Mercerization and acetylation treatments were applied to sisal fibers to enhance adhesion with polymer matrices in composites. The structures of the untreated and treated fibers were assessed with scanning electron microscopy. The waste from sisal-fiber clecortication consisted of mechanical, ribbon, and xylem fibers, and their ultimate cells varied considerably in size and shape. After mercerization and acetylation, the fibers and conductivevessel surfaces were successfully changed. The parenchyma cells were partially removed, and the fibrils started to split, because of the alkali action. This increased the effective surface area available for contact with the rnatrix. The mercerized and acetylated fibers were coated with cellulose acetate by the grafting of the acetyl group in the fibrils. The treatment used to remove lignin and hemicellulose caused changes in the fiber surface but did not damage the fiber structure because the fibrils remained joined in a bundle. (C) 2004 Wiley Periodicals, Inc.