This time we took shavings as thin as 200 micron from Ezomatsu (a kind of spruce in Hokkaido, Japan) and cooked them through prehydrolysis sulphate process. We measured the amount of removed lignin, pentosan and cellulose. Each amount was contrasted with the result of sulphate or sulphite. cooking.
Through water-prehydrolysis (2 hrs. at 160°C), the wood-hcmieellulose like pentosan was selectively hydrolysed and extracted partly, while cellulose and lignin remained unchanged. The dissolving rate of pentosan through prehydrolysis sulphate cooking is similar to the rate in case of sulphite process.
The content of alpha-cellulose in pulp reaches the highest (96.74 %) at a certain period of alkaline digestion when the lignin in the wood has not yet been removed enough for the wood-fibres to be easily separated each other. If we are to avoid over-cooking and excessive degradation of cellulose, it is required to adjust the rate of removal of lignin with that of hemicellulose.
The above fact leads us to the conclusion that higher yield or better quality of prehydrolscd sulphate pulp will be obtained by finding the way to remove the part of lignin in the wood chips during prehydrolysis or to accelerate further the removal of lignin during sulphate cooking.