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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