Deinked secondary fibers

Deinked secondary fibers are usually bleached in a bleach tower, but may be bleached during the repulping process. Bleach chemicals may be added directly into the pulper. The following are examples of chemicals used to bleach deinked secondary fibers hypochlorite [HCIO, NaOCl, Ca(OCl)2], hydrogen peroxide (H202), and hydrosulphite (NaHS03). 

Pulp mills. These separate the fibers of wood or other materials, such as rags, Enters, waste-paper, and straw, in order to create pulp. Mills may use chemical, semichemical, or mechanical processes, and may create coproducts such as turpentine and tall oil. Most pulp mills bleach the pulp they produce, and, when wastepaper is converted into secondary fiber, it is deinked. The output of some pulp mills is not used to make paper, but to produce cellulose acetate or to be dissolved and regenerated in the form of viscose fibers or cellophane. 

Contaminant removal processes depend on the type and source of secondary fiber to be pulped. Mill paper waste can be easily repulped with minimal contaminant removal. Recycled postconsumer newspaper, on the other hand, may require extensive contaminant removal, including deinking, prior to reuse. Secondary fiber is typically used in lower-quality applications such as multiply paper-board or corrugating paper. 

Use Continuous conditioning and batch washing of paper machine felts. Paper-mill system boil-outs. Deinking of secondary fiber. 

In recent years, less chlorine and more sodium hydroxide have been used for bleaching. At present, chemical pulps and the deinking of secondary fibers are the primary users of chlorine bleaching techniques. The European paper and pulp industry uses ozone, oxygen, and peroxide in place of chlorine. 

The product from a secondary fiber preparation plant for white grades is usually called DIP (Deinked Pulp) as there is at least one process step for ink removal integrated in the system. In most of the cases this deinking step is done by selective flotation. Washers may be used for deinking in special cases when very finely dispersed printing inks (like water-based flexo inks) are present in the recovered paper or when not only the ink, but also the major share of the ash content needs to be removed, as is true e. g. for tissue grades. 

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