Evaluating the Effects of Variability on the Mechanical Performance of Nanocellulosic Fibers

There have been significant research efforts on the topic of fabricating continuous fibers (filaments) from nanocellulose with impressive mechanical properties[1-3]. To use these in engineering applications such as e.g. fiber-reinforced composites, there are several additional requirements apart from the mechanical properties, such as stiffness and strength. One example is to understand and control the presence and effects of defects, the variability in internal structure and diameter, or the fiber-matrix interphase that provides the connection between the bulk fiber and bulk polymer matrix in the composite. In addition, the effects of ambient conditions such as humidity are of interest since they influence the performance of the fibers as well as fabricated composites.<br/><br/>To understand and quantify these effects, a significant effort has been made to carefully characterize nanocellulosic fibers spun using the micro-fluidic concept of flow-focusing[4] and evaluate the effects of, e.g., variability on mechanical performance. Several routes have been pursued to try to couple failure to variability and process conditions: laser diffraction to provide 3D tomograms representing the surface of the spun filaments, X-ray scattering for characterizing the internal variability, as well as effects of humidity and temperature during fabrication and in the use phase. The results are put in the context of conventional reinforcement fibers such as natural, glass, and carbon fibers.<br/><br/>1. M. J. Lundahl, V. Klar, L. Wang, M. Ago, O. J. Rojas, Spinning of Cellulose Nanofibrils into Filaments: A Review. <i>Ind. Eng. Chem. Res.</i> <b>56</b>, 8-19 (2017).<br/>2. T. Rosén, B. S. Hsiao, L. D. Söderberg, Elucidating the Opportunities and Challenges for Nanocellulose Spinning. <i>Adv. Mater.</i> <b>33</b>, 2001238 (2021).<br/>3. N. Mittal<i> et al.</i>, Multiscale Control of Nanocellulose Assembly: Transferring Remarkable Nanoscale Fibril Mechanics to Macroscale Fibers. <i>ACS Nano</i> <b>12</b>, 6378-6388 (2018).<br/>4. K. M. O. Håkansson<i> et al.</i>, Hydrodynamic alignment and assembly of nanofibrils resulting in strong cellulose filaments. <i>Nature Communications</i> <b>5</b>, (2014).