Laboratory Scale Two-loop Deinking Trials

Abstract

Here we describe our work on the design of a laboratory-scale two-loop deinking process with inclusion of a low-speed high shear kneading step in between two flotation steps. Our approach was then applied to evaluate the deinkability of MOW (mixed office waste) and mixtures of MOW with various amounts of digital print products (where liquid electrophotographic (LEP) prints were used as an example of digital print products). The process conditions at respective stages were optimized to closely mimic that of representative mill-scale processes. The effect of deinking chemistries was also evaluated, with a particular emphasis on nonionic surfactant-based neutral chemistries. The evolutions of dirt area, dirt counts, speck size and optical properties with respect to process stages were monitored to determine the efficacy of our approach. We show that with controlled flotation yields (∼ 80% in the pre-flotation, ∼ 97% in the post-flotation), the kneading step facilitates noticeable reduction in dirt area. The average speck size was noticed to fall within the perceived deinkable range (i.e. 5-200 microns). It is noteworthy to observe that the two-loop process successfully brings the dirt area for MOW with LEP prints (5% and 20%) to a satisfactory level.