ANALYSIS OF THE CHANGES IN CHEMICAL PROPERTIES OF DISSOLVING PULP DURING THE BLEACHING PROCESS USING PIECEWISE LINEAR REGRESSION MODELS

摘要

Dissolving wood pulp is a chemically bleached wood pulp that has a cellulose content of more than 90%. Such pulp has certain properties of industrial value according to the products it can be used for. Raw pulp, which comes after acid bisulphite pulping, goes through a number of bleaching processing stages, each with a specific role, to produce dissolving pulp. These processing stages have different effects on the pulp depending on the type of wood genotype that is being processed. The bleaching processing stages are considered as time points for repeated measurements of the following chemical properties viz., viscosity, lignin, gamma-cellulose, alpha-cellulose, copper number, glucose and xylose. Piecewise regression models were used to compare the behaviour of the chemical properties of the seven genotypes throughout the bleaching processing stages. In order to cut costs on the chemicals used for processing, it is important to identify species/genotypes that have similar chemical properties under the chemical pulping process in order to mix them together for optimised processing. It was established that when trying to classify different timber species/genotypes for the purpose of finding which ones can be mixed together, viscosity is not an important variable to consider. The other variables viz., lignin, gamma-cellulose, alpha-cellulose, copper number, glucose and xylose should be used for classification as they were found to be important for that purpose. It is suggested that these properties can also be used in multivariate classification procedures.