Studies on the Color of Sulphate Pulp (IV)

Abstract

The color of alkaline pulp is influenced by the time of pre-heating up to the maximum temperature of cooking. The time of pe-heating decreases, the color of pulp becomes deeper. The time of cooking at the maximum temperature increases, the main wave length of color of pulp increases, and the purity of color of pulp decreases. While cooking the brightness of pulp decreases at first, and then improved rapidly. If the time of cooking are equal, the color of soda pulp is always brighter than that of sulphate pulp. In a comparison of the two kinds of alkaline pulp whose lignin contents are equal, the above relation is no always in existence.
The dark color of alkaline pulps is mainly attributed to lignin, namely while cooking a part of lignin darkened is removed gradually. So the brightness of pulp may be influenced by the rates of removal of the lignin.