Initiation of wood defibration in groundwood pulping, single asperity indentation and scratching

Abstract

SUMMARY:To understand how the energy requirements of the mechanical pulping process can be reduced, the fundamental mechanisms behind fiber separation in Norway spruce were studied experimentally and analytically. Single tip scratching in heated water was used to reproduce initial defibration mechanisms found industrially. The resulting scratches were then compared with surfaces ground in a real industrial process. Moreover, the mechanical behavior of the wood microstructure was monitored with X-ray computed microtomography as a single hard tip was pressed into it. Subsequent digital image correlation was applied to estimate the strain field in the region around the indenting tip. Regions in the wood with high tensile or shear strains were identified, i.e. where cracking and fiber separation is believed to initiate. ADDRESSES OF THE AUTHORS: Magnus

Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale

“…On the other hand, treating wood as a continuum and instead focusing on the loading mechanisms, accurate global fracture paths have been predicted by, for example, Holmberg et al (1999). In an attempt to bridge the gap between high-resolution cell models and continuum models, Isaksson (2015) applied a gradientenhanced elasticity continuum theory, which was shown to better capture the strain fields of wood under an indenter (see also the work by Heldin et al 2016). This method is not, however, suited to study the deformation and strain of the individual cells under an indenter, as such displacements occur in a scale below.…”