Computer-assisted quantification of the multi-scale structure of films made of nanofibrillated cellulose

Films made of nanofibrillated cellulose (NFC) are most interesting for use in packaging applications. However, in order to understand the film-forming capabilities of NFC and their properties, new advanced methods for characterizing the different scales of the structures are necessary. In this study, we perform a comprehensive characterisation of NFC-films, based on desktop scanner analysis, scanning electron microscopy in backscatter electron imaging mode (SEM-BEI), laser profilometry (LP) and field-emission scanning electron microscopy in secondary electron imaging mode (FE-SEM-SEI). Objective quantification is performed for assessing the (i) film thicknesses, (ii) fibril diameters and (iii) fibril orientations, based on computer-assisted electron microscopy. The most frequent fibril diameter is 20-30 nm in diameter. A method for acquiring FE-SEM images of NFC surfaces without a conductive metallic layer is introduced. Having appropriate characterisation tools, the structural and mechanical properties of the films upon moisture were quantified.