Paper pulp

See also: Paste

The pulp paper is the Raw material of the manufacture of the Papier.

The preparation of the paste consists in insulating the cellulose Fiber S contained in the Bois while preserving the best possible their mechanical properties, Optique S and morphological and while seeking to eliminate the Lignine the other the made up main thing from the Bois. For that, there exist two great processes:

The mechanical way: the logs are grated by a grinding stone or the chips pass through discs disintegrators.

The chemical way: cooking of wood and addition of chemicals to dissolve the Lignin and to recover fibers of Cellulose.

There exist several hybrid processes, combining in a variable way the purity of the chemical paste and the good output of the mechanical paste.

Paper can be made starting from rags of cotton, or any materials fibrous plant rich in cellulose (bamboo, herbaceous, corn straw.). The famous paper-bible , end, flexible and durable, is manufactured starting from fibers of Chanvre.

Mechanical paste

The mechanical paste has a Rendement from 90 to 96%. This good performance is due to the chemical absence of handling on the matter. The organic compounds of wood, the cellulose, hemicelluloses and lignin, are preserved. Nevertheless, certain products, of good part of the extractable matters (resins, tannins, dyes, waxes, alkaloids, etc), have a reduced point of boiling and evaporate. Indeed, that it is by the use of a disintegrator (grinding stone) or a refiner (discs), the temperatures easily exceed the 100 degrees Celsius because of friction.

This type of paste is generally used directly on the site, drying degrading fibers. According to the use, the paste can be bleached by explanation by chemically modifying the grouping chromophoric of lignin. It is used in the Newspaper, the edition, with less measure to papers of graphic use, the paperboard S and papers of medical use.

Characteristics

  • average physical Resistances
  • high Output
  • Good opacity
  • Puffing out (weak density)
  • Good Printing quality
  • Bad ageing (tendency to yellowing, the acidification and embrittlement)

Chemical paste

The chemical paste is obtained by two processes: with the Bisulfite (Acid) and with the Sulfate (Alkaline), one speaks then about Kraft paper.

The chemical treatment of the raw material makes it possible to manufacture a paper pulp close to qualities of the paste of pure rag.

With this intention, it is necessary to eliminate to the maximum the undesirable components of wood: lignin, gums, resins to preserve only cellulose fiber.

The preparation of the paste is done in large lessiveurs, with high temperature 100 with 175°. Wood is cooked under pressure in the presence of chemical compounds of 2:00 to 5:00 the fibers leave there flexible and individualized. The active products are poured in lessiveurs and dissolve the undesirable elements during cooking.

It any more but does not remain to wash them, rinse, purify and, possibly, to bleach.

Several processes are used for the preparation of the chemical paste.

The process called to bisulfite.

The process called to bisulfite rests on the action of the sulfur dioxide which transforms lignin into soluble matter. The paste is collected at the exit of the lessivor, it then puffed up or is disintegrated then washed and purified.

The pastes with bisulfite use mainly the wood of coniferous tree except for the maritime pine too rich in resin.

The process with sulfate

The process with sulfate was a long time forsaken because them difficulties encountered to bleach the paste. This problem having been solved, the process present of many advantages. It makes it possible to treat the most various plants: wood of leafy trees and coniferous trees, wood tropical and equatorial, annual plants, canes with sugar, reed…

The chemical agent which one exploits the properties is soda. The chemical paste is of dark aspect. For papers of quality which require a high degree of whiteness, the paste will undergo a chemical bleaching.

They are used for the Emballage, paper with impression and paper with writing when they are bleached or in mixture.

Characteristics

  • better mechanical resistance
  • compact paper
  • bad opacity
  • good ageing, because absence of difficult Lignin
  • Bleaching, especially paper with sulfate.

Environmental impact

Paper is a material whose manufacture consumes much water and energy, but which can be several times recycled. Its environmental impacts come especially from the dyes and inks, its transport and the transport of wood, as of fungicides which are often added to the paste to lengthen of it the conservation during its transport (for example of Canada in Europe). Another impact comes from the conversion of primary forests or secondary rich person into Biodiversité into intensive plantations of trees (resinous, eucalyptus, poplars. ) intended to produce paper pulp.

Trees GMO

INRA produced in France a Peuplier transgenic which in 2007 is cultivated in outside and is in phase of test for Industry. Canada tests on its side a score of transgenic stocks of poplars (low in lignin, and producing for some a insecticie). These experiments worry the specialists in the biodiversity and worry the environmental ONG (of which Greenpeace and WWF) which evoke also tests of trees resisting the Salinisation tested in the USA (but which consuming much more water than the normal). One fears in particular a genetic Pollution normal trees by pollens of transgenic species, and the environmental phenomena of toxicity whenever the produced tree of LT, in the rhizosphère in particular, which does not exclude from the fast adaptations of xylophagous insects (because the poplars and trees low in lignin are less resistant vis-a-vis the insects).

See too

External bonds

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