Lamellar cracks, do they appear during radial compression of wood?

Abstract The development of flexible fibres in the refining of mechanical pulps requires large amounts of energy and it is important to find means of making this process more efficient. One way to obtain flexibility is thought to be by the initiation of cracks parallel to the cell wall. This process was studied during sinusoidal radial compression (10 Hz) of softwood at 20 and 95°C. Sections of compressed specimens were observed in a light microscope, or ESEM (Environmental Scanning Electron Microscope). To create a contrast, i.e. to enhance the damaged areas, Simons' stain was used for light microscopy and swelling in dimethylsulfoxide (DMSO) for ESEM. However, no parallel cracks were observed in any of the compressed specimens by the methods used, even after up to 10000 compressions. There was, however, a slight tendency towards a weakening in the structure at the cell corner area observed as parallel cracks in specimens dried in their compressed state. This could be an indication of the initiation sites for the permanent deformation of fibres in refining.