Functional Wood Materials Characterization
Densified Cellulose Composites
Ultrastructural and mechanical characterization of native and functionalized plant cell walls via atomic force microscopy
Wood represents a unique hierarchical biological material with excellent macroscopic properties originating from the specific structural arrangement of the constituents on the micro- and nanoscale. For a detailed analysis of the corresponding structure-property relationships high resolution analytical techniques, beyond conventionallyused SEM, TEM and nanoindentation, are needed. In this regard atomic force microscopy (AFM) can push the limit of resolution down to the nanoscale in terms of imaging the topography and mechanical properties. So we have adapted the so-called quantitative imaging mode (JPK instruments) based on recording a force distance curve in every pixel for the nano-scale structural respectively mechanical characterization of wood cell walls without the need of embedding. Thereby, it was possible to differentiate for the first time between the different cell wall layers, (CML, S1, S2, S3) on a spruce cross section on the basis of their mechanical properties. Furthermore, we have visualized the change in micro fibril angle in the transition zone from the S1 to the S2 layer characterized by a stiffness gradient, and proven the model of a concentric lamellar arrangement of the constituents within the S2 layer.
Quantitative imaging is not limited to the structural/mechanical analysis of natural unmodified plant/wood cell walls. Moreover, it additionally represents a powerful analytical tool for the detailed characterization of modified/functionalized wood. QI enabled for example the visualization of a homogeneous polyelectrolyte layer by layer buildup on wood surfaces already within the first nm thick layers based on differences of the adhesion values of the differently charged polyelectrolyte layers. Thus, it was possible to gain new insights into the stability of polyelectrolyte coatings on a complex biomaterial surface.
Characterization of wood adhesive and primer systems on a cell wall level
The gained knowledge in this project will unravel fundamental information concerning wood-glue-primer interactions and potentially help to improve the formulation of adhesives in the future.
This project is performed in close collaboration with Henkel, engineered wood.
 Casdorff, K., Keplinger, T., Bellanger, H., Michen, B., Schön, S., Burgert, I.: High-resolution adhesion mapping of the odd-even effect on a layer-by-layer coated biomaterial by Atomic-Force-Microscopy, ACS Applied Materials & Interfaces; 2017
 Casdorff K., Keplinger T., Burgert I.: Nano-mechanical characterization of the wood cell wall by AFM studies – comparison between AC- and QITM mode; Plant Methods; 2017
 Casdorff K., Kläusler O., Gabriel J., Amen C., Lehringer C., Burgert I., Keplinger T.: About the influence of a water based priming system on the interaction between wood and one-component polyurethane adhesive studied by Atomic Force Microscopy and Confocal Raman Spectroscopy Imaging; International Journal of Adhesion and Adhesives; 2017