Advances in steam explosion pulping

The effect of different forms of chemical pretreatment on steam explosion p ulping was studied. Pretreated aspen chips were cooked at 190 degrees with saturated steam for 4 min. and subsequently refined in the laboratory. The chemical systems used were Na2SO3 (8%) alone or with 1% NaOH, 1% MgCl2, 1% NaHCO3 or 1% MgCO3. The presence of NaOH or NaACO(3) or MgCO3, in compariso n to Na2SO3 alone, leads to a strength increase as well as to a drop in the relative specific refining energy. The enhanced strength, when NaHCO3, NaO H or MgCO3 is used, is correlated to the higher ionic content of resulting pulps and the higher oxygen/carbon ratio on fiber surface, as confirmed by ESCA analysis. A study of the effect of high temperature during steam explosion pulping (S EP) of sulfonated aspen chips on the fundamental physico-chemical changes o f fibers was also carried out. The following changes have been evaluated: c rystallinity using X-ray diffractometry; phase structure by FTIR and Raman Spectroscopy; physicochemical changes by CP-MAS C-13 NMR and IR; surface ch emical composition with ESCA. Physico-chemical changes due to temperature v arying from 190 to 200 degrees were compared to those found hi CTMP (128 de grees and CMP (150 to 170 degrees). The better bonding of SEP is explained by lower percentage of lignin on fiber surface, by a higher sulfonation lev el of surface lignin, lower percentage of disordered cellulose ii and highe r percentage of ordered cellulose I.