Variation of Cellulose Microfibril Angles in Softwoods and Hardwoods—A Possible Strategy of Mechanical Optimization

Abstract

Position-resolved small-angle X-ray scattering was used to investigate the nanostructure of the wood cell wall in two softwood species (Norwegian spruce and Scots pine) and two hardwood species (pedunculate oak and copper beech). The tilt angle of the cellulose fibrils in the wood cell wall versus the longitudinal cell axis (microfibril angle) was systematically studied over a wide range of annual rings in each tree. The measured angles were correlated with the distance from the pith and the results were compared. The microfibril angle was found to decrease from pith to bark in all four trees, but was generally higher in the softwood than in the hardwood. In Norwegian spruce, the microfibril angles were higher in late wood than in early wood; in Scots pine the opposite was observed. In pedunculate oak and copper beech, low angles were found in the major part of the stem, except for the very first annual rings in pedunculate oak. The results are interpreted in terms of mechanical optimization. An attempt was made to give a quantitative estimation for the mechanical constraints imposed on a tree of given dimensions and to establish a model that could explain the general decrease of microfibril angles from pith to bark. 1999 Academic Press

A close-up view of wood structure and properties across a growth ring of Norway spruce (Picea abies [L] Karst.)

“…Only the first tissue slice showed a slightly higher MFA. However, these findings were contrary to other observations indicating different MFAs in earlywood and latewood Lichtenegger et al 1999). Lichtenegger et al (2003) have shown that MFAs which are measured by cross-field pitting are likely to be overestimated in earlywood.…”

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.…”

Variation in wood properties among five full-sib families of Norway spruce (Picea abies)

“…3b) even if it is less significant in comparison to the findings in loblolly and radiata pine [4,29]. However, the observed MfA values, with a mean of 11 • and a variation from 8 • to 20 • , indicates that the majority of wood measured has reached maturity in respect to MfA [26,41,42]. The boards were extracted between ring 4 and cambium, which varied to be 13-21 rings from pith.…”