Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to the pressure impregnation of
wood with water-borne wood treatment materials to improve the
properties of the wood. More particularly, the invention relates
to a process for the impregnation of wood in which water-borne
wood treatment materials are deposited within the wood, as by
precipitation or chemical affixation, in a manner that combines
the effectiveness and other advantages of the full-cell process,
with low residual liquids in the wood ohtainable with empty-cell
processes.
BACKGROUND OF THE INVENTION
The present invention con-templates the use of what basic-
ally may be considered to be an "empty-cell" impregnation process,
as distinguished from a "full-cell" process. The essential
difference between these two processes lies in the fact that in
the full-cell process, the liquid forced into the wood is retained
by the wood after impregnation, while in the empty-cell process
most of the treatment fluid is expelled from the wood after
impregnation. The terms "full" and "empty" derive from the fact
that the cells of the wood are substantially filled with impreg-
nants in the full-cell process, but tend only to be coated with
the impregnant in the empty-cell process.
The full-cell process makes use o a vacuum/pressure
impregnation c~cle in which the wood is Eirst placed under vacuum
and then, without admitting air, the treatment vessel is filled
with the treatment liquid. Ater the wood is fully immersed in
the liquid, the pressure is increased to perhaps ten atmospheres
or so and the liquid is Eorced into the wood. After the wood
has been treated to the point of refusal, or until a predetermined
gross absorption of the treatmeht li~uid has been achieved, the
pressure is relieved and the treatment fluid is drained from the
vessel. Usually a short vacuum cycle follows to remove excess
8~
fluid from the surface o~ the wood.
q'he distinctive feature of the empty-cell process is
that at the end of the process, the pressure is reduced to, and
preferably below, the initial pressure within the wood prior to
impregnation so that a kickout of treatment liquid will result.
The most common way to achieve this is to place the wood under
initial pressure prior to the time that it is contacted with the
treatment liquid. This initial pressure is maintained during
the time that the treatment vessel is filled with the treatment
l.iquid and then the pressure is increased to a second, higher
pressure, forcing the treatment liquid into the wood against the
air pressure initially established within the wood. As a result
when the pressure is relieved, the air compressed within the
wood expands and expels much of the liquid that was forced into
the wood. Equivalent results can be obtained by starting the
impregnation while the wood is at or slightly below atmoshpheric
pressure and then pulling a vacuum at the end of the treatment
cycle. In any event, it is common to establish a vacuum in the
treatment vessel after the impregnation pressure has been relieved
to increase the recovery of the treatment liquid and shorten the
period of time in which liquid will exude from the surface of the
wood. The liquid expelled from the wood by the difference between
the internal and external pressures is referred to as '~kickout"
liquid which term is used the meaning so defined throughout the
following description.
The empty-cell process is especially advantageous as
compared with the full-cell process for treating wood with water-
borne materials which may be toxic since the wood, after treatment,
is ready for economical shipment, for further treatment, or for
immediate use since there is no need to dry the wood to remove
the treatment liquid from the interior surfaces of the wood.
Despite the inherent advantage of ending up with "dry"
2 -
wood, the empty-cell process has not, for some purposes, been of
practical utility in impregnating wood for a number of different
reasons. For example, when treating wood with water-soluble pres-
ervatives - for example chromium/copper/arsenic salts known as
"CCA" salts - the kickout that is inherent in empty-cell processes
cannot economically be reused since the kickout fluid will include
water-soluble reducing substances leached from the wood, such as
hemicelluloses, which, it is generally believed, react with the
CCA salts to precipitate a dense sludge that fouls the equipment.
This makes it impossible to recycle without periodically removing
insolubles, and further, the kickout cannot be discharged as
waste because of its toxicity and the danger it poses to the env-
ironment. For these and other reasons, such as the preerential
rate at which CCA salts are e~tracted from solutlon, it has become
standard practice to avoid problems attendant with recycling or
otherwise disposing of depleted CCA solutions by using full-cell
techniques and simply letting the treatment liquid remain in the
wood, until it evaporates, which may take up to several months of
drying in air.
In addition to CCA salts, another effective and commonly
used wood preservative that is difficult to use in ernpty-cell
processes is chlorinated phenol, most commonly the tetra- and
penta-chlorophenols (collectively referred to as "PCP"). PCP is
not soluble in neutral or acid solutions and, in order to orm an
impregnating solution, it is conventional to dissolve PCP in
hiyh-boiling petrochemicals, Stoddard's solvents, kerosene, and
the like. Empty-cell impreynation methods are sornetimes used to
coat the cell walls with the preservative solution since the
hydrocarbon solvents must be recovered to make the process econ-
omical and to prevent bleedlng of the oil-based solution which
would make it impossible to apply conventional ~inishes to the
wood. However, even though most of the treatment solution is
~L~2~
removed from the wood in empty-cell processes, the amount of
solvent consumed represent.s the major portion of the cost of
materials in impregnating the wood with PCP.
To reduce the cost of the oil-based solvents, other proc-
esses have been replacing the empty-cell methods in which the
solvent is a low-boiling liquid that may be recovered and reused.
Typically, in these processes, low-boiling aliphatic hydrocarbon
solvents for PCP are volatilized after impregnation, leaving a
water-insoluble residue of PCP within the wood. These processes
are not without attendant disadvantages which include the increa-
sed cost of treatment apparatus, the need to recover the gasified
solvents, both for purposes of economy and environment protection
and, as has been suggested in the literature, the protection
afforded the wood is less lasting when volatile solvents are used.
A further disadvantage in the use of low-boiling hydro-
carbon solvents is that the protection afEorded the wood at its
outer surfaces is sometimes less than satisfactory. It has been
suggested that the reason for this lies in the fact that during
volatilization, some of the PCP adjacent the surface of the wood
is carried away and the amount of PCP left at this region is
inadequate to protect the wood.
SUMMARY STATEMENT OF THE INVENTION
The present inventlon is directed to providing an improved
process Eor pressure-impregnation oE wood with a water-borne
preservative treatment material, wherein an aqueous solution of
treatment liquid is forced into the wood at a pressure greater
than the ini-tial internal pressure of the wood, the treatmen-t
liquid is retained within the wood under an elevated pressure and
a temperature at least 65C for a time of at ]east one hour and
sufficient to allow a major weight proportion of the preservative
treatment material to become affixed to or deposited within the
wood, and then the pressure is reduced to allow the spent
~,Zff~J~
treatment liquid to be expelled or exude, and then be collected.
It is contemplated that the inventive process as outlined
will be practiced with aqueous solutions of wood-preserving subst-
ances, which substances may comprise salts of copper, chromium or
arsenic or a mixture thereof, or a sodium chlorophenate, or an
alkaline solution of sodium pentachlorophenate.
It is further contemplated that the inventive process as
above recited be performed with heating of the wood to a tempera-
ture from about 65C to about 120C, which heating may be effected
variously by heating the treatment fluid, or by steam, or by the
application of a second heated treatment liquid while maintaining
the elevated pressure.
In a further aspect the invention is to be understood to
include use of a second treatment liquid which may contain wood
treatment agents selected from the group consisting of coloring
agents, wood-softening agents, antichecking agents, film formers,
flame retardants, antistatic agents, polymerizable mixtures and
additional wood preservatives~
It is also contemplated that the process according to-the
invention include the step of pretreatment of the wood with an
acid, which acid may be acetic acid, or with metal ions to
precipitate sugars within the wood.
From yet another aspect the invention may be seen to
include the provision of the step of irnpregnating woocl with a
solution of pentachlorophenol and a low-boiling hydrocarbon or
chlorinated solvent for the pentachlorophenol before the aqueous
treatment liquid is introduced into the vessel, such aqueous
treatment fluid containing CCA salts.
In yet another aspect, the invention is to be understood
to provide the further step of impregnating the wood following the
steps of impreynation and pressure reduction, with creosote.
By the practice of the invention as above outlined, the
-- 5
amounts of treatment materials retained within the wood are maxi-
mized and the retention of liquids within the wood following the
process is reduced to a minimum.
In the case of treatments with CCA salts, the process of
this invention is of particular utility since the kickout liquid
is substantially depleted o~ metal ions hence recovery or disposal
problems are largely avoided. Further, the treated wood is dis-
charged from the treatment vessel in substantially dry state,
thereby permitting of immediate use, shipment, or even subsequent
treatment such as impregnation with creosote ~o meet requirements
for marine applications.
Recognition of the fact that the treatment materials can
be reacted in situ during pressure impregnation makes it possible
to protect wood, using PCP preservatives, without the use of
hydrocarbon solvents. Rather, in the practice of this invention,
sodium penta- or tetra-chlorophenate is dissolved in an alkaline
solution, the wood is impregnated with the solution, and the
solution is held within the wood without permitting kickout of
spent liquid to occur until the natural acidity of the wood
causes precipitation of water-insoluble PCP within the wood. If
the acidity of the wood is not sufficient to precipitate PCP at a
useful rate, the wood may be first treated in an empty-cell proc-
ess with an acid, such as acetic acid, prior to impregnation with
the sodium penta-chlorophenate solution. It is believed that by
acidifyi.ng the penta-chlorophenate to form the insoluble PCP
precipitate in situ in the wood, the retention of the PCP and
protection o:E -the wood is made more lasting than can be achieved
when using either volatile or nonvolatile petroleum-based solvents.
~s would be expected, the reaction between the treatment
materials and the wood is greatly accelerated when the wood is
heated during the time the impregnating solution is held within
-- 6 --
q7
.". . ~:
, 2'h4P~
the wood. Suitable times and temperatures will vary substantially
depending upon the species of wood being treated and the nature
of the treatment liquid, but can easily be determined by simple
experimentation.
DESCRIPTION OF PREFERRED_EM~ODIMENTS OF THE INVENTION
In Examples I to IX detailed process steps are recounted
exemplifying practical modes in which the invention may be put
into effect, and tabular data is presented showing retention of
preservative materials in the treated wood~.`
As the examples will show, the treatment of Southern pine
with CCA salts at varying temperatures of the wood has been found
to be most efficient in the range from about 65C to 121C. At
temperatures lower than these, the reaction rates are inconveniently
slow, and at higher temperatures, damage may be done to the wood.
A preferred temperature range for treating Southern~Pine with
CCA salts is from about 81C to 116C and, more preferably, from
about 93C to 110C.
Treatment times will vary considerably and, depending on
the temperature used in the treatment cycle, satisfactory results
have been obtained using treatment times of from about one to
seven hours. Longer times can, o~ course, be used, but in the
interest of productivity of the process, no purpose is served in
prolonging the treatment time after the desired reactions have
neared or reached completion..
EXAMPLE
A charge o kiln-dry Southern pine tomato stakes having
15~ moisture content, and of yrape stakes of the same wood and
moisture content, was ~iven a modified empty-cell treatment
with a 2.0~ (oxide basis) solution of CCA as follows.
I'he charge comprised thirty tomato stakes measuring 2,5 cm by
2,5 cm by 183 cm (0.035 Cubic meters) and 15 grape stakes
7 --
' ' ~ ,
measuring ~,1 cm by 4,1 cm by 183 cm (0.046 cubic meters).
An ini-tial pressure of 0,7 kg/cm of air above one atmos-
phere was introduced into the treatment vessel and held for five
minutes. The vessel was then filled with the CCA solution
without relieving the initial pressure, and the pressure was
i.ncreased to 7 kg/cm in a forty-~ive minute period by increasing
the pressure 0,7 kg/cm at five minute intervals.
Excess preservative liquid was removed from the vessel
while maintain ng cylinder pressure at 7 kg/cm .
The gross absorption of the CCA solution during the press-
urization period was 575 Kg/M .
The charge was steamed 1.5 hours at 7 kg/cm pressure
with the maximum temperature of 116C being reached in one hour,
and then held at this temperature for 0.5 hours
A kickback sample taken at the end of the steami.ng cycle
had a pH of 3.1.
The charge was exposed to 660 mm Hg vacuum for one hour
before being removed and weighed to determine net solution reten-
tion. The net solution retention obtained during treatment was
164 ~g/M .
Analysis of the original treating solution and kickbackresulting from the treatment Oe this charge gave the ol:Lowing
result:
Sample pH CuO Cr~3 ~S~05 % reduction of:
CuO CrO3 AS25
Treatment 1.5 0.345 0.9580.718 - - -
solution
Kickback 3.1 0.021 0:0160.01993.9 98.3 97.4
_
E~LE II
Precipitation of Cu and Cr from acid copper chromate in
.2æ~s~
in kiln-dry Southern pine (20% moisture content) by steaming
before permitting the kickout to occur.
A piece of kiln-dry Southern pine of diameter 16,5 cm by
45 cm long was impregnated as follows:
A. Preservative Solution:
The solution of acid copper chromate was prepared in 2.38%
strength (oxid~ basis) from a commercial con~entrate "CELCUR~"
providing 3.84% copper sulfate (anhydrous), 5.01% sodium
dichr~mate (anhydrous), and 0.20~ chromic acid (anhydrous) by
dilution with water. The pH of this fresh solution was 3.4
B. Impregnation Cycle:
A pressure of 2,8 kg/cm2 of air atmosphere was initially
held for five minutes, after which the treatment vessel was filled
with the preservative solution at this pressure, and the pressure
was then increased to 9,8 kg/cm and held for two hours.
Excess preservative solution was drained from the vessel
while maintaining the c~linder pressure at 9,8 kg/cm2.
A~kickout sample was taken at the end of the pressure period
but before starting tha steaming, by momentarily reducing the
pressure slightly. The pH of this kickout sample was 3.85.
The gross absorption of preservative during the pressure
period was 469,4 Kg/M3.
The sample was steamecl at 100C Eor three hours while
maintaining 9,8 kg/cm vessel pressure.
A kickout sample taken at the end oE the steaming cycle
had a pH oE 5.45.
The sample was exposed to 660 mm Hg vacuum ~or one hour
before being removed and ~eighed to determine net solution
retention.
A sample of the drip obtained during the Einal vacuum had
g _
a pH of 5.50.
The net solution retention obtained during treatment was
145.7 Kg/M so that the gross retention was reduced by over
320,5 Kg/M .
A disc obtained from the middle of this sample after
treatment was dried i.n an oven to determine its average moisture
contentO Its moisture content expressed as a percentage of oven-dry
weight was 40.3%.
Analysis of the samples obtained during the treatment of
this sample for Cu and Cr yave the results indicated in the table
below~ In this table, Sample I was the original treatment solution;
Sample 2 was the kickout after impregnation but before steaming;
Sample 3 was the kickout after impregnation and steamin~; and
Sample 4 was the dr;p from the wood during the final vacuum.
Sample pH %Cu %reduction % CrO3 % reduction of
of CuO Cr~3
_
1 3.~0 0.717 ~ 1.661
2 3.85 0.628 12.41 1.527 8.07
3 5.45 0.014 98.06 0.027 98.37
4 5.50 0.025 96.58 0.009 99.46
_ .
The disc obtained from this sample after treatment and
steaming indicated complete penetration by the preservative.
E AM LE III
Wood was given an empty-cell pre-treatment with a 0.5~
Barium hydroxide solution prior to treatment with CCA -to determine
i.f the sugars could be precipitated in the wood so that they
would not conta.minate the kickout.
Analysis of the kickout after the CCA impregnation cycle
showed that the reduction oE the trea.tment solution in CuO was
-- 10 --
100.00% and 99.56% in CrO3 and As2O5.
Enough CCA concentrate was added to a porkion of the
kickout to bring its concentratinn up to 2.0~ (oxide basis). No
precipitate occurred in this sample after two weeks' storage in the
laboratory, indicating that the wood sugars were precipitated in
the wood and did not contaminate the kickout -to any observable
extent.
EXAMPLES IV, V AND VI
Samples of Southern pine wood were tre~ted with CCA salts
under varying process conditions t as shown in the following table.
Column headed "Initial Pressure" in the table denotes the pressure
to which the wood was exposed prior to impregnation. Column headed
"Impregnation pressure" indicates the pressure that was established
within the treatment vessel after the vessel was filled with the
treatment liquid. "Steaming Temperature" denotes the ultimate ~-
hlgh temperature reached, over a period of about one hour, after ~-
the impregnation pressure was imposed. "Holding Time" denotes the
period of time during which impregnation pressure and steaming
temperature was maintained within the vessel.
The other columns indicate the percentage of the active
ingredien-ts in the initial treatment solution, the kickout, and
the percentage of the active ingredients that were retained within
the wood. Note that in EXAMPLES IV and V where the temperature
oE the treatment vessel was not increased above ambient, the
deposition of the CCA salts did not begin to approach completion
even aEter a holding time of as long as six hours. In contrast
to thisl EXAMPLE VI shows th~t at a steaminy temperature of 98C
well over 95% of the CCA salts were deposited in the wood after a
holding time of onl~ two hours.
-- 11 --
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- 12 --
",,"
EXAMPLE VII
A piece of kiln-dry Southern pine 14,6 cm in diameter
and 45 cm long was impregnated as follows:
A. Preservative Solution: 1.50% technical grade
~ sodium penta-chlorophenate in water; original p~I = 10.3.
B. Impregnation Cycle:
The wood was placed in a pressure treatment vessel wh~ch
was then pressurized with air at 2.1 kg/cm2. Without relieving
this pressure, the vessel was filled with the preservative
solution and the air pressure was increased to 10.5 kg/cm2 which
was held for two hours. ~ .:
The preservative was drained away from the wood while the
cylinder pressure was maintained at 10.5 kg~cm . Gross absGrp-
tion of preservative during the pressure period was 523 Kg./~3.
The wood was then steamed for three hours at 100 C while
maintaining 10.5 kg/cm pressure in the cylinder. A kickout
sample taken by momentarily reducing the pressure at the end of
the steaming period had a pH of 5Ø The wood was placed under
a vacuum of 660 mm Hg for one hour and was then removed from the
cylinder and weighed. The net solution retention by gain in
weight during treatment was 122 Kg/M3 which means that the
amount of kickout expressed as a percentage of total gross
absorption was 76.6%.
A sample of the drip recovered during the final vacuum
had a pH of 5.15.
C. Analysis of Borings ~or PCP:
Three increment cores were taken near midlength of the
sample at 120 intervals around the circumference. The cores
were zoned .into 1,~5 cm segments and assayed for PCP by the lime
ignition method. The results of the analyses are tabulated on
the next page.
- 13 -
L2Z~
Depth from Surface, cm. PCP Content, Kg/M
0.0 - 1.25 6.33
1,25 -2.54 2.47
2,54 - 3,8 3,12
3,8 - 5,0 2,47
D. Analysis of Original Treating Solution and Kickout
After Steaming for PCP:
Samples of the original treating solution and kickout were
analyzed by the lime igni-tion method Eor PCP with results as
follows:
Original Treating Soluti~n.......... 1O143% PCP content
Kickout after steaming.............. 0.026~ PCP content.
The percentage reduction in PCP (i.e., retained in the wood)
was 97.7%,
E. Test For Fixation of PCP to Wood:
A disc of axial length 1,90 cm in length was cut from
the midlength of the treated pole section. A strip 1,90 cm wide
was sawn from this disc so -that the pith was in -the center of the
strip. The outer 7,6 cm on opposite sides of the pitch in this
strip was sectioned into 1,25 cm incremen-ts for the acid test and
into 2,54 cm increments for the pH determination.
To test for acid, each block w~s splintered into 3,1 mm
square pieces and covered with 50 ml of boiling disLilled water.
The mixture was shaken for -thirty minu-tes and fil-tered through
Whatm~n 1~541 Eilter paper. 3 ml of the filtrate was placed in a
test tube and dilute HCl was added to determine if any PCP precip-
itated upon addition of the MCl. The sensitivity o~ the method
related is 100 ppm.
The results of the acid test are shown by table in the
following page.
- 14 -
Sample Distance From Wood Surface Precipitate
measured in cm Occurrence ::
Present Absent
- ,
0.0 to 1,25 very slight
1,5 to 2,54 yes
2,54 to 3,8 yes
3,8 to 5,0 yes
5,0 to 6,3 yes
6,3 to 7,6 yes
F. Moisture Content After Treatment:
A disc 1,90 cm thick was sawed from the middle of the
treated pole section and oven-dried to determine the average
moisture content immediately after treatment. The moisture
content of this disc was 38.6%.
EXAMP~E VIII
The acidity of the wood being treated was relied on
solely in this Examp~e to reduce the pH of the treatment solution
to precipitate PCP within the wood. The wood was first treated
with acetic acid in a modified empty~cell process prior to
impreynation with the pentachlorophenate solution to determine
if the added acidity would make the process more efficient.
A sample of Southern pine wood was placed in a treatment
vessel and placed under 0,7 kg/cm2 air pressure above atmosphere~
W:ithout relieviny the pressure, an 0.8 molar solution o.E ~lacial
acetic acid was introduced :into the vessel and the ai:r pressure
was lnc~reasecl to 8,4 ]cg/cm and held Eor two hours. The acetic
acid was drained away :Erom the wood while maintaininy 8,4 ky/cm2
air pressùre and the wood was then steamed for three hours
at 99C. The pressure was then relieved and a vacuum pulled for
one hour.
Immediately following the above acid treatment of the wood,
- 15 -
4~
the identical process operations were repeated as recited in
Example VII using a 4% alkaline solution of sodium penta-chloro-
phenate as the impregnate.
~ fter treatment with PCP r the kickout was found to contain
less than 0,008% PCP thus indicating -that over 99.8% of the PCP
in the treatment solution was deposited in the wood. A test for
leachable PCP as described in Example 1 above was run, and the
results were negative, indicating that the PCP precipitated in
the wood could not be leached in observable quantities (i.e.,
greater than 100 ppm) by boiling the treated wood in water.
Borings were made in the -treated wood and the amount of
PCP depoeited in the wood was determined at various depths by
lime ignition:
_ Sample PCP, Kg/M
0,0 to l,25 cm 17,75
l,25 to 2,54 13,56
2,54 to 3,8 12,68
3,8 to 5,00 12,28
; . n
The preceding Examples VII and VIII demonstrate that
the chemically precip~tated PCP is tightly held and is not
leachable, if at all, except in tract amounts. It is at once
obvious that b~ achieving this fixation o~ -the PCP within the
wood, the e~ectiveness oE the wood preservative will be maint-
ained over prolonyed periods of -time.
~ secon~ar~ bene~it whi.ch is yained in afEixiny the PCP
within the wood lies in the Eact that the potential danyer of PCP
to the environment is greatly reduced when the PCP is tightly
held within the wood. In contrast to the results obtained
through the practice of this invention, when conventional high-
boiling petrochemical solvents are used and PCP is not precipitated
- 16 -
in the wood but i5 held in solution by organic solvents, the
PCP may leach from the wood over a period of time, depending on
such factors as the type of soil and other yround conditions
to which the wood is exposed, changes in temperature, barometric
pressure, humidity, and other ambient conditions.
EXAMPI,E IX
_
A charge of air-dried pine fence posts with 25~ moisture
content was placed in a pressure vessel . The posts were of
dimensions lO cm diameter by about 260 cm length. An initial
air pressure of 1,4 kg/cm2 above atmosphere was introduced into
the treatment vessel and held for about five minutes.
The vessel was then filled with a CCA solution of 2%
strength (oxide basis) as in EXAMPLE I without relieving the
initial vessel pressure. The pressure was increased to over
9,8 kg/cm over a period of about 55 minutes. The temperature
of the CCA impregnating solution was about 32C and the gross
absorption achieved was about 503 Kg/M .
When the re~uired gross absorption had been obtained, steam
was admitted to the coils in the cylinder and the CCA solution
in the cylinder was heated to about 88C within 30 minutes and
this temperature was maintained for 60 minutes. No precipitating
of CCA salts from the treatment solution was noted during this
heating cycle.
At the end of the heating period, the CCA solution was
removed from the cylinder wi-thout permitting the pressure on the
system to chanye, following which the pressure on the system was
released to collect the kickout separate e rom the CCA solution.
The temperature Oe the kickout solution was 82C. A final
vacuum of 60 minutes at 655 mm Hy followed after releasing the
pressure on the system.
The wood was removed from the cylinder and weiyhed. It
was determined tha-t the net preservative solution retention was
- 17 -
4~
112 Kg/M .
Results of analyses performecl on the CCA be:fore treatment,
after -treatment and heating, and on a sample of the kickout
solution after heating, are contained in the table below:
SOLUrION p~:[ METAL CO2~T~, % OXIDE BASIS
CuO CrO3 AS205 rrotal Salt
CCA before -treatment 1.92 0.304 0.870 0.643 1.817
CCA after treatment 2.03 suhstantially the same as ahove
and heating
Kickout 4.18 0.008 0.017 0.022 0.047
An increment core was taken from midlength of each post
for analysis for Cu, Cr and As retention after treatmentO The
cores were cut into 1,25 cm segments and similar segments were
combined for analysis. Results for these analyses are contained
in the table below:
Depth From Surface, cm. Retention of Metals Kg/M
~Oxide Basis)
CuO CrO3 As2O5 Total Salt
0.o to 1,25 2.58 5.64 4.02 12.26
1,25 ~o 2.54 1,97 3,91 0.30 6.17
2.54 to 3,8 1,18 2,84 2,24 ~,24
rrhe modi:Eied empty-cell process of this invention has
been descrihed primarily w:i.th regard to -the impreynation of wood
w:ith sodium chlo:r:i.natecl phenates and CC~ salts, but it can
readily be unclerstood hy those of ordinary skill in the wood
treatment arts that the invention is of utility in treating wood
with other wood conditioners. For example, the water-borne
materials may include such things as wood-softening agents, antl-
checking agents, film-formers, coloriny ayents, flame retardants,
30 antistatic agents, dimensional stabilizers, and other wood-treating
-- 18 --
: :
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agents. The process of this invention may also be used to leach
materials, such as sugars, from wood or conversely to precipitate
sugars in the wood prior to a subsequent preservation step. The
pH of the treatment liquid can be adjusted to maximize solubiliz-
ation of the sugars and, if it is the object to fix the sugars
in the wood, cations such as barium or copper may be included in
the treatment liquid to form insoluble products with the sugars.
The modified empty-cell process of this invention makes
it possible to conduct a plurality of sequential impregnations
without the intervening drying or curing steps required in the
full-cell process. For example, substantially immediately after
wood is treated with CCA salts in accordance with this invention,
it may be impregnated with an oil-based preservative. Another
example would be to follow the CCA treatment with a PCP treatment.
This increases the degree of protection for the wood and is
advantageous if arsenic salts must be excluded from the treatment
liquid because of environmental hazards.
In a further modification of this invention, CCA salts
can be de~osited at the surface regions of wood while the wood is
being treated with a solution of PCP and liquefied hydrocarbon.
When the pressure is relieved on the system, volatilization of
the hydrocarbon will cause kickout of the CCA treatment liquid.
In the above examples, the treatment solution was removed
Erom contact with the wood, while maintaining impregnation
pressures, prior to the time that the wood was heated. This is
not essential and, if desired, the temperature of the wood may be
raised by heatiny the impregnating solution, as by steam coils,
prior to the time it is drained from the vessel. Ln another
variation of the practice of this invention, the treatment
solution may, in some instances, be heated prior to the time it is
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l~Z~
introduced into the vessel. Also, the treatment liquid may be
drained from the vessel while maintaining sufficient pressure to
avoid kickout, and s-team or a second liquid used to heat the woodO
In this latter regard, a liquid may be intxoduced;' into
the vessel while maintaining sufficient pressure to prevent
kickout. If a hot water bath is used for this final treatment,
it may prove advantageous to include water-borne wood treatment
materials such as the above-mentioned wood-softening agents,
anti-checking agents, film-formers, coloring agents, flame
retardants, antistatic agents, dimensional stabilizers, and
other wood-treating agents. Also, if the first treatment was
with PCP, a dilute solution of CCA salts may advantageously be
included in the water to provide additional protection to the
surface of the wood. Since the CCA salts will tightly adhere
to the wood, this additional protection may prove to be of value
to protect against any possible loss or migration of the PCP
from the surface areas of the wood. Thus, it can be understood
that this final treatment step may serve not only to aid in
precipitating or affixing the preservative to -the wood, but also
to improve at least the surface properties of the wood.
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