Use of sodium dithionite for controlling kiln brown stain development in radiata pine sapwood

Kiln brown stain develops during the drying of radiata pine sapwood due to translocation and accumulation of water-soluble sugar and nitrogen containing compounds to near the wood surface, where they react to form a chocolate-brown sub-surface stain. In the current study, methods were investigated for improving treatability and penetration of freshly sawn radiata pine with sodium dithionite to control kiln brown stain. Kiln brown stain development was reduced but not entirely eliminated in treated radiata pine. Chemical analysis of treated radiata pine indicated that either chemical uptake of sodium dithionite was too low for in situ inhibition of kiln brown stain precursors or conditions prevailing during or prior to chemical treatment induced irreversible changes that led to kiln brown stain during subsequent drying. Furthermore, pre-steaming changed the drying characteristics, which resulted in longer drying times compared with untreated radiata pine. It is concluded that development of an industrial process using sodium dithionite for control of kiln brown stain is unlikely to be practical because of the inherent difficulty in achieving sufficient penetration of radiata pine sapwood.

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