Colloidal stability of Pinus radiata wood extractives Part 1: Effect of extractives composition and process variables

This paper presents the results of a study undertaken to investigate the interaction between the various key factors that have been identified to affect wood extractive colloid stability and pitch deposition of wood extractives released in thermomechanical pulp of Pinus radiata. These key factors are temperature, soluble calcium, pH, dissolved carbohydrates and wood extractive concentration and composition. Very little work has been undertaken to study the effect of composition and seasonal changes in Pinus radiata wood extractives on their colloidal stability and pitch deposition. Two different compositions of the wood extractives, representing the maximum and minimum in ester to acid ratio (EAR) that occur during the summer and winter periods, were investigated. The EAR of the extracts was found to significantly affect the wood extract colloidal properties. Low EAR (EAR = 0.31) extracts, typical of the summer period, were found to be more unstable and more susceptible to deposition and destabilisation by soluble calcium than higher EAR (EAR = 0.66) extracts, typical of the winter period. Complex interactions between the various process variables were found. In particular, the dissolved organic matter (DOM) level was found to cause both stabilisation and destabilisation depending on the concentration and the pH. This was more apparent in the higher EAR extract.