Bleaching of softwood kraft pulps using an ethanol-based partial sequence

Previous findings showed that acid ethanol extraction (A(E)) can remove residual lignin from a chlorine dioxide (D-0) treated kraft pulp. Preliminary tests indicated that an ethanol-based (DA(E)) partial sequence using the D-0 effluent as the A(E) medium generally afforded pulps with lower residual lignin and higher brightness levels than the DA(E) sequence. However, A(E) was less efficient and selective at removing lignin than aqueous caustic extraction (E). (DA(E)) pulps were more difficult to brighten with an aqueous D-1-stage than aqueous DE pulps. Apparently, the (DA(E)) sequence changes the residual lignin character in a way that negatively impacts D-1 bleachability.