WO2008145146A1

WO2008145146A1 - An oil/oil/water type emulsion and method of using the same for preservative treatment of pine wood

Info

Publication number: WO2008145146A1
Application number: PCT/EE2008/000014
Authority: WO
Inventors: Tiit Kaps; Rein Reiska; Urve Kallavus; Üllar LUGA; Pille Meier; Arne-Enn KÖÖSEL; Margus Koolme; Kairi Otto
Original assignee: Tallinn University Of Technology; Kivilo, Marko
Priority date: 2007-05-30
Filing date: 2008-05-30
Publication date: 2008-12-04
Also published as: EE00686U1

Abstract

An oil/oil/water type emulsion and a method for impregnation of pine wood. Water phase of the emulsion comprises a water solution of boron compounds (borax, boric acid) and quaternary ammonium compounds. First oil phase comprises rapeseed oil as the dispersed phase and an emulsifier (an unsaturated fatty acid or their mixture). Second oil phase comprises polysiloxane particles dispersed on the surface of the first oil phase to improve hydrophobisation. Emulsion is prepared by emulsifying polysiloxane with rapeseed oil and the emulsifier. Then the mixture is emulsified with a water solution by pulsation-type emulsif ication device at a pulsation frequency from 800 to 1,200 Hz. Wood impregnated by this method has good antiseptic properties against wood-decaying and wood-colouring fungi as well as reduced wash-out of the active agents. Its surface can be covered with non-transparent or transparent coating, and the electrical properties are similar to unimpregnated wood.

Description

AN OIL/OIL/WATER TYPE EMULSION AND METHOD OF USING THE SAME FOR PRESERVATIVE TREATMENT OF PINE WOOD

Background of the invention

Technical field

The invention belongs to the field of wood treatment, more precisely among the methods and emulsion-type preservatives used to protect pine (Pinus L.) wood against fungal damages.

In Estonia increasingly more attention is paid to upgrading wood in different ways, e.g. by vacuum drying and impregnation.

Background art

A known method for preservative treatment of wood is using of creosote oil, the advantages of which is effective protection and low price. A disadvantage of this method is the negative environmental impact of the treated wood, the smell, the insufficient speed of diffusion of creosote oil and the short period during which the active substance stays in wood. These disadvantages have been, to some extent, alleviated by using water emulsions of creosote oil (US5098472); however, the smell and smearing quality of the solution still remain a problem. These negative qualities have been avoided by using animal or plant oils (e.g. WO2006047819) as the bearers of the active agents. To improve the diffusion, petroleum products (white spirit, etc.) had to be used, in which case implementation of the VOC directive (on the control of volatile organic compound emissions) must be taken into account.

The use of emulsion preservatives is increasing, the oil phase of which consists of several plant oils and products based on these (EP0227430B1, WO2004022291) - tall oil, linseed oil, rapeseed oil, soybean oil, coconut oil, etc. - however, with these oils hydrophobisation of wood is not sufficient and, therefore, the indicators of wash-out of the active agents are impermissibly high. There are known solutions (WO2007022114, WO2006031743) wherein the hydrophobity of a plant or animal oil has been improved by adding waxes, but the indicators of diffusion of such mixtures in wood are not sufficiently good. Using pentachlorophenol (GB 1354298) in the oil phase is even more problematic as it may form supertoxins when leaking into the environment.

A well-known method is the use of a classical substance complex Cr-As-Cu (GB 1069640, PT92836), which is today very strictly regulated with EU directive 2003/02/EC (06.01.2003). If plant oils are used in the composition an emulsion preservative ensuring a technologically acceptable diffusion speed must be considered.

Another known method is the use of boron compounds (US6494941) or boron compounds and quaternary ammonium salts (CA 1257752) in the water phase of emulsion preservatives. A disadvantage of these solutions is the high level of wash-out of the active substances and the resulting negative impacts on the environment and decrease in antiseptic properties of the treated wood as well. Wood preservative described in EE 199800416 comprises, in addition to a quaternary ammonium compound, carboxylic acid anions supporting the diffusion of the active agent. Possibilities to use this solution are limited because of the high level of wash-out of the agent. The antiseptic properties of the active substance have been adjusted by the use of an extra long-chain ammonium compound (16-50 C atoms) which also includes N₅ O, S and halogen atoms (US20060251915). These are complex compounds, the extensive use of which for preservative treatment of wood is problematic. There have been successful attempts at antisepticising wood by saturating it with an organosilicon liquid (US4400326). The antiseptic effect of the active ingredient is based on physical isolation of wood from air moisture and requires great economic expenses. It has been tried to alleviate the problem by emulsifying an organosilicon liquid (US2007042124, US2006121300); however, such emulsions are produced on the basis of complex-structure organosilicon oils. There is also a known method in which polyorganosiloxane of a simple chemical structure and a water solution of boron compounds with decylether of polyoxyethylene or another surface active agent gave an emulsion-type wood preservative (US20070134423). The emulsion proved stable, but the fact that the emulsion required distilled water and the stability of the system depended heavily on the pH level of the surrounding environment was noteworthy. An analogous emulsion-type preservative consisting of a water phase (containing inorganic substances, incl. boron compounds and/or organic substances) and an organic substance phase (copolymer) is described in US6494941. The novelty of the invention is that the known water-soluble active agents tebuconazole and propiconazole are included in the organic substance phase by adding a suitable copolymer, synthesised on the basis of three monomers, in the formula. A disadvantage of the solution is the fact that the organic phase of the emulsion - copolymer - is a synthetic product, making which requires technological precision as it is necessary to produce a component with predetermined qualities.

Considering environmental protection, it is better to use a renewable natural product - e.g. rapeseed oil - as the oil phase. A copolymer generated on the basis of a synthetic monomer passes through its polymerisation process in a reactor, which is a process that cannot considerably continue in impregnated wood. Rapeseed oil, on the other hand, contains unsaturated fatty acids and undergoes thus the oxidative polymerisation in wood. It results in drying of the plant oil, which hinders water from penetrating the wood and washing out the active substances, and ensuring a long-term antiseptic effect of the preservative. The formula of the invention presupposes the use of volatile solvents (acetone, methyl ethyl ketone, etc.), which, however, may cause timber companies problems with implementation of the EU VOC directive. Emulsification of plant oils requires no easily volatile solvents and the oils themselves are not volatile either. In addition to that, the invention uses microemulsions containing dispersed particles with a diameter of 0.1 μm. Achieving such a dispersion level under industrial conditions may prove highly complicated. But the stability and diffusion qualities of the emulsions produced on the basis of plant oils are sufficient with the diameter of the oil phase particles ranging from 1 to 8 μm, which is realisable under industrial conditions. In the known solutions discussed there are no data about antiseptic properties of the treated wood or the extent of wash-out of the components of the preservatives. A known macroemulsion-type preservative (US20060057300) whose important component is tebuconazole and whose oil phase consists of a plant oil and unsaturated fatty acid with the addition of emulsifiers and zinc carbamate as the water- repelling component. The solution can basically be viewed as an emulsified analogue of a typical water-based preservative. Zinc as a heavy metal may, however, cause problems with environmental protection.

An important issue here is thus the problem of locking the active agents into the wood. A method known from literature (E. Baysal et al, Bioresource Technology, 97, 2271-79 (2006)) helps reduce wash-out of boron: wood is first impregnated with boric acid in a polyethylenglycol-400 medium and borax suspension and, following drying for three weeks, impregnated with a monomer - styrene, methyl methacrylate or an isocyanate. The positive result gained with the method is, unfortunately, shadowed by the technological impossibility of the method. Another solution successful for reducing washing out of boron compounds (T. Fiiruno et al, Journal of Wood Science, 49, 344-8 (2003)) was after- treatment of wood impregnated with boron compounds by treating it with solutions of heavy metals (zinc or lead), which is not an acceptable method from the position of environmental protection. There is a known method for locking boron compounds into wood by means of amino oxide-type compounds (EP1298997B1), but due to the complex structure of the method there are not many usage prospects for it from the economic aspect.

Disclosure of the invention

The objective of the invention is a new oil/oil/water type emulsion for wood preservation which would ensure antiseptic properties of wood under EN 113 criteria and whose active ingredients would, at the same time, be washed out less compared to wood impregnated with the oil/water-type emulsions known so far. Another objective is a method for preparing such emulsion as well as using such emulsion for wood preservation.

To achieve the aims set, an impregnation method and a formula for an oil/oil/water type emulsion has been elaborated where the water phase consists of a solution of boric acid, borax and quaternary ammonium salts, the first oil phase is rapeseed oil, the second is polysiloxane and the emulsifier is either a single unsaturated fatty acid or a mixture of unsaturated fatty acids with glycerides of the same acids and lecithin.

To produce the emulsion preservative - a milky liquid - according to the new method, the emulsifier and polysiloxane are, before dispergation, mixed with rapeseed oil. Dispergation can be achieved by means of a pulsation-type emulsification device (with a pulsation frequency ranging from 800 to 1 ,200 Hz) and is recommendable no sooner than 8 hours, preferably 2 to 3 hours, before impregnation. The components of a repeatedly used emulsifier diffuse in wood proportionally to the formula. The diameter of dispersed particles in the emulsion varies from 1 to 8 μm, being usually between 2 to 6 μm.

The invention avoids using heavy metals by adding boron and nitrogen compounds in the formula; use rapeseed oil - a renewable natural resource - as the drying plant oil in the formula; use a single unsaturated fatty acid or a mixture of fatty acids with glycerides of the same acids and lecithin as the emulsifϊers; use sapwood of the genus pine wood (Pinus L.) as the wood impregnated by regulating the humidity of the wood by the vacuum drying method; achieve an antiseptic effect of the preservative both on wood-decaying and wood- colouring fungi; provide wood with hydrophobic properties by means of oil phases consisting of rapeseed oil and polysiloxane to ensure a low level of wash-out of the active agent from the wood; produce impregnated wood that can be covered both with a non- transparent or transparent coating; to achieve electrical properties of wood similar to unimpregnated wood.

Examples for carrying out the invention

Several examples of the invented emulsion with different ingredients as well as the characteristics of pine wood samples treated by such emulsions are shown in Table 1.

The emulsion has undergone laboratory tests in the framework of the project "An advanced technology for preservative treatment of pine wood" supported by Enterprise Estonia (EAS) in the period from 2005 to 2007. During the implementation of the project, half- industrial test devices were built for producing the emulsion preservative, and test impregnation of 1 m long vacuum dried wooden work pieces was carried out. The results corresponded with the laboratory tests.

The bioresistance of the laboratory-impregnated pine wood sapwood to wood-decaying fungi was determined at the Latvian State Institute of Wood Chemistry (according to EN 113 and EN 84) and the bioresistance to wood-decaying and wood-colouring fungi at the Centre of Material Research of Tallinn University of Technology by using an express method. The results proved that the subjects of the invention - the wood preservation method and the emulsion — ensured the bioresistance of pine wood sapwood to wood- decaying fungi (mass loss under 3%) and protection from wood-colouring fungi.

The level of wash-out of the active agents was determined by soaking the impregnated wood and sprinkling it with water. The concentration of boron compounds washed out was determined in the Laboratory for Residues and Contaminants of the Agricultural Research Centre. The results revealed that, regarding the washing out of the agents, the oil/water emulsion has its advantages over the water solutions and the oil/oil/water emulsion over the oil/water emulsion. The tests showed that two contrary tendencies have to be taken into account when devising a formula for an emulsion.

On one hand, reducing the mass of the oil phase improves the diffusion of the preservative in wood and thus the antiseptic properties of the wood after its impregnation. If the emulsion contains less oil, the movement of the water phase in wood is less hindered as the walls of wood cells are less hydrophobisised. But, at the same time, the initially good antiseptic properties are not permanent as the active substances are not sufficiently protected from wash-out.

On the other hand, relative increase of the oil phase mass reduces the diffusion of the preservative in wood and, due to the lower concentration of the agent, the antiseptic properties of the wood are not so good. However, in this case, the level of antiseptic properties is more lasting as the agents are better protected from wash-out.

With the described impregnation method and emulsion there has been achieved a high antiseptic level of pine wood sapwood: e.g. the mass loss with the wood-decaying fungus Coniophora puteana (EN 113) was in the range between 0.7 to 2.5%. Further tests for determining the bioresistance at the Latvian State Institute of Wood Chemistry by aging wood with wash-out according to standard EN 84 resulted in mass loss of 0.1%. The fact that the quaternary ammonium salts chosen for the formula of the emulsion can repel the spread of wood-colouring fungi in impregnated wood was also confirmed.

The results of assessing the bioresistance of impregnated wood by three methods have been presented in Table 1 :

Method 1 - the mass loss of wood (in percentage points) after treatment with the wood- decaying fungus Coniophora puteana (EN 113);

Method 2 - the surface (in percentage points) of wood covered with fungal fruit-bodies after its 4-week contact with the wood-decaying fungus Coniophora puteana;

Method 3 - the surface (in percentage points) of wood covered with fungal fruit-bodies after its 4-week contact with the wood-colouring fungus Aspergillus sp. Table 1

The electrical resistivity of unimpregnated wood (with humidity content 29%) was 311 kΩ, with the potential difference being 500 V; the resistivity of pine wood treated with the emulsion was, with other conditions being equal, 345 k'Ω. The colour characteristics (L, a and b) of wood impregnated with the emulsion, determined calorimetrically with a Minolta 2600 device and the adhesion of colour on the surface determined by ISO 1518 are presented in Table 2.

Table 2

(*The scale: 1-5 points; the highest: 1 point)

In Estonia ca. 170 thousand m³ (2007) of impregnated wood is produced yearly and most of it is exported. The environmentally-friendly and competitive product would enable increasing our sales on the international market. Upon implementation of the invention, the estimated growth of turnover of Estonian timber companies would be ca. 240 million kroons in 2011, including export for 142 million kroons. Implementation of the invention means introduction of a more environmentally- friendly preservative whose one component - rapeseed oil - is connected with an important development trend in Estonian agriculture. Impregnated wood produced on the basis of the invention and timber products made of it are more environmentally- friendly than the solutions known so far as the material of the invention is remarkable for the low extent of wash-out of the active agents.

Claims

1. An oil/oil/water emulsion for preservative treatment of pine wood, comprising a water solution of boron compounds as a water phase of said emulsion, a dispergated phase consisting of rapeseed oil as a first oil phase and polysiloxane particles dispergated on the surface of the first oil phase to improve hydrophobisation as a second oil phase.

2. The emulsion as in claim 1, wherein said water phase contains at least one quaternary ammonium compound.

3. The emulsion as in claims 1 to 2, wherein said water phase is a water solution of boric acid, borax and at least one quaternary ammonium compound.

4. The emulsion as in claims 1 to 3 wherein said first oil phase includes an unsaturated fatty acid type emulsifier to stabilise the emulsion.

5. The emulsion as in claim 4 wherein said emulsifier is a single fatty acid or a mixture of unsaturated fatty acids, forming at least 55 mass percentage points of composition of said emulsifier, and glycerides of these fatty acids, forming up to

40 mass percentage points of composition of said emulsifier, and lecithin.

6. The emulsion as in claims 1 to 5 wherein said emulsion contains 1 to 6 mass percentage points of rapeseed oil and 0.3 to 3.5 mass percentage points of polysiloxane.

7. A method for preservative treatment of pine wood, comprising preparing an oil/oil/water type emulsion and treating pine wood with said emulsion, characterized in that said water phase of the oil/oil/water emulsion is a water solution of boron compounds, a first oil phase is a dispergated phase consisting of rapeseed oil and a second oil phase are polysiloxane particles dispergated on the surface of the first phase to improve hydrophobisation.

8. The method as in claim 7, comprising preparing said emulsion by emulsifying polysiloxane with rapeseed oil and an emulsifier and then emulsifying the mixture produced with a water solution by means of a pulsation-type emulsification device at a pulsation frequency ranging from 800 to 1,200 Hz.

9. The method of claims 7 to 8 wherein the water phase contains at least one quaternary ammonium compound.

10. The method of claims 7 to 9 wherein the water phase is a water solution of boric acid, borax and at least one quaternary ammonium compound.

11. The method of claims 7 to 10 wherein the first oil phase uses an unsaturated fatty acid type emulsifier to stabilise the emulsion.

12. The method of claim 11 wherein the emulsifier used is a single fatty acid or a mixture of unsaturated fatty acids, forming at least 55 mass percentage points of the composition of the emulsifier, and glycerides of these fatty acids, forming up to 40 mass percentage points of the composition of the emulsifier, and lecithin.

13. The method of claims 7 to 12 wherein the emulsion contains 1-6 mass percentage points of rapeseed oil and 0.3-3.5 mass percentage points of polysiloxane.

14. The method of claims 7 to 13 wherein the wood is dried by vacuum drying making the passages in wood accessible for the emulsion.

15. The method of claims 7 to 14 wherein the impregnated wood is further treated with a non-transparent or transparent coating.