Application of X-ray diffraction to assess the microfibril angle of green and dry Eucalyptus grandis wood

Key message X-ray diffraction allows indirect measurement of the microfibril angle (MFA) in green and dry wood, revealing that there are statistical differences between the MFAs of these woods. Wood drying is essential for most wood uses; however, the removal of water from wood can lead to defects. Although it is consolidated that water removal to below the fibers saturation point causes a decrease in the distance between cellulose microfibrils, little is known about how the microfibril angle (MFA) behaves in dry wood in terms of the cell wall ultrastructure. The hypothesis investigated in this study is that with the reduced distance between cellulose microfibrils after drying, there is a simultaneous decrease in MFA. Therefore, the objective of the work was to estimate the microfibril angle of dry and green wood using X-ray diffraction (XRD) and then to compare the MFA of the wood in both conditions mentioned. The basal discs from stems of Eucalyptus grandis with age of 22 years were used to produce the samples used in the measurement of MFA by polarized light microscopy and of the T value by XRD. The mean MFA measured by polarized light microscopy was 7.0 degrees. MFA could be estimated by T value obtained from XRD using the cubic model. The mean MFA estimated by this model was 9.0 degrees for green wood and 7.5 degrees for dry wood, concluding that the MFA in dry wood is slightly lower than in green wood.