submicron VGCFs were used in cement-matrix composites, an application wherein they could be amazingly valuable, because of the relative minimum cost and simple process ability [41]. With a fiber heap of just 1.5 vol%, they accomplished the most noteworthy electromagnetic interference (EMI) shielding effec-

Composites based on VGCF-mats were made and heat-treated at 2800°C and their thermal conductivity was studied [45]. It was acquired that the 36 vol% composite exhibited a room-temperature thermal conductivity of 564 W/mK. This

Aluminum matrix and carbon-carbon composites based on VGCFs were fabricated and compared [46]. For the aluminum-VGCF composites at 36.5 vol% the thermal conductivity of 642 W/mK was found. An outstanding value of 910 W/mK was observed for a 70 vol% carbon-VGCF composite which is double the value of copper.

value is some extent higher than that of copper (+/− 450 W/mK) and it was

the heat treatment expands the fiber conductivity by a factor of 50. The heat-treated fibers rank among the best thermal conductors available, at room temperature. Besides, it was demonstrated an immediate connection between electrical resistivity, thermal conductivity and tensile modulus of carbon fibers. The strong correlation between thermal conductivity and electrical resistivity was elucidated by comparative fiber structural effects dominating these properties. This, in blend with the recently pointed out connection between fiber structure and tensile modulus [34], could prompt the expectation of the properties legitimately from

In recent times, there has been a developing enthusiasm for the utilizations of VGCF in carbon and polymer matrix composites. The primary thermoplastic submicron-size VGCF composites, utilizing polycarbonate and nylon as a matrix was reported [36]. The growing mechanical and thermal properties were calculated with fiber volume fraction, despite the fact that this increase is less than could be theoretically expected. The composites were compression molded utilizing a straightforward set-up bringing about a fiber arrangement that was believed to be irregular in three dimensions. It was anticipated higher properties if a process like

The process ability of submicron VGCFs in thermoplastic matrices was analyzed by extruding polycarbonate-VGCF composites in a single screw extruder and subsequently melt-drew the composites to induce fiber orientation. It was concluded that the dispersion of the fibers in the matrix was very poor at 2 vol% fiber fraction and turned out to be much less fortunate when the fiber content was expanded to 5 vol%. It was recommended that grinding or melt-blending the fiber with the

*DOI: http://dx.doi.org/10.5772/intechopen.92300*

fiber structural considerations.

**9. Applications of VGCFs**

fractions as low as 0.6 vol%.

to acquire planar isotropy [44].

**9.1 In composites**

#### *Vapor-Grown Carbon Fiber Synthesis, Properties, and Applications DOI: http://dx.doi.org/10.5772/intechopen.92300*

the heat treatment expands the fiber conductivity by a factor of 50. The heat-treated fibers rank among the best thermal conductors available, at room temperature.

Besides, it was demonstrated an immediate connection between electrical resistivity, thermal conductivity and tensile modulus of carbon fibers. The strong correlation between thermal conductivity and electrical resistivity was elucidated by comparative fiber structural effects dominating these properties. This, in blend with the recently pointed out connection between fiber structure and tensile modulus [34], could prompt the expectation of the properties legitimately from fiber structural considerations.
