Extraneous materials in wood


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Extraneous materials in wood
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Mixed Material
Ritter, George J
Forest Products Laboratory (U.S.)
University of Wisconsin
U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory ( Madison, Wis )
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aleph - 29325049
oclc - 756039771
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U. S. Department of Agriculture, Forest Service


In cooperation with the University of Wisconsin





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GZCRE' J. RITT3F,_ Chemist

All species of woods contain materials other than wood sub-
stance and water. Although such materials are not an integral part of
the wood structure, nevertheless, they affect the properties of the wood
as a whole. _.-joy are referred to under the all-inclusive term, extraneous
materials. These materials vary over a wide range both in amount and
composition nmong the different species of woods, among different trees
of the same species, and even among the various parts of the same tree.
Consequently, an infinite amount of painstaking chemical work would be
required to describe and identify all the compounds included in this
group of substances. In this short article a general account of only a
few of them is given. In general, except for some dyes that require
oxidizing treatments to remove them from wood, most of the r.:.t-d.inr
extraneous materials can be divided into tw.o classes: (1) those soluble
in water and (2) those soluble in such neutral organic solvents as ether,
alcohol, or mixtures of alcohol-benzene.

Anong the water-soluble materials is a class of compounds known
as tannins. Some of these are toxic toward wood-destroying fungi and thus,
when present in sufficient quantities, act as natural wood preservatives.
Although tannins are present in only minute quantities in most woods,
in a few, such as hickory, oak, and redwood, they are more plentiful;
their main source of supply for commercial use is chestnut wood and hem-
lock bark. They are extracted from the wood or the bark by means of water
which is subsequently evaporated to obtain a concentrated tannin liquor
or a dry powder, depending on the process employed. Th..se concentrated
tannins are used in the leather and fur industry as they have the property
of reacting with the proteins in hides, making them resistant to putre-

Another water-soluble extraneous material is galactan. It
occurs in large quantities in western larch and can be converted by
hydrolysis to a sugar, galactose, which in turn can be converted to mucic
acid. This acid is adapted for use in the manufacture of baking pc.v.d:-r,
self-rising flours, effervescent salts, and soft drinks. Still another
water-soluble extractive is pinite. This sulir-like substance has been
found in a few conifers. In sugar- pine it is plentiful enough to concen-
trate as a white powder on the surface of the lumber during seasoning in
the kiln and the yard. Then, too, sugar maple is known to contain sugars
and esters which are concentrated from the sap to form such well-known
products as m';ple syrup arnd maple sugar.


Under certain conditions wat r-soluble extractives produce un-
desirable effects in wood, whereas under others they increase its value.
Some of them darken on prolor,-:d exDosure to the atmosphere or to
elevated temperatures. During the seasoning of some species of lumber,
especially by improperly controlled artificial means, these materials
produce, near the surface of the stock, intense discolorations which
cause heavy degrades to otherwise select stock. On the other hand,
some extractives in conjunction with the natural dyes impart harmonious
colors to wood and thereby cnharce the value of lumber. A knowledge
of the ch-.i:-; of these colors du-ring natural or artificial aging
of wood is invaluable to tne architect in selecting the woods best
suited, from an artistic point of view, for the innumerable types of
wood construction.

Compounds found in the class of extraneous materials that are
soluble in neutral organic solvents, in general, are resins, oils, fats,
and waxes. In most of the pines the resinous materials consist of a
mixture of oils and rosin. HoM'errer, in Jeffrey and digger pines the
oily portion is principally noirrmal heptane viwhich belon to a different
class of compounds than do turpentine oils. i'i:-re is a ;o present An
the oily portion minute amounts of aldehydes which are thought to impart
a fruitlike odor, but the rosin is similar to that in the other pines.
Thus far, turpentine oils and oils belonging to the heptane class have
been found only occasionally in the same species. The crude distillate
of oleoresins from Jeffrey and digger pines was early 11ouwn as abieiene,
and it has been used locally in California as a cleansn'tg agent; an
insecticide, and as a constituent of chewing gum, cough syrup, and other
medicinal preparations. A recent new use has arisen fur heptane as a
constituent of a standard fuel for the measurement of "knock" in automo-
bile engines.

A high resin content in lumber is undesirable because it inter-
feres with the proper surfacing of the stock and with the pleasing
appearance and the wearing qualities of surface finishes. In one process
developed for removing the excess resin, the lumber is stacked on trucks
which are pushed into a fairly air-tight shed. The lumber is then sub-
jected to a treatment with turpentine fumes which condense on thp stock
and dissolve the resin on and near the surface of the lumber. The resin
solution then trickles to the floor from which it is conveyed by gravity
to a heated retort. There the turpentine is again vaporized and con-
ducted to the lumber, leaving behind the concentrated rosin for use in
paper sizing and other commercial processes.

A process for recovering resins from wood waste having a high
resin content has been used extensively. In this process the turpentine
is recovered by steam distillation of the wood waste and the rosin is
then dissolved by means of gasoline from which it is recovered by vapor-
izing the solvent. Turpentine and rosin obtained from conifers by this
procedure supplement the gum oleoresins obtained from living trees as
sources of supplies for naval stores.


Fats are also present in the ether extractives of woods.
Some of them are similEr to the solid fats that occur in lard whereas
others are oils at ordinary temperatures. Both fats and oils are formed
by the combination of fatty acids and glycerine. Another class of
compounds closely related to fats and oils are waxes. Th-ese materials
are formed by the combination of free fatty acids and sterols which are
classed as alcohols having a high molecular weight.

Research studies have shown a general distinction between the
ether extractives of the young second-growth sapvood and the heartwood
of southern pines. The content of the sapwood extract is considerably
less than that of the heartwood extract. Moreover, the major portion of
the sapvwood extract consists of fats, waxes) and fatty acids and is
semiliquid in nature. In contrast the major portion of the heartwood
extractives consists of resins and is solid in character" It is likely
that the lower ether-solble extractive content and the more liquid
state of the extractives in the sap-wood than in the heartwood account
for the difference in the pulpLrg qualities of the two types of wood.
These differences in the extractives v:ould seem to expl in whl, the sap-
wood can be pulped by the sulphite process: whereas the heartwood
requires an alkaline process for its successful conversion into pulp.

From this brief discussion it is evident that wood is both
a finished raw product and a storehouse of raw material-. A knowledge
of the chemical composition of the extraneous materials in conjunction
with that of the wood itself offers a direct aid in the silvicultural
control of wood and its properties. Such knowledge forms a scientific
basis for selecting, handling, seasoning, surfacing, finishing, preserv-
ing, and converting wood into pulp and other products -- in short, it
affords a rational cooperative means by which our forests can be more
economically utilized than at present.



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