Evaluation of APMP and BCTMP for market pulps from South American eucalyptus

Eucalyptus grows fast, and it has been used in mechanical pulping for years. However, its wood is darker than North American aspen. To be used for tissue and printing and writing grades, the eucalyptus pulp will have to reach brightnesses of 85% ISO or higher. In this study, E. grandis from Argentina and E. grandis and E. saligna from Paraguay were used as sources of fiber. Pulps were produced by two processes, APMP (alkaline peroxide mechanical pulping) and BCTMP (CTMP with post bleaching). These two processes were compared for energy consumption, pulp property development, effluent characteristics, and post bleachability. The pulps from the three fiber sources were similar in the way they responded to changes in process conditions. All three demonstrated good potential for high-brightness grades. The APMP and CTMP processes are comparable in energy consumption, pulp strength development, and effluent loading. However, BCTMP produced more COD discharge than did APMP at the same final brightness. Furthermore, it was difficult to bleach the CTMP pulp to 85% ISO, but the APMP pulp could be bleached to 89% ISO when the bleaching chemicals were properly distributed over two stages of chip impregnation.