Dewatering evaluations of FBB Filler Ply stocks and their reinforcement pulps

The FBB filler ply typically contains a significant amount of mechanical pulp such as BTMP, BCTMP, CTMP, etc. This is usually reinforced with either refined broke from the same PM line and converting process, or by utilizing traditional BKP. There has been a trend towards reducing the refining of mechanical pulp compensated with additional refining of the reinforcement stock related to the filler ply. In response to the drive for increased bulk, reduced basis weight, and minimized energy consumption, papermakers have experimented with various options and strategies. In between the common approaches, choices have been made between reducing the refining of the mechanical pulp, increasing the broke refining (more frequently practiced on the production scale), or increasing the BKP refining (a potentially superior choice).
The present study focused on a simplified approach to assess the impact on dewatering of three reinforcement stock refining conditions. As the reinforcement stock HWBKP was used at the SR levels of 30-35, 50-55 and 70-75. The reinforcement stock was added to the core stock for the FBB filler ply – a mechanical pulp that was either BTMP SR35 or BCTMP SR25. The proportions of HWBKP were 20% of 30-35 SR, 10% of HWBKP 50-55 SR and 5% of HWBKP 70-75 SR. The intention behind using varying percentages of reinforcement pulp was to attain a controlled internal bond while enhancing bulk through increased mechanical pulp content. The dewatering of the stock mixture was assessed at three distinct vacuum levels —estimated, 7, 14, and 28 kPa— which are possible values employed in progressive stages within production-scale forming sections.
This study provides indicative changes for dewatering responses of basic FBB filler ply stock composition and suggests possible optimal strategy to deal with reinforcement stock.