Preparation of Dissolving Pulp by Totally Chlorine-free Bleaching：Roles of Hardwood Syringyl and Guaiacyl Lignins

Abstract

Dissolving pulp was produced from four diff erent hardwoods by prehydrolysis-kraft cooking and totally chlorine-free (TCF) bleaching using oxygen (O) ，peroxymonosulfuric acid (P sa) ，and alkali extraction with hydrogen peroxide (E p) in an O-P sa-E p-P sa-E p sequence. The hardwood lignin structures were characterized by the nitrobenzene oxidation method, which provided syringaldehyde (S a) to vanillin (V a) molar ratios (S/ V ratios) of the lignin. Eucalyptus globulus wood had the highest S/V ratio of 5.81 and a combined yield of S a and V a of 3.04 mmol/g-lignin, while the Acacia hybrid wood exhibited the lowest S/V ratio and the combined yield. The E. globulus wood provided a fi nal pulp with an acceptable level of viscosity 7.0 mPa•s, a weight-average molecular weight (M w) 3.04 × 10 5 g/mol, a number-average molecular weight (M n) 5.56 × 10 4 g/mol, polydispersity (M w /M n) 5.47, a high brightness of 90.1% ISO, and an α-cellulose content of 94.2%. It is attributed to the high S/V ratio and the high combined S a and V a yield, which is suggestive of a less-condensed lignin structure compared to the other hardwoods tested. No signifi cant diff erences in the cellulose crystallinities of the bleached pulp produced from the four hardwoods were observed.

Effects of Soluble Anthraquinone Application on Prehydrolysis Soda Cooking of Acacia crassicarpa Wood

“…The results of chemical analysis indicated that A. crassicarpa wood consists of 41.1％ glucan, 10.9％ xylan, 31.5％ lignin, and 2.1％ acetone extractives (Table 1) . Compared with the contents of lignin and extractives for Eucalyptus globulus wood (27.6％ and 0.6％, respectively) as stated in a previous report 20) , these were high, and nitrobenzene oxidation of A. crassicarpa wood showed that the lignin had a less syringyl and non-condensed structure. In addition, the xylan to glucan ratio of A. crassicarpa was lower than that of E. globulus (0.265 and 0.310, respectively) , and that is an advantage for dissolving pulp materials.…”

“…There was a tendency of increasing brightness based on increasing AA dosage for cooking (A) for all processes, and the soda cooking showed higher brightness than kraft cooking, except for one point of AA 20％ without SAQ because of high kappa number (23.6) . When brightness was compared at the given kappa number (16)(17)(18)(19)(20) , soda cooking indicated higher brightness (3.8-3.9 points) than the kraft process (B) . A recent study on radiata pine 1) reported that the prehydrolysis process also made cellulose strength vulnerable, but significantly increased the brightness of the pulp.…”