Imaging of the helical arrangement of cellulose fibrils in wood by synchrotron X-ray microdiffraction

Abstract

A complete image of the helical arrangement of cellulose ®brils in the S2 layer of adjacent wood cells of Picea abies (Norwegian spruce) was obtained by applying position-resolved synchrotron X-ray microdiffraction on cells in cross section. In contrast to conventional ®ber diffraction studies, the incident beam was parallel to the longitudinal cell axis, resulting in a glancing angle " far from 90 with respect to the cellulose ®brils. This special choice of diffraction geometry allowed us to take advantage of an asymmetry effect in the two-dimensional diffraction patterns arising from the curvature of the Ewald sphere to obtain information on the local orientation of the cellulose ®brils. The small size of the beam, smaller than the thickness of a single cell wall, allowed mesh scans over intact transverse sections of adjacent wood cells with a microscopic position resolution. The scan yielded a map of diffraction patterns that could readily serve as a microscopic image. Each of the diffraction patterns was then used to evaluate the local orientation of the cellulose ®brils at the actual beam position. The combination of these results gave an image of cellulose ®brils forming (Z) helices in several adjacent wood cells.

The fracture behaviour of single wood fibres is governed by geometrical constraints: in situ ESEM studies on three fibre types

“…In terms of wood tissues tension buckling of the individual fibre within the tissue is impeded by neighbouring cells because of their mostly rectangular shape and the z-helical orientation of the cellulose microfibrils, which results in counterrotating cellulose fibrils of two adjacent cell walls, glued together by the compound middle lamellae, (e.g. Booker 1996;Lichtenegger et al 1999). …”

A Sinusoidally Architected Helicoidal Biocomposite

“…Similar observations have been made with respect to the periodic region of the dactyl club and helicoidal structures found within most arthropod cuticles as well as other Submitted to 8 natural composite materials including lamellar bone, cell walls of wood and fish scales. [17,18,[28][29][30][31][32][33] Crack deflection is an extrinsic form of toughening that is well-documented in natural composite materials, specifically biomineralized tissues. [3] The periodic nature of hard and soft interfaces, in this case between alpha-chitin fibrils and hydroxyapatite crystals, results in a crack-tip shielding effect that changes the crack driving force and thereby arresting crack propagation.…”

A new experimental station for simultaneous X-ray microbeam scanning for small- and wide-angle scattering and fluorescence at BESSY II

“…Thus, scanning SAXS/ WAXS experiments on hierarchical tissues such as bone or wood require a beam size adapted to the hierarchical level of interest. Several studies have been performed so far with laboratory equipment with beam sizes of % 200 mm (Fratzl et al, 1997;Jaschouz et al, 2003), and with synchrotron radiation with beam sizes from % 20 mm (Ž ižak et al, 2000; Ž ižak et al, 2003) down to about 1 mm (Lichtenegger et al, 1999;Wagermaier et al, 2007) in recent years. The principle of the technique having been well demonstrated and elaborated, one of the needs is now to install dedicated synchrotron instruments for routine high-throughput scanning SAXS/WAXS experiments similar to existing laboratory instruments (Jakob et al, 2003), but with a considerably smaller beam size and shorter data acquisition time.…”