Large-scale and high-resolution visualization of static mechanical properties of wood-adhesive interphase utilizing nanoindentation mapping

To improve the mechanical performance of wooden engineered composites, more information is needed to understand the relationship between adhesive infiltration and mechanical properties of wood-adhesive interphase. Nanoindentation mapping (NI Mapping) was hereby used to achieve large-scale and high-resolution visualization of mechanical properties of wood-adhesive interphase for establishing the basic understanding of such correlation, and it showed the convincible reliability (variation less than 3% as compared with commonly applied NI methodology) and exceptional efficiency (180 min of total analysis time as compared with more than 3000 min using the commonly applied NI methodology). Successful investigation into the distribution of mechanical properties of wood-phenolic resin (wood-PF) and wood-polyurethane (wood-PUR) interphases using NI Mapping has confirmed that gradient elevation in mechanical properties of cell wall in wood-adhesive interphase is related to adhesive infiltration. PF adhesive exhibits favored infiltration which led to the enlarged wood-PF interphase region (over 60 μm) and improved micro-/macro-mechanical properties. NI Mapping was also applied for revealing mechanical performance of early wood-adhesive interphase which cannot be characterized by commonly applied NI methodology due to its small size. The mechanical properties of cell wall in early wood-adhesive interphase are poor; however, the interphase region would be enlarged due to the large lumen of early wood. NI Mapping can be a powerful tool to provide significant insights into the mechanical properties of wood-adhesive interphase, and thus, to improve the knowledge of the adhesive infiltration and mechanical properties of cell wall.