WO2013064724A1

WO2013064724A1 - Preservative element, method for localized wood preservation, and wood obtained by the method

Info

Publication number: WO2013064724A1
Application number: PCT/FI2012/051013
Authority: WO
Inventors: Risto Rahkola
Original assignee: Kemira Oyj
Priority date: 2011-10-31
Filing date: 2012-10-23
Publication date: 2013-05-10
Also published as: FI20116064A0; FI20116064L

Abstract

The present invention relates to a preservative composition comprising a water-soluble preservative agent and rosin as a water permeable solidifying agent. The preservative composition may be in the form of a fused body. The present invention also relates to a method for treating wood by applying said preservative composition to an opening in said wood. The present invention also relates to wood obtained with said treatment method.

Description

PRESERVATIVE ELEMENT, METHOD FOR LOCALIZED WOOD

PRESERVATION, AND WOOD OBTAINED BY THE METHOD

Field of the invention

The present invention relates to a method for localized wood preservation. More specifically the present invention relates to a preservative element containing preservative composition, which may be used for treating wood.

Background of the invention

Wood-destroying organisms are attracted by moisture in ground contact and may reduce wood service life significantly. In certain areas termites are a significant problem for untreated wood. As an example preservative-treated poles have decades' service life with only one specific exception, which is the ground line zone. In this area that is 0.2 m above ground and 0.4 m below ground there are perfect conditions for decay to grow. At the same conditions today's preservatives are not as good as forbidden old-timers, such as CCA. For example Finnish Road Admin- istration no longer accepts NTR - A class copper treated light poles (unofficial information from pole manufacturer 201 1 ).

In the past, pentachlorophenol (PCP) or chromated copper arsenate (CCA) were superior wood preservatives, but environmental and health concerns have been changing legislation to ban any chlorophenols or arsenic compounds in this appli- cation. CCA was banned by the European Union in 2006. Creosote is remembered from railway sleepers and transmission poles but also from polluted treatment sites. Its use is heavily controlled by authorities.

Borates are considered acceptable wood preservatives from a human health and an ecological perspective because of very low toxicity to both mammalian and aquatic organisms. Borates are effective preservatives against both fungi and insects and even considered more effective than copper or zinc compounds.

Borates are inexpensive, colorless, odorless and non-corrosive. Unfortunately, borate solubility reduces its use in outdoor applications, since high moisture will dissolve boron from wood. There are small differences in classification of wood in different countries when treated with preservative. Below are listed EU requirements according to EN 335: (according to Ullmann's Encylopedia of Industrial Chemistry, Wiley-VHC). Use Class 1 - above ground, covered (dry)

Use Class 2 - above ground, covered (risk of wetting)

Use Class 3 - above ground, not covered

Use Class 4 - in contact with ground or fresh water

Use Class 5 - in salt water

In principle boric acid or borate is suitable to be used in class 1 , when wood is in a dry atmosphere without risk of wetting. If boron would be fixed properly in the wood, the treated wood would be applicable in any class.

Boron in wood is typically expressed as boric acid equivalent (BAE) and it repre- sents all boron compounds in wood preservation including borates, polyborates etc. In numerous researches the effective level of BAE is typically between 0.2-1 .0 BAE % (wt/wt) depending on the wood material, boron preservative and wood attacking organism.

According to New Zealand standard NZS 3640, treatment level of 0.8% BAE (wt/wt) meets the hazard class 3.1 (exposed to the weather, above ground), if sufficient protective surface treatment has been done.

Wood preservative or treated wood should meet several requirements (Suolahti, Osmo: Laho ja sen torjunta. Porvoo, Helsinki WSOY (1961 ), pages 75-76): effective against wood destroying organisms and insects; harmless for mammals, ver- tebrates and cultivated plant; easily and fast impregnated into the core of wood; non-toxic, non-flammable for wood handlers; effective in service for years or even decades; non-corrosive for metals which are in contact with wood or which are used in impregnation; not deteriorating mechanical properties of wood; not affecting ignition properties and in case of fire, not releasing toxic gases; odorless, col- orless, non-staining; not preventing painting or other post treatment; easily analyzed at least qualitatively; relatively cheap and available for large scale; nontoxic waste after use; easily reclaimed for example as energy.

There are elements available for treating wood called impel rods, which are prepared by fusing borate compounds in hot temperature (above 1000^QC) and formed to round bars. These rods are applied in drilled wood as solid in certain dimensions. This material is soluble in water and when the moisture of wood exceeds about 25%, the boron rods start to dissolve and release boron preservative in the surrounding wood material. However, the boron leaches rapidly from the wood material causing boron loss and resulting in poor protection (Mitsuhashi et al., Forest Products journal (2007), vol. 57, No 12).

GB2008640B discloses a fused body of wood preservative material including boric oxide, said fused body being shaped to fit a cavity into which in use it is to be in- serted.

US4661 157 discloses a process for the production of a shaped body, comprising one or more boron compounds, suitable for use as a preservative insert in structures liable to biological attack, characterized by forming a paste comprising water and one or more boron compounds capable of binding water by hydration, shaping the paste and allowing the shaped paste to solidify by the binding of at least a portion of the water therein to form the shaped body.

WO9218007 discloses a shaped body for use as a wood preservative insert comprising at least one boron compound and at least one fluorine compound.

US491 1988 discloses a shaped preservative element in the form of a rod or pellet, for timber or masonry, which contains a solid organic boron ester having a melting point of about 50-200^QC, which is hydrolysable in the presence of water.

WO8303997 teaches using liquid preservative and fused borate rods in drilled holes. It is claimed that untreated wood requires liquid preservative since borate will not diffuse in dry conditions. Synthetic resins like melamine or phenolic resins require hot temperatures and high pressures to polymerization. Thermoset plastics are possible to mix with borate or other biocide. One example is CA2429914.

Freitag et al. (Holzforschung, Vol. 65, pp. 429-434, 201 1 ) have studied the long- term performance of fused borate rods for limiting internal decay in Douglas-fir utility poles. Fused borate rods are produced by heating disodium octaborate to molten state so that it can be poured into molds. The borate hardens into a glasslike rod as it cools, and the rods are put into drilled holes, which are then plugged with tight fitting, copper naphtenate-treated wooden dowels.

The prior art has several drawbacks. In many cases expensive special machinery is required. Further, generally the fusing is carried out at very hot temperatures, such as over 500^QC. When using a rod-shaped body, the rod gives support to the wood material in the beginning, but as soon as the dissolving starts from the sur- face, the strength is lost in an unpredicted way. Also the drilled hole requires a cap to prevent direct contact with outside moisture and it is a challenge to ensure the cap's tightness for many years. In general, many known applications increase the cost of wood too much. Glue or plastic mixes tend to influence only on material that is hardened, because there is no practical preservative release in the surrounding material. Outdoor wood handling is difficult since curing requires pressure.

There is a need for a "smart weapon" especially for wood which is in contact with moist ground or termite population. It should be efficient against wood destroying organisms, such as decay fungi, and keep the required properties for a long time. It should also be environmentally friendly, for example in use above groundwater areas. Neither extreme temperatures nor specific machinery would be needed. In addition to excellent properties, low cost would be an asset.

Summary of the invention This invention relates to a melted mixture which after solidifying step creates constant release of preservative. Melted material fills every pore in a drilled hole and mechanical strength is perfectly suited for application. It was surprisingly found that when using a suitable solidifying agent it is possible to use water-soluble preservative agents. Traditionally it is desired to use only non-water soluble agents to bind the effective agents to the wood and to avoid the leaching therefrom.

The mixture comprises a preservative agent, which is leachable in water (or water- soluble or water-borne), for example boron salt or monocarboxylic acid salt. The mixture also includes a solidifying agent. Solidifying material is rosin, which is a resinous compound, especially tall oil rosin or its biopolymer derivatives. It is re- markable that tall oil rosin is an extractive from pine, and pine is the most used material for poles and other treated wood in the market. The aim is environmental friendliness and controlled biodegradability over a long time. Rosin or rosin biode- rivatives are preferred because they have certain water permeability and ensure preservative controlled release. The present invention provides a preservative composition containing a water- soluble preservative agent and rosin as a water permeable solidifying agent.

The present invention also provides a method for treating wood by applying said preservative compound to a hole in said wood. The present invention also provides the wood obtained with said treatment method.

The composition of the invention is suitable for example against surface moulds, blue stain fungi and wood-rotting fungi, and also for the inhibition of damage caused by termites and the like.

One advantage of the invention is that it is durable and simple to apply. Rosin as the solid material provides a controlled release of the preservative. Preservative element acts as storage for biocide and it releases the active substance only when material gets wet i.e. in conditions which facilitate the microbial growth. Further, the amount of released compound may be adjusted by controlling the composition of the preservative element. Rosin also helps supporting the shape of the preservative element, such as a rod, inside the wood when the preservative agent starts releasing. Rosin also maintains its mechanical strength when wetted unlike many other materials, such as plain octaborate rods, which will leach on their surface and lose their strength.

Another advantage of the invention is that it is environmentally beneficial. Still another advantage of the invention is that it is economical. Brief description of the drawings

Figure 1 shows a leaching test for boron: full immersion in water without agita- tion, boric acid and rosin elements, procedure like AWPA E-1 1 (upper graph) versus Mitsuhashi et al., Forest Products journal (2007), vol. 57, No 12, disodium octaborate impregnated in wood (adapted), test AWPA E-1 1 (lower graph).

Figure 2 shows a leaching test for boron: full immersion in water without agitation, boric acid and rosin elements, procedure like AWPA E-1 1 (upper graph) ver- sus US2008/0131717, boric acid, test AWPA E-1 1 (lower graph).

Figure 3 shows a comparison of different preservative elements wherein different compositions of tall oil rosin and boric acid were compared using Araldite and boric acid as a control.

Detailed description of the invention The present invention provides a preservative composition, such as a melting preservative composition, comprising a water-leachable preservative agent and a wa- ter permeable solidifying agent. The preservative composition may be in a form of a melting body which is capable of filling and solidifying in open wood structures.

The mixture comprises a preservative agent, which is leachable in water or water- soluble/water-borne (hydrolysable in the presence of water), for example boron salt or monocarboxylic acid salt. The preservative agent may be selected for example from disodium octaborate, boric acid, sodium pentaborate, calcium borate, sodium formate, potassium formate, calcium formate, ammonium formate and mixtures thereof. Other water-borne preservative agents include for example chro- mated copper arsenate (CCA), alkaline copper quaternary (ACQ), copper azole, ammoniacal copper zinc arsenate (ACZA), copper xyligen, copper borate and other copper compounds such as copper sulfate; sodium silicate based preservatives; potassium silicate based preservatives; and certain cobalt salts.

The water permeable solidifying agent is rosin, which is a resinous compound. Rosin is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid ter- pene components. The rosin may be selected for example from wood rosin, gum rosin, tall oil rosin, its biopolymer derivatives or mixtures thereof.

Tall oil rosin is considered as a low-cost side product from the distillation of crude tall oil (CTO). Crude tall oil is a by-product obtained from the kraft paper making process. Normal delivery form is hot molten, but in this application tall oil rosin can be used as solid. Alternative rosin is obtained from aged pine stumps which are chipped and soaked in a solvent; this extracted form of rosin is called wood rosin. Yet applicable rosin in a preservative is gum rosin obtained from living trees.

Tall oil derivatives are effective preservatives against decay especially with high loading in wood. In the invention the preservative agent concentration, such as boron concentration, may be less with rosin additive than it would be in bare (boron-based) preservative to reach the required preservative properties.

In one embodiment the preservative agent is a boron salt. When using boron salts together with the rosin as the solidifying agent a synergic effect was observed. The water permeability and the controlled release of the boron salt in the presence of water were especially suitable for use as a preservative composition.

In one embodiment the composition is can be melted, such as at a temperature of about 100-200^QC, for example at 100-150^QC. In one embodiment the composition is in the form of a fused body or insert, for example an elongate body, such as a rod, a stick, a pellet or some other shaped object. In another embodiment the composition is in a form of powder, which can be melted at the place of treatment, such as by a hot glue gun or the like, and delivered to the wood to be protected i.e. to an opening in a wood structure, such as a hole, for example a drilled hole. The hole may be plugged with a fitting, such as a wooden dowel.

Therefore the present invention also provides a method for treating wood comprising applying said melting preservative composition to a hole, aperture or any suitable opening in said wood. Examples of such openings include drilled holes, cracks, natural openings and the like. The preservative composition may be ap- plied as a solid body or as molten. In the latter case the molten composition will fill and solidify in the open wood structure.

The present invention also provides a method for preparing said solidified (fused) wood preservative body. Said method comprises mixing the water-soluble preservative agent and the water permeable solidifying agent to form a powder mix- ture, heating said mixture at a suitable temperature to melt the mixture to form a homogenous liquid (or paste) mixture, and forming said homogenous liquid (or paste) mixture into a body. The body may be formed by shaping the molten material by pouring it into a mold and letting it solidify to obtain the preservative body.

In one embodiment the composition contains about 50-80% (w/w) of the water- soluble preservative agent, such as boric acid. In another embodiment the composition contains about 50-60% (w/w) of the water-soluble preservative agent. Substantially the rest of the composition comprises the solidifying agent, such as the resinous agent, for example tall oil rosin.

In this context, the term wood refers to all materials and products containing ligno- cellulosic material, including raw timber, sawn timber, wooden construction materials and elements and wood-plastic composite products, and further, various processed wood products such as round logs, like utility poles, all sawn timber such as boards, planks, laths, flat elements such as laminates, for example chipboard, plywood or LVL products (Laminated Veneer Lumber), panels, slabs, wall ele- ments and the like, furniture for indoors and outdoors, window and door framings, joint ends, flooring, roofing, deck and other wooden articles and objects. The wood containing preservative product may also be present in immobile structures, particularly outdoors, such as wooden buildings, fences, framings, pillars, bridges, piers, railway sleepers etc. In one embodiment the wood material is a wooden collision safe pole, such as lighting pole, telegraph pole, electrical pole or the like. The preservative composition or body/bodies thereof applied into the drilled holes in the pole have a dual function. It preserves the pole wood from decay, but also weakens the structure of the pole just enough to create a collision safe pole. In one example, when a vehicle hits the pole, blocks in the pole's body disengage, reducing the collision energy and allowing the vehicle to stop slowly and safety. In another type of such safe pole the structure of the pole withdraws when a vehicle hits it. Collision safe lighting poles are generally known in the art (for example KAPU and TURVA safe poles by Sahko-Jokinen, Finland; see also instructions concerning collision safe poles by The Finnish Transport Agency, ohjeita 14/2010).

Examples

Examples 1 and 2

Figures 1 and 2 show results from leaching tests for boron wherein the test ele- ments (boric acid and rosin elements) were fully immersed in water without agitation. Procedures used were (Example 1 , Figure 1 ) procedure like AWPA E-1 1 (upper graph) versus Mitsuhashi et al., Forest Products Journal (2007), vol. 57, No 12, disodium octaborate impregnated in wood (adapted), test AWPA E-1 1 (lower graph), and (Example 2, Figure 2) procedure like AWPA E-1 1 (upper graph) ver- sus US2008/0131717, boric acid, test AWPA E-1 1 (lower graph).

Example 3

Five different preservative elements were prepared. Tall oil rosin (TOR) elements were prepared by melting with boric acid in 100-150^QC. 80% boric acid did not create an element; instead it remained in a powder form. Other compositions con- tained 40, 50 and 60% of boric acid. Elements were cylinders with a diameter of 20 mm and height of approximately 10 mm. A comparative element was made from synthetic epoxy polymer (Araldite Rapid) as bar in dimensions of 1 10 mm x 15 mm x 8 mm.

All the elements were immersed in 500 ml of water separately for two weeks. After that, analysis was made from the water to check boron content by titration (Figure 3).

As the result, there is a certain mixture which works excellently as a preservative agent releasing element. According to the example such a mixture contains about -80% of boric acid and the rest is tall oil rosin. Synthetic polymer fixing agent release only some boron from its surface.

Claims

1 . A preservative composition comprising a water-soluble preservative agent and rosin as a water permeable solidifying agent.

2. The preservative composition of any of the preceding claims, characterized in that the rosin is selected from wood rosin, gum rosin, tall oil rosin, its biopolymer derivatives, and mixtures thereof.

3. The preservative composition of claim 1 or 2, characterized in that the preservative agent is a boron salt.

4. The preservative composition of claim 3, characterized in that the boron salt is selected from disodium octaborate, boric acid, sodium pentaborate, calcium borate and mixtures thereof.

5. The preservative composition of claim 1 or 2, characterized in that the preservative agent is a monocarboxylic acid salt.

6. The preservative composition of claim 5, characterized in that the monocarboxylic acid salt is selected from sodium formate, potassium formate, calcium for- mate, ammonium formate and mixtures thereof.

7. The preservative composition of claim 1 or 2, characterized in that the preservative agent is selected from chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), copper azole, ammoniacal copper zinc arsenate (ACZA), copper xyligen, copper borate and other copper compounds such as copper sulfate; sodium silicate based preservatives; potassium silicate based preservatives; and cobalt salts.

8. The preservative composition of any of the preceding claims, characterized in that the composition contains 50-80% (w/w) of the water-soluble preservative agent.

9. The preservative composition of any of the preceding claims, characterized in that the composition is in the form of a fused body.

10. The preservative composition of any of the preceding claims, characterized in that the composition is in the form of powder.

1 1 . A method for treating wood comprising applying the preservative composition of any of the preceding claims to an opening in said wood.

12. The method of claim 1 1 , characterized in that the composition is applied as a solid body.

13. The method of claim 1 1 , characterized in that the composition is applied as molten.

14. Wood obtained by the method of any of the claims 1 1 -13.

15. A wooden collision safe pole, such as a lighting pole, obtained by treating said pole with the method of any of the claims 1 1 -13.