Improved Deinking Flotation of Water-Based Ink

ABSTRACT
Deinking flotation is the most widely used method of removing fine ink particles from printed papers. While
flotation is effective for oil-based inks, the same approach does not work well for water-based inks as the pigments
are generally hydrophilic, small in size, and most importantly poorly liberated from the paper fibers. In the present
work, several approaches were taken to systematically address these challenges and improve the efficiency of waterbased
ink flotation. First, the degree of liberation between the ink particles and fibers was determined through a series
of hyperwashing tests and ζ-potential distribution measurements using the method of Huang et al. (in press). The data
showed that the liberation of water-based ink particles is initially quite poor, however, it can be substantially improved
by using dispersants in the pulping step. Second, a series of novel flotation collectors were developed to dramatically
increase the hydrophobicity of the water-based ink particles. The results obtained from contact angle measurements
show that the contact angle of water-based ink is increased from ~0 to over 140o in the presence of the novel collectors.
It is also found that the size of water-based ink particles can be increased by increasing particle surface hydrophobicity,
which is likely due to hydrophobic coagulation. After identifying a suitable reagent suite (i.e. dispersant and collector),
deinking flotation tests were conducted in a laboratory flotation unit using a furnish consisting of printed office paper.
In these tests, the brightness gains due to flotation were improved by three-fold relative to that of industrial standard
reagent, without compromising fiber yield. This work provides insight on increasing the recycling paper printed with
water-based ink, which can in turn lead to reduced embodied energy and CO2 emissions for paper feedstocks. 

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