Uses of virgin carbon fiber -Activated carbon fibers (ACF)-(3)

Molecular sleeves: Oak Ridge National Laboratory has developed a carbon fiber composite molecular sieve designed specifically to absorb CO2 emitted from coal fired power plants and gas turbines. Petroleum pitch based chopped fiber is bonded with a phenolic resin and activated in steam, O2, or CO2 at 850C, to form a product with a large surface area and pore volume with mesopores of 2-50 nm, capable of absorbing CO2. There are also macropores which allow sufficient fluid flow with low pressure drop. It also has potential to be used for removal of CO2 from natural gas for fuel cells.

Catalysts: A porous carbon fiber carbon composite with a density >0.2 g/cm3 with a significant volume of mesopores and macropores which allow excellent fluid flow with minimal pressure drop has potential as catalyst support. Fortafil P200 PAN based carbon fiber was slurried in water with a phenolic resin, vacuum molded, dried at 50C, cured for 3h at 130C and carbonized in a flow of N2 at 650C. In this process, O2, CO2, H2O and CO were trapped inside the micropores during carbonization and gasified the surface of the PAN fibers, resulting in large surface areas and mesopore volumes, a possible candidate for a catalyst support.

Biomedical applications: The use of carbon materials and carbon fiber reinforced composites for medical application is examined. Carbon fibers are first considered, looking at their physical and chemical properties in vitro; the properties and histology of two commercial carbon fibers in vivo; and the histology of carbon cloth in vivo. The use of carbon-carbon composites in medical applications is then examined.

Any material used in a surgical medical application has to be proved safe and the material to be implanted for an extended period of time must be non-toxic, non-carcinogenic and unaltered by the body environment. Where a mechanical movement is involved, the implant must have good fatigue resistance and be unaffected by corrosion due to body fluids and the implanted material must not suffer a rejection process.

Jenkins, at the University Hospital of Wales, Cardiff worked on implants for the heel tendons of sheep and rabbits and knee ligaments for sheep using HM carbon fiber, chosen because of its higher purity and probable better biocompatibility. A 10k tow was twisted and doubled and subjected to pressure steam sterilization prior to use. The results were quite successful and after two months, it was virtually impossible to tell which limb the sheep had been operated on, as there was no tissue rejection and the filaments acted as a scaffold for collagenous growth. After 3 months, the twisted tow was completely engulfed in new tissue, which forced apart the filaments in the tow and assisted the transfer of load from the carbon fiber filaments through to the newly formed collagen tissue. The cells tended to grow in a spiral fashion along the manipulate, it was replaced with Type A fiber, which was stronger, more readily handled and exhibited no ensuing biocompatibility problems.

Veterinary applications were pursued at the University of Bristol on racehorses. When a racehorse rupture a tendon, the effect was far reaching and usually resulted in the horse being destroyed, so there was every encouragement to establish whether carbon fibers could induce tendon and ligament growth in racehorses.

A hernia repair with carbon fiber, ligament repairs and the introduction of carbon fiber pads in the knee have also been reported. One problem with the knee pad is that the carbon fiber does tend to get ground away and not all surgeons favour carbon fiber implants, preferring to use items from a tissue bank.

Park and Vasilos fabricated carbon fiber reinforced calcium phosphate composites, made by hot pressing to give a ceramic with significantly improved ductility albeit with a slight decrease in ultimate flexural strength. The failure strains of the composites and the monolithic calcium phosphate ceramics were 0.36 and 0.21%, respectively. It was demonstrated that carbon fiber reinforced calcium phosphate composites would be good biomaterials for bone replacement.

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