Mechanical performance of cellulose nanofibril film-wood flake laminate

Homogeneous and transparent CNF films, fabricated from the (2,2,6,6- tetramethylpiperidin-1-yl) oxyl (TEMPO)-modified CNF suspension, were laminated onto wood flakes (WF) based on phenol-formaldehyde (PF) resin and the reinforcement potential of the material has been investigated. The focus was on the influence of CNF film lamination, relative humidity (RH), heat treatment, and anisotropic properties of WF on the CNF-WF laminate tensile properties (elastic modulus, ultimate tensile strength, strain to failure). Results demonstrated that CNF-WF laminates had improved mechanical performance as compared to the neat WF. In the WF transverse direction, there were gains of nearly 200% in Young's modulus and 300% in ultimate tensile strength. However, in the WF axial direction, the reinforcement effect was minor after PF modification of the wood and the presence of the CNF layers. The effective elastic moduli of the CNF-WF laminates were calculated based on the laminated plate theory, and the calculation in both axial and transverse directions were in agreement with the experimental results.