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Sunday, April 6, 2008

Papermaking Process

Papermaking is a continuous process that begins with the tree and ends with the cut sheet of paper.

Although wood fiber is the basic ingredient, only a little more than half of the fiber used comes from trees cut specifically for paper manufacture. The remaining fiber is made up of secondary material obtained by recycling used newsprint, spent packaging, and other waste paper. The waste residues of lumber operations and wood chips from saw mills provide additional materials.



Pulp Processing


The principle functions of pulping are gather end to separate the fibers. The logs that will be reduced to pulp to through one of two processes: either they are mechanically ground into pulp, or they are reduced to a pulp by being chipped and then cooked in a chemical solution. Cheaper grades of paper are generally produced from mechanically made pulp, which often contains some unwanted residues. Chemical methods remove more of residues. In the chemical process, wood chips are first cooked in a digester, a closed tank operated at high temperature and pressure. In the sulfite solution of sulfite salt; in the sulfate, or kraft process, the chemical solution consist of caustic soda and sodium sufide. In both processes, the lignin, the material that hold wood cells together, is dissoved, and the cellulose fiber separate.



In order to make the fiber more flexible, thereby increasing their matting, or felting, capacity, the pulp next goes through a mechanical pounding and squeezing process called beating, which is carried out with high speed conical or disc beaters, or refiner. Pigment or dyes are added to the pulp at the beating stage, along with filler materials that help to preserve the paper or give it a better opacity and finish. Sizing materials, such as rosins, starches, and gum that will make the paper resistant to the water in water based writing inks may also be added during beating.

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