Studies on the Color of Sulphate Pulp (I)

Abstract

In order to investigate the color of pulp caused by the sulphate cooking, following experiments were carried out.Three kinds of samples varried extremely in the content of cellulose, hemicellulose and lignin namely groundwood, holocellulose and bleached sulphite pulp were cooked with the liquors of various sulphidities, and the colors developed on these samples were compared by means ofI.C.I.system.(1) Irrespective of the sulphidity of cooking liquor, increase of the cooking time caused increase of the dominant wave length and the purity of pulp, and caused decrease of the brightness of pulp.The rates of increase of the dominant wave length on the three samples were as follows : Sulphate pulp<Holocellulose<Groundwood.The rates of increase of the purity and of decrease of the brightness were also in the same order.In the case of groundwood, rich in lignin, the purity curve plotted for the cooking time had a maximum point which could not he recognized in the case of the other samples.(2) From the results it may be concluded that lignin and hemicellulose, especially the former, play an important role in colouring of alkaline pulps.(3) The soda pulps and the sulphate pulps, prepared by the cookings in which the cooking conditions were controled as the same as possible except the sulphidity of cooking liquor, contained almost equal amount of pentosan, and less lignin was found in the sulphate pulps. Against the expection from the comparison of composition of the two kinds of pulp, the sulphate pulps apparently gave longer wave length and lower brightness.Therefore it is considered that the deep color of the sulphate pulp is partly due to the sulphur combined with lignin of pulp.