Activated carbon fibers from Nomex by chemical activation with phosphoric acid Original Research Article

The preparation of activated carbon fibers (ACFs) by phosphoric acid activation of Nomex [poly(m-phenylene isophthalamide)] polyaramid fibers was studied. Nomex pyrolysis in the presence of phosphoric acid was followed by thermogravimetry and infrared spectroscopy in order to establish the nature of transformations involved. Then, ACFs were obtained by impregnating Nomex with different amounts of phosphoric acid, followed by pyrolysis and washing with water. The porous texture of the resulting ACFs was characterized by N2 and CO2 adsorption. Phosphoric acid has a strong effect on Nomex degradation, reducing the number of decomposition steps and lowering the temperature range at which the decomposition takes place. The resulting ACFs bear P-containing functionalities like acid phosphates and polyphosphates. The impregnation ratio strongly influences the porous texture of the ACFs, but they remain microporous even at high impregnation ratios, when, as shown by SEM, the fibrous morphology is lost due to agglomeration. The results obtained suggest the practical feasibility of the process of phosphoric acid activation of Nomex polyaramid fibers. ACFs are obtained with high yields and they exhibit a well-developed porosity restricted to the micropore range and with P incorporated in form of functional groups. A major drawback identified (fiber fragmentation and agglomeration) can be avoided by using low or intermediate impregnation ratios.