Note: Descriptions are shown in the official language in which they were submitted.
9~z
FIELD OE THE INVENTION
This invention relates to the treatment of wood to
enhance its properties. More particularly it relates to the
impregnation of wood with resin and optionally with various
additives such as preservatives and fire retardants.
DESCRIPTION OF THE PRIOR ART
It is well established that wood expands and contracts
depending upon the degree of swelling of its cell walls.
The wood cell walls exhibit varying degrees of swelling
depending upon the particular solvent or solvent vapor it is
exposed to and its affinity for this solvent or solvent
vapor. Thus, exposure to water or water vapor causes a high
degree of swelling, and exposure to less polar solvents or
solvent mixtures such as ethanol-xylene mixture causes its
cell walls to dehydrate resulting in shrinkage.
Additionally, when the wood cell wall, consisting
mainly of cellular chains, is swollen it has maximum porosity --
that is, the free space between actual cellular chains is
large, and when it is not swollen the porosity is very low.
Conse~uently, the size and amount of molecules that can be
deposited within the wood cell walls is dependent upon the
degree of swelling of the cell walls.
The above property of wood has been used in a
variety of ways to impart specific properties to wood. Thus
water soluble poly-glycols, such as polyethylene glycol
having a molecular weight of about 3000 to 6000 can be
introduced into wood cell walls in their wet or swollen state.
(See "New and Better Ways to Dimensionally Stabilize Wood",
A.J. Stam, Forest Products Journal, 9(1959):3,107-110, and
"PEG of the Woodworker's Heart", Harry C. Leslie, Man Society
Technology, A Journal of Industrial Arts Education, 33(1):13-
16, Sept., Oct., 1973). Such polyglycols have a low vapor
pressure and, unlike water, evaporate only very slowly.
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Consequently, the above treatment is very effective in
preventing checking and cracking of wood. Such a treatment
is often used to treat wood engravings, statues, etc., giving
these wooden pieces a long life even when stored in dry
atmosphere. How~ver, poly-glycols remain water soluble and
leach out when wood treated with these is exposed to wet
conditions. The usefulness of this treatment is therefore
very limited.
Using somewhat the same concept, water soluble low
molecular weight phenolic and urea resins have been used to
treat wood. (See U.S. Patent Nos. 3,968,276, 3,519,476 and
3,493,417). To fix these resins within the wood cell walls
subsequent heat treatment is required to cure the phenolic
resin to make it water insoluble. Very often a combination
of heat and pressure is used to further densify the wood.
Such a treatment, though effective, requires special equipment
and is thus practiced only for industrial production of
~pecial articles where water or chemical resistance or
structural strength or a combination of these is needed.
Many other polymers have been used to impregnate
,
wood. Some of these include the use of acrylic type monomers
(U.S. Patent No. 3,663,261), polyisocyanate (U.S. Patent No.
3,539,386), and dibromopropyl glycidyl ether (U.S. Patent
No. 3,483,021). All of these treatments require a secondary
treatment of wood after the impregnation step to polymerize
the monomers in situ to fix it in the wood. The secondary
treatment most often used is to heat the impregnated wood,
although in the case of vinyl type monomers such as the
acrylics, gamma ray exposure may also be used. The requirement
of a post impregnation secondary treatment is expensive and
cumbersome. Consequently, none of these techniques have
found a wide acceptance in industry.
Even when the wood cell walls are in a wet or
swollen state, only relatively small size molecules can
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penetrate the wood cell walls. The actual size of the molecule
that will penetrate the wood cell walls is dependent upon
the degree of swelling and the species of wood. Polymers
which are large in molecular size will not penetrate even
a swollen wood cell wall. Thus for example, polyvinyl acetate
and polyacrylate emulsions have been used for years to produce
adhesives and paints for wood. Unlike condensation polymers,
such as the phenolic resin mentioned earlier, these emulsions
are produced by free radical or chain polymerization and do
not contain any appreciable quantities of low molecular
weight components. (See Text Book of Polymer Science, F.W.
Billmeyer, Jr., Interscience Publishersj 1966). Consequently,
when wood is treated with these emulsions, the wood cell
walls swell due to the presence of water but the polymer
molecules are too large to penetrate even the swollen wood
cell wall. Consequently the wood gets a protective coating
but its other properties such as resistance to checking and
cracking are not affected. It is therefore not useful to
use a water borne polymer of large molecular size to achieve
the objectives of this invention.
Low molecular weight vinyl resins such as acrylic
resins are known but their utility for the treatment of wood
cell walls to improve check resistance, dimensional stability
and other properties has not been recognized. For example,
such resins have been suggested for use in floor polishes as
a leveling aid.
Alkyds are condensation polymers and contain an
appreciable quantity of low molecular weight components
(Text Book of Polymer Science, supra). Moreover, alkyds
crosslink and cure, that is, become solvent resistant and
partially infusible, by reacting with air. In the past only
alkyds soluble in organic solvents, were standard items of
commerce. The organic solvents in these alkyds do not swell
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the wood cell walls Many of them actually shrink the wood
cell walls by displacing water and reduce the porosity of
wood.
In the last decade or so, alkyds that are soluble
in water or a water polar solvent mixture have been extensively
used in industrial finishes such as coatings for washing
machines, refrigerators, automobiles, etc. However, it was
not realized that they also form a basis for imparting the
so highly sought properties of reducing checking and cracking,
introducing dimensional stability, and of substantially
permanent fire retardant and preservative treatment of wood
without a secondary post impregnation treatment of heating
or exposure to gamma rays. Simple exposure to air is sufficient
to crosslink them to form a polymer in situ. Moreover,
being in water, and containing an abundant amount of small
but reactive molecules, they have excellent penetration into
wood cell walls.
SUMMARY OF THE INVENTION
... .
In the preferred embodiment the present invention
permanently deposits specific chemical mixtures within the
cell walls of wood fibers, the combination of chemicals to
be deposited having been solubilized in water or water-water
miscible solvent combinations~ so as to swell the wood cell
wall and thus achieve maximum penetration of the chemicals
into the wall itself. The chemicals selected are such that
at least one of the components of the mixture comprises
molecules of a small size capable of entering the ree space
in the cell walls in the presence of the solvent and which
are capable of being converted at ambient conditions, either
by itself or aided by the presence of other chemicals that
may act as catalysts, to a water insoluble form, simultaneously
trapping other water soluble chemicals which may be present
in the mixture, thus eliminating or greatly reducing the
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tendency of the entire mixture to leach out on subsequent
treatment of the wood with water of water containing solutions.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The chemical capable of being converted to a water
lnsoluble form used in-this invention may be a water dilutable
alkyd or a modified water dilutable alk~d. Examples of such
alkyds are long, medium or short oil water dilutable alkyds
presently commercially available from a number of different
manufacturers and which are well known to the industrial
coatings industry. Modified alkyds such as urethane modified
alkyds are also commercially available and well known in the
art. Such alkyds or modified alkyds are generally soluble
in water or water-polar solvent mixtures in near neutral or
slightly alkaline solutions. Examples of polar solvents are
butanol or higher alcohols, ketones, butyl cellosolve, butyl
carbitol, propasol, and N-methyl pyrrolidone.
By way of background, it is known that alkyd resins
are made by combining synthetic dibasic acids such an phthalic
anhydridé, isophthalic anhydride, trimelytic anhydride with
s~nthetic or natural fatty oils, i.e;, glycerides of fatty
acids. The fatty acids or their glycerides used generally
contain mixtures of fatty acids of varying chain lengths and
varying degree of unsaturation in the chain.
Alkyds may be additionally modified by combining
them with various glycols. Examples of glycols commonly
used are pentaerythritol diethylene glycol. More drastic
changes in alkyd properties can be produced by crosslinking
them by the addition of isocyanates such as toluene di-iso-
cyanate. The latter alkyds are commonly called urethane
modified alkyds. Urethane modified alkyds dry to much harder
finishes than alkyds not so modified. Other examples of modified
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alkyds include modification by reacting them with natural
resins such as rosin, or with other synthetic resins such as
phenolics, amino resins, silicone resins, or by reacting
them with imides, styrene, and the like.
The final molecular weight or the degree ofpoly~erization
of the alkyds is controlled by adding controlled amounts or
an excess of one of the reactants -- fatty acids or glycols.
Consequently the finished alkyds generally contain small
amounts of unreacted hydroxyl, or acid groups, or both.
Alkyds produced by using relatively low ratios of synthetic
polybasic acid to fatty acid are called long oil alkyds,
those produced with very high ratio are called short oil
alkyds, and those produced with intermediate ratio are called
medium oil alkyds.
The alkyd resins of the above type are soluble in
both aromatic or aliphatic hydrocarbon solvents, and insoluble
in most polar solvents such as water, methanol and butanol.
More recently, alkyd resins have been reacted with various
chemicals to improve their solubility in polar solvents.
This may be achieved by incorporating highly polar groups
into the alkyd structure. As an example, alkyd may be made
by using an excess of acid with the final product having an
acid number ranging from about ten to one hundred, preferably
around 20 to 60. The acid groups are then partially or
wholly neutralized using an amine or ammonia or a combination
of amines and ammonia. The products so made are then soluble
in such polar solvents as methanol, butanol, carbitol, butyl
Cellosolve (ethylene glycol monobutyl ether) and mixtures of
such solvents with water. To achieve full solubility, mixtures
of the above type solvents may have to be used. For example,
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~9~382
some of these alkyds have greater solubility in higher boiling
solvents such as butyl Carbitol (diethylene glycol monobutyl
ether) or butyl Cellosolve, and addition of such solvents
may increase the amount of water that can be used as a part
of the solvent system. It is these alkyd resins that ~ave
been modified for dissolving in polar solvents that are
useful in the present invention and are referred to herein
as water dilutable alkyds.
Aside from simple alkyds, short, medium or long
oil length, alkyds modified by reacting them with isocyanates,
acrylics or other suitable chemicals commonly used to modify
alkyds may be used for practicing the present invention.
These modifications are the same as those used with organic
solvent based al~kyds and which have been further modified
with neutralizable acid groups for solubility in polar solvents.
It should be noted that the present invention is
not limited to the types of modified alkyds discussed. Any
water dilutable polymeric system that is soluble in polar
solvents, or mixtures of polar solvents, or mixtures of
polar solvent and water, and capable of being converted to a
water ~insoluble stage such as through curing by exposure to
air, by evaporation of water, or by volatilization of a
water solubilizing amine component under ambient conditions
of temperature and pressure, may be used to practice the
invention. For best resultsj whatever resin that is selected
should contain at least 5 weight percent of molecules having
a molecular weight lower than about 1000, preferably 10
weight percent of molecules having a molecular weight below
about 1000. Thïs will promote entry into the free space
of the wood cell wall. The larger molecules which are too
large to enter the free space of the wood cell wall form a
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protective and decorative layer on the wood surface.
While all water dilutable polymeric systems as
described above are broadly useful in the present invention,
it should be understood that some resins may be more satisfactory
than others in a particular application. For example, stability
of the resin solvent systems differ and resin precipitation
may occur more quickly in some systems than in others. It
has been observed that the choice of resin is more critical
with respect to stability in more dilute resin solutions
containing less than about 20 weight percent of resin. In
such solutions several resins may be tried to select one
having optimum properties. Example III given below illustrates
a resin-solvent system having relatively long term stability
at low resin concentrations.
Like oil or organic solvent dilutable alkyds, the
water dilutable alkyds or modified alkyds react with oxygen
in the air and crosslink to form a water insoluble product.
The rate of crosslinking can be substantially increased by
adding small quantities, generally 0.05 to 1.0 weight percent,
of catalysts such as driers. Examples of driers that may be
used are calcium, cobalt, manganese and zirconium naphthenates
or chelated salts of calcium, cobalt, manganese or zirconium.
It has been surprisingly found that the above
water dilutable alkvd solutions, when applied to wood, penetrate
the wood cell wall and on subsequent exposure to air become
water insoluble. They can therefore be used to stabilize
the wood cell walls, thus imparting greatly improved dimensional
stability or reduced tendency to expand and contract with
changes in humidity.
It has also been surprisingly found that other
chemicals that are normally water soluble or soluble in the
above alkyd solution, when used in conjunction with these
xi
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alkyd or modified alkyd solutions, also penetrate the wood
cell walls and on subsequent air curing of the alkyd or
modified alkyd become fixed in the wood and are substantially
water non-leachable.
Thus, in addition to imparting dimensional stability
to wood, this discovery can be used to treat wood with a
number of chemicals that give wood long lasting and other
special properties. Thus, normally water soluble fire retardant
chemicals may be used to give treated wood durable non-water-
leachable fire retardant properties. Similarly, water solublewood preservatives, both organic and inorganic, may be
introduced into wood and upon curing of the alkyd or modified
alkyd become non-leachable giving wood the capability of
retainin~ these compounds even under wet and humid conditions
of use.
The present invention can be used in a variety of
ways. For example, if it is desired to impart check resistance
and dimensional stability to wood, a simple treatment with a
solution of a water dilutable alkyd containing suitable
driers followed by air drying may be sufficient. The amount
of material deposited in the wood cell walls is proportional
to the concentration of the material in the treating solution.
This applies to the binder polymer as well as to other
ingredients such as wood preservatives or fire retardants.
The binder polymer used may be as concen~rated as
about 70 weight percent or a low as about 5 weight percent
in concentration. Generally mixtures of about 5 weight
percent to about 30 weight percent are preferred as above
this concentration range the viscosity of the solution is
very high. Very viscous solutions take a long time to soak
into the wood. The viscosity may be lowered somewhat by
heating the solution. However, from a purely practical
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viewpoint it is more convenient to use room temperature and
lower concentration ranges. While concentrations of about 5
weight percent of resin binder show definite improvement in
dimensional stability of treated wood and in ixing of other
additives therein, a concentration of at least about 8 weight
percent of resin should be used if substantial avoidance of
water leaching of additives is sought.
The amount of wood preservative or mixtures of
wood preservatives used again depends upon the degree of
protection desired. Pentachlorophenol for example may be
used in concentration ranges of about 0.5 to 6 weight percent,
preferably about 2 to 5 weight percent. Tributyltin oxide
adducts, on the other hand, are generally used at concentration
ranges of about 0.1 to 0.5 weight percent. Similarly fire
retardants or mixtures of fire retardants may be used in
concentration ranges of about 2 to 15 weight percent again
depending upon the degree of protection needed. Other wood
treating chemicals contemplated are copper-8-quinolinolate
and copper ammonium borate.
The wood may be treated sequentially or concurrently
with preservatives, fire retardants and resin binder. Where
wood is first treated with fire retardant or wood preservative
and then with the binder of the present system, hlgher levels
of protection may be obtained than would be possible with a
concurrent treatment. For example, a fire retardant such as
borax may be compatible with the present binder system up to
only 4 weight percent and a greater quantity is needed to be
deposited in the wood for the level of fire protection desired.
Under such circumstances wood could first be treated with 10-
15 weight percent borax in water and subsequently with the
binder of the present system to fix the higher concentration
of borax in the cell walls.
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The resin binder and other wood treating chemicals
may be contacted with the wood by any suitable technique.
Conventional methods such as brushing, spraying, dipping, or
subjecting the wood to vacuum followed by the treating solution
under pressure at ambient or elevated temperature are all
contemplated depending upon the wood and extent of penetration
desired.
Conventional pigments, dyes, thickeners, flattening
agents and extenders, both organic and inorganic, may be
included in the formulations as desired.
EXPERIMENTAL
....
Example l
The enhancement of wood properties by the present
invention is reflected in the resistance of wood to dimensional
change with changes in moisture content, and also the dimensional
change in wood its~elf. For samples of maple of about 1.5 cm
impregnated with 20, 40 and 60% (by weight) concentration
solutions of resin and air dried for two weeks, the following
percentage changes in dimensions at saturation moisture level
and at dry state were found.
Resin in Tangantial Radial
Solution (~)* (%)*
(wt. %)
0 112.18 105.46
110.25 103.86
109.24 103.34
104.94 101.83
*Dimension at saturation x 100
Dimension on oven drying
The above results were obtained by soaking the wood
samples overnight in the resin solutions in the following
table. After the two week air drying period they were resoaked
in water overnight. Oven drying was at 150C until a constant
weight was obtained -- usually in about three hours.
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Ingredients
(by weight) 60% 40~ 20
Medium oil water dilutable
alkyd. 80% in butyl Cellosolve627.0 412.0 200.0
(trade mark)
Ammonium Hydroxide 28~36.024.0 12.0
Butyl Cellosolve
(trade mark) 34.6 77.6120.0
Water 138.4 310.4480.0
6~ Cobalt Naphthenate*4.0 2.7 1.3
18~ Zr Naphthenate* 2.0 1.3 0.7
Activ-8* (trade mark) 2.8 l.g 0.9
BYK 301**
~trade mark) 6.0 4.0 2.0
TOTAL 836.0 824.0812.0
*6~ Co Naphthenate, 18~ Zr Naphthenate an
Activ-8 (trade mark) are driers.
**BYK 301 (trade mark) is a wetting agent.
It is obvious that the impregnation of wood
with the solution has resulted in great enhancement of
dimensional stability and that the dimensional stability
imparted in the tangantial direction is greater. It is
also significant that the treatment results in equal-
izing the dimensional changes in both the tangantial
and radial direction. The improvement in dimensional
stability also shows that there is actual cell wall pene-
tration of the polymer.
Similar results were obtained when bass wood,
sugar pine, yellow poplar samples were treated with
the above solutions.
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In this study it was also found that wood after
treatment with the resin solution, followed by air curing for
a week, did not return to its original dimensions. Percent
change in dimensions on such treatment for maple is given
below:
Resin
Concn. Tangantial Radial
(wt %) (~)* (~)*
O O O
10. 20 103.4 101.45
103.86 102.15
105.81 102.64
*Length of treated sample (oven dry) x 100
Length of untreated sample (oven dry)
This is additional evidence of the fact that the
polymer does indeed penetrate the wood cell walls.
.~
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EXAMPLE II
Aside from imparting dimensional stability
the present treatment of wood also results in greatly
enhanced check resistance. This was demonstrated by
taking three equivalent samples of red oak, ' ,
Sample Xl was kiln dried only and is relatiyely
free of checks.
Sample ~2 was kiln dried, water saturated by
soaking in water for about 20 minutes, and then oven
dried. Numerous checks are visible.
Sample #3 was kiln dried and then soaked in the
polymer system set forth in the table below. Upon oven
drying, only a few small checks are visible.
Ingredients
(b wei ht) ''
Y g
Medium oil water dilutable
alkyd 80~ in butyl Cel~osolve 248.70
(trade mark)
Ammonium Hydroxide, 28~ 15.00
Butyl Cellosolve
(trade mark) 59,51
Water ' 493.93
Tinuvin 328* (,trade mark) 4.46
6% Cobalt Naphthenate 1.24
18~ Zr Naphthenate 0,62
Active-8
(trade mark) 1.36
BYK 301
(trade mark) 2.60
TOTAL 827.42
*Tinuvin 328 (trade mark) is a
u.v. absorber.
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~9~382
EXAMPLE III
It has been mention earlier that wood Preservatives
and fire retardants that normally leach out of wood on exposure
to water, for example rain, can be substantially fixed in
the wood and made non-leachable by this invention.
Pentachlorophenol is commonIy used as a preservative
for wood. For this application pentachlorophenol is generally
dissolved in a solution of aromatic and aliphatic hydrocarbons.
Blocks of wood treated with pentachlorophenol on leaching
with water lose the preservative at a very fast rate. Thus
a l cm3 block of wood was treated with 5 weight percent
pentachlorophenol and its chlorine content analyzed before
and after leaching with water (one month) using Energy-Dispersive
X-Ray Analysis (EDXA). Analysis for the absence of chlorine
in the leached sample clearly shows that most of the pentachloro-
phenol was leached out. Another 1 cm3 block of wood was
treated with a solution of 5 weight percent pentachlorophenol
and 14 weight percent water dilutable alkyd. The block was
air dried for 30 days. Again its chlorine content was analyzed
using EDXA before and after water leaching (one month). The
results clearly show that very little chlorine was lost --
the polymer having fixed the pentachlorophenol within the
wood.
This same method can be used to add other chemicals
to wood such as fire retardants and to make them non-leachable.
*The treating solution was prepared from the
combination of Mixes A and B set forth in the
following table.
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Mix A
Pentachlorophenol 823
Butyl Cellosolve
(trade mark) 3837
Ammonia 28% 180
4840
Mix B
Arolon* 385
(trade mark) 955
Ammonia 28~ 22
Butyl Cellosolve
(trade mark) 64
Cobalt Hydrocure
(trade mark) 6.5
Activ-8
(trade mark) 4.0
Mix A 1190
Mix for 15 minutes
and add:
Water 2700
Adjust pH to 8.5 with ammonia (28%)
*water dilutable alkyd resin sold by
Ashland Chemical Company
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Example IV
This example shows that, like the preservative of
Example III, a fire retardant may be deposited within the
wood cell walls and fixed against water leaching by the
resin.
The procedure of Example II was repeated except
that to the binder mixture of Example II was added 42 gms
(5~) of sodium borate. The wooden blocks used were 5cm x
10cm x l/2cm. Subsequent to treatment the block was air
dried at room temperature for two weeks. It was then cut
into half along its width. One of the halves was repeatedly
washed with water and air dried. The water washed and the
unwashed portions of the block were exposed to a lighted
torch held at a distance of 10 cm from the end grain side of
the block. Both blocks took 8 minutes to start charring.
As a comparison an untreated block under identical conditions
started charring in 4 minutes.
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The foregoing discussion and experimental
work primarily illustrates the present invention with
water dilutable alkyd resins. As indicated, the invention
may be practiced with any water dilutable polymeric
system that is soluble in polar solvents or mixtures of
polar solvents and water while being thereafter conver-
table to a water insoluble stage. In this regard water
dilutable film forming resins made from vinyl monomers
have been found to have advantageous properties in this
invention. These vinyl monomer derived water dilutable
resins are converted to a water insoluble form by water
evaporation and film formation and/or by volatilization
of ammonia or an amine that has been reacted with acid
groups in the resin.
The vinyl monomer based water dilutable resins
are advantageous in that they can be formulated with
much less organic polar solvent than the water dilutable
alkyd resins. In fact, certain types of these vinyl
resins require no organic solvent at all and are formu-
lated with water alone as the solvent as disclosed and
claimed in commonly assigned United States patent
4,285,997, issued August 25, 1981.
In the present case small quantities of water
miscible organic solvent may be employed in order to
provide a vinyl resin which will form a film under
ambient conditions. The use of only small quantities
of organic solvent (generally less than about 10~ by
weight, and preferably less than 5~ by weight, of the
formulation) has both environmental and economic bene-
fits. The functional benefits are most significant.
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9~382
In this connection the organic cosolvents utilized
to impart water dilutability to the alkyd polymer mixture
are alsogood solvents for some of the dark colored chemicals
naturally present in wood. Consequently, the application of
these solutions to the wood brings these dark color compounds
to the surface, darkening the wood and detracting from its
natural beauty. In addition, the water miscible organic
solvents create difficulties with respect to certain types
of water soluble chemicals such as wood preservatives and
fire retardants which are added to the formulation for permanent
disposition in the wood treated with the formulation. The
addition of certain of these compounds to a formulation
containing larger quantities of organic solvent separates
the mixture into two layers -- a resin cosolvent layer and a
wa~ter-wood preservative and/or fire retardant layer. This
phenomenon excludes the use of most water soluble compounds
for formulating a unitary wood treating solution and the
systems containing larger amounts of organic solvent are
thus useful only when used in conjunction with chemicals
which have a fair amount of solubility in the mixture, such
as pentachlorophenol or fire retardants soluble in polar
solvents. Such compounds are expensive compared to water
soluble compounds and often are not as effective in like
amounts. The use of resins formed from vinyl monomers which
permit the use of a relatively small amount of organic cosolvents
avoid the foregoing problems present in systems which require
larger amounts of organic cosolvents.
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Polymers formed from vinyl monomers such as acrylic
polymers, both copolymers and homopolymers are generally
produced by reactions which result in a relatively narrow
molecular weight distribution. As with the alkyd resins,
the selected vinyl based resin should contain at least 5
weight percent of the resin molecules present having a molecular
weight lower than about 1000 and preferably at least about
10 weight percent of resin molecules having a molecular
weight below about 1000. In the preferred embodiment it is
desired to have in the formulation sufficient larger molecules
that cannot ~enetrate the wood cell wall and therefore form
a protective and decorative outer surface coating. To this
end the preferred formulations will usually, involve combining
two different vinyl polymers, one having the small molecules
for penetration into the wood, and the other having relatively
larger molecules for film forming on the surface of the
wood. The larger molecules will generally have a molecular
weight of about 20,000-200,000 with a typical formulation
having 95% of the molecules in a molecular weight range of
90,000-110,000.
It has been fou,nd that most emulsions made by
emulsion polymerization of vinyl containing monomers may be
used to formulate the treating solution. Examples of monomers
that contain a vinyl group are vinyl acetate, methyl methacry-
late, ethyl ethacrylate, acrylamide, acrylonitrile, styrene,
isoprene, and malic anhydride. These monomers may be polmerized
by themselves to form homopolymers. Preferably, however, a
judiciously selected mixture of monomers is used to control
such properties as minimum film forming temperature, the
~.
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9~382
hardness of the dried film, etc. The polymerization is
generally carried out in the absence of oxygen using a free
radical initiator such as a peroxide, the monomer or monomer
mixture being suspended in water, by agitation and its
temperature controlled above the temperature needed to
decompose the initiator.
Many acrylic emulsions sold commercially contain
organic cosolvents which serve as thickeners and/or coalescing
agents. When water soluble wood preservatives or fire retardants
are added to these, flocculation of the emulsion or one or
more of the additives may occur.
Examples of emulsions that are found suitable are
given later. Other emulsions that are film formers at or
below room temperature and are stable in the presence of the
additives may be used.
The low molecular weight polymers, either in the
emulsion form or as clear solutions are synthesized much
like the polymerization reaction described above, except
that a suitable chain transfer ingredient is included in the
reaction mixture.
Emulsion polymers having a large or small molecular
weight, when made by using an acid, such as acrylic acid or
methacrylic acid, or a mixture of such acids, as part of the
monomer mixture, tend to form clear solutions when amines or
ammonia are added to them to raise their pH to the alkaline
side, generally above 8 or 8.5.
Although soluble in this form, when used as binders
or film formers, they lose the ammonia or the volatile amine
(if a volatile amine is used to adjust the pH) by evaporation
and become water insoluble.
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ms~rr~ln
, :
9~3~Z
When a mlxture of a high molecular weight polymer
and a low molecular weight polymer are used, the low molecular
weight polymer, together with water and the additives penetrate
the wood cell walls and on the evaporation of water become
deposited therein. The high molecular weight fraction is
added to form a film on the outer surface, thus protecting
it from the elements, and also adding an aesthetic appeal.
The inclusion of this surface film former component also
enables the addition to the treating solution of pigments
and dyes, thus providing a wood treating and a wood coating
or staining system in a single mixture. The wei'ght ratio
of high molecular weight resin to low molecular weight resin
will generally be from 95:5 to 50:50 and more usually from
about 90:10 to 70:30.
When such pigmented systems are used the pigments
also serve as ultraviolet (W) light abs'orbers. It is well
known that W light degrades wood. Consequent]y the inclusion
of the pigment further serves to enhance the life of wood.
In clear coatings the same objective can be achieved by the
addition of UV abs'orbers. Typical examples of UV absorbers
are given in the preceding examples.
The following examples illustrate typical formulations
employing resins formed from vinyl monomers and which can be
formulated with a relatively small amount of organic polar
cosolvent. In Example V both the large and small molecular
weight resins have a~plurality of acid groups which are
neutralized with the ammonium hydroxide. The result is a
very soluble water white transparent solution Example VIII
illustrates the ability of the formulation to incorporate
inorganic fire retardant and preservative salts without
causing phase separation because of the relatively low concen-
tration of organic polar cosolvent.
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9982
EXAMPLE V
Rhoplex B-505*
(trade mark) 45.00
Acrysol 527**
(trade mark) 4.44
Ammonium Hydroxide, 28%*** 1.00
Water 46.56
Methyl Carbitol
(trade mark) 3.00
Total 100.00
*Rhoplex 505 (trade mark) is a high molecular
weight acrylic copolymer manufactured by
Rohm & Haas Company, 40~ n.v.
**Acrysol 527 (trade mark) is an all acrylic
(low molecular weight) resin solution manu-
factured by Rohm & Haas Company, 45% n.v.
***Ammonium Hydroxide is used to adjust pH and
obtain clarification
Total resin solids of above formula is 20~.
The ratio of Rhoplex B-505 (trade mark) to Acrysol 527
(trade mark) on solids basis is 9.0:1Ø
EXAMPLE VI
Synthemul 40-450*
(trade mark) 32.65
Acrysol 527 (trade mark)8.88
Ammonium Hydroxide 28% 2.00
Water 52.47
Butyl Carbitol (trade mark)4.00
Total 100.00
*Synthemul 40-450 (trade mark)ic a polyvinyl
acetate, acrylic copolymer emulsion, 49~ n.v.,
produced by Reichhold Chemicals Inc.
Total resin solids = 20~
Synthemul 40-450 (trade mark)/Acrysol 527
(trade mark) ratio = 80:20
~r
- 23 -
mab/
EXAMPLE VII
E-1630 (trade mark),
45% n.v.* 40~00
Acrysol 527 (trade mark) 4.44
Water 52.06
Methyl Carbitol
(trade mark) D ' 3.50
Total 10~0.00
*E-1630 (trade mark) is an experimental
acrylic emulsion manufactured by Rhom
& Haas Company, n.v. = 45%
10 E-1630 (trade mark)/Acrysol-527 (trade mark)
ratio = 90:10
Total resin solids: 20
EXAMPLE VIII
E-1630 (trade mark) 40.00
Acrysol 527
(trade mark) 4.44
Fire retardant* 10.00
Nylate-10**
(trade mark) 2.00
Water 40.56
Methyl Carbitol
(trade mark) 3.00
Total 100.00
*Fire retardant is produced by the com-
plete neutrilization of dimethylamine
with phosphoric acid.
**Nylate-10 (trade mark) is a wood pre-
servative manufactured by Seymore
Chemicals Co. The active ingredient
is copper-8-quinolinolate.
X - 24 -
ma~/
9~82
Example IX
The formulation of Example VIII was used to apply
to two blocks of yellow cedar 4"x8". The wood was soaked in
the formulation for 15 minutes and then allowed to air dry
overnight at room temperature. One of the boards was then
washed under running tap water for 6 hours and again redried
overnight at room temperature. The boards were then exposed
to the flame of a blow torch held 6" from their sur~ace. -
~either of the two boards supported any flame after the blow
torch was removed. However, local charring was visible
after a period of 3 minutes. In a control block of wood
which was not treated at all, the wood caught fire within 1
minute when exposed to the flame, and the fire continued to
burn after the torch was removed. This experiment shows
that the fire retardant was effective in reducing the flame
spread and had become non-leachable even though originally
it was a water-soluble compound.
X
-- 25 ~
mc / v ~f / ~,
9~82
EXAMPLE X
A block of white oa~ approximately 1-1l/2"x3"x
4" was soaked in the formulation of Example VIII for 12
hours and air dried for 24 hours. An identical size
block was used as an internal control. The treated
block and the control block were then soaked in water for
2 hours and dried in an oven at 250F. On examination
of these dried blocks it was found that the untreated
block had checked along the ray cells whereas the treated
block showed no checking whatsoever. This experiment -~
shows that the formulation of Example VIII had effec-
tively stabilized the wood.
The entire experiment was repeated, except
that the Acrysol 527 (trade mark) was omitted from the
formulation of Example VIII. In this case it was found
that both the control and the treated blocks checked
on oven drying. This experiment shows that the high
molecular weight acrylic polymer alone did not effectively
stabilize the wood.
X - 26 -
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