Pulp (paper)

As a pulp raw material is referred to, which is used for the manufacture of certain paper grades. It is made from wood and contains, unlike pulp for high-quality papers, large amounts of lignin. The high lignin content leads to yellowing of the paper ( wood-containing paper ) so that wood pulp for newsprint and magazine paper ( engl. "light - weight coated paper" ( LWC ) ) and other paper briefly used is employed. Economically important species are wood pulp, groundwood, pressure groundwood and TMP ( thermomechanical pulp german / thermomechanical pulp ).

It is produced by mechanical and / or thermal and / or chemical processes for pulping.

  • 2.2.1 Thermomechanical pulp (TMP )
  • 2.2.2 Chemithermomechanical pulp (CTMP )
  • 4.1 advantages
  • 4.2 disadvantages

History

Earlier paper was obtained primarily from rags ( rags ). Because of the limited availability of this raw material were sought from about 1700 for alternatives. In the 19th century process for recovering pulp and the high-order, but more complicated to be produced pulp have been developed.

Production

Pulp is made ​​of wood as raw material, consisting mainly of lignocellulose, won. Lignocellulose consists of cellulose molecules that are assembled into fibers. A matrix of lignin by the effect of cellulose, such that a pressure-resistant and tear-resistant composite is formed. In the manufacture of wood pulp defibration of the wood is carried out by various methods. Due to the almost complete use of raw material, high yields are possible. In the manufacture of pulp, however, the lignin is removed by chemical methods, so that at lower yields and higher costs of higher pulp is extracted, which consists almost entirely of cellulose. Most roundwood or wood spanking is used, with softwood is preferred because of Langfaserigkeit. Different methods lead to different pulp grades.

Grinding process

Cut - products are produced by pulping of wood by means of grinding stones.

Groundwood

The manufacture of wood pulp is done mechanically. Debarked wooden club ( meters of wood ) are pressed and zerschliffen with the addition of hot water on rotating grinding stones. Can be followed by a further grinding to adjust the fibers.

Pressure groundwood

A more modern production variant is the pressure groundwood. Compared to conventional wood pulp, which is produced at a temperature below 100 ° C, allows the encapsulation of the grinder at a higher pressure and thus a higher temperature. This softens the Ligninmatrix. This allows the output easier pulped wood and a greater length of the cellulose fibers are obtained.

Pulping process,

In the pulping process, first a comminution in wood chips, and after further process steps, the defibration in the refiner.

Thermomechanical pulp (TMP )

In the TMP - generation chips are at temperatures up to 140 ° C between the edges of a refiner shredded ( Faserstoffmahlung ). At this temperature, the lignin and the composite softened dissolves to form long fibers. Thus, the properties approach those of the more expensive part of the pulp, such as higher tensile strength of the paper produced therefrom.

Chemithermomechanical pulp (CTMP )

A variant of the TMP is the chemo- thermal mechanical pulping (CTMP ), in which the wood chips are also chemically treated. The product is darker by the chemical pretreatment as TMP. CTMP can be bleached and is then referred to as the BCTMP.

Depending on the desired paper quality ( opacity ( light scattering ability ), volume ( stiffness ), brightness, surface properties, binding and strength properties ) and after economic aspects are used different wood materials. There is often also a combination with other raw materials, such as with recycled paper or long-fiber pulp from softwood, rather than to achieve the desired paper quality.

Chemical detection

Pulp can be detected by red staining of the lignin contained with hydrochloric acid phloroglucin and so distinguished from pulp.

Pros and Cons

Benefits

  • Pulp is much more advantageous than wood pulp for cardboard production because the lignin in the pulp composite gives added rigidity. Also for newsprint is ligninfreies paper from pulp unsuitable. The manufacture of wood pulp is also easier and more cost-efficient than the production of pulp, as the complex cooking process eliminates the lignin.
  • The yield based on the use of wood is wood pulp at about 90 %, since almost all of the ingredients of the wood, including lignin in wood pulp are available virtually unchanged. In the cellulose production, the yield by the removal of the lignin is significantly lower ( about 50 %).

Disadvantages

  • The biggest disadvantage of wood pulp in many applications is to lignin content. Under light and oxygen influence yellowed the lignin. Paper with a high pulp content discolored quickly find themselves ( newsprint).
  • The visible paper quality pulp is poorer than that of pulp, since there is a much stronger floc formation, whereby the formation is impaired.
  • For the grinding process much energy is required to drive the wheels and Häckselanlagen. The energy requirement is dependent on the intensity of grinding and is 1500-3500 kWh / t. This high energy demand and the availability of cheap paper have led to the manufacture of newsprint for use by almost 100% recycled paper in Central Europe. Within Europe, TMP is processed only in Scandinavia newsprint.
  • Paper from wood pulp has low strength values, since the fibers are damaged during production. By mixing with the pulp, the strength can be increased.
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