RE-PULPING OF FLASH-DRIED HARDWOOD AND SOFTWOOD BCTMP

A common question for a paper mill using market flash-dried chemi-thermo-mechanical pulps (BCTMPs) is how to re-pulp them effectively. To address this question, three commercial flash-dried BCTMPs from maple, aspen, and spruce were selected for a re-pulping study. The main objective of this research was to evaluate the effects of re-pulping variables on final pulp properties, including freeness, bulk, physical, and optical properties. The re-pulping variables in this study include re-pulping temperature, pH, agitation time, and retention time. The results presented here show that re-pulping is an important process for market flash-dried pulp. With a correct re-pulping procedure, flash-dried pulp can regain the properties lost during the flash-drying process and bring fibres back or close to their never-dried state. In general, for all three BCTMPs, the flash-dried pulps, after proper re-pulping, can regain their original pulp properties, unlike flash-dried reference pulps after standard hot disintegration. Note that there are some differences between hardwood and softwood BCTMPs. Flash-dried maple and aspen BCTMPs are relatively easy to re-pulp. Their pulp properties after re-pulping are very close to those before drying. On the other hand, flash-dried spruce is relatively difficult to re-pulp. Measures should be taken to reduce the residual latency of flash-dried spruce BCTMP to make sure that the pulp is properly re-pulped.