Dynamic-mechanical properties of wood-fiber reinforced polylactide:: Experimental characterization and micromechanical modeling

Wood-fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. When designing new materials of this kind, it is useful to measure the influence of fiber-matrix interface properties on macroscopic mechanical properties. In particular, a quantitative measure of the dynamic stress transfer between the fibers and the matrix when the material is subjected to cyclic loading would simplify the development of wood-fiber composites. This is obtained by comparing the mechanical dissipation of the composite with a value predicted by a viscoelastic micromechanical model based on perfect interfacial stress transfer. The loss factors predicted by the model are 0.12 and 0.16 at dry and humid conditions, respectively, which amount to 63 and 66% of the experimentally determined values. For Young's moduli the predicted values are 1.01 and 0.88 GPa, which correspond to 92% of the experimentally determined values. The mismatch between the predicted and experimental values may be attributed to imperfect interfaces with restrained stress transfer. Loss factors are also determined for specific molecular bonds using dynamic Fourier transform infrared (FT-IR) spectroscopy. These values show the same trends with regard to moisture content as the macroscopically determined loss factors.