Elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching of colored broke

Six different colored broke samples were bleached by elemental chlorine-free (ECF) and totally chlorine-free (TCF) bleaching processes. Colored broke samples were bleached either individually or in blends, or mixed with brownstock. CIE's L*a*b* numbers were used to rank the efficiency of various bleaching processes. Single-stage TCF bleaching with hydrogen peroxide, ozone, or formamidine sulfinic acid (FAS) did not provide bright pulp suitable for use in premium-grade papers, such as those for laser printers. Chlorine dioxide is the most efficient chemical in bleaching colored broke and their blends, as is hypochlorite. Single-stage bleaching of broke in may instances provided a lightness (L*) value of 90.0 but failed to meet the ''chroma'' specification of root a(*2) + b(*2) less than or equal to 10.0 that is important to use them in high-grade papers. Multistage bleaching of colored broke, broke blends, and broke blends mixed with brownstock resulted in pulps with a brightness of greater than or equal to 85% ISO, a lightness of greater than or equal to 90.0, and a chromacity of root a(*2) + b(*2) less than or equal to 10.0. These pulps are suitable for use in white, near-white, and color paper grades. Gold- enrod-, cherry-, and pink- colored broke are difficult to bleach, while blue- and green-colored broke were bleached easily either individually or blended among themselves or with brownstock.