Removing fungal stain from ponderosa pine by caustic bleaching

The potential of peroxide-based bleaching systems for removing fungal stain was investigated on ponderosa pine sapwood. Image analysis of specimens before and after treatment indicated that the use of 2 percent hydrogen peroxide at 50? or 60?C for a minimum of 60 minutes appeared to produce significantly more improvement in whiteness of the test specimens than all other treatment combinations. The sodium hydroxide:sodium silicate ratio in the treatment solution, which acted as a buffer, could be manipulated between 0:12 and 1:6 with little effect on final specimen whiteness. The pH of the bleaching solution at higher NaOH:Na2SiO3 ratios exceeded 12, resulting in a considerable loss of peroxide and reduced bleaching efficiency. A preliminary analysis of the results suggests that peroxide bleaching could be an economical method for improving the grade of stained ponderosa pine sapwood. Further trials are recommended.

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