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1. What is meant by recycling and deinking of papers?

The EU definition for recycling taken from the EC Waste Framework Directive: "Recycling means any recovery operations by which waste materials are reprocessed into products, materials or substances whether for the original or other purpose.” With respect to paper recycling, this can mean the ability to recycle paper into a new paper of the same type or into a different, type of paper or paper product. The typical definition of recyclability in most eco-label requirements is that the paper product should be able to be re-pulped into individual fibers without significant fiber bundles and foreign material.

Deinking is a process step sometimes used in recycling papers. The deinkability of papers is a reference term and a measure of how effectively ink can be removed from paper for recycling in a deinking process. Deinkability performance can vary greatly depending on ink type, paper type and processing conditions.

2. Is paper printed using water-based inkjet ink deinkable?

Generally speaking, yes, however this depends very strongly on the ink-paper combination, the process used, and end use requirements. Some ink-paper combinations show good to excellent deinkability, while some combinations do not provide acceptable deinkability. Small quantities of problematic ink-paper combination inkjet prints mixed with conventional printed papers will likely not lead to a significant reduction of the quality of the recycled pulp under practical conditions in an industrial deinking plant.

3. What is the deinking process and why is it a potential issue for inkjet printing?

Deinking is the key step used in paper recycling processes for graphic papers that incorporates an air flotation process to separate inks from paper fibers. After chemical and mechanical re-pulping of the paper for recycling, air bubbles are generated and mixed with the pulp. These bubbles attach to ink particles and float them to the surface for removal. The flotation step was designed primarily for hydrophobic particulate inks. Dye based aqueous inks are water soluble and need attachment to special paper coating particles in order to be removed by the flotation method alone. Additional process steps may be required for the de-colorization of dye based inkjet inks. Pigment based inkjet inks are sometimes removable in a flotation deinking process, depending on the printing substrate used.

4. So what is the concern from the deinking industry?

Already today, dirt and residuals present in the collected paper lead to problems in the recycling process and resulting products. It is, therefore, in the best interest of the paper recycling industry to reduce the amount of any additional substances that may further disturb the deinking process, even if the contribution is small. In this context, the concern from deinkers is that water soluble inks will discolor or darken the recovered pulp fibers. Additionally, the process water used in the deinking facility may become darker over extended periods of time. Recycling facilities minimize their water usage by recycling this process water.

The presence of residual colorants in the pulp is common for all inks since flotation is not 100% efficient. Generally, residual colorants are not an issue when recycled pulp is used in packaging and similar applications. If the intended use is for the production of higher brightness graphic papers, the recovered pulp is bleached as a normal process. For newsprint deinking, some systems use only flotation technology, so in these systems, the flotation deinkability of the printed paper is critical to achieving the final paper product quality.

5. What are the other process steps used in deinking plants?

If higher brightness is required, there are many secondary processes used today to brighten deinked pulp. While single loop flotation deinking is the most basic method, most paper recyclers today have a two loop flotation system, and some have even a three loop system. Depending on the desired end product to be produced from the recycled fiber, flotation deinking can be complimented with washing and/or bleaching steps that remove residual colorants and enhance the pulp properties. Most tissue manufacturers utilize these additional steps to achieve full cleaning of the recycled pulp.

6. Are there other activities that the DPDA is pursuing?

The Digital Print Deinking Alliance (DPDA) has been active with all stakeholders in the recycling industry. We have conducted research with paper mills, chemical companies, research organizations, and within our own facilities.

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by Dr. Radut