Large-area TEM imaging for characterization of fibrillated cellulose across microscale to nanoscale

Abstract Fibrillated cellulose, such as micro- and nanofibrillated cellulose (MNFC) and fines, plays a significant role in papermaking. However, characterizing its complex morphology across multiple scales remains challenging due to the limitations of conventional microscopy. Optical microscopy lacks the resolution to detect nanoscale fibrils, and electron and atomic force microscopy are limited by the trade-off between resolution and field of view. To overcome these limitations, we employed large-area transmission electron microscopic (TEM) imaging. The automatic stitching of thousands of images generated a single image as large as 523 × 886 µm 2 , enabling the visualization of both fibril length and width across multiple scales, from micrometers to nanometers. Moreover, large-area TEM imaging revealed distinct morphological differences between two samples that have previously been considered comparable by a standard optical method: one, slender and fibrillar, prepared by the aqueous counter collision method; the other, sheet-like with a broader size distribution, prepared by a grinder.