The Covid-19 crisis has resulted in significant structural changes in recycled fiber stream collection and availability due to the move toward work from home. In particular, sorted office papers (SOP)/mixed office waste (MOW) generation has been significantly reduced with some estimates suggesting that collection of this stream has declined by 30-50%. Supply shortages and rising MOW prices are the result. In the current market conditions, many recycled fiber (RF) tissue makers are either having to supplement their fiber supply with virgin content or, in some cases, having to switch over completely. Moving your base sheet fiber mix from RF to virgin presents both opportunities and challenges to the tissue maker.
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The fiber that most tissue makers are turning to is southern cone Eucalyptus (EUC). EUC is known for possessing advantages in product handfeel characteristics over recycled fiber, but it is significantly more expensive than the deinked pulp streams that integrated tissue mills produce from MOW. It is worthwhile to ensure that if more expensive virgin fiber must be used, it is done in a way that maximizes benefits and minimizes operational upsets so that production efficiency and quality can be maintained.
This article will concentrate on the two key areas where operational and quality impacts result from the fiber mix changes and best practices to deal with them.
The first thing to be understood is the difference in basic fiber characteristics. The cell wall thickness and overall fiber length is vastly different for EUC vs the northern hemisphere hardwoods that are used to manufacture office papers. This difference is much greater for the softwoods. Replacing MOW with eucalyptus results in a drastically different base fiber. This difference means the tissue maker has to adjust the way he generates strength. The initial temptation is to achieve the strength needed via higher refining intensities, but the following negatives cascade from this approach: increased fiber cutting, higherfines generation, increased dusting and sheet densification, reduced caliper/bulk and decreased softness. Fines also reduce drainage and increase the drying load on the tissue machine. Where drying capacity is limited, this can result in reduced production capacity.
The negative impact can be reduced but not eliminated with lower intensity refining, however this approach requires more available refining capacity, or in some cases, completely different equipment. The best way to circumvent this problem is to employ an enzyme-based technology to modify the fiber. This technology allows for maximum fibrillation of the fiber with minimal input of refiner energy. The result is the ability to maximize tensile generation without the fiber cutting.
The tissue maker gets the strength required while preserving bulk to basis weight, absorbency and handfeel, all of which suffer when the base sheet is densified.
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