A Mechanistic Approach to Crystallite Length as Related to Cell-Wall Structure

A tentative mechanistic model is proposed that relates variation in crystallite length in wood to some physical conditions under which the crystallite may have been formed, namely the curvature and ultrastructure of the microfibril. Over most of the experimental data range, representing both hardwood and softwood samples, the model allows reasonably good prediction of the effect of crystallite orientation angle and radial distance from the cell center. As the angle increases and radial distance decreases, the average crystallite length becomes smaller

Mathematical Description of the Change in Properties of Casuarina Wood Upon Exposure to Gamma Radiation. 1. Changes in the Compressive and Tensile Strength

Casuarina cunninghamiana specimens were exposed to gamma-radiation doses ranging from 104 to 108 rad and tested in compression and tension parallel to grain. The percentage values of the irradiated specimens relative to that of the matched control (Y) were determined. The relationship between (Y) and log gamma radiation dose (X) was represented mathematically by the equation: Y = aXbcx. This equation described the change in compressive and tensile strength very well as was detected from the high correlation coefficients. Generally these properties increased slightly at low levels of radiation, reached a maximum, then decreased gradually thereafter. The reduction in tensile strength was more pronounced than in compressive strength.The threshold dose, i.e., the dose beyond which the properties began to decrease, was calculated. This dose ranged from 3.69 x 106 to 3.76 x 106 rad for compressive strength properties and from 1.51 x 106 to 1.70 x 106 rad for tensile strength properties. This indicated that irradiated casuarina wood had a greater resistance to compression than to tension

Short-Term Creep as Related To Microfibril Angle

Relationship between creep response and microfibril angle within the S2 layer of some coniferous wood tissues was examined. Constant loads corresponding to predetermined initial strain levels of 3,000 μinches/inch (A) and 6,000 μinches/inch (B) were applied to small wood strips. Microfibril angle was measured by the mercury impregnation method.A positive linear relationship was found between microfibril angle and total creep (r = 0.82 and 0.83 for samples tested at constant loads corresponding to strain levels (A) and (B), respectively). A phenomenological approach is presented to explain the role of microfibril angle of the S2 layer in controlling creep response. Total creep was also found to be positively correlated with magnitude of applied load corresponding to a given deformation

A Direct X-Ray Technique for Measuring Microfibril Angle

A texture goniometer was utilized for measuring the azimuthal intensity distribution of the (040) meridional diffraction from some coniferous wood tissues. A computerized iterative fitting method was used to generate mathematically the experimental diffraction curve and to resolve the (040) diffraction pattern from the composite profile. The mean microfibril angle was then estimated from the shape of the resolved (040) profile.The technique developed herein is a direct and simple method for determining the mean microfibril angle with a generally satisfactory level of precision. In addition, the technique is applicable to material with a wide range of microfibril angles