TEM (Fig. 4) confirmed the presence of nanofibers. The TEM images suggested that the chemical and mechanical treatments removed hemicelluloses, lignin, and pectin (the cementing materials around the fiber-bundles). To determine the diameters of the fibers, we used an image processing analysis software (ImageJ) to process the TEM images. The cellulose nanofibers had diameters between 10.9 and 22.6 nm, showing that all the treatments effectively isolated the banana fibers in the nanometer scale (Table 1). The diameters were similar to the nanosized structures derived from other sources such as nanofibers from rice straw (12–35 nm) (Abe and Yano 2009) and wheat straw (15–35 nm) (Chen et al. 2011), and smaller than nanofibers from sugarcane bagasse (30 nm) (Bhattacharya et al. 2008) and sugar beet (30–100 nm) (Leitner et al. 2007).