Secondary fiber pulping

Table 21.3 presents an overview of wood pulping types by the method of fiber separation, resultant fiber quality, and percent of 1998 U.S. pulp production.1112 Many mills perform multiple pulping processes at the same site, most frequently nondeink secondary fiber pulping and paper-grade kraft... 

E. Hamilton and B. Leopold, eds.. Pulp and Paper Manufacture, Vol. 3, Secondary Fibers and Non-Wood Pulping, Joint Textbook Committee of the Paper Industry, Tappi, Adanta, Ga., 1987. 

Secondary Fiber. Increasing costs of taw fiber, legislative mandates for recycling (qv), and avadabdity of inexpensive waste papers have contfibuted to the increased use of recycled fibers. The use of secondary fiber in the United States has grown from 22% of pulp from all sources in 1978 to close to 31% (24 x 10 metric tons) in 1993 (3). Recycled fibers ate sometimes used in special writing papers, but the principal use is for the manufacture of linetboatd, newsprint, tissue, cereal boxes, towels, and molded paper products such as paper plates and egg cartons (see Packaging materials, containers AND INDUSTRIAL materials). 

P. E. Shick, paper presented at TAPPI Conference on Alkaline Pulping and Secondary Fibers, Washiagton, D.C., Nov. 7—10,1977. 

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. 

Secondary fiber nondeink Nonwood chemical pulp... 

Debarking, slashing, chipping of wood logs and then screening of wood chips/ secondary fibers (some pulp mills purchase chips and skip this step)... 

The types of furnish used by a pulp and paper mill depend on the type of product produced and what is readily available. Urban mills use a larger proportion of secondary fibers due to the postconsumer feedstock being close at hand. More rurally located mills are usually close to timber sources and thus may use virgin fibers in a greater proportion. 

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. 

Strazdins, E. (1984), Chemical aids can offset strength loss in secondary fiber furnish use. Pulp and Paper, March. 

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. 

Soure From Touzinsky, G.F. Laboratory paper machine runs with Kenaf thermochemical pulp, TAPPI, 1980, 63(3), 109 Touzinsky, G.F. Kenaf, In Pulp and Paper Manufacturing, Vol. 3., Secondary fibers and non-wood pulping. Chapter 8, TAPPI Press, Atlanta, GA 1987,106. 

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. 

In secondary fiber preparation, peripheral systems are very important for the runn-ability of the whole plant as well as for cost minimization and environmental issues. Peripheral plant components are the reject system, sludge treatment and water handling (see Fig. 4.56-4.60). Coarse rejects from the pulping section, heavy particle separation and hole screening are dewatered to a dry content of approximately 60%. If thermal treatment is involved for these rejects, metal components have to be removed and the particle size adapted to the burning process by means of shredding. 

Newsprint represents an important subgroup. It consists primarily of a mixture of primary and secondary fibers (0-100%). The primary fibers include groundwood and small amounts of chemical pulp, which are used to increase strength. The main field of application is newspaper production. Other uses are, e.g., paperbacks, calculating-machine roUs, and interleafing paper. 

In order to meet the high strength requirements, these papers consist of primary or a mixture of primary and secondary fibers of kraft pulp. They are used predominantly for packaging purposes. 

Mixed soda pulp-paper is made predominantly from secondary fibers and kraft pulp (70-35 g m ). 

These novel organic polymers were not developed solely for the CW or BW treatment market but are for much wider application. These same value-adding process additives are regularly incorporated into products for industrial and domestic cleaning, concrete, pulp and paper, metal finishing, paints and surface coatings, wastewater, seawater distillation, drilling muds, secondary oil-recovery, plastics extrusion, fibers, rubbers, and a host of other areas. 

Fig. 1-15. Ballooning of a sulfate pulp fiber (Pinus sylvestris). Note the ribbonlike, unrolled primary wall (P) and the swollen secondary wall. S, is the swollen outer layer of the secondary wall, under which the microfibrils of the middle layer, nearly parallel to fiber axis, are dimly visible. S3 is the inner layer ot the secondary wall (llvessalo-Pfaffli, 1977).

Cellulose acetate is usually produced by the so-called solution process with exception of the fully acetylated end product (triacetate). In the solution process the pulp is first pretreated with acetic acid in the presence of a catalyst, usually sulfuric acid. The purpose of this activation step is to swell the fibers and increase their reactivity as well as to decrease the DP to a suitable level. Acetylation is then performed after addition of acetic anhydride and catalytic amounts of sulfuric acid in the presence of acetic acid. After full acetylation the final triacetate obtained is dissolved. This "primary" acetate is usually partially deacetylated in aqueous acetic acid solution to obtain a "secondary" acetate with a lower DS of about 2 to 2.5. 

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