In this work, polypropylene (PP) fiber waste was modified by the reaction with concentrated H2SO4. IR, TG, Raman, CHN, acid titration, SEM, and XRD suggested that sulfuric acid at about 105 degrees C reacts with PP to produce mainly surface sulfonic groups. The kinetic experiments showed that these SO3H groups decompose to form SO2 gas leading to an aromatization of the polymer to form amorphous and graphitic carbon. Adsorption isotherms of the cationic model molecule methylene blue showed that the modified PP fibers have a great potential as ion-exchange adsorbent. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3586-3591, 2010