Cellulose is present in the cell walls of wood in the form of partially crystalline microfibrils, with a thickness of 2–3 nm. Lateral aggregation of the microfibrils into bundles, also termed macrofibrils, in the secondary cell walls has been reported by various methods (Sarkar et al. 2009; Adobes-Vidal et al. 2020), including atomic force microscopy, electron microscopy and electron tomography. The lateral size of microfibril bundles is usually in the range 15–20 nm, with some hemicelluloses and water ncluded within the bundle. However, none of the methods used so far has been able to observe these structures in their truly native state, as part of an intact cell wall structure and hydrated by liquid water.
Neutron and X-ray scattering are excellent tools for non-invasive characterization of the hierarchical structure of wood and other cellulosic materials (Rongpipi et al. 2019). With these methods, the properties of cellulose crystals and the packing of microfibrils can be analysed under various external conditions such as different humidity levels (Penttilä et al. 2020a). In the current work, we utilized small-angle neutron scattering (SANS) together with contrast variation by poly(ethylene glycol) (PEG) to assign a specific contribution in the SANS intensities of native wood to the outer dimensions of cellulose microfibril bundles (Penttilä et al. 2020b). This allowed us to detect the presence of microfibril bundles in the cell walls of different types of wood and to determine their diameter also in wood samples without PEG.
Keywords: microfibril, cellulose, wood structure
Authors
Paavo Penttilä
Aalto University, Department of Bioproducts and Biosystems, Espoo, Finland
Michael Altgen
Aalto University, Finland
Muhammad Awais
Aalto University, Department of Bioproducts and Biosystems, Espoo, Finland
Aleksi Zitting
Aalto University, Department of Bioproducts and Biosystems, Espoo, Finland
Monika Österberg
Aalto University, Department of Bioproducts and Biosystems, Espoo, Finland
Ralf Schweins
Institut Laue–Langevin (ILL), Large-Scale Structures Group, Grenoble, France
Lauri Rautkari
Aalto University, Department of Bioproducts and Biosystems, Espoo, Finland
Login to download the PDF