New Trends on Raw Material: Effects on Recycled Pulp and Paper Processes
July 1, 2006 By Pulp & Paper Canada
Within the next four years, North American consumption of office paper will shrink by 1 million tons, or 2-3% per year. This reduction can largely be explained by the increasing use of computers and t…
Within the next four years, North American consumption of office paper will shrink by 1 million tons, or 2-3% per year. This reduction can largely be explained by the increasing use of computers and the Internet to read the news, documents, mail, etc.
Over the last 20 years, optical properties of recycled pulp (fluorescence and consequently brightness) have gradually increased. In 2005, the new brightness trends have forced the fine papers industry to drastically increase brightness of certain paper grades by 4 to 6 points. To keep the cost increase and the impact on the process at a minimum, papermakers have increased the fluorescence level of these grades by adding fluorescent whitening agents (FWA’s) at the size press. Consequently, this industry change has significantly increased the fluorescence level as well as the brightness of recycled pulp dedicated to fine papers. Another strategy is to increase the concentration of fillers in paper, to decrease costs and/or improve optical properties. However, the real effect of this strategy has been, so far, only partially observed in the recycled pulp industry.
Trends on raw material
In 2004, the recovery rate (the ratio of total office paper recovered to supply) reached an unprecedented level of 49.1% in the United States (Figure 1). Compared to 47.8% in 2000, we would be inclined to think the availability of recovered material is higher. Contrarily, in the last year, exportations have increased by 28% while domestic consumption has grown by a meagre 3%, mainly due to the tissue industry increasing demand.
In the recovered office paper industry, another important modification that can be observed is the increasing level of shredded raw material. In 2002, only 25% of office paper was shredded. In 2005, it soared to 50% and is predicted to reach 85% in 2008. The events of September 11 and the Enron and Worldcom scandals, leading to the creation of the Sarbanes Oxley law can largely explain this. Not only are business documents today destroyed with small personal shredders but also increasingly specialized recyclers shred, or pulverize the paper mix. This new practice eliminates the possibility of sorting this type of material, leaving mechanical fibres (newsprint), unbleached fibres (old corrugated containers) and paper containing high levels of PSA (pressure sensitive adhesives), such as envelopes, in the total mix.
Furthermore, the remaining full sheets of office paper are in high demand by Asian countries. For example, China pays a premium price for full sheet unsorted office paper that comes from both the west and east coasts. This raw material is sorted at a cost, which is about two orders of magnitude cheaper than that in North America.
Trends in recycled pulp and paper processes
Regarding fine paper mills, the increasing level of fluorescence of recycled pulp has allowed, on one hand, to decrease the FWA’s addition cost but, on the other hand, has negatively altered the efficiency of retention aids and production costs. For example, the addition of 10 kg FWA’s (as received) per ton has decreased filler retention from 60-65% to about 55%. Variability of the fluorescence of recycled pulp is sometimes more critical than the fluorescence level itself, which makes the control of the optical properties of paper difficult.
This trend is likely to continue over the coming months, until the effect of new brightness targets is totally observed. Moreover, because a European producer is targeting 175% whiteness to increase its exportations to North America, the whiteness and fluorescence of paper will likely be pushed to an even higher level
This trend leads to another technical concern, the grey point, which is observed at high fluorescence levels. Brightness loss of about 1-2% can be observed, as well as a decrease of the CIE a* (greenish tint of paper). Interestingly, the increase of Fibres Breakey’ pulp brightness over the last seven years can be explained by the increase of fluorescence, and the rate of change has significantly increased over the last year (Figure 2). Consequently, we speculate that the issues related to grey point of paper will increase in the coming years.
Other major process effects might be observed, such as the shut down of a bleaching stage. Although this seems positive from an economic point of view, it can certainly decrease the stability of recycled pulp optical properties. It is clear that sequential bleaching (ex. peroxide/hydrosulfite) leads to higher brightness and increased stability of optical properties than does single stage bleaching.
Moreover, the increasing proportion of shredded raw material puts more pressure on cleaning and bleaching stages of the deinking processes. However, because shredded material cannot be sorted, high levels of contaminants (stickies, mechanical and brown OCC fibres) are found, which decrease the quality and the stability of wood-free deinked pulp. Non-fibrous material present in this unsorted material will reduce the yield and create upset conditions in the management of waste. Bleaching conditions will have to be modified to treat the mechanical fibres, as well as unbleached chemical and semi-chemical fibres, to maintain the quality of recycled pulp. Moreover, if the concentration of pulverized material increases, we have to ask ourselves how it will affect the fibre length and the strength of the recycled pulp.
Finally, the above trends will provide, for many years to come, challenges and opportunities for the pulp and paper industry to solve these changes and adapt, just as it always has.
Roger Gaudreault, Ph.D. is the General Manager, R&D, and Guillaume Bouvier, Eng. is the Director, R&D Centre at Cascades Canada Inc.
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