Carbon Fibers orientation effect

In the previous symposium, we reviewed mesophase mechanisms involved in the formation of petroleum coke ( 2 ). Since 1975, two significant developments have been the use of hot-stage microscopy to observe the dynamic behavior of the carbonaceous mesophase in its fluid state (3-6), and the emergence of carbon fibers spun from mesophase pitch (7-9) as effective competitors in applications in which high elastic modulus or good graphiticity is important. This paper focuses on mesophase carbon fibers as an example of how the plastic mesophase can be manipulated to produce fibers with intense preferred orientations and elastic moduli that approach the theoretical limit for the graphite crystal in the a-direction. 

High molecular orientation is generally considered to be an indispensable prerequisite for good carbon fibers. As mentioned in Section 3.3, there is evidence in the literature that molecular order in the precursor fiber may take effect on carbon fiber properties. 

It should be noted from Figure 9.12 that the magnetic permeability increases as the effective aspect ratio increases. Conductive thermoplastics, which contain carbon fiber, have a maximum injection rate above which electric conductivity will not increase. These composites also depend on fiber orientation which increases the... 

Orientation of fiber is detrimental to performance of composites which contain carbon fibers (Figures 11.16 and 11.17). T ensile strength of composites containing fibers oriented in a direction parallel to the surface is not affected by moisture content. Composites which have fibers oriented in a direction perpendicular to the surface, lose tensile strength as moisture increases (exception — carbon fiber/PEEK composite). Similar effects on tensile modulus, compression modulus and elongation have been observed. 

So the effect of following a uniform treatment process to complete the oxidation stage resulted in a product with an inhomogeneous structure the skin is oxidized then cyclized, whilst the core is cyclized and then oxidized. The diffuse boundary can be considered as a third zone, where the rates of the two reactions are fairly compatible. The final structures are not the same and will result in carbon fiber with graphite crystallites exhibiting different orientations relative to the fiber axis and different stacking distances. 

Comonomers do have a significant effect on the stabilization process, enhancing the segmental mobility of the polymer chains [22,23] resulting in better orientation and mechanical properties of the precursor and resulting carbon fibers. Comonomers can also reduce the temperature of initiation of cyclization [24,25]. 

Amide comonomers have a less pronounced effect than acid comonomers. Acrylate comonomers do not initiate the cyclization reaction [78,79], whilst MMA results in a lower carbon yield than MA. The bulky side groups of an ester comonomer lower the crystallinity and crystal size but improve the segmental mobility of the polymer chains [22,23]. The size of the ester molecule also affects the structural parameters of the precursor and the resultant carbon fibers have a lower average orientation and mechanical properties [21]. 

Synergism between the conductive networks was examined, and the effects of fiber orientation and fiber length on composite resistance were evaluated. The resistance of the composites containing both carbon fiber and carbon black fillers was also compared with that of composites containing only carbon black or carbon fibers. 

Table 9.4. Effect of the Orientation of Carbon Fibers on the Properties of Carbon Polymer CompositesI l...

Table 9.5 shows the effect of two types of polymer matrices, epoxy and PEEK, on the mechanical properties of a carbon-fiber composite with two different fiber orientations 0° (unidirectional) and 45° (three layers at 0°, 45° and 90° respectively). The fracture strain of the PEEK 45° composites is considerably larger than that of the others. 

The inherent properties of CNT assiune that the structure is well preserved (laige-aspect-ratio and without defects). The first step toward effective reinforcement of polymers using nano-fillers is to achieve a uniform dispersion of the fillers within the hosting matrix, and this is also related to the as-synihesized nano-carbon structme. Secondly, effective interfacial interaction and stress transfer between CNT and polymer is essential for improved mechanical properties of the fiber composite. Finally, similar to polymer molecules, the excellent intrinsic mechanical properties of CNT can be fully exploited only if an ideal imiaxial orientation is achieved. Therefore, during the fabrication of polymer/CNT fibers, four key areas need to be addressed and imderstood in order to successfully control the... 

Zamel et al. presented a study on the estimation of effective thermal conductivity of carbon paper GDL stmctures based on the aforementioned DNS formalism (Eq. 9.12). The 3D carbon paper GDL microstractures were reconstracted using the stochastic method by Schulz et al. They investigated the influence of fiber orientation, anisotropy, compression and binder fraction. Figure 9.27 shows the representative effective thermal conductivity prediction along with experimental data available in the literatirre." " ... 

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