Inducing large deformation in wood cell walls by enzymatic modification

It has been shown recently that wood with a high cellulose microfibril angle in the S2-layer, e.g. compression wood, shows permanent plastic deformation without significant mechanical damage to the matrix. This molecular stick-slip mechanism was explained by a gliding of the cellulose fibrils, after a certain shear stress in the matrix was exceeded [1]. Such a material behaviour would be desirable for various applications, for instance, to cover complex geometries with highly deformable veneers as needed in the automotive industry. However, veneers that are typically used for these purposes have a rather brittle failure behaviour, which leads to breakage, and drastic quality and productivity losses. A better deformability of such veneers might be achieved when the underlying deformation principles are conferred by modifying the wood cell wall components, in particular the cellulose fibrils and their matrix coupling. Enzyme treatments were performed on mechanically isolated wood fibres to plastify the entire lignified secondary cell wall. Cellulase Onozuka R-10 from Trichoderma viride (E.C.3.2.1.4) with activity on cellulose and xylan was utilized. Micromechanical tests and FT-IR microscopy studies revealed the change of mechanical properties and nanostructural features of the cell wall. An extended deformability was achieved for two of ten of the modified fibres.