A new method of determining moisture gradient in wood

Moisture gradient in wood and wood composites is one of most important factors that affects both physical stability and mechanical performance. This paper describes a method for measuring moisture gradient in lumber and engineering wood composites as it varies across material thickness. This innovative method employs a collimated radiation beam (x rays or gamma rays) emitted from a radiation source that discretely scans the material in steps or continuously through its thickness direction. A radiation detector on the other side detects intensities of the transmitted beam, which directly relates to the material density profile through scanning direction. Moisture gradient can be calculated by contrasting it to the ovendried density profile. A series of solid wood samples were tested to verify the accuracy of this technique. The estimated moisture content (MC) gradients measured using the radiation method were compared with the actually measured MC gradients using the ovendry method of microtomed sections. The high correlation between the two MC gradient methods proved that the radiation method could provide an accurate and prompt estimation of internal wood MC gradient.