Residual Lignosulfonic Acid in the Unbleached Deciduous Sulfite Pulp
On the Mechanism of Pulp Bleaching VII
1962 Volume 16 Issue 2 Pages 109-113
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1962 Volume 16 Issue 2 Pages 109-113
In this series of the investigations on the residual lignin in unbleached sulfite pulp only that in soft wood unbleached sulfite pulp was investigated until now.
In the previous paper (Part II), it was shown that the residual lignosulfonic acid in unbleached sulfite pulp (RLS) was dissolved by intensive beating, although more than half of the total amount of the residual lignosulfonic acid in the pulp remained undissolved by this treatment. This isolated RLS has almost half as much sulfonic acid group as the ordinary lignosulfonic acid (LSA) and has no chemical bond with carbohydrate.
In part IV, it was shown that this residual lignosulfonic acid remaining in the beaten pulp could be dissolved further by dimethylsulfoxide (DMSO), and the non-existence of chemical bond between this lignin and carbohydrate was also confirmed.
The RLS obtained by the above mentioned process has a smaller diffusion coefficient i. e. higher molecular weight than LSA.
It was thus concluded that the reasons for the difficulty of the dissolution of RLS from the unbleached sulfite pulp lie in too high molecular weight of the RLS to diffuse out from the fiber cell wall.
It is the problem of the present paper to investigate the residual lignosulfonic acid in “ deciduous ”unbleached sulfite pulp.
Birch unbleached sulfite pulp was beaten in water, and the residual lignosulfonic acid (BRLS) dissolved was isolated pure in a form of barium salt, yield of the BRLS being 24% of the total amount in birch unbleached sulfite pulp.
The BRLS thus obtained has sulfonic acid group only 0.18 per C9unit, and the content of the phenolic hydroxyl group was low, being 0.10.08 per C9unit. The amount of phenolic hydroxyl group of BRLS was nearly half of the ordinary birch lignosulfonic acid obtained from sulfite waste liquor, and has very large amount of type II phenolic hydroxyl group, the ratio of type I and type II phenolic hydroxyl groups being 1 : 1 in BLSA and 1 : 3 in RLS.
When beaten pulp was extracted with absolute dimethyl-sulfoxide, a DMSO extract consisting 11% of lignin and 50% of carbohydrate was obtained. From the results of the paper electrophoresis of DMSO extract, it was concluded that almost no chemical bond exists between these two components.
The diffusion coefficients of BRLS and BLSA measured by McCarthy's method are 12.8 and 16.2mm2/day respectively. It was thus confirmed that the molecular weight of BRLS is higher than that of BLSA.
The amount of BRLS dissolved by beating is 2530%and the same extracted with DMSO is 811%, showing that about 40% of BRLS is isolatable by beating and by DMSO extraction.
Thus, we may say, just as in the case of softwood, the BRLS thus obtained has smaller amount of sulfonic acid group, higher molecular weight, no chemical bond with carbohydrate and about a half of the total amount of BRLS could be dissolved from the fibrillated fiber by intensive beating in water followed by DAISO extraction.
It has thus fully confirmed again in the case of deciduous sulfite unbleached pulp that the residual ligno-sulfonic acid remained undissolved because of the too high molecular size of the acid to diffuse out from the fiber cell wall structure.
