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Intelligent resource usage is one of the most challenging tasks for the wood-based panels industry. With respect to this issue, leather shavings, derived during leather preparation, are a promising new raw material, as they offer not only high availability, but also potentially enhance material properties such as panel fire retardancy. In order to improve the performance of these emerging panel binder materials, an understanding of chemical interactions between the different constituents is crucial. This paper investigates the chemical changes that occur during hot-pressing of wood and leather in combination with lignin by means of solid state 13C NMR spectroscopy. These constituents, their binary mixtures, and the influences of panel pressing temperature and pressure commonly used in panel production were investigated. The study showed characteristic chemistry and features of these constituents, quantifying the impacts of both heat and pressure on their interactions. Primarily, analysis revealed that lignin readily connects with both the wood and leather components. Lignin induces chemical change within the protein structure of leather, resembling tanning reactions, or protein complexation. By analogy, it was deduced that this interaction also takes place between leather and the lignin-rich wood fibre surface. This effect may be beneficial in industrial-scale production through improving resin binding properties during panel consolidation.

Besides other ligno-cellulosic materials such as straw, rice husks, or bagasse, wet blue particles from leather production are a promising new raw material stock for wood-based panels, as they offer not only a high availability, but increase the properties of the panel with regard to fire resistance or mechanical characteristics. A panel with a mixture of 42.5% wood fibers, 42.5% wet blue leather particles, and 15% lignin adhesive was produced, and an inhomogeneous sample was prepared. An area of 9 x 10 mm was rasterized and scanned by means of Raman Spectroscopy. Furthermore, the reference spectra of the constituents, i.e. wood fiber, wet blue leather particle, and lignin powder were recorded. The obtained data were treated and analyzed using chemometric methods (principal components analysis PCA and cluster analysis). An important finding was that the reference data were not directly represented in the panels’ spectra, and the correlation matrix of the PCA was not applicable to the panel data. This indicated that chemical changes might take place during the pressing. After processing the panel Raman spectra with the help of PCA and cluster analysis, three distinctive clusters were obtained, discriminating wood, leather, and mixed regions. With the assigned spectral information, it was possible to create a spectral image of the surface.

Wet-white and wet-blue leather shavings were investigated as promising new raw materials as they seem to offer a high availability and cost competitiveness compared to wood, and they also show some interesting new properties. In order to determine a new field of application for the leather shavings and to understand the fiber particle interaction, boards with a density of 700 kg/m³ and a resin load of 12% were produced with varying contents of wood fibers, wet-blue and wet-white leather particles. These panel composites were characterized with regard to their internal bond, modulus of elasticity, and modulus of rupture. Furthermore, the micro-structure of selected panels was investigated by X-Ray computed tomography (CT). Different phases within the CT data were segmented using thresholding algorithms, and the pore size distribution of the panels was analyzed. A substantial difference was found between the panels produced due to the incorporation of leather particles. The internal bond strength increased with rising leather particle content, whereas other mechanical properties dropped. The CT analysis showed a huge difference in the pore size distribution and the number of pores for the different materials. This indicates that the differences visible in mechanical testing were induced by the different geometry of the constituents.