Note: Descriptions are shown in the official language in which they were submitted.
35~
Background of the Invention
The present invention relates to a process for impregnating wood and
other porous materials with impregnants. More particularly, this invention
I~,relates to a process and composition for impregnating wood and other cellulosic ~
'~porous materi dlS Wi th impregnants to preserve these materials, .~ :
Impregnants like wood preservatives, fire retardants, dyes, water
repellants, and other wood treating compositions have been added to wood for.. many years. The degree of penetration of the impregnant into the wood varies ~ .
from treatment to treatment. The treatment that gives the maximum penetration
is a pressure treatment. In a pressure treatment a positive external pressure
is applied -to the wood to -force lhe impregnating fluid into the pores of the
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wood. In many pressure treatments it is customary to use an impregnating f'luid
consist;ng of an impregnant dissolved in solution. The solution may be com-
posed of certain solid organic compounds dissolved in petroleum distil1ates
, or composed of halogenated hydrocar~ons.
il There are certain inherent dlsadvantages when an imprègnant is
applied to the wood in such a non-aqueous solution. One disadvantage is migra-
'l~ion which is a phenomenon where the impregnant, after being deposited in the
'Iwood, moves to the peripheral areas of the wood due to the movement of residual
llsolvent remaining in the wood. Another disadvantage which is related to migra-~'tion is blooming. Blooming is a phenomenon where the impregnant deposited in
;the wood crystallizes out of the solvent onto the surface of the treated wood.
This phenomenon is believed to be caused by the migration of the solvent in the
treated wood to the surface of the treated wood and this migrating solvent
~¦brings along with it the dissolved impregnant which forms crystals on the sur-~face of the treated wood. Since some lmpregnant is lost because of blooming,
,Ithe amount of impregnant used to treat the wood must be greater than the amount
;,that is desired to be retained in the wood. In addition to waste, this situ-
llation leads to a problem in treating thin pieces of wood with impregnant when
I 'a volatile solvent is used. Another disadvantage is the difficulty in obtain-
2n ',ing a treated wood that has a controlled distribution of the impregnant within
~!the treated areas.
The art has tried to overcome some of these disadvantages by using
anti-blooming agents or by removing the solvents from the wood once the im-
pregnant is in the wood. Anti-blooming agents usually have a relatively high
llviscos'ity and a high'solvency for the impregnant~ and do not readily volatilize
jlfrom the wood. These agents may also contribute to water repellency, and act
as an auxilliary solvent. Typical anti-blooming agents that are used when the
impregnant is pentachlorophenol are polypropylene glycol, trixylylphosphate,
linseed oil, ester gum, long oil alkyl, and o-dichlorobenzene. The removal of
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the solvent from the treated wood ostenslbly leaves only the impregnant in the
treated wood. Recovery of the solvent reduces the amount oF blooming and makes
; an impregnation process more economical by saving expensive solvents that can
ibe reused, but when the solvent is removed it brings some of the impregnant
Iwith it. Also, it is difficlllt to remove all of the solvent because some of
the solvent is retained in the wood due to entrapment, and this leads to post-
treatment blooming.
l There are several processes where the impregnant is mainly a preser-
il
¦vative that is deposited in the wood by a pressurized impregnation treatment
lin order to reduce to some degree the dlsadvantages of migration and blooming.
One example of such a process, United States Patent No. 3,200,003, (Bescher),
discloses impregnating wood with a solution comprised of a carrier, a co-
solvent, and a preservative. The carrier is an aliphatic hydrocarbon solvent,
~Iwhich boils below the boiling point of water and which readily liquifies and
llwhich contains the co-solvent to assist the preservative into solution. The~
~co-solvent has less than 10% water solubility and greater than 25% solubility
for the preservative and a solubility in the solvent used as the carrier for
the preservative. One example is the use of the preservative, pentachloro-
' phenol, dissolved in the co-solvent, isopropyl el;her, and both are dissolved
in the bulk liquid carrier, butane.
An example of a pressure treatment which uses a solvent as a bulk
~liquid carrier for the preservative is Canadian Patent 863,885, (Dunn et al.~.
This patent teaches impregnating wood with a fluid containing a halogenated
hydrocarbon solvent and optionally one or more modifying agents. The modifying
. ,j ~ .-
agents are those solvent-soluble or solvent dispersible chemical compounds and
~resins which are non-volatile below about 250F. (121C.). Examples of such
modifying agents are polymerizable ingredients like styrene, acrylic monomers
and copolymers ~or dimensional stabilization, fire retardants for thermal pro-
tection, dyes for color and preservatives for protection from decay. All of
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the modifying agents are soluble in the halogenated hydrocarbon solvent which
acts as the bulk liquid carrier. After the fluid penetrates the wood the
halogenated solvent is removed from the wood by heating the impregnated wo~d
with steam.
Another example where a pressure treatment is used and where a sol-
vent is used as a bulk liquid carrier for the impregnant is United States
Patent No. 3,785,770 (Hudson). A wood treating composition is produced by treat
ing wood with pentachlorophenol dissolved in a narrow boiling range of mineral-
spirits which acts as a solvent carrier. A small amount of polypropylene glycol
is added as an anti-blooming agent and a thermoplastic hydrocarbon resin is
added as a water repellent. Also, di-octylphthalate may be aclded to aid in
suppressing blooming. After this wood treating composition has impregnated the
wood, the mineral spirits solvent is removed from the wood.
Impregnation of wood with an impregr,ant by the above desc~ibed pres-
sure treatments purport to reduce blooming, but the wood treated by these pro-
cesses generally nnust be washed after impregnation to remove some oF the bloom-ed particles present immediately after impregnation.
It is well known in the art that wood can be impregnated with vinyl
monomers such as styrene, methyl methacrylate, acrylonitrile and vinyl acetate. ~ -
Subsequently, these monomers are polymerized in situ to improve the dimensional
stability of tne wood. Polymerization is induced either by action of a high
ener~v radiatiGn or a thermal decomposition of a chemical free radical precur-
sor like benzoyl peroxide.
The art has not developed a method of impregnating wood with an im-
pregnant that results in a controlled distribution of impregnant in the treated
wood witn little or no blooming. The above-mentioned processes of United
States Patents Nos. 3,~00,003 and 3,785,770, and Canadian Patent No. 863,885,
purport to reduce blooming but the treated wood must be washed after impregna-
tion to remove some of the bloomed particles which appear on the surface of the
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wood immediately after impregnation. Also, the treated wood is subject to post
treatment blooming since all of the so1vent which acts as a bulk liquid carrier
can not be removed during the process.
The object of this invention is to provide a process and composition
l for more permanently depositing an impregnant in the wood by a controlled re-
¦¦action which allows for better retention and controll~d distribution of the im-
¦¦pregnant in the wood and which reduces the amount of blooming with its concom-¦itant loss o~ impregnant and which facilitates recovery of the bulk l;quid
carrier and which obviates the need of washing treated wood after treatment 1~ ;~
and which does not affect the strength or appearance of the wood.
.
Summary of the Invention
¦ In accordance with this invention, ;t has been found that an i~preg-
¦nant for wood can be more permanently deposited in the wood with controlled
¦distribution and still be effective when after penetrating the wood the impreg-nant is immobilized from the solvent or solvents used to facilitate penetration
¦of the wood. Accordingly, the process of thi.s invention in its broadest as-
pects involves treating wood with a single phase non-aqueous system containing~ :~
an impregnant, and a reactive solvent so that both the impregnant and reactive
solvent penetrate the wood, and then,.reacting the reactive solvent so that
the impregnant is substantially insoluble in the reacted reactive solvent. A .`
liquid carrier ~s used with the impregnant and the reactive solvent to
facilitate the penetration of the wood, the reactive solvent being
soluble in this liquid carrier while the impreynant is substantially insoluble
in the liquidi carrier. : .
The impregnants used in the process of this invention are wood treat-
Iling agents that are put in~o the wood to protect the wood from damage and de- :
j¦terioration. Examples of such wood treating agents are preservatives and fire,¦retardants, dyes, water repel~ants, and other wood treating compositions. Thel ~
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amount of impregnant used is the amount necessary to treat the wood effectively.This eff`ectlve amount is the amount of impregnant which suffices to impart
preservative, flame retardant, dye or water repellant character to the wood.
,The effective amount of impregnant will vary depending upon the impregnant
used and the end-use of the impregnated wood. The effective amount for a
part~cular impregnant and end-use can be deter~ined by consulting the literatureto determine the threshold value of that impregnant for protection of soil
blocks. Then the effective amount is at least equal to or around the amount
of the threshold value. The threshold value for soil blocks may be obtained ' lo ',from the literature, for example, American Wood Preservers' Association Stan-
dards and American Wood Preservers' Association Journal, British Wood Preserv-
ers' Assoclation Standards, Forest Product Reserach Society Journal, Journal
of Wood and Fiber, Journal Institute of Wood Science, and Holzforschung.
The reactive solvent is a non-aqueous compound or mixture of
compounds that keeps the impregnant in solution and that can be reacted so
the impregnant is caused to be substantially insoluble in the reacted
reactive solvent. A liquid carrier is used in addition to the solution of
impregnant and reactive solvent, and the reactive solvent keeps the
impregnant dissolved in the three component non-aqueous impregnating system
of impregnant, reactive solvent and liquid carrier. The reactive solvent
is solu'ole in the liquid carrier while the impregnant is substantially
insoluble in the liquid carrier. Examples of types of reactive solvents I -
are water insoluble polymerizable monomers, insoluble complex-forming agents,
and decomposition product-forming agents. The amount of reactive solvent
that is needed is the amount necessary to keep the impregnant solubilized
before the reactive solvent is reacted. The impregnant is immobilized by
being substantially insoluble in the reacted reactive solvent and liquid
carrier.
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The liquid carrier should be an inert liquid in which the
reactive solvent is soluble but the impregnant is substantially insoluble.
Additionally, the liquid carrier should have a low viscoslty and a high
penetrating ability in wood. The amount of liquid carrier needed is at
least that amount necessary to dissolve the reactive solvent.
The contacting of the w~od by the process o~ this inv2ntion is
carried out at superatmospheric pressure. A full cell or an empty cell
process may be utilized. The contacting must be in such a way to allow
penetration or impregnatior~ of the wood by the impregnant, the reactive
solvent and the liquid carrier.
_ .. . , . _ . .
The manner in which the reactive solvent is reacted so that the im-
pregnant is insoluble in the reacted reactive solvent and the liquid carrier
and any other solvent used differs with the type of reactive solve~t used.
When the reactive solvent is a polymerizable monomer or a mixture thereof~ it
is reacted by subjecting the ;mpregnated wood to high energy radiation or heat.
In an addition polymerization the quantity of high energy radiation or heat
needed to effect polymerization may be lessened by using an initiator. This
use of an initiator can avoid the possibility of the wood being damaged ~rom
the large quantity of high.energy radiation or large quantity of heat needed
to effect polymerization. The initiator need not be a true catalyst because
some of the initiator may take part permanently in the reaction and appear
chemically combined with the resulting polymer. The initiator may undergo
¦¦decomposition by heat, or decomposition as a photosensitizer under the influenc~
¦of a photon for surface layer reaction, or decomposition by high-energy elemen-l tary particles, such as electrons, protons, alpha particles or neutrons. This
i decomposition forms a free radical which attacks the monomer in such a way as
to form polymers. When the polymers are formed the reacted reactive solvent
no longer keeps the impregnant dissolved in solution; consequently, the polymer
is a non-solvent for the impregnant
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The liquid carrier ~lsed with the impregnant and reactive
solvent is removed from the treated wood after the reactive solvent ~orms
a non-solvent for the impregnant. The rea~tive solvont is solubl~ in the
liquid carrier but the non-solvent or the re~cted reactive solvent-may or
may not be soluble in the liquid carrier.
When a reactive solvent is used that remains in the wood after
it is reacted to become a non-solvent for the impregnant, a wood product
is produced that contains the impregnant and the reacted reactive solvent.
The solution used to contact the wood in order.to produce such a wood
product is composed of an impreqnant dissolved in solution of a reactive
solven~ which is soluble in the liquid carrier but the impregnant is
substantially insoluble in the liqu.id carrier. The contacting solution may
also contain cosolvents which aid in dissolving the reactive solvent into
the liquid carrier or which aid in dissolving the impregnant into the
reactive solvent.
1~ . ..
Description of the Invention
Generally, in the process of this invention the i~pregnant used to
l treat the wood is a preservative or fire retardant. The preservative may be
! any o~ the solvent soluble toxic preservatives which are often referred to as
20 l¦toxic salts. These toxic salts, of which some are not salts in the technical
~sense, generally include what is referred to as the oil-borne preservatives. P
¦IExamples of the solvent soluble toxic preservatives include chlorinated organic ~.
compounds, metal organic compounds and inorganic compounds. The chlorinated
llorganic compounds include pentachlorophenol; 2,4-dinitrochlorobenzene; chloro-ilnaphthalene; l,-chlorobetanaphthol; 2,4-chloroalphanaphthol; trichlorobenzene;!! tetrachlorophenol; 2,4,5-trichlorophenol; 2,4,6-trichlorophenol; chloro-2-
phenylphenol; 2-chloro-4-phenylphenol; tetrachloro-naphthalene-pentachloropheno
I
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and 1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a - octahypro-1,4-endo,
` ¦ exo-5,8-dimethanonaphthalene which is better known as "Dieldrin". The metal
.. lorganic compounds include copper naphthenate, copper resinate, copper abietin-
. ate, zinc naphthenate, zinc resinate, zinc abietinate, ethyl mercuric acetate,
; 5 ethyl mercuric chloride, ethyl mercuric oleate, phenyl mercuric acetate, phenyl
ercuric chloride, phenyl mercuric oleate, solubilized copper-8-quinolinolate,
¦ copper pentachlorophenol, pentachlorophenol-zinc-naphthenate, sodium penta-
chlorophenol, and tributyltin acetate and tributyl lead acetate and tributyltin~oxide.
~, 10 When a polymerizable monomer is used as the reactive solvent the
monomer is a solvent for the preservative. By being a solvent for the preser-
, vative, the reactive solvent contains the preservative and keeps the preserva
I ¦tive in solution in a three component non-aqueous impregnating system of
¦`preservative, reactive solvent and liquid carrjer. Any monomer that is water
¦¦insoluble and a solvent for the preservative~ and can undergo addition polymer-
¦¦ization, condensation polymerization, homopolymerization, copolymerization or
: ~!ionic polymeri2ation may be used as the reactive solvent. For example, when
the preservative is pentachlorophenol, examples of suitable polymerizable
monomers are styrene, vinyl acetate, acrylonitrile, bu~yl acrylate, methacrylo-
Initrile and methyl acrylate. Also, mixtures of these compounds like a styrene-
~ llacrylonitrile mixture may be used. Also a cosolvent may be used to aid in
I ~¦dissolving the pentachlorophenol into the polymerizable monorner. Good co-
solvents are rnethanol, toluene, benzene, nitrobenzene, di- and tri-chloro-
~jbenzenes, alkyl benzenes, hydroxybenzenes, xylene, ethyl ether9 isopropyl
~: 25 ¦ ether, vinyl ethyl ether, dibutyl ether9 dibutyl ketone, diisobutyl ketone,
methylisobutyl ketone, benzonitrile, decalin, ~etralln, butyraldehyde, iso-
butyraldehyde and polymerizable monomers that act as reactive solvents. When
the cosolvent is not a reac~ive solvent the efficiency of the process of this
invention is decreased. This decrease may result in a small arnount of blooming
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but this small amount of blooming would still be an improvement over the prior
- llart processes.
I Other specific preservatives or fire retardants may be used with sui~-
able monomers. Tributyltin acetate or tributyl lead acetate may be used with
1 5 styrene or acrylonitrile or methacrylonitrile or mi~tures of these compounds.
;~ The preservative "Dieldrin" may be used with such monomers as vinyl acetate,
`,1' acrylonitrile, butyl acrylate, methacrylonitrile, or methyl acrylate or mixtures
of these compounds. The dibasic fire retardant magnesium phosphate may be used
with the reactive solvent acryionitrile, and the liquid carrier, pentane. A
- ~ 10 Ithree component non-aqueous impregnant system with basic magnesium phosphate
includes 5 percent by weight magnesium phosphate, 5 percent by weight acrylo-
~, ~nitrile and 89.9 percent pentane and 0.1 percent by weight benzoyl peroxide.
These examples of specific preservatives and fire retardants being used with
specific monomers are not limitations on the scope of this invention. Any non-
IS aqueous polymerizable monomer may be used for any solvent soluble impregnant
as long as the impregnant is known by those skilled in the art to be soluble
i in the monomer.
¦ For monomers that undergo addition polymerization, initiators such
as: peroxides, like acetyl peroxide, benzoyl peroxide, and lauroyl peroxide;
¦ or hydroperoxides, like cumene hydropero~ide or azo compounds, 1ike 2,2`bisazo-
¦ isobutylnitrile may be used. These initiators decompose under the influence
of heat, or high energy elementary particles such as electrons, protons, alpha
,particles or neutrons to form free radicals which initiate polymerization of
¦the monomer. Certain vinyl type monomers do not respond to free-radical initi-
:: : , . :
Iation but these monomers like propylene, isobutylene, and most vinyl ethers can~
be initiated by Friedel-Crafts-type catalysts. Catalysts of this type known
¦to those skilled in the art are boron ~rifluoride, aluminum chloride, stannic
chloride and aluminum bromide with co-catalysts of water and acetic acid.
Other initiators that are known to those ski11ed in the art may be used.
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¦ The liquid carrier used to facilitate the impregnation of wood with
the reactive solvent and the preservative is a non-aqueous compound in the
!~ liquid state in whlch the reactive solvent is soluble but the preservative isllsubstantially insoluble. This liquid carrier should be easy to recover so it
¦¦can be reused, if desired. Examples of such a liquid carrier are aliphatic
¦Ihydrocarbon compounds which boil below the boiling point of water at ambient
!' atmospheric pressure and liquify readily at ambient atmospheric temperatures
when placed under elevated pressure. When pentachlorophenol is the preserva-
tive such liquid carriers as liquified petroleum gas, liquified propane,
10 i!butane, iso-butane and pentane are particularly recommended. Pentachlorophenol
, .
¦lmay be slightly soluble in these liquid carriers. This solubility skill is
¦insignificant enough so that the pentachlorophenol is substantially insoluble
in these compounds. Other examples of liquid carriers that can be used with
specific impregnants include: aromatic hydrocarbons, petroleum distillates or
, any liquid wh~ch is inert to the impregnant and reactive solvent and in which
I-the impregnant is insoluble.
j The impregnant and the reactive solvent are added to the wood
in conjunction with a liquid carrier. The use of a liquid carrier
I reduces the amount of reactive solvent used. Also, the liquid carrier
can be recovered and reused.
.,~ 11
The three component non-aqueous impregnating system of impregnant and
I'reactive solvent and liquid carrier can be added to the wood by either a full
¦cell or empty cell process. This solution system must be injected into the
¦¦woo-d under pressure at a temperature lower than that needed to react the re-
active solvent. If more heat is used, the reactive solvent wou1d react before
maximum penetration of the wood could be obtained and maybe beFore any of the
impregnant could penetrate the wood.
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The empty cell procedure allows the recovery of some liquid carrier
that may remain in the wood after the bulk of the liquid carrier is removed
by volatilization. This remaining liquid carrier is removed from the wood by
the expansion of a non-condensable ~as which is placed in the wood before the
¦ impregnant, reactive solvent~ and liquid.carrier. Compressed air may be used
I as the non-condensable gas, but because the liquid carrier may have a combus-
¦¦tible nature, an inert gas like nitrogen may be used. In the empty cell pro-
~cedure the wood is placed in a ~ressure v~ssel, commonly a horizontal cylinder,lland inert gas like nitrogen is introduced into the cylinder before the impreg-1 10 ¦nant solution. In this manner a cushion of inert gas is formed within the wood
¦under the impregnant solution.
~1 An impregnant solution is then forced into the cylinder and into the
- Ilwood. Pressures of up to 100-200 pounds per square inch may be used to force
¦Ithe impregnant solution deep into the wood. A pressure is maintained even
~Iwhile the impregnant solution is r~moved from, the cylinder. While still fully. I saturated with solution and under pressure, the wood is heated for a sufficient
time in order to cause the reactive solvent to react. The wood may be heated
. by any manner known to those skilled in the art. Heating mediums that can be
used include hot butane vapors or hot butane liq~id or water or steam. The
2~ 1 high pressures in the wood prevent any absorption of water and still allows
the treatment to be dry. Once the reactive solvent is reacted and immobilized,
vapor recovery and vacuum phases can be used to recover as much of the liquid
carrier as possible. A vacuum can be applied so the compressed inert gas ex-
pands in the wood cells and forces any remaining liquid carrier out of the
wood. There is no loss of impregnant in this procedure because the impregnant
i¦is substantially insoluble in the liquid carrier and the reacted reac~ive sol-vent- Some, all or none of the reacted reactive solvent may be removed with
the llquid carrier depending upon what type of reactive solvent is used.
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1 In the full cell procedure a high vacuum is applied initially to the
pressure vessel containing the wood. An impregnating solution is added to the
I cylinder and surrounds the wood while the vacuum is maintained. Positive pres-
; sure is then applied to force the impregnant a'long with the reactive solvent
and liquid carrier into the wood. This positive pressure step is still a modi-
¦ fied heat pressure step, i.e., the amount of heat used cannot exceed the heat
¦ required to react the reactive solvent. If the positive pressure needed cannot
be reached by using the limited amount of heat, then other methods of develop-
ing pressure must be used. The positive pressure is held to allow penetration
of the wood by the impregnant, reactive solvent and liquid carrier. The
cylinder is emptied while a sufficient pressure is maintained to keep most of
th'e penetrated impregnant, reactive solvent, and liquid carrier in the wood.
The cylinder is then heated so that the reactive solvent reacts and the im-~
pregnant becomes immobilized in the wood. The cyllnder lS emptled of the heat
transfer medium which can be any heat transfer medium known to those skilled
n the art. Vapors are recovered by any manner known to those skilled in the
art and a final vacuum can be applied to vaporize most of the liquid carrier
from the wood.
A pre'ferred mode for commercially carrying out the process of this
~ invention to preserve wood involves using pentachlorophenol as the impregnant,¦ and acrylonitri`le as the reactive solvent, and iiquefied butane as the liquidcarrier. Any amount of pentachlorophenol may be used but it is customary ~o
use 5% by weight of the total solution as the effective amount of pentachloro-
phenol for treating wood against decay. The amount of acrylonitrile required
i is at least that amount which will dissolve an effective amount of pentachloro-
phenol. The amount of acrylonitrile that will disso'lve a 5%` amount of penta-
¦ chlorophenol is at least 7% by weight of the total solution and preferably an
I amount in the range of 8% to 12% to avoid'any problem with precipitation of the
~¦pentachlorophenol. This solution may be warmed at mild conditions for short
,
1085106
periods of time to further avoid any problem of pentachlorophenol precip.itation.
The amount of butane used is in the range of that needed to dissolve the acrylo-
',nitrile usually in the range of 79-88% by weight.
' In order to polymerize acrylonitrile at relatively moderate conditions
,an initiator is used. Such initiators are known in the art but the preferred
,initiator is lauroyl peroxide. The amount of lauroyl peroxide is that amount
,needed to give favorable decomposition characteristics between 20C. and 100C.'
'The preferred amount of lauroyl peroxide used is in the range of 0.05% to 0.80%
by weight of the three component system. An example of another initiator that ''
may be used is the azo compound, azobis-isobutyronitrile. The decomposition
rate of this azo compound is slightly lower than lauroyl peroxide at the same
,temperature. Consequently, longer heating periods or higher heating tempera-
tures may be required when azobis-isobutyronitrile is used as the initiator.
The above three component system of 5% pentachlorophenol, 7-12%
;acrylonitrile and 0.05-0.80% lauroyi peroxide and 79-88~ butane can be applied
to wood in either an empty cell or full cell procedure. Since acrylonitrile is
present in the solution any procedure used should be conducted in equipment
which does not contain any copper or brass. Acrylonitrile corrodes copper and
;brass and once the copper is in solution it forms a red complex precipitate
with pentachlorophenol. This precipitate represents a loss of penta from the
~three component non-aqueous impregnating system.
, The preferred procedure is a full cell procedure. The wood to be im-
~1 . .
pregnated is enclosed in a hermetically sealed pressure cylinder. The cylinder
is purged to remove the oxygen to below 3Y so as to avoid reaching the explosiverange with butane. Vacuum is then pulled on the wood to remove all non-condens-'able gas'from the wood cells to enable as much preservatiye as possible to pene-
~trate the wood. Any initial deposition of pentachlorophenol in the cylinder
~may be prevented by first introducing pure butane ;nto the cylinder until the
equilibrium vapor pressure at the boiling temperature of,the impregnating mix-
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ture is reached. The cylinder is filled with the above-described three compo-
jlnent non-aqueous impregnating system which is pre-mixed by mixing pentachlorQ-Iphenol with acrylonitrile in the presence of heat to aid in the dissolution of
: !the pentachlorophenol and then diluting this mixture with butane and then
¦adding the polymerization catalyst. This is the preferred order of mixing,
I ¦but other mixing orders may be used, The pressure is then raised with an inert
I Igas to a preferred pressure of 125 pounds per square inch. Additional impreg-
lnating system may be pumped into the cylinder if necessary during processing.
i IlThe pressure is held until sufficient pentachlorophenol has been put into the
: 10 lwood. This time varies depending on whether comple~e or near complete penetra-
¦~tion is desired and on what species of wood is used.
~I When sufficient pentachlorophenol has been put into the wood for pro-
¦Itection against decay, the cylinder is emptied while a pressure is maintained .
llthat is greater than the vapor pressure of the butane so as to keep the impreg-
¦Inating system in the wood while the cylinder is emptied, The cylinder is then
; !filled with butane which acts as the heat transfer medium. It is filled just
; !to cover the steam coils on the bottom of the cylinder to produce hot vapors of
butane or it is filled to completely cover the wood to heat the wood with hot
liquid. The impregnated wood is heated to a preferred temperature in the range
i : 20 ~of 1~0F. (60C.) to 185F. (85C.). At this temperature the lauroyl peroxide
decomposes and inltiates the polymerization of acrylonitrile. The polymerized ..- ¦~acrylonitrile is not a solvent for the pentachlorophenol and the-pentachloro-
j,phenol is substantially insoluble in butane so the pentachlorophenol is immo-
bi1ized in the wood. This immobilization allows for a more permanent deposition :.
lof pentachlorophenol in wood. Vapor recovery and vacuum phases are used to re- .
cover as much butane as possible. A vapor pump is used to remove the vapors in
. Ithe cyllnder. The vapor pressure is reduced at a rate that will not damage the
'lwood. After the butane and any other gases which are contained in the impregna-
llted wood have been evaporated, condensed, and placed in a storage tank, the
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cylinder is subjected to a final vacuum to remove last traces of hydrocarbons,
then the cylinder is purged with inert gas to reduce hydrocarbon vapor to less
¦ than 4 percent. The cylinder is then opened and the impregnated wood removed.
I An alternative embodiment is ~he empty cell procedure where a combus-
Itible gas is used. The wood is enclosed in a hermetically sealed cylinder, the
¦air evacuated, and an inert gas, such as nitrogen, is introduced at a relativel~
low pressure, and forced into the wood. On top of this gas the three component
¦impregnating system of pentachlorophenol, acrylonitrile and butane impregnates
the wood, resulting in a cushion of inert gas under pressure within the wood
under the system solution. When the above described impregnating and reacting
cycle is ended, the butane is returned to a pressure storage tank. The quantit~
, of solvent retained in the wood during fu11 cell treatment is less than solvent
, retention of prior art processes which use organic solvents in full cell treat-
`i ments, thus solvent recovery is enacted more quickly and the cylinder can be ;
~¦ ~ opened ear1ier.
; ~ Both the above-described full cell and empty cell procedures yield a
treated wood that contains an effective wood preserving amount of pentachloro-
phenol immobilized in the treated wood. The treated wood also contains the
polymerized polyacrylonitrile. The polyacrylonitrile does not interfere with
the effectiveness of the pentachlorophenol as a wood preservative, therefore
the polyacrylonitrile need not be removed from the treated wood. The treated
-~ wood produced from the above-described procedures contains both pentachloro- ~;
phenol and polyacrylonitrile and the surface of the treated wood is clean and
need not be subjected to a washing step.~ I
~25 ll ~ For a better understanding of the inventlon reference should be had
to the following examples:
¦ Table I presents examples of impregnating non-aqueous system formula-
~tions which crn be used by the process of this inventlon to treat wood.
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- ~I The percentage of pentachlorophenol was maintained at 5.0 percent
¦ in tests a-i. This percentage of pentachlorophenol is customary in the wood
` i preserving art, but the percentage of penkachlorophenol can be varied below and
¦ above the value of 5.0 percent. Also, examples of 5.0% formulations of other
wood preservatives are shown. The formulations in Table I were prepared by
adding at room temperature the reactive solvent and the preservative to the
` ¦ liquid carrier, then the catalyst was added and the mixture was stirred for
I ¦ around 0.5 hours. The system solution obtained was clear with the consistency
-, of the liquid carrier and with a color ranging from yellow to brown.
,,. I .
!I Table I
Impregnating Mixture Formulations
~ Preservative Reactive Solvent Agent Catalyst1 Liquid Carrier
`i a) 5.00% penta 8.00% acrylonitrile 0.20% BP0 ~6 80% pentane
b) 5.00% penta 11.00% acrylonitrile 0.22% LP0 83.78% butane
- c) 5.00% penta 10.00% acrylonitrile 0.20% AIBN 84.80% butane
d) 5.00% penta 13.7% mPthacrylonitrile 0.28% LP0 81.02% pen~ane
e) 5.00% penta 2,0% styrene 0.20% BP0 85.80% butane
7.0% acrylonitrile
¦f) 5.00% penta 40.00% styrene 0.80% BP0 54.20% pentane
g) 5.00% penta 14.00% yinyl acetate 0.30% BP0 80.70% pentane
h) 5.00% penta 16.00% butyl acrylate 0.32% LP0 78.64% pentane
) 5.00% penta~ 13.50% methyl acrylate 0.27% LP0 81.23% pentane
''j) 5.00% 15.0% styrene 0.30% LP0 79.70% pentane
1, ',tributyltin ,
¦¦acetate
,jk) 5.00% dieldrin 10.0% methacrylonitrile 0.20% LP0 84.80% pentane
5 00% dieldrin 15.`0% vinyl acetate 0.30% LP0 79.70% pentane
¦ 1. BP0 = benzoyl peroxide, LP0 = lauroyl peroxide; AIBN = 2,2'azobis-
isobutyronitrile
1,1
l' -17-
11 , `~
5106
Example I
Southern yellow pine (SYP) blocks were treated by the full cell pro-
I , cess on a bench scale with a pressure hydrometer jar used as a treating cylinde~ .
Three-quarter inch SYP blocks were treated with a 5% penta solu~ion using pen-
tane as the liquid carrier and either a styrene-methanol mixture or a styrene-
acrylonitrile mixture as the reactive solvent. After an initial vacuum period,
pure pentane was introduced until equilibrium vapor pressure was reached.
Enough solution was added to cover the blocks. The pressure was increased to
i I atmospheric or 15 pounds per square inch absolute and the pressure period was
maintained for 30 minutes. The impregnant solution was withdrawn and pentane
added to the bottom of the cylinder making sure that it did not touch the
blocks. Then, the entire apparatus was heated in a hot water bath at 70C.
for 2-4 hours. The hot pentane vapors that were generated heated the blocks
to cause the reactive solvent to react. No surface crystals were visible on
! any blocks treated in the above described manner. Table II presents data from
X-ray analysis to show penta retentions on the blocks treated in the above
~described manner. No surface crystals were visible on any blocks treated by
¦this technique and blooming did not occur after treatment with this technique.
¦¦The treated blocks were clean, dry, natural appearing9 and did not need to be
washed. I
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I -18- -
ii
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Table II
Retentions of 3/4-Inch SYP Blocks Treated With Imprecinant Solution
I li Containinci 5~ Pentachlorophenol
i¦ Weight Weight Weight Retention
; I Before After After of Penta-
Test Reactive Treatment Impregnation Reaction chlorophenol Retention
No~ Solvent _ (gm) (gm) (Clm) (~) (pcf)*
1 Styrene 4.84 8.66 -- 3.95 1.26
!l
2 Styrene 4.47 8.44 4.65 4.45 1.42
methanol
I ~1 3 Styrene 4.49 8.81 4.75 4.80 1.53
¦ methanol
' ~ Styrene 5.04 8.76 5.29 3.67 1.17
acrylonitrile
Z 5 Styrene 4.63 8.42 4.85 4.07 1.30
¦ acrylonitrile
- i 6 Styrene 4.81 8.24 5.03 3.57 1.14
acrylonitrile
:
* Based on oven dry weight of southern yellow pine of 32 pcf ~pound per cubic
foot). ` `
Example II
I! Douglas fir heartwood lumber whlch was end-sealed to simulate the
lltreatment of commercial lumber was treated with the noniaqueou$ impregnating
¦¦mixture on a pilot plant scale in an 8-inch diameter cylinder. The impregnant
5ilwas pentachlorophenol and the reactive solvent was a polymerizable monomer and
the liquid carrier was either butane or pentane. The boards treated with this
solution had clean surfaces and an appearance of untreated wood. The results
i¦of treating Douglas-fir lumber with such an ~mpregnant mixture are summarized
in Table III. Cross sections from each sample board were cut and retentions
10¦Iwere determined by X-ray analysis.
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None of the boards had crystals on their surfaces a~ter treatment.
~! For these boards the temperature was maintained at at least 76C. for at least
1.5 hours. Th;s time and temperature were sufficient to react all of the re-
¦active solvent, therefore, preventing the formation of crystals on the surface
- llof these boards.
;`'`, 1'
¦ Example III l
.
~- 1.' Further pilot plant tests were conduc~ed in 3 ft. and 18 in. diametèr
cylinders to determine the applicability of the process of this invention
to the treatment of poles. The impregnating mixture consisted of 3.6-4.7%
lipentachlorophenol as the impregnant, 7-12% acrylonitrile as the reactive sol-
! vent, and 83-89% butane as the liquid carrier along with 0.15-0.25% benzoyl `
peroxide as an initiator for polymerization.
In this series of tests 6-ft. pole sections were trea~ed. Th~e total
volumes of these pole sectlons varied between 2.5 and 3.2ft.3. The po,les were
~' 15 end-sealed prior to treatment to mlnimize end penetration effects and simulate
- Itreatment of commercial stock. Douglas fir poles were used primarily because
this species represents the~most serious crystal blooming problems. One charge
of a Southern Pine pole section was treated. The results o~ this series of
treatments are reported in Table IV.
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Example V
Four SYP blocks (3~4 inch) were treated with an impregnating mixture
of 5% pentachlorophenol as the preservative, acrylonitrile as the reactive sol-
vent and butane as the liquid carrier. After the treatment three of the blocks
were placed in ovens at temperatures ranging from 50 to 90C. for up to one
~` week. This treatment determined that there was no post-treatment bloominy or
.. i ~
~crystal formation on the surface of the blocks during a one week period of
,., I
observation at elevated temperatures. One block was sliced into sections and
submitted for x-ray analysis of pentachlorophenol. These sections were then
!subjected to a leaching test. This test consisted of soaking the sections in
distilled water for two hours, heating in an oven at 50C. for six hours and
~being at room temperature for the rest of the day. Thls 24 hour cycle was re-
peated for three weeks. The sections were submitted for pentachlorophenol (PCP),analysis at the end of this test to determine if any pentachlorophenol was
~` 15 llost. The results are given in Table V. The results show that only a minor
amount of PCP was lost.
;'i~ !
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Table V
Oriyinal PCP Final PCP
Sections Content Content
Sample A % pcf % pcf
~ ' 1 2.350.75 2.230.71
- i 2 2.610.83 2.460.78
i 3 2.120.68 2.060.65
I 4 2.100.67 1.960.63
~ ~ ~ Based on average density of dry SYP being 3? pcf.
,:. ,
Example VI
To show that the impregnant, here pentachlorophenol, is not rendered
ineffectiYe as a result of the process of this invention, soil block tests were
~performed3 The soil block tests were conducted to determine the effectiveness
of pentachlorophenol by exposing treated blocks to Lenzites trabea for twelve
-23-
: ~ !
:'.. .. ~ . `. ..
59 ~)6
:` ,
,weeks. Any significant loss of weight would indicate that the blocks were de-
cayed by the organism.
A series of soil blocks were treated with the impregnating mixture of
~pentachlorophenol, a mixture of styrene-methanol in a weight ratio of 7:2 as
the reactive solvent with methanol as a co-solvent and pentane as the liquid
carrier. The series was composed of three sets of blocks. The first set was
treated with an impregnating mixture having a pentachlorophenol concentration
of 2.0%. The second and third sets were treated with an impregnating mixture
~having pentachlorophenol concentrations of 1.3% and 0.6% respectively. A
fourth set of blocks was treated containing the styrene reactive solvent but no
pentach10rophenol. A fifth set of blocks were untreated and served as controls.
Half of the total number of blocks in each set were subjected to the standard
American Wood-Preservers' Association (A.W.P.A.) two week weathering cycle.
This cycle is described in Proceedings Sixty-Nineth Annual Meeting of the
~American Wood-Preservers' Association, American Wood-Preservers' Association,
Washington, D.C., Volume 69, page 116. One of the weathered and unweathered
blocks from each set was ground and analyzed by x-ray analysis for pentachloro-
phenol content. Because of the variation in solution pick up For different
blocks, the results from x-ray analysis could only be used as a check for
approximate pentachlorophenol retentions. Analysis of all the individual
blosks for pentachlorophenol retentions were conducted at the end of the test.
The remaining blocks that were not ground and analysed in each set were equili-
-~ brated at constant temperature and humidity, weighed and exposed to Lenzites
~- trabea for 12 weeks. After the twelve week incubation period the blocks were
reweighed. Any loss in weight greater than 3~ indicates attack by the decay
organism. A slight increase in weight is ;nsignificant and due to variations
-~ .
in moisture content of the blocks. The unattacked blocks had retentions rangin
from 0.13 to 0.33 pounds per cub;c foot (pcf). Results are summarized in
Table VI.
,. ~,
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-24-
!
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~` ! 1085~L06
~ !1
¦ Table VI
Pre-exp Post-exp Reténtion
Block Weight Weight Weight % Wt. (pcf) Post-exp
Set No. (gm) (gm) Loss oss Weatherin~ X-ra~
'! A 1 5.052 5.0280.024 0.5 U 0.27
/ A 2 5.429 5.3800.049 0.9 U 0.20
I A 3 4.744 4.7430.001 0. W 0.33
A 4 4.795 4.7720.023 0.5 W 0.30
I B 1 5.023 4.8530.170 3.4 U 0.130
i B 2 4.356 4.3370.019 0.4 U 0.167
~ ~' B 3 5.198 5.206+0.008 +0.2 W 0 199
: ¦ B 4 5.188 5.1500.038 0.7 W 0 213 ;
C 1 4.930 4.7570.173 3.5 U 0.113
C 2 5.~26 4.7430.483 9.2 U 0.093
I C 3 5.508 5.1590.349 6.3 W 0.078
`` I C 4 4.867 3.7781.089 22.2 W 0.026
; ,I D 1 4.345 1.6672 678 61 6 U -
i! D 2 5.499 3.4522 047 37 2 U
I! Control
j 1 4.405 2.5201.885 42.8 U I -
2 4.400 1.4382 962 67 3 U -
- 3 4.24g 1.3012 948 69 4 W -
4 4.091 2.6641.427 34.~ ~ -
~ ' l ,
Group A - 2.0% pentachlorophenol treating solution.
Group B - 1.3% pentachlorophenol.
I , Group C - 0.6%ipentachlorophenol.
ii ~ Group D - 0.0% pentachlorophenol.
W = weathered.
U = unweathered.
,.
",,,, . ,
By practicing the process of this invention, and using either the ~i~
empty cell or full cell procedure, better penetration, retention and uniformity
of treatment are obtained and blooming is prevented or`substantially reduced
from that of prior art processes. Even though the process of this inventibn
jhas the capabiiity of a more uniform treatment, ;t still can be used to effect
a gradient of concentration of the impregnant in wood. A major reason for the
¦benefits of the process of this invention is that the impregnant is deposited
in the wood by a controlled reaction. The impregnant does not attach to or
Ideposit in the wood as the impregnant first contacts the wood. The impregnant,~ :., l
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reactive s.olvent, and liquid carrier move into the wood and, when the desired
penetration is reached, the reactive solvent is reacted and the impregnant is
'deposited in the wood.
.1 According to the provisions o~ the patent statutes we have explained
~the principle, preferred cohstruction and mode of operation of our invention
and have illustrated and described what we now consider to represent its best
. llembodiment. However, we desire to have it understood that within the scope of
.. - ~the appended claims, the invention may be practiced otherwise than as speci- .
~ ~fically illustrated and described.
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