摘要：

The processing of wood particle, fiber, and flake products by pressing of a felted mat generally results in a density gradient from one surface of the product to the other. Measurement of density gradients through the thickness of a pressed wood product has traditionally been performed through calculation of volume and weight changes of specimens which are incrementally planed on each surface. This technique is time con-suming, has limited resolution, and destroys the speci-men. The primary objective of this study was to develop and test a simple and fast method of determining ma-terial density gradients to replace the tedious planing (or sanding), weighing, and thickness measurement technique. Density gradients were determined by in-crementally measuring the amount of radiation (from an Americium 241 source) which passed through a sample. The influence of adhesives and moisture on the radiation attenuation was investigated, as well as defi-nition of the mass attenuation coefficient for cellulosic materials. The primary objective of this work was to assemble and test a gamma radiation-based density gradient measurement system to replace the accepted gravi-metric method of obtaining density gradients from re-constituted products. Modeled after the radiation-based system described by Ranta and May (6), the gamma radiation technique provides a nondestructive means of measuring density gradients for researchers and manu-facturers of wood composite materials. A survey of methods for determining density gradi-ents is presented, followed by a discussion of the theory and equipment required when using a gamma radiation source. Tests of the system are detailed to determine the mass attenuation coefficients needed to obtain densities of reconstituted products, and to investigate the system inaccuracies caused by the resin and moisture in these products.

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