The investigation upon the degradation of wood carbohydrates during the latter part of commercial bisulfite cooking was carried out by using the holocellulose prepared from red pine (Pinus densiflora) by a subsequent process: namely very mild bisulfite cooking, further defibrating and finally delignifying by repeated treatment with NaClO
2.
Thus prepared holocellulose was further hydrolyzed in Ca-bisulfite-sulfurous acid solution (bisulfite cooking liquor: total SO
2 5.7% and combined SO
2 1.5%), at max. temp. 140°C, changing the reaction time.
With these treated samples, the chemical analysis was carried out and the leveling off DP was determined by such modification of Maeda's method as each sample was hydrolyzed in 3 N-HCI, CH
3OH solution and also the swelling state of these samples in 79% phosphoric acid was observed by the same method described in Part VIII. The pH-value of reaction liquor at elevated temperature was determined by Rydholm's method. The results were as follows:
1. The hydrolysis reaction rate in pure Ca-bisulfite-sulfurous acid solution seemed to be relatively slow, however in the progress of the reaction, SO
2 was consumed despite of absence of lignin, further the acidity of reaction liquor increased by forming sugar sulfonic acid or sulfuric acid without lignosulfonic acid, consequently the degradation of carbohydrates was accelerated autocatalytically.
2. The leveling off DP of samples decreased with the progress of hydrolysis in proportion to their original DP, therefrom it was suggested that acid hydrolysis at such high temperature and high pressure influenced upon the fine structure of wood cellulose.
3. The swelling state of samples in phosphoric acid was improved more remarkably at the latter part of hydrolysis reaction than in usual sulfite cooked pulp having same average DP. This result seemed to be due to uniform contact of fibers with the reaction liquor, starting from defibrated holocellulose.
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