SOFTWOOD DELIGNIFICATION BY MSS-AQ IN ONE AND 2 STAGES - PULP CHARACTERISTICS

The rate of delignification of maritime pine by sodium sulphide and su lphite solutions with anthraquinone reaches a maximum at a sulphidity of 10 to 15%, The pulps are obtained in yields 6 to 10% greater than k raft pulps at the same kappa indexes. They have equivalent strength pr operties except for tear strength, which is inferior by 10%. This rema rkable result is linked to the properties of sodium sulphite. In addit ion to lignin sulphonation, an excess of sulphite ions in the cooking liquor makes the tracheids more flexible via solvation of cell wall ca rbohydrates and much more amenable to fibrillation during beating. The removal of some mannans during the second stage of the treatment (by alkaline pulping or enzymatic hydrolysis) again increases the flexibil ity of tracheids, giving pulps with better properties than kraft pulps at the same yield.