Stabilization of carbon Fibers

The stabilization of carbon fiber precursors is done in an air atmosphere, and oxygen is required all through the fiber, for the chemical reactions going on (cf. Sect. 3). 

Methods of filler pretreatment lignin treated by methylolation decreases the rate of cure of phenolic adhesives " carbon fiber was anodicaUy oxidized and subjected to various treatments with coupling agents to improve interfacial interaction with phenolic resins and oxidative stability of carbon fibers titanate coupling of oxidized fibers resulted in improved adhesion to matrix and enhanced thermal stability of fibers ... 

J D Nam and J C Seferis, Anisotropic thermo-oxidative stability of carbon fiber reinforced polymeric composites , SAMPE Quart October 1992,10-18. 

What is the reason for the superior thermal stability of carbon fiber reinforced phenolics ... 

J.P. Bonal, C.H. Wu, Neutron irradiation effects on the thermal conductivity and the dimensional stability of carbon fiber composites, Phys. Scr. T64 (1996) 26—31. 

The morphology of these modified carbon fibers was studied using scanning FEI QUANTA 2000) and transmission JEOL JEM 2000FX Electron Microscope) electron microscopy. Thermo gravimetric analysis Pyris Diamond DTA/TGA, Perkin Eimer, USA) of as received-and modified carbon fibers was done to see the effect of carbon nanotubes coating on the thermal stability of carbon fibers. 

Mechanical Properties and Stability at Elevated Temperature. One increasingly important characteristic of carbon fibers is their excellent performance at elevated temperatures. Strength tested in an inert environment remains constant or slightly increases to temperatures exceeding 2500°C. Amoco s high modulus pitch carbon fiber P-50 maintains approximately 80% of room temperature modulus at temperatures up to 1500°C, then decreases more rapidly to 30% at 2800°C (64). The rapid decrease in modulus is a result of increased atomic mobiHty, increa sing fiber plasticity. 

An unusual application involves the use of carbon fiber to reinforce cement. This results in improved tensile and flexural strength, high impact strength, improved dimensional stability, etc. 

Vinyl bromide (VBr) as a comonomer does not improve the solubility to the same extent. Evidently, the smaller molecular volume of CH2=CHBr is responsible. The molecular order of PAN is less perturbed by this comonomer. As a consequence, more severe conditions are required to get a copolymer AN (96%)/VBr(4%) in solution. However, since color formation is evidently not a problem in the case of carbon fibers (color formation actually signals the onset of the stabilization reactions aimed at, cf. Sect. 3), dissolution of AN/VBr copolymers can be achieved at high temperature (110-120 °C). 

Simitzis has reported elemental analyses of carbon fibers made from PAN or AN/MA copolymers, and stabilized for 3 hours at 250 °C. The fibers were carbonized for 5 minutes at different temperatures (Table 3). It follows that, under these conditions, a temperature of 1600 °C is necessary to transform the stabilized fiber to a >99% carbon fiber. 

Table 3. Elementary analyses of carbon fibers. Stabilization 3 h, 250 °C time of carbonization 5 min...

Table 11. Sonic modulus and tenacity of precursor fibers, and sonic modulus of carbon fibers (where determined under standard stabilization conditions cf. Fig. 9).

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