Bleaching with new reductive chemicals: Replacement of hydrosulphite

We studied the bleaching potential of various highly selective reducers, boranamines, on a spruce-fir high yield pulp. Our spectroscopic study shows that boranamines selectively attacks lignin's aldehyde structures and greatly lowers the light absorption coefficient, thus increasing brightness. Lignin's coniferaldehyde type chromophores are modified by boranamines in various chemical species that absorb light below 300 nm. It seems that aromatic ketones and quinones are so far unaffected. Boranamines can be used between pH 4 to 10, but are most effective at acidic pH. They can also be used in multi-stage bleaching with hydrogen peroxide. An ISO brightness as high as 76% was observed. Even if the cost of boranamines is actually very high, an increase in the use of these chemicals will undoubtedly lower the prices. Boranamines are more effective than sodium borohydride, and even sodium hydrosulphite, the most widely used reducing chemical in the pulp and paper industry.