Applied and Structural Aspects of Lignin in Novel Wood Composites and Plywood

Self-binding high-density fibreboard is formed using grey alder (Alnus incana L. Moench) steam-exploded (SE) fibres without addition of synthetic adhesives. The selfbinding high-density grey alder fibreboard and birch (Betula Pubescens) plywood with application of SE lignin shows sufficient mechanical properties comparing to commercial composites (Table 1 and Table 2). In developing new binderless materials relationships between structure, function, and properties is a key issue. The main role play segregate lignin particles during SE. Cellulose consists of micro-fibrillated nano-structures of high stiffness and strength (whiskers). The state of lignin nanostructures is not so clear. The Riga group has formulated hypothesis of the fractal character of primary nanostructures of lignin [1]. The experimentally observed (TEM, SEM, 13 C NMR in solid state, SAXS, USAXS) nanoparticles make new cell wall modifications. However, SE primary nano-particles in short time aggregate making secondary larger particles. As a rule, self-binding wood composites from structural viewpoint are hierarchical materials at different size scales. Using small and ultra-small-angle synchrotron X-ray scattering (SAXS and USAXS) [2] the average shape of a lignin particle that cannot be characterized by some exact molecular formula has also been determined (Fig. 1 and 2).