PAPERmaking! g FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 2, Number 1, 2016
INTRODUCTION Recycled pulp is an important raw material used in paper products. The use of recycled pulp has increased globally in recent years (Ibarra et al. 2012). Recycled pulp from old newspapers (ONP), old corrugated containers (OCC), old magazines (OMG), white ledger, and mixed office wastes (MOW) is widely used in the manufacture of paperboard. The production of paperboard accounts for 50% of the paper products created by the Korean paper industry. Duplex boards or white lined chipboards are used to package food, pharmaceuticals, detergents, textiles, clothing, and more (Kiviranta 1997). Wood powder and other organic fillers have been added to the middle ply of duplex boards to reduce production costs in Korean duplex board mills (Lee et al. 2014a; Park et al. 2015). Reducing the use of virgin pulps is the first step toward lowering production costs and protecting domestic environments in Korea. The replacement of virgin pulp with recycled pulp is beneficial to the Korean paper industry and to the domestic environment. A duplex board is typically made of many plies. The top ply generally consists of bleached kraft pulps (BKP), white ledger, and ONP. Other plies are made of recycled pulp of lower quality (Kiviranta 1997). Though the ratio of BKP is lower than that of other recycled pulp in the top ply of a duplex board, BKP must be replaced with white-grade recycled pulp to reduce production costs. White ledger consists of general office paper that is non-glossy and is either printed or unprinted; this office paper may include typing paper, copy machine paper, or white notebook paper. The production of white ledger has increased steadily as various printing technologies have developed. White ledger, which is of high quality in terms of its white colour, brightness, and strength, contains a higher portion of chemical pulp and a lower content of recycled materials compared with other recycled pulp (Lee et al. 2015). However, the quality of white ledger has decreased because papermakers have increased the use of high-yield pulp (Zhai and Zhou 2014) and inorganic fillers (Jung and Seo 2015) in general office paper to reduce production costs. The high ash content of other recycled pulp has reduced the yield of raw materials and paper strength (Zhao et al. 2008). Therefore, it is necessary to improve the first-pass retention and paper strength of duplex boards that are made from white ledger and that have high ash content. This study explored the ideal conditions of cationic polyacrylamides (CPAMs) to improve the retention and strength of white ledger stock. The properties of white ledger used at an actual mill of duplex boards were analysed and compared with the properties of recycled pulp from the same mill. Next, the first-pass retention of white ledger stock was measured by adding six types of C-PAMs with different charge densities and molecular weights. After determining first-pass retention values, the handsheets were constructed, and their strength was measured. EXPERIMENTAL CONDITIONS Materials Pulp slurries were collected from the Kleannara mill (Cheongju, Korea) where six-ply duplex boards were produced. The pulp was classified as either recycled pulp or virgin pulp, both of which were used for the manufacture of duplex boards. The recycled pulp included white ledger, ONP, and OCC. The virgin pulp consisted of mixed BKP, which combined softwood BKP and hardwood BKP at a ratio of 5:5. Bleached chemo-thermo mechanical pulp (BCTMP) was also included.
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Article 1 – Improving Retention and Strength
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