Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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mechanical wood pulp

A papermaking pulp produced by mechanical means only. The resultant fibers, which are produced by abrading the de-barked logs against a grinding wheel, are short, the average length being about 3 to 4 mm, with an average diameter of about 0.03 mm. Paper made from 100 mechanical wood pulp has relatively low strength, discolors fairly rapidly upon exposure to air and light (possibly because no lignin is removed from the fibers), and has very little permanence. It does, however, possess good bulk, opacity, and compressibility, which are desirable characteristics in some boards, book papers, and printing or writing papers. The wood used is almost always one of the softwoods, although in certain instances hardwoods are also used. The most important physical properties of mechanical wood pulp are freeness, relative length of fiber, uniformity of fiber length, strength, color, and cleanliness.

This type of pulp is generally used with a proportion of chemical wood pulp, the percentage ranging from about 15 to 50. Chemical tests for determining the presence of mechanical wood pulp include the iodine-zinc chloride test, which gives a yellow result, as does aniline sulfate, and phloroglucinol, which gives a bright red. (17 , 143 )

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