BLEACHING WITH NEW REDUCTIVE CHEMICALS - REPLACEMENT OF HYDROSULFITE

We studied the bleaching potential of various highly selective reducer s, boranamines, on a spruce-fir high yield pulp. Our spectroscopic stu dy shows that boranamines selectively attacks lignin's aldehyde struct ures and greatly lowers the light absorption coefficient, thus increas ing brightness. Lignin's coniferaldehyde type chromophores are modifie d by boranamines in various chemical species that absorb light below 3 00 nm. It seems that aromatic ketones and quinones are so far unaffect ed. 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 hyd rogen 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 industr y.