Interactions of Optical Brightening Agents With High Yield Pulps

Abstract

The interactions of Optical Brightening Agents (OBA) with High Yield Pulp (HYP) fibers under two methods of OBA addition were evaluated on a softwood TMP and hardwood (aspen) HYP: OBA added to the peroxide bleach liquor (Method A), and OBA added conventionally at the wet end (Method B). The treated pulps were fractionated and OBA retention and efficiency in each fraction were determined. Adding OBA to the bleach liquor gave a higher OBA retention than adding OBA at the wet end; the hardwood HYP had a higher OBA brightening efficiency than the softwood TMP. The results are explained in terms of pulp morphology, lignin content, and process conditions (temperature and contact time). Adding OBA to the mechanical pulp also improved the brightness stability during the light-induced yellowing process.