From Wikipedia,
the free encyclopedia
Resin acids are
protectants and
wood preservatives that are
produced by
parenchymatous
epithelial cells that surround
the
resin ducts in trees from
temperate coniferous forests.
The
resin acids are formed when
two- and three-carbon molecules
couple with
isoprene building units to
form mono-, sesqui-, and
diterpene structures. Resin
acids have two functional groups,
carboxyl group and double
bonds. Nearly all have the same
basic skeleton: a 3-ring fused
system with the empirical formula
C19H29COOH.
Natural occurrence
Pines contain numerous
vertical and radial resin ducts
scattered throughout the entire
wood. The accumulation of resin in
the
heartwood and resin ducts
causes a maximum concentration in
the base of the older trees. Resin
in the
sapwood, however, is less at
the base of the tree and increases
with height.
Natural resins are
water-insoluble mixtures of
compounds, many of which have a
hydroaromatic structure. Mixtures
of isomeric
carboxylic acids, such as
abietic and
pimaric acids, which occur in
rosin in nature in
solvent-free form, in the form
of
tree sap or wood rosin such as
pine
oleoresin, where they are
dissolved in
terpenic
hydrocarbons. They can also be
present as
fossil
coal or
copal resins, in old pine tree
stumps, etc.
Chemical characteristics
Resin acids occur in pines in a
number of isomeric forms having
the molecular formula C19H29COOH
and in some related structures.
The most prevalent resin acids
are:
Abietic-type acids
Pimaric-type acids
Pimaric acid
Production in tall oil
(chemical pulping byproduct)
Commercially, the manufacture
of
wood pulp grade chemical
cellulose using the kraft chemical
pulping processes releases these
resin acid compounds. The
Kraft process is conducted
under strongly basic conditions of
sodium hydroxide,
sodium sulfide and
sodium hydrosulfide which
neutralizes these resin acids,
converting them to their
respective sodium salts, sodium
abietate, ((CH3)4C15H17COONa)
sodium pimarate ((CH3)3(CH2)C15H23COONa)
and so on. In this form, the
sodium salts are insoluble and,
being of lower density that the
spent pulping process liquor,
float to the surface of storage
vessels during the process of
concentration, as a somewhat
gelatinous pasty fluid called
kraft soap, or
resin soap.
Kraft soap can be reneutralized
in the presence of concentrated
sulphuric acid to restore the
acidic forms
abietic acid,
palmiric acid and their
isomers which form the resin acid
component of a pulping byproduct
called
tall oil. Other major
components include fatty acids and
unsaponifiable
sterols.
Resin acids, because of the
same protectant nature they
provide in the trees where they
originate, also impose toxic
implications on the effluent
treatment facilities in pulp
manufacturing plants. Furthermore,
any residual resin acids that pass
the treatment facilities add
toxicity to the stream discharged
to the receiving waters.
Variation with species and
biogeoclimatic zone
The chemical composition of
tall oil varies with the species
of trees used in pulping, and in
turn with geographical location.
For example, the coastal areas of
the southeastern United States
have a high proportion of
Slash Pine (Pinus elliottii);
inland areas of the same region
have a preponderance of
Loblolly Pine (Pinus taeda).
Slash Pine generally contains a
higher concentration of resin
acids than Loblolly Pine.
In general, the tall oil
produced in coastal areas of the
southeastern United States
contains over 40% resin acids and
sometimes as much as 50% or more.
The
fatty acids fraction is
usually lower than the resin
acids, and unsaponifiables amount
to 6-8%. Farther north in
Virginia, the resin acid
content decreases to as low as
30-35% with a corresponding
increase in the fatty acids
present.
Still farther north in
Canada, where mills process
Lodgepole Pine (Pinus
contorta)
Jack Pine (Pinus banksiana),
Eastern White Pine (Pinus
strobus) and
Red Pine (Pinus resinosa),
resin acid levels of 25% are
common with unsaponifiable
contents of 12-25%. Similar
variations may be found in other
parts of the United States and in
other countries. For example,
resin acid values from
Scots Pine (Pinus
sylvestris) in
Finland may vary from 20 to
50%, fatty acids from 35 to 70 %,
and unsaponifiables from 6 to 30%.
In 2005, as an infestation of
the
Mountain pine beetle (Dendroctonus
ponderosae), devastated the
Lodgepole Pine forests of northern
interior
British Columbia, Canada,
resin acid levels three to four
times greater than normal were
detected in infected trees, prior
to death.
