Revealing the structures of cellulose nanofiber bundles obtained by mechanical nanofibrillation via TEM observation

To reveal the structures of cellulose naonfiber bundles extracted from lignocellulosic pulps and prepared by mechanical nanofibrillation methods, the samples were systematically investigated by transmission electron microscopy (TEM) observation. First, high magnification and high resolution TEM images were obtained starting from one end of the bundles. The imaging position was then carefully shifted along the length of the bundles until the other end was reached. Finally, a series of TEM images were integrated through image processing and analyzed. The cellulose nanofiber bundles displayed ribbon-like structures, which were organized with parallel aligned cellulose nanofibers 2-5 nm in width. The length of the bundles was >11 μm. The bundles were interconnected with other nanofibers and nanofiber bundles, forming entangled, web-like networks in suspension. Evidence demonstrating the existence of twisted bundle morphologies was also presented.