Characteristics of High Yield Pulp and Its Effect on Some Typical Wet-End Issues

In this paper, some of the recent results are reviewed on the characteristics of BCTMP-based high-yield pulp (HYP) and its effect on the wet-end operations of the papermaking process in the production of printing and writing paper, including internal sizing, filler retention, and OBA/dye addition. Compared with bleached kraft pulp (BKP), the HYP contains more fines, lignin and anionic trash, as well as more carboxylic and sulfonic groups. Due to these differences, substituting HYP for BKP may have some impacts on the wet-end chemistry of the papermaking process. Generally, HYP has higher response to AKD sizing than BKP due to the higher anionic group content and self-sizing capability of HYP, although HYP fines and anionic trash can affect the sizing adversely. The addition of cationic polymers, such as PEI, can eliminate the negative effect of HYP anionic trash on internal sizing and filler retention. Under the optimized conditions, a partial substitution of BKP with HYP can lead to improved filler retention. OBA/dye can be used to improve the optical properties of HYP and HYP-containing furnish.