The application of nanoindentation for determination of cellulose nanofibrils (CNF) nanomechanical properties

Nanocellulose is a polymer which can be isolated from nature (woods, plants, bacteria, and from sea animals) through chemical or mechanical treatments, as cellulose nanofibrils (CNF), cellulose nanocrystals or bacterial celluloses. Focused global research activities have resulted in decreasing costs. A nascent industry of producers has created a huge market interest in CNF. However, there is still lack of knowledge on the nanomechanical properties of CNF, which create barriers for the scientist and producers to optimize and predict behavior of the final product. In this research, the behavior of CNF under nano compression loads were investigated through three different approaches, Oliver–Pharr (OP), fused silica (FS), and tip imaging (TI) via nanoindentation in an atomic force microscope. The CNF modulus estimates for the three approaches were 16.6 GPa, for OP, 15.8 GPa for FS, and 10.9 GPa for TI. The CNF reduced moduli estimates were consistently higher and followed the same estimate rankings by analysis technique (18.2, 17.4, and 11.9 GPa). This unique study minimizes the uncertainties related to the nanomechanical properties of CNFs and provides increased knowledge on understanding the role of CNFs as a reinforcing material in composites and also improvement in making accurate theoretical calculations and predictions. (paper)