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.