Background and Challenges:

· The mill produces premium coated white paperboard using 100% recycled pulp (OCC + MOW) as the base layer and virgin chemical pulp as the top layer.

· The main challenge was the high anionic trash content in the base pulp, which resulted in unstable performance of traditional single-component retention aids.

· The retention rate of fillers (kaolin and calcium carbonate) was low (approximately 52%), resulting in cost waste and sedimentation problems. The whitewater system was highly closed, and the total solids content (TSS) continued to rise, affecting operation of paper machine.

Solutions:

· A microparticle retention system of "bentonite + cationic polyacrylamide (CPAM)" was adopted.

· A high-charge-density cationic coagulant (such as polyamine or poly-DADMAC) was initially added to neutralize the anionic trash.

· CPAM was then added to form initial flocs.

· Finally, bentonite is added, leveraging its large surface area and charge properties to break down the initial large flocs into smaller, more uniform, and more robust micro-flocs.

Performance Data:

· Filler Retention: Increased from 52% to 72%, significantly reducing raw material consumption.

· First Pass Retention Rate (FPR): Increased from 65% to over 82%, reducing white water concentration and improving system cleanliness.

· Paper Machine Operation: Web breaks were reduced by approximately 15%, and machine speeds were increased by approximately 5%.

· Finished Product Quality: Improved inter-ply bond strength and reduced side-to-side variation, providing an optimal substrate for subsequent coating.