CA1304893C - Method of protecting wood - Google Patents

Abstract

ABSTRACT

A method of protecting wood that comprises applying to the surface of the wood a solution of sodium carbonate and sodium borate. In a further aspect wood is protected against fungal growth by applying to the sur-face of the wood a solution of sodium carbonate.

Description

~30~ 93 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.

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-` ~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 ,.~ .,~, .

.

~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.

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Table 2 Formulation Infected Area (~ at5_Months) With Wax Without_Wax Water (Control 100 100 C10B2 o o 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.

~" 131~ 3 Table 3 Formulation Infected Areas (~) _ _ _ Water (Control) 100 _ _ 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.

: . .. , .. ~ , 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.

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 ~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 . .

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.

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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 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-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.

Claims (9)

1. A method for protecting wood against fungal attack and fire that comprises applying to the surface of the wood a solution consisting 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 water.

2. A method as claimed in claim 1 in which the solution is applied by dipping the wood into the solution for at least ten seconds.

3. A method as claimed in claim 1 in which the solution is applied by spraying.

4. A method as claimed in claim 1 in which the pH is in the range 10 to 11.

5. A method as claimed in claim 1 in which the solution contains a wax.

6. A method as claimed in claim 1 in which the solution contains a pigment.

7. A composition useful in the protection of wood against fungal attack and fire and consisting essentially of about two parts by weight of sodium borate, about 4 to 30 parts by weight sodium carbonate and the balance about 100 parts by weight water.

8. A composition as claimed in claim 7 in which the solution also contains a wax.

9. A composition as claimed in claim 7 in which the solution also contains a pigment.