The purpose of this study was to develop practical and reliable small-angle x-ray scattering and x-ray diffraction methods to study the nanostructure of the wood cell wall and to use these methods to systematically study the nanostructure of Acacia mangium wood grown in Sabah, Malaysia. Methods to determine the microfibril angle (MFA) distribution, the crystallinity of wood, and the average size of cellulose crystallites were developed and these parameters were determined as a function of the tree age and the distance from pith towards the bark. The mean MFA in Acacia mangium increases rapidly as a function of the number of the year and after the 7th year-old it varies between 6° and 10°. The thickness of cellulose crystallites for Acacia mangium appears to be constant as a function of the tree age after 10-year-old. The obtained mean value is 3.20 nm. The size of the cellulose crystallites was also quite constant after 11 year-old. The maximum value of the width of the crystallites for Acacia mangium was 2.34 nm at the pith region, while the minimum value was 0.290 nm at the bark region. The mass fraction of crystalline cellulose in wood is the crystallinity of wood and the intrinsic crystallinity of cellulose. The crystallinity of wood increases from the 3nd year-old to the 10th year-old from the pith and is constant after the 10th year.

Partially crystalline cellulose microfibrils are wound helically around the longitudinal axis of the wood cell. A method is presented for the measurement, using small-angle X-ray scattering (SAXS), of the microfibril angle, (MFA) and the associated standard deviation for the cellulose microfibrils in the S2 layer of the cell walls of Acacia mangium wood. The length and orientation of the microfibrils of the cell walls in the irradiated volume of the thin samples are measured using SAXS and scanning electron microscope, (SEM). The undetermined parameters in the analysis are the MFA, (M) and the standard deviation (σФ) of the intensity distribution arising from the wandering of the fibril orientation about the mean value. Nine separate pairs of values are determined for nine different values of the angle of the incidence of the X-ray beam relative to the normal to the radial direction in the sample. The results show good agreement. The curve distribution of scattered intensity for the real cell wall structure is compared with that calculated with that assembly of rectangular cells with the same ratio of transverse to radial cell wall length. It is demonstrated that for β = 45°, the peaks in the curve intensity distribution for the real and the rectangular cells coincide. If this peak position is Ф45, Then the MFA can be determined from the relation M = tan-1 (tan Ф45 / cos 45°), which is precise for rectangular cells.

The term microfibril angle (MFA) in wood refers to the angle between the spiralling cellulose fibrils and the long axis of the tracheid cell wall. Diffraction patterns arising from crystal planes of various sample forms of wood trees had attracted scientific research in determining the crystallographic measurements. As such the tropical hard wood in Sabah, Acacia mangium was chosen for experimental data. Age-contributing factors were measured; the angle of reflection (θ), relative intensity, full width at half maximum (FWHM), the nearest between two neighbouring atoms in the crystalline structure (d-spacing) and the peak height, had been taken into account at different ages, pith and bark of tree. Regressions were done in comparing the microfibril angle, MFA at different ages using the least-square method and cubic-spline interpolation. The latter was able to interpolate a polynomial up to the third order. The range of the optimum angle was found to have benefited foresters in deciding the time for tree cropping and harvesting.