Predicting microfibril angle in Eucalyptus wood from different wood faces and surface qualities using near infrared spectra

International audienceThe microfibril angle (MFA) of crystalline cellulose in the wood cell wall along the stem axis has major effects on stiffness and longitudinal shrinkage of wood and is of key importance to timber quality. The aims of this study were: (i) to develop partial least square (PLS) regression models for microfibril angle (measured on tangential sections by Xray diffraction) based on NIR spectra measured on tangential and on radial surfaces; ii) to develop PLS regression models for such wood trait based on radial NIR spectra collected from wood surfaces of different quality; and (iii) to verify the reliability of these PLS-R models by external validations. T values were recorded by X-ray diffraction on tangential section while NIR spectra were taken on tangential and radial wood surfaces. PLS-R calibrations for MFA based on tangential NIR spectra were better (R²p=0.72) than those using radial NIR spectra (R²p=0.64). The key role of the chemical components and the effect of surface quality of wood on NIRS calibrations are discussed. Considering the differences between experimental conditions, these findings showed the robustness of the NIR-based models for predicting MFA in Eucalyptus wood, even using spectra taken from different wood faces, and surface qualities

RADIAL VARIATION OF MICROFIBRIL ANGLE AND WOOD DENSITY AND THEIR RELATIONSHIPS IN 14-YEAR-OLD Eucalyptus urophylla S.T. BLAKE WOOD

The orientation of cellulose microfibrils in the cell wall along the stem axis has major effects on stiffness and longitudinal shrinkage and is of key importance in wood quality. The aim of this study was to investigate the radial variability of MFA and wood density (ρ) and their relationships in Eucalyptus urophylla wood. Three MFA values were estimated by X-ray diffraction at three points of each one of the 175 tangential sections, and the basic density was measured. A decrease of microfibril angles from pith to bark can be observed in most samples; however, some radial strips presented different patterns of variation. For basic density, a linear significant increase from pith to bark was confirmed. There was no significant correlation between microfibril angle and density. The relationships among the three MFA estimated on tangential sections of wood were strong. The “curvature effect” due to the growth rings had a negligible effect on the three measurements of tangential sections cut near to the pith. This study showed that a single T value measurement by X-ray diffraction, preferably at the centre of the tangential section, is precisely sufficient to estimate the mean MFA of Eucalyptus urophylla wood

Relationships between microfibril angle, modulus of elasticity and compressive strength in Eucalyptus wood

Many traits are known to be important in determining the value of Eucalyptus wood as sawn tim-ber. The commercial importance of the microfi bril angle (MFA) for wood quality is well established for a range of softwoods, but is less clear for hardwood species. For instance, the relationships of MFA with wood stiffness and compressive strength are unknown in Eucalyptus. Therefore, the aim of this study was to evaluate the correlation between MFA and the modulus of elasticity (Ec0,m) in compres-sion parallel to grain and compressive strength (Fc0,k) using juvenile wood of Eucalyptus grandis from fast-growing plantations. The correlation between wood stiffness and compressive strength was high (0.91). The cellulose microfi bril angle presented a correlation of -0.67 with wood stiffness and of -0.52 with compressive strength in Eucalyptus juvenile wood. MFA was found to be important in de-termining the mechanical behaviour of wood and appears to be a useful parameter to indicate wood stiffness and strength in juvenile Eucalyptus from short-rotation plantations