Traditionally, the field of advanced nanocomposites has relied on a fairly limited set of building blocks; many with low reactivity and of limited variability. These limitations have been addressed by the creation of functionalized nanometer-scale aramid structures, in the form of nanofibers and nanosheets. These were obtained by deprotonating macroscale, commercial Kevlar yarns using potassium hydroxide in dimethyl sulfoxide to yield stable dispersions of nanometer-scale aramid fibers that were then hydrolyzed using phosphoric acid (PA). To illustrate the use of these functionally-active nanostructures as building blocks for nanocomposites, they were crosslinked by glutaraldehyde (GA), and formed into macroscopic thin films by vacuum-assisted filtration. It was shown that the mechanical properties of these PA/GA treated films can be tuned by varying the amounts of PA and GA used during synthesis, adjusting the relative amounts of hydrolysis and polymerization. These results are the first demonstration that aramid nanometer-scale fibers can be used to form versatile nanometersized building blocks that can then be crosslinked to fabricate a wide variety of nanostructured aramid materials with tailorable properties.