A study has been carried out to determine the influence of chemical pretreatments on the physical properties of chemithermomechanical pulps (CTMP) made from hardwood chips which were chemically treated with sulfite liquors at the range from pH 1.8 to 13.0.
Of the chemical pretreatments investigated, neutral sulfite (pH 9.8) and bisulfite (pH 4.1) appeared to offer the greatest potential for strength development to produce CTMP from hardwood chips. Alkaline sulfite (pH 13.0) and acid sulfite (1.8) treatment, on the other hand, have little effect on the strength properties of CTMP.
As far as energy requierment is concerned, pretreatment with sulfite liquor at low pH (4.11.8) leads to a substantial reduction in refining energy. However, there are distinct differences in the long fiber contents between acid sulfite CTMP and bisulfite CTMP. In the case of acid sulfite-and bisulfite-pretreatments, The strength properties of CTMP from birch wood were higher than those of CTMP from oak wood.
The ultraviolet microscope was used to follow the delignification visually during acid sulfite-and bisulfite-pretreatment of birch wood. When the birch wood was delignified with bisulfite, the topochemical effect was not detected, while topochemical preference for the removal of lignin from the secondary wall was found in the case of acid sulfite-pretreatment.
Furthermore, it was found that total pore volume and median pore width of cell wall treated with bisulfite was larger than that of cell wall treated with acid sulfite.
