Abstract
Abstract Alkaline delignification of wood tissue is the core of the global pulping technology and the most prominent large-scale separation of the main wood components. This work aims at improved understanding of the interplay between the topochemistry of alkaline pulping and the associated morphological changes. Morphology and chemical structure of partially soda-delignified wood chips were studied combining X-ray tomography (XRT), X-ray diffraction analysis and compositional characterization (lignin and carbohydrate content). The XRT studies of wet samples (providing 3D structural information without interfering drying effects), allowed observation of the cell wall separation as an increasing amount of lignin was removed with the increasing pulping time. Comparison between the microstructure of the surface and the central parts of the treated chips showed a more delignified microstructure at the surface, which highlights the dependence of the delignification process on the mass transport (hydroxide ions and lignin fragments) through the wood tissue. The crystallite size of cellulose increased in the <200> crystal planes during the early stage of pulping while there was little effect on the <110> plane.
Highlights
Climate change, and the associated necessity to reduce the use of fossil-based fuels, materials and chemicals, is one of the most urgent problems the world is currently facing
The structural changes in wood during soda pulping have been studied using standard approaches combined with high-resolution X-ray micro-tomography and X-ray diffraction
During the stage I, the cooking liquor passes through the lumen and pits of the tracheids and saturates the inner surface of the cell walls, which results in an initial removal of hemicelluloses and lignin from the secondary wall
Summary
The associated necessity to reduce the use of fossil-based fuels, materials and chemicals, is one of the most urgent problems the world is currently facing. During the last decades, there has been an increasing number of initiatives to develop new sustainable energy and material resources (Christopher 2013; De Bhowmick et al 2017; Lew et al 2012; Mattsson et al 2017). Wood is the most abundant biomass on land and is already one of our most important raw materials for the production of a large number of products used in our daily life, ranging from sawn timber (wood construction, furniture etc.) and fiber-based materials (paper, board, viscose) to chemicals (e.g. cellulose derivatives and lignosulfonates). The largest industrial use of wood is in the form of sawn timber and paper/board
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