Developing a bio-based, continuous fibre reinforcement to push the impact energy limits of engineered wood in structural applications

Abstract

Laminated birch veneers were reinforced with a layer of unidirectional, continuous filaments for an investigation on the potential increase in fracture toughness. By proposing a new type of reinforcement based on regenerated cellulose filaments, an alternative for conventional glass fibres was introduced featuring a reduction in carbon footprint and enabling a circularity perspective in combination with engineered wood. Impact bending tests based on ISO179-1/2 were performed to assess the mechanical potential of such a novel reinforcement. Two sources of fibre reinforcement were considered for a comparison; glass fibres (E-glass) and high-tenacity viscose filaments. Based on biomimetic considerations, structural features such as yarn twist and a partial impregnation of the yarn were implemented to foster a tough composite failure. A Finite Element (FE) model was proposed to describe the effect of cellulosic reinforcements under dynamic loading, considering the impregnation with different adhesive systems. The results indicated a strong influence of the fibre impregnation. With a mean impact strength of 38.6 kJ/m² cellulose filaments impregnated with epoxy showed only a moderate improvement compared to 34.7 kJ/m² for non-reinforced wood. When impregnated with an emulsion polymer isocyanate, impact strength more than doubled to 88.9 kJ/m². This was traced back to the partial impregnation of the yarn cross-section. A comparison of the FE simulation with the experimental data showed consistency in the failure behaviour and the quantitative effect of reinforcement. This novel reinforcing approach and its underlying model demonstrated a considerable progress in increasing the crash-safety of wood by means of a bio-based and easily applicable solution.