Because the manufactured nanocellulose products were matted and not individualized as seen in FESEM images, the nanoparticles size and morphology of CNCH2SO4 and CNCCr(NO3)3 were confirmed by transmission electron microscopy (TEM). This technique is considered one of the most accurate methods for direct measurement and observation at a nanoscopic scale. Under the controlled hydrolysis conditions, the non-crystalline regions of cellulose were cleaved transversely by H2SO4 and Cr(NO3)3 hydrolyzing catalysts with heat treatment. The average diameter of the nanocellulose fibers was calculated by ImageJ software for at least 200 measurements. The results showed that the macro-sized native cellulose fiber diminished to the nanometer scale after the hydrolysis reaction. However, it can be clearly observed that the morphology of the nanocellulose obtained for both hydrolysis procedures exhibited noticeably different structures: CNCH2SO4 displayed a rice-shape structure (Figure 5a) and CNCCr(NO3)3 revealed a spider-web-network-like structure (Figure 5b), confirming a successful extraction of nanocellulose from MCC. However, part of the CNCH2SO4 and CNCCr(NO3)3 samples were observed in a somewhat agglomerated form, as bundles of particles with some dispersed individual fibrils present. In fact, it was challenging to obtain separated nanocellulose fibrils due to the presence of strong hydrogen bonding and the high surface area between these fibrils fosters agglomeration, overlapping and assembly. This phenomenon occurred mainly during the evaporation of the dispersing medium in order to dry the particles for TEM imaging . Similar observation has been previously reported .