syntans
A contraction of "synthetic tannins," which are
chemicals that combine with, or affect, the
protein constituents of hides and skins and
produce a product that is flexible, porous, and
has the desirable qualities of leather. The most
widely known syntans are made by treating aromatic
substances, e.g., cresols, phenols, naphthalenes,
etc., with formaldehyde and sulfuric acid. There
are many variations in the ingredients of syntans,
relative quantities used, and methods of
manufacture. Syntans produce white or buff-colored
leather, depending on the ingredients, which
darken upon exposure to light, and generally
behave much like vegetable-tanned leathers.
Although syntans do exist which can be used alone
to produce leather (so-called exchange or
replacement syntans), many syntans lack the
filling power of vegetable tannins and produce an
undesirably thin, "papery" leather. They are also
more expensive than the natural tannins. Syntans
do have desirable properties, however, and are
widely used in both chrome and vegetable tannages.
When used in conjunction with other tanning
agents, where they are known as "auxiliary
syntans," they perform the following functions: 1)
the presence of 5% syntan helps dissolve solid
vegetable tannin extracts and reduces any tendency
to form REDS
(condensed tannins) or BLOOM (pyrogallol
tannins); 2) a pretannage with 5 to 10% syntan
improves the shade, i.e., makes it paler, and the
levelness of color of a subsequent vegetable
tannage; 3) a pretannage with a syntan or
admixture with a vegetable tannage improves
penetration of tannin into the skin; 4) when
syntan is used with a vegetable tannin the leather
develops a more uniform but paler color upon being
dyed, hut the syntan generally prevents the
development of deep, full shades: 5) some types of
syntan may be adjusted with an alkali to a pH of
6.0 to become "neutral syntans," often called
synthetic mordants (but should be called
"synthetic leveling agents") which have value in
dyeing leather: and 6) some syntans retard mold
growth and/ or remove iron stains. (248 , 291 , 306 , 363 )
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