The term microfibril angle, MFA in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall, S2 layer of fibres and tracheids and the long axis of the cell. In this study, the mean MFA of the cell walls were determined for thin samples of thickness 200.0 µm from pith and outwards, for eight ages of Acacia mangium wood. The determination of MFA was based on a diffraction pattern arising from cellulose crystal planes of the type 002 generated by x-ray diffraction and recorded using an electronic detector. The results show an inversely relationship between MFA and age of tree in Acacia mangium wood. MFA decreased from 26.13° at age 3 year-old to 0.20° at tree of age 15 year-old for the pith region. The most significant drop occurred from 16.14° at age 7 yearold to 11.30° at age 9 year-old. An inversely relationship between MFA and storage modulus E’ was evidence in Acacia mangium at age 10-year-old. The results showed that about 76.22% variation of loss modulus E” was attributed to the MFA, while about 66.4% of the variation of glass transition Tg was explained by MFA under the same experimental conditions.
Pontamine fast scarlet 4B is a red paper and textiles dye that has recently been introduced as a fluorescent probe for plant cell walls. Pontamine exhibits bifluorescence, or fluorescence dependent on the polarization of the excitation light: Because cellulose is aligned within the cell wall, pontamine-labelled cell walls exhibit variable fluorescence as the excitation polarization is modulated. Thus, bifluorescence measurements require polarized excitation that can be directly or indirectly modulated. In our confocal microscopy observations of various cellulose samples labelled with pontamine, we modulated excitation polarization either through sample rotation or by the confocal's scanfield rotation function. This variably rotated laser polarizations on Leica confocal microscopes, but not those from other makers. Beginning with samples with directly observable microfibril orientations, such as purified bacterial cellulose, the velamen of orchid roots and the inner S2 layer of radiata pine compression wood, we demonstrate that modelling the variations in pontamine fluorescence with a sine curve can be used to measure the known microfibril angles. We then measured average local microfibril angles in radiata pine samples, and showed similar microfibril angles in compression and normal (opposite) wood. Significantly, bifluorescence measurements might also be used to understand the degree of local cellulose alignment within the cell wall, as opposed to variations in the overall cellulose angle.
Small-angle X-ray scattering (SAXS) was used to investigate the nanostructure of the microfibrils of cell wall in Acacia Mangium wood. Parameters, such as the fibre length (L), surface area of the single fibre (S), the correspondence distance from the center of the fibre to the center of its neighbor and the shape of the fibre were determined as a function to the distance from pith towards the bark. The results indicate that the fibre length ranged from 53.44 nm to 13.72 nm from pith to bark. Surface area of the single fibre varied from 0.65 nm 2 to 4.36 nm 2 , the highest being found at the end of bark region. The mean value of the correspondence distance is 13.95 nm. Surface structure analysis from scattering graph showed a rod shape of fibre in the pith region of Acacia Mangium wood. The use of SAXS technique and scanning electron microscope (SEM) micrographs gives the most reliable dimensions values.