Tamer A. Tabet

Cellulose Microfibril Angle in Wood and Its Dynamic Mechanical Significance

The orientation of the cellulose microfibrils in the S2 layers of the cell walls of softwood has a significant influence on the mechanical properties of wood. The angle between the cellulose fibrils and the longitudinal cell axis, the microfibril angle, MFA was found to be a critical factor in determining the physical and mechanical properties of wood (Cave, 1997). For this reason, considerable effort has been directed towards the measurement of the cellulose MFA. Direct measurement of MFA has been made by highlighting microfibrils in individual cell walls with iodine staining, but the most widely adopted techniques use either wideangle X-ray diffraction or small-angle X-ray scattering The pioneering work of Cave (1966) and Meylan (1967) led to the use of the ‘T’ parameter derived from the curve distribution of the intensity diffracted by the (002) planes of the cellulose fibrils.

Regression models on the age-affecting and microfibril angle of Acacia mangium

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.

Modeling Microfibril Angle and Tree Age in Acacia Mangium Wood Using X-Ray Diffraction Technique

 Abstract—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. Acacia mangium classified as a hardwood 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.

Simulation of temperature dependent characterization of charge transport in organic transistor

In this paper, we present a simulation work in organic transistors using technology computer-aided design (TCAD) Sentaurus tool. A pentacene as an active semiconductor layer is used to simulate and design a top contact structure of p-channel organic transistor. The electrical characterization on these devices was investigated at temperature (T) ranging from 70 to 300 K to estimate the effects of Meyer-Neldel rule (MNR) for charge transport mobility (μ_MN). In the linear region of output characteristics for T = 70, 100, 140, 180, 220, 260 and 300 K, simulation showed maximum drain current (I_ds) for temperature of 70 K is 0.394 μA and for 300 K is 3.54 μA. The transfer characteristics exhibit threshold voltage values ranging from 18.3 to 24.6 V at 70 K to 300 K range, using IEEE1620 Standard. Then, the MNR model reveals low E_a has high μ_mn of 0.0093 cm² V¹ s^-1 at T_MN = 208 K, while higher E_a values of 63.8 meV has lower μ_MN = 0.0034 cm² V¹ s^-1, which shows an inverse relationship between E_a and μ_MN.