ROSIN SOAP SIZING WITH FERRIC AND FERROUS-IONS AS MORDANTS

Ferric and ferrous ions were investigated as mordants for rosin soap s ize.While ferric ion at pH 3.0-4.0 and ferrous ion at pH around 5.5 ar e able to induce a very high level of sizing to unbleached Douglas-fir kraft pulp, they have virtually no effect on bleached Douglas-fir kra ft pulp and bleached hardwood chemical pulp. The reason is believed to be due to the difference in lignin content of the unbleached and blea ched pulps. Two possible structures of the complex formed between thes e transition metal ions and lignin are postulated. The formation of hi ghly stable five-member chelate rings between lignin units and iron io ns and the high bond dissociation energy of eta6 arene polyhapto ligan d-metal ion bonds are thought to be the reasons why their Hercules siz e test values with 1% formic acid ink or neutral ink are extraordinari ly high compared to the optimal condition when alum is used as the mor dant. The excellent sizing results achieved by iron ions in mechanical pulp strongly support this hypothesis. Although the paper is darkened to some extent when iron ions are used, it is recommended that ferrou s or ferric ions be used in rosin soap sizing instead of alum in unble ached chemical pulp and mechanical pulp in cases where the color of pa per or paperboard products is not a concern. Iron mordants would also act as effective mordants for some dyes to deeply color mechanical pul p, such as in black or darkly colored construction paper.