Bleachability of kraft pulps treated by ethanol-based chlorine dioxide delignification sequences

Kraft pulps delignified with ethanol-based chlorine dioxide (D-0) stages yi elded pulps with higher brightness levels than aqueous D-0 stages. However, when these pulps were subjected to aqueous extraction (E) stage, the ethan ol D-0 pulps were more difficult to brighten with a second chlorine dioxide (D-1) stage than were aqueous D-0 pulps. The pulps from a combination of e thanol Do and acid ethanol extraction (A(E)) stages were also more difficul t to brighten than aqueous D0E pulps. An A(E) stage was less efficient and less selective at removing lignin than an aqueous caustic extraction. Appar ently, chromophores are developed in ethanol-based D-0 and A(E) stages that negatively impact D-1 bleachability.