RELEASE OF POTENTIAL ANIONIC TRASH IN PEROXIDE BLEACHING OF MECHANICAL PULP

The release of anionic carbohydrates, potentially detrimental to paper making, was studied by analyzing suspensions of unbleached and peroxid e bleached Norway spruce TMP. Cationic demand (CD) was used as a measu re of the anionic polymers in the TMP suspensions and was determined b y polyelectrolyte titration with streaming current detection. The CD o f a 1% suspension of peroxide bleached TMP (3% hydrogen peroxide on o. d. pulp) was threefold compared to that of an unbleached suspension. T he contribution from dissolved and colloidal substances (DCS) to the t otal CD of the bleached TMP suspension was about 25%. The DCS from ble ached TMP were much more capable of consuming cationic papermaking pol ymers than the DCS from unbleached TMP. Hemicelluloses rich in galactu ronic acid (polygalacturonic acids) were effectively flocculated by ad dition of polybrene to DCS from bleached TMP. Pectinase treatment of b leached TMP substantially decreased the CD of the DCS. Polygalacturoni c acids contributed to about 3% of the total dry matter of the DCS in a 1% suspension of bleached TMP. However, they accounted for about hal f of the total CD of the DCS from the same suspension. It was conclude d that potential ''anionic trash'' is released from spruce mechanical pulp in alkaline peroxide bleaching and that the major part of these s ubstances are polygalacturonic acids.