Formation of resin acids during thermomechanical pulping

A series of chip, pulp and process water samples from various stages of a t hermo-mechanical pulping process have been collected and analysed, and the mass balance of total resin acids produced during the process calculated. T he 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 remarkab le loss of resin acids during pulping and this is believed to be due to che mi-mechanical degradation or loss as volatiles with steam (which was not in cluded in the mass balance). The distribution of individual resin acids in the wood, pulp and process wa ter from various stages of the TMP process indicated that pimaric type resi n acids were more chemically and biologically stable than abietic type resi n acids and dehydroabietic acid. The level of resin acids in the aqueous ph ase was higher than the solubility of the acids and suggests that they are present in a partly colloidal dispersed form.