REVIEW: Colloidal stability and removal of extractives from process water in thermomechanical pulping

This paper reviews the literature on the colloidal stability of wood extractives and evaluates different processes used to remove the colloidal wood extractives from thermomechanical pulping (TMP) process water. The mechanisms giving rise to colloidal stability of wood extractives present in process water are briefly reviewed. Different analytical methods to study the colloidal stability of extractives are described. The problems caused by wood extractives (pitch) during the TMP process are discussed in relation to their colloidal stability. Mechanical pulping pre-treatment and impregnation technology are discussed in relation to reduction of the amount of extractives from the wood chips as early as possible in the beginning of the TMP process, in order to reduce their detrimental effects.