Cellulose microfibril orientation of Picea abies and its variability at the micron-level determined by Raman imaging

Abstract

The functional characteristics of plant cell walls depend on the composition of the cell wall polymers, as well as on their highly ordered architecture at scales from a few nanometres to several microns. Raman spectra of wood acquired with linear polarized laser light include information about polymer composition as well as the alignment of cellulose microfibrils with respect to the fibre axis (microfibril angle). By changing the laser polarization direction in 3° steps, the dependency between cellulose and laser orientation direction was investigated. Orientation-dependent changes of band height ratios and spectra were described by quadratic linear regression and partial least square regressions, respectively. Using the models and regressions with high coefficients of determination (R2 > 0.99) microfibril orientation was predicted in the S1 and S2 layers distinguished by the Raman imaging approach in cross-sections of spruce normal, opposite, and compression wood. The determined microfibril angle (MFA) in the different S2 layers ranged from 0° to 49.9° and was in coincidence with X-ray diffraction determination. With the prerequisite of geometric sample and laser alignment, exact MFA prediction can complete the picture of the chemical cell wall design gained by the Raman imaging approach at the micron level in all plant tissues.

Variation in Mechanical Properties within Individual Annual Rings in the Resonance Spruce Wood (Picea abies (L.) Karst.)

“…However, the obtained MFA values correspond to the values reported by other authors (e.g. Lichtenegger et al, 1999;Gierlinger et al, 2010), who proved that the MFA in the spruce wood, especially in rings placed further from the pith, may be close to 0°. Bearing in mind that the correlations between MFA and modulus of elasticity and tensile strength are negative (Fig.…”

Microspectroscopy as applied to the study of wood molecular structure

“…This is due to the orientation of the cell wall polymers, especially the cellulose. In the analysis of spectra, this has to be taken into account and one can even extract orientational information (Gierlinger et al 2010). By inserting a polarizer in the beam path of the IR microscope, this method can also be used to extract information on the orientation of the wood polymers (Stevanic and Salmén 2009).…”

Silica replication of the hierarchical structure of wood with nanometer precision

“…55 The compound middle lamella that contains much more lignin than the cell S2 layer appeared to be excessively damaged. 19,56 Also, the overall thickness of the cell wall was reduced to 4.2 6 0.8 lm, indicated in literature as the removal of lignin. 57 The delig 2inf samples again showed thicker cell walls (6.3 6 2.3 lm) than their extr 2inf counterparts [ Fig.…”

“…In the dominatingly thick S2 cell wall layer of normal spruce early-sapwood, the cellulose fibrils are arranged parallel and their angle with respect to the cell axis is between 3°and 5°. 19,20 They, therefore, form a group of helices wound around the cell lumen.…”