Note: Descriptions are shown in the official language in which they were submitted.
~30~ 93
1592-104
This invention relates to a method of pro
tecting wood, more particularly, a method of protecting
wood to prevent stain and decay and to improve its fire
retardance~
Because wood is an organic substance with a
high carbohydrate content, it is an ideal nutrient for
fungi and is also susceptible to destruction by fire.
The ability of wood products to inhibit both the growth
of fungi and spread of fire have long been important con-
cerns.
The majority of wood species which constitute
the main volume of commercial lumber have low resistance
to sapstain, mold and decay in the green condition. In
the warm sum~er months, green sapwood will be attacked by
sapstain fungi in 2 or 3 weeks, producing black and/or
blue stains which affect mainly the aesthetic value of
the lumber. Further growth of fungi results in decay
which weakens the wood structure. Antistain and decay
treatment are therefore very important in lumber stored
before drying or when shipped in the green condition,
especially when shipped by ocean transport to inter-
national markets under warm, humid conditions over
several months.
- 1 - .
-` ~30~1~il93
There are many commercial practices for
sapstain and decay prevention in lumber. The penta-,
tetra-, and tri-chlorophenols in admixture with caustic
and~or borax are the most effective, but their toxicity
to humans and fish has been a health and environmental
concern for a considerable time. The discovery of safer
treatments is an urgent requirement of the wood industry.
Fire hazard is still one of the major problems
with wood products. The development of treatments which
will increase fire resistance of wood is highly desirable
to reduce fire losses.
The discovery of treatments that can be bifunc-
tional by both improving resistance to biological attack
and increasing fire retardancy is of major importance to
the wood industry.
Prior art known to applicant includes United
States Patents 4,461,721 to Goettsche; 4,269,875 to
Bechgaard; 4l234,340 to Pellico; 4,154,818 to Kanada;
3,214,453 to Stern; 3,305,298 to Chapman; 806,540 to
Hager and 4,061,500 to Hager. Goettsche shows use of
boric acid, sodium salt and an organic amine as a means
of preserving wood. Bechgaard shows the use of boric
oxide as a wood preservative. Pellico features a wood
preservative composition including a number of organic
~L3~ 33
compounds. Kanada features a product useful against
marine organisms and includes a number of relatively
complex organic compounds. Stern is an example of rela-
tively complex compounds being used in wood preservation.
Chapman discloses a composition of some considerable
complexity. Hager in 806,540 shows a wood preservative
and Hager in 4,061,500 shows a composition including a
fatty acid.
It follows from the above that there is a need
to simplify compositions of the preservation of wood,
both from the point of view of chemical complexity and
toxicity,
This invention proposes to use a bifunctinal
chemical treatment to substantially reduce the biological
staining attack on wood and to improve its fire retar-
dancy properties. Experimental results with sodium
carbonate-sodium borate treatment solutions were found to
be very satisfactory in this regard, while sodium car-
bonate by itself was also effective to a lesser degree.
To enhance water resistancy, water repellent wax can be
added to the antistain solution.
The anti-biological stain concept is based on
the ability of the chemical treatments to inhibit the
growth of fungi by high alkalinity, by modifying wood
13~9~
4l495-~04
sugars through boron complexes and by forming a laye:r of
inorganic e:lemen-ts in the wood surface to isolate food :Erom
the fungal spores and fungi, thus clenying nutrients to -the
fungi.
The fire retardant concept of this invention is basecl
on the abili-ty of the c`hemicals to produce carbon dioxide
and to release structural water to re-tard the growth of
fi.re. In addi-tion, the boron-sugar complexes should
con-tribute to a higher kindling point.
Accordingly, the present invention provides a
method of protecting wood against fungal a-t-tach and fire
that comprises applying to the surface of -the wood a
solution consis-ting essentially of about 4 to 30 parts by
weight of sodium carbonate, about two parts by weight of
sodium borate and the balance of the solution being about
100 parts by weight wa-ter.
The effec-tiveness of the chemlcal or chemical mixtures
to inhibit fungal growth on and improve fire re-tardancy of
wood is performed by disso:Lving the chemicals in water and
then we-tting the wood through dipping or spraying. A
series of :Labora-tory experiments were conducted to examine
-the validity of this concept in prevention of fungal grow-th
and i.mprovement in fire retardancy.
In the following experiment reference is made to the
drawings, in which:
:
:3 3~
Figure 1 is a graph relating stain index to
defined treatment as discussed in Example 6;
Figure 2 is a graph relating burning time to
treatment as discussed in Example 8; and
Figure 3 is a graph relating flame spread and
burning time; and
Figure 4 is a graph relating flame growth and
treatment as discussed in Example 10.
ANTI BIOLOGICAL STAIN PROPERTIES
-
Example 1: Antistain Effectiveness on Spruce-Pine-Fir
Eleven concentrations of sodium carbonate in
water solution were prepared at 0, 1, 2, 4, 6, 8, 10, 12,
15, 20 and 30 g/100 ml water. Two percent sodium borate
by weight (2 g/100 ml of solution) was added to each.
After complete dissolution of the inorganic chemicals,
the pH level was measured by pH meter. The results are
shown in Table 1.
-` 3L3Q4~3
.. . . ..
Table 1
~ _ . .
Formulat ion pHInfected Area ( ~ )
Water ~Control) 6.2 100
GOB2 9. 3 27
ClB2 9.9 8
C2B2 10.1 5
C4B2 10. 3 0
C6B2 10. 4 0
C8B2 10.5 0
C10B2 10.6 0
C12B2 10.6 0
C15B2 10.7 0
C20B2 10 . 8 0
C30B2 10l9 0
~ = Sodium Carbonate
B = Sodium Borate
The number~ in the formulation~ repre3ent the ehemical
concentratlonq.
~3~ 3
The pH level of sodium carbonate by itself in
water solution measured 11.4 to 11.6 at a chemical con-
centration of 1 to 20~. The borate addition reduced the
pH of the sodium carbonate solutions as a result of the
buffering effect of the sodium borate.
These results indicate that high concentrations
of the sodium carbonate-sodium borate mixture can be used
to effectively coat the wood surface without too high a
pH, that is, without a high health or environmental
hazard.
To confirm the antistain effect of the chemi-
cals, one sample of sapwood veneer (12 in. by 12 in.) was
eollected from eaeh of 20 logs of spruee-pine-fir at a
plywood mill. The average moisture eontent was 1115
(bone-dry wood basis) (standard deviation 50.9%).
Eaeh veneer sample was eut into 12 strips (1
in. wide by 12 in. long). One strip from eaeh veneer was
randomly selected and placed in a group. Thus a total of
12 strip groups with matehed veneer was established.
Each ~eneer group was then sprayed with one of
the chemieal formulations, air dried for 4 hours and then
sprayed with a fungal spore solution. The veneer groups
were incubated at 22-25C for observation of fungal
~ 3~ 9~3
growth. Fungi started to grow on control veneers by the
fifth day of incubation. By the seventh day, about 60~
and by the twelfth day, 80% of the control veneers were
infected. However, a-t this time all treated groups
showed no signs of growth. After 5 months' incubation
the control veneers showed 100% of the surface areas
infected with fungi, while COB2, ClB2, and C2B2 treat-
ments showed only 27, 8 and 5~ area infection respec-
tively, the treatments at greater concentration showed no
signs of growth. The results of the treatments are shown
in Table 1. The sodium carbonate-sodium borate mixtures
are thus demonstrated to be effective for stain fungi
inhibition at concentrations of C4B2 and above.
Example 2: Effective _ss of Sodium Carbonate Alone
Similar to Example 1, three groups of spruce-
pine-fir veneers were prepared and treated with C6 and
C12 only without the addition of sodium borate.
Observations after L~ months showed that the percent
fungal growth on the wood surfaces was 100~ for the
control, 25~ for C6 and 0~ for C12. These results
suggest that the sodium carbonate by itself is also an
effective chemical for suppression of fungal growth.
Example 3: Antistain Effectiveness on Ponderosa Pine
Ponderosa pine is well known for its suscep-
tability to fungal attack. A 2-foot length of a 2 in. by
8 in. cross section of air dried sapwood, which had been
previously subjected to biological stain was used in this
experiment. This piece of lumber was planed to have two
smooth surfaces along its length and then cut into
thirty-six 2 in. by 2 in. by 1 in. thick blocks.
Eight solutions of the new chemical treatments
with differing concentrations of sodium carbonate and
sodium borate were prepared as before. The formulas are
shown in Table 2.
Eight hundred ml of solution was prepared for
each of the above formulations. Four hundred ml was used
as prepared and the remaining 400 ml was mixed with a 4%
commercial wax with a trace of yellow iron oxide pigment
added. Thus, sixteen formulations were prepared plus one
control. In addition to the above formulations, one con-
taining 0.8% tetrachlorophenate with 4~ wax and pigment
in water solution, similar to a commercial antistain dip,
was prepared.
Two blocks of ponderosa pine were assigned to
each treatment. The blocks were submerged for one to two
_g _
~econd~ to thoroughly ooa~ khe ~urf~ce and alr drled at
room temperature overnlght. A water ~olution o~ fungi
was prepared by ~oaking fun~ally inrected wood in water
for one week and the water ~olution decanted. The
treated and control ~ample blocks were ~prayed with the
fungal Qolution (pH 5.2) and incubated at room tem-
perature in~ide a covered gla~q container. The block~
were qprayed with water dail~ to maintain the moisture
content and in~pected weekly with a stereomicroscope to
record fungal growth.
One week following treatment only the control
block~ had ~old growth. At two weeks, the control blocks
not only had mold but al~o Yta~n fungi and the C2B2 and
C4B2 w~th wax and pigment ~howed very minor blue ~old
vi~ible only through the mieroscope. Howeverg C2B2 and
C4B2 without ~ax or p~gment showed no ~lgn of growth9 a3
did all higher concentration treatment~ with or without
wax. The 0.8~ tetrachlorophenate-wax-pigment treatment
showed Qome mold growth with the appearance of black
fungal ~tain.
After 30 day~, the control and 0.8~ tetrach-
lor~phenate treated block~ showed ma~ive sur~ace growth
of black fungi, while the C2B2 block had Aome mold fungi
(pH indicator ~howed the ~urface o~ thi~ block to be
--10--
,.~ .,~, .
.
~L3~4l5~3
about 5). The mold on the C4B2 block had disappeared.
The 5-month results on percent fungal infection area are
shown in Table 2. All the treatments were highly effec-
tive. The formulations containing wax and pigment gave
practically similar results to those which did not. It
appears that C6B2 or higher concentrations completely
inhibited the growth of the fungal species under the con-
ditions of the experiment. The effectiveness of the
sodium carbonate-sodium borate combination was again
substantiated.
-~ ~3~
Table 2
Formulation Infected Area (~ at5_Months)
With Wax Without_Wax
Water (Control 100 100
C2B2 4 7
C4B2 2 0
C6B2 1 0
C8B2 0 0
C10B2 o o
C15B2 0 0
C20B2 0 0
C30B2 o o
.. .. _ _ . . _ .
C = Sodium Carbonate
B = Sodium Borate
The numbers in the formulations represent the chemical
concentrations.
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., .
.. .. .
,' ,, ;
..
3[3~3t;~3
Example 4: Treatment of Aspen Wood
Ten samples of 12 in. by 12 in. aspen veneer
(1/10 in. thickness) were obtained, one each from 10 dif-
ferent logs. These sample veneers were split into 1 in.
by 12 in. strips and separated into 11 groups. All
groups had 10 veneer strips, each from a different log.
One of the groups was used as a control and the others
treated with the same chemical combinations and incubated
under the same conditions as described in Example 1.
Five months later, the controls showed complete coverage
with white decay fungi. The treated sample results are
shown in Table 3.
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~" 131~ 3
Table 3
Formulation Infected Areas (~)
_ _ _
Water (Control) 100
COB2 28
C1B2 5
C2B2 8
C4B2 42
C6B2 40
C8B2 30
C10B2 8
C12B2
C15B2 6
C20B2
_ _
The above results indicate that fungal growth
on aspen (a hardwood) was different from that found with
softwood species. The control was covered with a white
decay fungi while treated spec;mens showed no such
growth. While the results show considerable variability
these chemical treatments are again proven to be effec-
tive on aspen, a hardwood, but its development trend was
different from that of softwood.
- 1 4
: . .. , .. ~ , j , : ,,
..... . ~ .
~3~4~93
Example 5: Antistain Effectiveness or Douglas Fir
One sample of Douglas fir sapwood veneer (12
in. by 12 in. by 1/10 in. thickness) was taken from each
of 5 logs. Each sample was then cut into three 4 in. by
12 in. strips. Three groups were made up of 5 samples,
one from each log. Two concentrations of treatment che-
micals, C8B2 and C15B2 were prepared as previously
outlined in Example 1. One group was kept as a control
and the other two treated with chemical and sprayed with
fungal solution as previously outlined in Example 1.
After 5 months incubation at 22-25C the infection areas
were 100~, 3~ and 0~ for the control, C8B2 and C15B2
respectively. The chemical formulations are again proven
to be effective for Douglas fir.
Example 6: Antistain Effectiveness on Western H_mlock
In laboratory experiments, three pieces of
hemlock sapwood lumber (2 in. by 6 in. by 2 ft.) were
selected green from the sawmill. These were cut into 2
in. by 1 in. by 1/2 in. blocks. The treatments and con-
ditions of spraying and incubation are the same as for
ponderosa pine described in Example 3. The results were
essentially the same as for ponderosa pine.
:. ;,~ ... . .-
~L3~ 3
With the accumulation of encouraging results in
the laboratory, a field trial was carried out at the
sawmill. About 100 pieces of green economy grade 2 in.
by 6 in. western hemlock 8-foot long were used for this
experiment. A package, 8 boards wide and 11 boards in
depth, was constructed as follows: layers 1 through 4
were untreated controls; layers 5 through 8 were treated
by spraying with C10B2 solution containing 4~ wax and
pigment made up as previously described; layers 9 through
to 11 were treated with C10B2 without wax and pigment.
The lumber pile was stored outdoors at a Vancouver,
Canada mill during the summer of 1986. It was covered
with a plastic sheet for the first three days and then
exposed to the weather.
After 5 month's exposure the pile was
dismantled and the average stain index measured by the
standard provided by Forintek Canada Corporation. (R.S.
Smith et al 1985. New Fungicidal Formulations Protect
Canadian Lumber. Forintek Can. Corp. Special Publication
No. SP-25. 18 P.).
Results are shown in Figure 1. The control
pieces were all stained with a stain index of 4.6 while
the treatments with and without wax were 1 and o.8
respectively.
~ ~3~9L~3~3
The chemical treatment is therefore shown to be
effective on western hemlock.
Example 7: Mill Run Trial_on Green Spruce-Pine-Fir
Two hundred pieces of green spruce-pine-fir 2
in. by 4 in. by 8 ft. long were cut two days before chem-
ical treatment. During that time it was stacked 3/4 in.
apart with wood spacers to provide an opportunity for air
borne fungal spores to contaminate the wood surface.
A total of 5 piles of 40 pieces of lumber were
prepared. One pile was left untreated as a control. Two
piles were treated by spraying with C5B2 chemical treat-
ment and the remaining two piles with C10B2. After
spraying with chemical, the lumber was packed without
spacers and completely wrapped in plastic and then paper
wrapped for storage. The lumber was stored for a period
of four months.
The stain index was determined as in Example 6.
Completely clean lumber is assigned O and completely
covered black stain 10. The control sample was not only
attacked by stain and mold fungi but was also infected
with white decay fungi. During this grading procedure a
three-person consensus was used to arrive at the results
which are shown in Table 4.
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13~3~3
Table 4
Treatments No. of Samples Average Stain Index
Control 40 6.40
C5B2 - Pile 1 40 0.08
- Pile 2 40 0.43
C1OB2 - Pile 1 40 0.42
- Pile 2 40 0.30
The above results clearly indicate the effectiveness of
these antistain treatments.
FIRE RETARDANT PROPERTIES
Example 8- Laboratory Candle Burning Test
Four chemical treatment formulations were pre-
pared as described in Example 1: C2B2, C6B2, C10B2,
C30B2. Two additional formulations, C12B2 and C6B2, con-
taining 4~ wax and pigment were similarly prepared
(Example 3). Pulp sheets were obtained from a nearby
pulp mill and cut into 1 in. wide and 6 in. long strips.
~3~g~8~3
They were conditioned in an oven at 800C for two days to
minimize moisture content. Three replicated pulp strips
were dipped into each of the chemical solutions and oven
dried at 800C for two days.
Control and treated strips were clamped upright
and the tops lit with a propane torch for 3 seconds to
initiate a flame. After removal of the torch, burning
time, regardless of flame/no flame, was recorded. The
length of strip consumed by the fire was expressed as a
percent of total length. Results of burning time are
shown in Figure 2.
The control samples were burnt totally while
the treated samples lost less than 5% of their length.
Figure 2 shows that the controls would continue burning
indefinitely while the treated samples extinguished them-
selves in finite time. These results demonstrate the
fire-retardant properties of the new chemical treatments.
Example 9: Laborator~ Flame Spread Test - Aspen Veneer
Aspen veneer (1/8 in thickness) was cut into 1
in. wide by 12 in. long strips. One end of each strip (6
in.) was dipped into either chemical treatment C6B2 or
C12B2 prepared as before. The other end of the strip was
left untreated and used as a control. The strips were
then dried in an oven at 800C for two days prior to
-19-
~41~
testing. The fire testing procedure was the same as in
Example 8.
The results showed that although the chemicals
only coated the surface, results were similar to the
treated pulp strips. The fire in the treated aspen went
out rapidly on removal of the fire source, while the
untreated controls stopped burning at the interface be-
tween the control and the treated ends showing the abil-
ity of the chemical treatment to stop the continuous
flame and eventually quench the fire altogether.
Example 10: _Laboratory Flame Test -_Douglas Fir Plywood
Three pieoes of Douglas fir plywood (3-ply) 12
in. by 12 in. in size were prepared. One-half of the
plywood (6 in. by 12 in.) was painted with C6B2 or C12B2
chemical treatment both with wax and pigment, prepared as
described previously. The other half of the face was
left untreated as a control. Samples were then oven
dried at 800C for two days.
A flame spread test was undertaken to compare
the treatments with the controls. Samples were placed on
a burning deck with a slope angle of 45 and a 4 in. pro-
pane torch flame applied to the end of the side of the
wood sample being tested. The length of the flame spread
-20-
. .
3l3~9~9~
was recorded every 10 seconds after torch contact. After
120 seconds contact with the plywood, the torch was
removed and total burning time recorded.
Figure 3 shows the results of the relationship
between the flame spread length and burning time. The
control flame spread was two times greater than that of
treated samples after 30 seconds of testing. The flame
of the control kept growing but the treated samples,
after reaching a peak, decreased.
The fire growth time, as shown in Figure 4,
suggests the infinitive for the control while less than
20 seconds for the treated samples.
The ef'fectiveness of the new chemical for fire
retardation is again proven.
Example 11: Commercial Flame Spread_Test
To confirm laboratory results, 20 pieces of 2
in. by 6 in. by 8 ft. long kiln-dried hemlock lumber (12
moisture content) were treated with C12B2 chemical con-
centration by spraying and tested in the Warnock Hersey
Certification Agency's 25-foot fire tunnel in accordance
with the Can.4 S102 M83 Standard.
The flame spread classification based on the
standard was FSC1 22.
~3L~
According to the Underwriter's Laboratory spe-
cification -- "To be eligible for classi~ication~ the
coating or system must reduce the flame spread of Douglas
fir and all other tested interior combustible surfaces
(having flame spread of 100 or greater by test) to which
it is applie~, by at least 50~ or to a flame spread of 50
or less, whichever represents the lesser spread of
flame." With a flame spread of 22, the new chemical
treatment should be acceptable as a fire retardant.
The Canadian National Building Code, 1980,
Appendix 11 (Section 3.1.12) Fire Retardant Treated Wood
Systems, requires a flame spread rating of 25. The above
rating of 22 would thus be acceptable for use in public
buildings.
Example 12- Fish Toxicity of the Treatment
Chlorinated phenols are the most common
antistain chemicals in commercial use. They are well
known to be extremely toxic to humans and to fish. Fish
toxicity is rated by the use of the 96 Hr. LC 50 Index --
being the concentration of the toxic component which will
be lethal to 50% of the test fish in a 96-hr. treatment
under a standard set of conditions (J.D. Davis and R.A.W.
Hoos, Use of Sodium Pentachlorophenate and Dehydroabietic
Acid as Reference Toxicants for Salmonid Bioassays, J.
~3~ g3
41S92-104
Fish. Res. Board Can. Vol. 32(3)411-16 ~1975).
Comparative toxicities for sodium pentachlorophenate
powder, an industrial polychlorophenate dip tank solution,
and the 6% sodium carbonate-2% sodium borate solution are
given in Table 5.
Table 5
Chemical Treatment 96 Hr._LC50_~m
Sodium Pentachlorophenate Powder 0.03 to 0.12
Industrial Dip Tank Solution 145
6% Sodium Carbonate-
2% Sodium Borate Solution 22,300
As can be seen from Table 5, the sodium carbonate-sodium
borate solution is less than 1% as toxic as the present
polychlorophenate solutions used in industrial antistain
dip tanks.
The experimental results support the claim that
sodium carbonate-sodium borate solution treatments prevent
fungal attack on wood and also contribute substan-
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A
~309~33
tially to the fire resistance of wood. In practica]
application, the solutions can be directly applied to
lumber by soaking or spraying.
Variations, departures and modifications lying
within the spirit of the invention or the scope as
defined by the appended claims will be obvious to those
skilled in the wood treatment art.
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