COMPRESSION-ROLLING REDUCES KILN BROWN STAIN IN RADIATA PINE SAPWOOD

Kiln-drying of radiata pine sapwood often causes the formation of a br own discoloration, commonly called kiln brown stain. Kiln brown stain develops just under the wood surface in a thin layer but subsequent ma chining of the lumber exposes the stain. The occurrence of kiln brown stain has caused substantial loss in revenue in New Zealand's high-val ue radiata pine export markets. In this study, the effect of compressi on-rolling of radiata pine prior to kilning was investigated as a pote ntial method to control the formation of kiln brown stain, along with its effect on thickness shrinkage and drying time. The results of the study demonstrated that regardless of kiln schedule, compression-rolli ng significantly reduced the formation of kiln brown stain in the kiln ing of radiata pine, but increased drying time. In the drying of radia ta pine at 90/60 degrees C, rather than at 71/60 degrees C, compressio n-rolling significantly increased thickness shrinkage from 4.9 to 6.0 percent. The mechanisms of compression-rolling on kiln brown stain for mation in the drying of radiata pine are discussed.