Effect of PPTA pre-impregnation with phosphoric acid on the porous texture of carbons prepared by CO2 activation of PPTA chars

Activated carbon fibers (ACFs) were prepared by CO2 gasification to different burn-offs of chars from the polyaramid fiber, poly(p-phenylene terephthalamide) (PPTA) pre-impregnated with 5 wt.% H3PO4. Thermogravimetric analysis showed that the addition of phosphoric acid produces a significant increase in the yield of solid residue. While the char yield of the pure polymer at 1000 degrees C amounted to 39.5 wt.%, it rose to 52.8 wt.% in the case of 5 wt.% H3PO4-impregnated PPTA. The chars and derived ACFs were characterized by physical adsorption of N-2 (-196 degrees C) and CO2 (0 degrees C). No significant differences were found as concerns chars porosity. At equivalent burn-offs, the surface area of the ACFs prepared by physical activation with CO2 Was up to 70% higher in the case of PPTA pre-impregnated with phosphoric acid, the pore size distribution being displaced towards somewhat wider pores within the 2-10 nm range. These results are in contrast with those obtained previously with the poly(m-phenylene isophthalamide) (PMIA) polymer, where H3PO4 pre-impregnation did not significantly affect the porosity of chars and ACFs. (C) 2008 Elsevier Inc. All rights reserved.