Mechanical performance of CNF films revealed by Raman spectroscopy

Films prepared using cellulose nanofibrils (CNF) possess high density and smoothness; they are lightweight with good mechanical performance and thus, can be considered as potential material alternatives for several application areas ranging from packaging to electronics. Strategies to produce CNF films have been developed allowing larger scale film production using industrially relevant unit operations. The film performance with respect to structural uniformity and strength can be improved by adding plasticizers and other strength additives. Here we present how the addition of sorbitol influences the mechanical performance of the CNF films prepared using cast coating. The role of the individual fibrils as well as the role of sorbitol as plasticizer on the evolution of the strength performance is revealed using Raman spectroscopy. A Raman band located at 1095 cm-1, associated with the CO ring stretching of the cellulose backbone, was used to quantify molecular deformation. Molecular strain in CNF films was measured by following a shift in the peak position of the Raman band at 1095 cm-1, which is then related to the sorbitol content in the films.