Abstract
Abstract•BackgroundIt is with increasing interest that wood materials are now being considered as a green resource. For improving the product performance of wood derived materials new ways of separating them from wood are required. Thus, there is a great demand for a better understanding of the ultrastructure of wood and how the components are interaction on a molecular level in building up its properties.•Material and methodBy the use of microscopic and spectroscopic techniques combined with mechanical forces, new knowledge regarding especially the role of the matrix polymers, the hemicelluloses and lignin, has been gained. This relates specifically to molecular interaction and orientation.•ResultsIt is here demonstrated that all of the wood polymers within the secondary cell wall exhibit a preferred orientation along the fibrils. The degree of orientation decreases in the order cellulose, hemicelluloses to the lignin which only shows a small degree of orientation, probably induced by structural constrains.•ConclusionThis orientation distribution is probably what has to be considered to better predict transverse cell wall properties. Moisture accessible regions are also aligned in a parallel arrangement in the cellulose fibrils explaining its high moisture resistance. The lignin is surprisingly inactive in the stress transfer in the secondary wall. This could perhaps be related to the function of lignin providing compressive, hydrostatic resistance in the lenticular spaces between fibrils, when longitudinally straining the fibre. This knowledge of the ultrastructural properties of the wood polymers, here presented, provides for a better understanding of the cell wall properties.
Highlights
Wood is one of the most abundant biomaterials on earth
It is well known that moisture cannot access the crystalline regions of the cellulose, which is why the structural arrangement of these in the fibril structure must be of great importance
It is clearly evident that the secondary cell wall of wood fibres is a highly intermixed composite material, in which the very detailed structure is not yet fully understood
Summary
Wood is one of the most abundant biomaterials on earth. For millions of years, trees have adapted to their environment to withstand incredibly diverse conditions, while the basic function of a tree trunk is to act as a strong supporting material and to serve as a transport mechanism and a store for the nutrients of the living tree. The arrangement is such, that the properties that exist in different directions are maximized so that they meet the requirements of the tree, while having the ability to adapt to a changing environment without adversely affecting the long-term performance of the structure This ability of the wood structure to withstand harsh changing conditions presents difficulties in making use of the wood material, when trying to break down its fibres in order to extract its different building components. There is large interest in the possible utilization of hemicelluloses as barrier films and of lignin as an inexpensive raw material source for carbon fibre production To separate these constituents in an economically feasible way, with good property performance, requires a deeper understanding of the structural features of the cell wall and its organization
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