Recycling of Colored Office Paper. Part I: Pre-bleaching with Formamidine Sulfinic Acid at Pulper

The possible use of formamidine sulfinic acid (FAS) for pre-bleaching of colored office paper in the stage of pulping was investigated. In addition, the effects of FAS pre-bleaching on different colors were examined. Colored office papers were mixed with white office paper at a 1:4 ratio. FAS was added as 0.25%, 0.50%, 0.75%, 1.00%, and 2.00% into the pulper. Reduction ability of colors with FAS were determined as yellow, red, green, and blue according to L*, a*, b*, ΔE, and reflectance spectrum at 220 nm to 900 nm wavelength. In other words, it was determined that FAS succeeded on the yellow, red, and green colored waste paper, but it failed on the blue colored waste paper at 10 minute pre-bleaching conditions. On the other hand, in mixed colored waste paper, which can better represent industrial applications, the color difference (ΔE) were calculated as 32.0 with 1% FAS pre-bleaching. This result is successful for pre-bleaching, which is an auxiliary process during re-pulping of waste paper.