Pulping Variables, Storage Time and Pitch Deposit

Abstract

The effects of pulping variable, wood classification and storage time on pitch deposition during kraft pulping of mixed tropical hardwood species growing in Nigeria were investigated. Storage time has effect on pitch deposition in all the groups. Pulp resin decreased from 0.535% in control experiment to 0.235% after the sixth month in group A. In group B, pulp resin decreased from 0.560% for the control experiment to 0.243% after the sixth month while in group C, pulp resin decreased from 0.529% to 0.277% after the sixth month. Pulp resin is also influenced by effective alkali concentration of the pulping medium. With increase in effective alkali concentration from 13% to 15%, pulp pitch is reduced. The interaction effect of storage and effective alkali concentration was not significant indicating that reduction in pulp pitch caused by effective alkali concentration in the different group occurs at about the same rate. However, interaction effect of maximum temperature and effective alkali concentration was significant. This occurs as the combination of high temperature and high effective alkali concentration causes saponification of triglycerides and esters of wood resin to fatty acids which tend to form liquid crystals. On cooling the cook below 100oC during washing, the crystals form micelles which dispersed and which are washed out of the pulp.

Keywords: resin, effective alkali concentration, storage, hardwoods, pulping.