Formation of resin acids during thermomechanical pulping

A series of chip, pulp and process water samples from various stages of a thermo-mechanical pulping process have been collected and analysed, and the mass balance of total resin acids produced during the process calculated. The result showed that most of the resin acids are solubilised in the first refiner stage of a two-stage TMP process. The mass balance shows a remarkable loss of resin acids during pulping and this is believed to be due to chemi-mechanical degradation or loss as volatiles with steam (which was not included in the mass balance). The distribution of individual resin acids in the wood, pulp and process water from various stages of the TMP process indicated that pimaric type resin acids were more chemically and biologically stable than abietic type resin acids and dehydroabietic acid. The level of resin acids in the aqueous phase was higher than the solubility of the acids and suggests that they are present in a partly colloidal dispersed form.