Nanocellulose Film Modulus Determination via Buckling Mechanics Approaches

Glassy polymer films are important materials in many manufacturing industries. The rapid and reliable characterization of the elastic modulus is essential for the implementation of these materials in industrial processes. In this study, a freestanding column buckling mechanics approach is utilized to determine the elastic moduli of glassy polymer films. To demonstrate the efficacy of this measurement approach, several types of nanocellulose films are measured (specifically, mechanically fibrillated cellulose nanofibers (CNF), 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibers (TOCNF), and cellulose nanocrystals (CNC)). Two different analysis approaches, the linear intercept (LI) method and the Southwell method, were used to determine the modulus of each film type for various thicknesses. The LI and Southwell methods determined similar moduli for each film type. However, when compared with tensile testing results, the moduli of the TOCNF and CNC films had similar experimental error and were more easily characterized by freestanding buckling mechanics. Modulus values determined via either buckling approach were found to be more reproducible for the geometrically stiffest (thickest) films, which are often the most difficult materials to characterize in tension. By the use of freestanding buckling mechanics, rapid and reliable modulus characterization was achieved for brittle nanocellulose films, demonstrating that this approach can be applied to brittle films in general.