An in-situ microscale investigation into the fracture of wood-adhesive interphase by nanoindentation

Green timber high-rises now taking off raises the desire to improve the mechanical performance and durability of engineered wood-based composites. It requires an in-depth understanding of the fracture mechanism of wood-adhesive interphase. Nanoindentation (NI) analyses in conjunction with finite element analysis (FEA) were conducted in this work to reveal the fracture behaviors and static mechanical properties of microscale woodadhesive interphases composed of different cell wall layers and phenol-formaldehyde (PF) adhesive. Results revealed the evident cracks and bending in microscale wood-adhesive interphase, which originates from the stress concentration at the interfacial interlock of the cell walls and PF adhesive. Deformation of compound middle lamella (CML) located far from the bond line was prior to other microscale wood-adhesive interphases. Prolongation of cracks contributes to the fracture of wood substrates, and brittle fracture of adhesive leads to the deconstruction of wood-adhesive interphase. Results also demonstrated that compact interpenetrating polymer networks (IPNs) impart the corresponding wood-adhesive interphase with the favored yield strength (281 MPa) because of the improved stress transferring. Therefore, building compact IPNs is beneficial for fabricating a strengthened and toughened wood-adhesive interphase in engineered wood-based composites.