[en] Full text: Acrylonitrile-butadiene elastomers (NBR) are widely used on the oil and automotive industries in hoses, sealing rings, gaskets, fuel pipes, and many other rubber products due to its good resistance to oil, apolar solvents and temperature. However, a NBR artifact needs to be vulcanized and reinforced with fillers in order to present those good properties. Carbon black is the most well-known and used filler for rubber, however other types of filler such as short length fibers are subject of recent studies. This study assesses different types of rock wool fibers (RWF) with different lengths; 100 μm and 300 μm, with and without surface chemical modification on NBR composites using X-ray computed tomography. The scans were carried out in a Bruker SkyScan 2211 multiscale Nano-CT with a 0.9 μm pixel size. Nine formulations with 10, 25 and 40 parts per hundred rubber (phr) of 03 different RWF types were prepared in a standard two-roll mixer based on the parameters described on ASTM D-3187. After the mixing procedures, rubber compounds were left 24 hours in a room with 23 ± 2 °C and moisture not higher than 50% to rest. Afterwards the compounds were vulcanized in a hydraulic press at 160 °C, 180 kgf/cm², using the optimum cure time (t90) obtained through their rheometric characteristics as time parameter (ASTM D-2084). The X-ray computed tomography analysis allowed us to evaluate three major parameters. The arrangement of the fibers in the rubber matrix, exposing whether a preferential orientation was achieved, the fiber volume fraction actually dispersed in the rubber matrix, and the aspect ratio (length/diameter) of the fibers, which is important to determine crosslink density using a fast method on a Rubber Process Analyzer instead of a high time consuming swelling test. The Mogno beamline at SIRIUS synchrotron facility will provide faster and more precise measurement with submicrometric resolution, which is essential for the future characterization of our samples. (author)