Process factors affecting colloid stability and depositudformation in manufacture of newsprint from TMPudand recycled fibre

摘要

Formation of pitch and sticky deposits through the destabilisation of colloidal material present in paper manufactureudcontinues to be a challenge in improving machine efficiency in newsprint manufacture from a furnish comprisingudthermo-mechanical pulp (TMP) and recycled fibre (RCF), and in an environment where water usage efficiency is at bestudpractice. Findings from laboratory studies that have investigated colloid structure, impact of multiple and multi-valentudcations, pH, temperature, shear and dissolved organic matter on Pinus radiata extractive colloid stability have beenudused , along with observations of process conditions in Norske Skog’s Albury mill to determine which properties areudmost important in maintaining colloid stability.udDevelopments in our understanding of wood extractive colloid structure have led to an explanation as to why pitchuddeposition is more likely during summer months. A parameter called the “ester to acid ratio” has been shown toudexhibit both short and long-term trends when applied to process stream extractive levels. This greater propensity foruddeposition during summer months is exacerbated by elevated soluble calcium levels during summer time. Dissolvedudorganic wood polymers also affect colloid stability and their behaviour is further modified by the presence of solubleudcalcium. More stable colloids are obtained under conditions of neutral pH, avoidance of downward temperatureudshocks and avoidance of shear forces.