Mechanical wood pulp

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Mechanical softwood at 200x transmitted light


A mass of wood fibers produced by physically grinding rather than chemically treatment. To produce mechanical wood pulp, bark-free, cut wood is sent to a sandstone abrasion-type grinding machine. It is then screened and filtered to remove large pieces and foreign material. The resultant pulp contains Lignin, Hemicellulose, Resin, and colouring materials which yellow and deteriorate the paper over time. Thus, the pulp is often bleached with Peroxide or hydrosulfite to improve whiteness. Groundwood paper is produced from coniferous trees. It is inexpensive and has low strength but high opacity and bulk. It is used for newsprint and other low cost printing papers. Groundwood paper is chemically unstable.

Mechanical softwood at 200x polarized light

Synonyms and Related Terms

mechanical wood-pulp; groundwood pulp

Physical an Chemical Properties

Tests used to determine the presence of mechanical wood pulp in a paper are: 1) Iodine-Zinc chloride test gives a positive yellow, 2) Aniline sulfate turns yellow for positive, 3) Paranitroaniline turns orange, 4) Phloroglucinol turns red (Roberts and Etherington 1982), 5) and Graff "C" stain will turn yellow due the presence of lignin.

Additional Images

Resources and Citations

  • R. J. Gettens, G.L. Stout, Painting Materials, A Short Encyclopaedia, Dover Publications, New York, 1966
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Walter Rantanen. "Fiber ID Course." Integrated Paper Services. June 2013. Lecture.