Damage of the cell wall during extrusion and injection molding of wood plastic composites

To study material damage in wood cells during any transformation process, one must consider the molecular architecture of natural cellulosic fibers, which may eventually impact the overall mechanical behavior of wood fibers. In particular wood species, anatomical features and mechanical properties of the cell wall may determine the potential for stress transfer in hybrid materials. In this study, we quantified wood cell damage in terms of the stiffness reduction of the S2 layer for the cell wall by measuring Young's modulus with nanoindentations of the cell wall before and after processing. We then propose and validate a modified rule of mixtures based on a damage parameter affected by the latewood proportion and cell wall properties.