Effect of Combining Neutral Flotation and Enzyme Treatments, 1999 Recycling Symposium Proceedings

T. Yaezawa, T. Yaguchi

The addition of chemicals, which agglomerates the fragmented inks, disperses them properly and prevents them from re-depositing on the fiber, in the de-inking process is one of the techniques that increases the de-inking efficiency. For example, neutral flotation is effective in the case of de-inking of flexo-printed paper and is usually suitable before alkaline soaking. However, the brightness gain is only a few points as compared with the conventional alkaline de-inking process, and also it is not effective in de-inking offset-printed paper.

In this study, we present the advantages of combining neutral flotation and enzyme treatment. The neutral flotation was performed by neutralization (after alkaline soaking) and also by enzyme treatments, such as cellulase, xylanase, mannanase, amylase, or amphoteric electrolyte. This combination agglomerated and removed the fragmented offset inks, and also enhanced the final brightness gain by 6-8 points (ISO) as compared to the conventional alkaline process.