NEW WOOD PROTECTING METHODS AND WOOD PRODUCTS PRODUCED WITH THE METHODS

Abstract

Disclosed herein is an environmentally friendly wood protecting method against biological deterioration such as fungal, bacterial and insect damage and non-biological wood deterioration such as weathering. The method comprises contacting a wood material with an aqueous solution of a zirconium salts which is followed by a heat treatment step, providing durable protection of wood against biodegradation and improving several other properties of the treated wood.

Claims

1. A method preparing a wood product, comprising a) contacting a wood material with a water-based composition comprising one or more zirconium salts; and b) heat treating the wood material at a temperature of between 100 to 220° C., more preferably between 115 to 200° C., most preferably between 135 to 185° C.

2. The method according to claim 1, wherein the composition comprises 0.01 to 30% (w/w), preferably 0.1 to 15% (w/w) and more preferably 0.2 to 6% (w/w) of zirconium ions from one or more zirconium salts, preferably the zirconium salt is zirconium acetate.

3. The method according to claim 1, wherein the composition comprises 70 to 99.99% (w/w) water and optionally at least one of a wetting agent, a defoamer, a conservative or a biocide, a dye, a pigment, a rheology modifier and a UV stabilizer.

4. The method according to claim 1, wherein the composition has a pH value of 2 to 13, preferably 2 to 11 and more preferably of 2 to 9.

5. The method according to claim 1, wherein the contacting step is performed by soaking, impregnating, padding, foularding, dipping, spraying, brushing, coating, rolling, foam-application, preferably by vacuum pressure impregnation.

6. The method according to claim 1, comprising a step of drying the wood material to a moisture content of less than 20% before heat treating the wood material.

7. The method according to claim 1, comprising a pretreatment step of drying the wood product to less than 40% moisture content before its contact with the water-based composition.

8. The method according to claim 1, comprising a pretreatment step of heating the wood product to temperatures of 5 to 250° C. before its contact with the water-based composition.

9. The method according to claim 1, comprising heating the water-based composition to less than 100° C. before contacting the wood material.

10. The method according to claim 8, comprising heating both the wood product and the water-based composition.

11. A wood product prepared by the method according to claim 1.

12. The wood product according to claim 11, comprising chemical bonds between zirconium atoms and hydrophilic functional groups selected from hydroxyl groups and carboxylic groups of the hemicellulose, cellulose or lignin in the treated wood material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0045] The invention is now described, by way of example, with reference to the accompanying drawings, in which:

[0046] FIG. 1 shows a model reaction of zirconium acetate (water soluble) with wood hemicellulose (water soluble) under curing conditions creating an insoluble reaction product.

[0047] FIG. 2 demonstrates moisture sorption of a wood material according to the invention.

[0048] FIG. 3 shows enhanced hydrophobicity of the wood and decreased moisture content by dipping a wood material according to the invention in water.

[0049] FIGS. 4 and 5 show 13C CPMAS NMR spectra of wood products treated or not treated with the present invention.

[0050] FIG. 6 shows crystallinity index for wood products treated and not treated with the invention.

[0051] FIG. 7 shows weight loss of impregnated and non-impregnated wood.

[0052] FIGS. 8 and 9 compare moisture content and mass loss of impregnated and non-impregnated wood.

[0053] FIG. 10 shows enhancement of the mechanical properties with the present invention.

DETAILED AND EXEMPLIFYING DESCRIPTION OF THE INVENTION

[0054] One of the most important features of an impregnating liquid (protection against rot fungus and insects) is that it stays within the wood and that leaching is prevented and kept to a minimum under natural/accelerated weathering conditions. This is a highly important feature in order to prolong the service lifetime of the treated wood. The present inventors have found that heat treatment (curing) of the impregnated wood was necessary in order to force the zirconium salt to create physical and chemical bonds with the hydroxyl and carboxyl groups of the wood. In order to elucidate the reaction of Zirconium salts with wood, a model reaction (FIG. 1) was devised where Zirconium acetate (water soluble) was reacted with extracted wood hemicellulose (water soluble) in a molar ratio of 1:1 (monosaccharide:Zr) and thereafter cured at 135° C. This resulted in a product that was not water soluble anymore due to the chemical reaction of the Zirconium acetate with the reactive groups of the hemicellulose (hydroxyl, carboxylic groups and similar). It was evident that there had been crosslinking between the structures. Therefore the same phenomena can be expected to occur in zirconium acetate impregnated and heat treated wood where the reactive groups in the chemical components of wood (Cellulose, Hemicellulose and Lignin) are reacted with zirconium salts.

[0055] General Procedures of the Composition Preparation 1-2 According to the Invention:

[0056] Method 1.

[0057] Step a) Mixing zirconium salt composition and water in any order of addition, Step b) Adding deformer, wetting agent and other optional component to the resulting mixture in step a, wherein the resulting mixtures in steps a-b are optionally mixed and/or optionally homogenized.

[0058] Method 2.

[0059] Step a) Mixing deformer, wetting agent and other optional component to the water Step b) Adding zirconium salt to the resulting mixture in step a, wherein the resulting mixtures in steps a-b are optionally mixed and/or optionally homogenized.

[0060] The apparatus for preparing the water-based composition is any kind of laboratory or industrial equipment using low and/or high shear forces for producing the homogenous composition of the invention. This might be a magnet stirrer, overhead stirrer with propeller or disperser or like, homogenizer with or without high pressure, in-line or external homogenizers, extruders, shaking equipment, mortar and pestle, blender type of instrument, any kind of mixer (static mixer, micro mixer, vortex mixer, industrial mixer, ribbon blender, V blender, continuous processor, cone screw blender, screw blender, double cone blender, double planetary, high viscosity mixer, counter-rotation, double and triple shaft, vacuum mixer, high shear rotor stator, dispersion mixer, paddle, jet mixer, mobile mixer, drum mixer, intermix mixer, planetary mixer, Banbury mixer or like), French press, disintegrator, mill (grinding by bead mill, colloid mill, hammer mill, ball mill, rod mill, autogenous mill, semiautogenous grinding, pebble mill, high pressure grinding rolls, buhrstone mill, vertical shaft impactor mill, tower mill or like), ultrasonic treatment, rotor-stator mechanical equipment, any kind of propeller or mixer, high temperature and/or high pressure bitumen emulsifiers or combinations of the above.

[0061] Table 1 below summarizes the examples demonstrating the invention in the following sections of the specification.

TABLE-US-00001 TABLE 1 Composition Ex preparation Wood Heat Number Composition method treatment Wood type treatment Ex 1 3% Zirconium acetate Method 1 Vacuum Scot pine 135° C. Powder (ZrO.sub.2~48%) pressure sapwood A.M.P.I. S.r.l impregnation Ex 2 3% Zirconium acetate Method 1 Vacuum Scot pine 135° C. Powder (ZrO.sub.2~48%) pressure mix sap A.M.P.I. S.r.l impregnation and heartwood Ex 3 3% Zirconium acetate Method 1 Vacuum Scot pine 185° C. Powder (ZrO.sub.2~48%) pressure sapwood A.M.P.I. S.r.l impregnation Ex 4 3% Zirconium acetate Method 1 Vacuum Scot pine 185° C. Powder (ZrO.sub.2~48%) pressure mix sap A.M.P.I. S.r.l impregnation and heartwood Ex 5 5% Zirconium acetate Method 1 Vacuum Scot pine 135° C. Powder (ZrO.sub.2~48%) pressure sapwood A.M.P.I. S.r.l impregnation Ex 6 5% Zirconium acetate Method 1 Vacuum Scot pine 185° C. Powder (ZrO.sub.2~48%) pressure A.M.P.I. S.r.l impregnation sapwood Ex 7 10% Zirconium acetate Method 1 Vacuum Scot pine 135° C. Powder (ZrO.sub.2~48%) pressure sapwood A.M.P.I. S.r.l impregnation Ex 8 10% Zirconium acetate Method 1 Vacuum Scot pine 135° C. Powder (ZrO.sub.2~48%) pressure mix sap A.M.P.I. S.r.l impregnation and heartwood Ex 9 10% Zirconium acetate Method 1 Vacuum Scot pine 185° C. Powder (ZrO.sub.2~48%) pressure sapwood A.M.P.I. S.r.l impregnation Comparative Scot pine 135° C. Ex 10 sapwood Comparative Scot pine 185° C. Ex 11 sapwood Comparative Scot pine Ex 12 sapwood Comparative Scot pine Ex 13 mix sap and heartwood Comparative 3% Zirconium acetate Method 1 Vacuum Scot pine  70° C. Ex 14 Powder (ZrO.sub.2 ~48%) pressure sapwood A.M.P.I. S.r.l impregnation

[0062] The described structural change in the wood due to the reaction with zirconium salts under curing conditions has several impacts on the properties of wood. These are exemplified in the following Examples:

Example 1

[0063] Decrease of the hydrophilicity of the wood by the reaction of zirconium salts with the hydrophilic functional groups in the wood:

[0064] As it can be seen in FIG. 1, a cloudy/opaque dispersion (not water soluble) was created by mixing water soluble components hemicellulose and zirconium acetate and curing at 135° C. The said property can be due to chemical bonding of the zirconium acetate with the hydrophilic functional group of the hemicellulose (hydroxyl, carboxylic acid and similar) and crosslinking of the saccharide based molecules.

Example 2

[0065] Enhanced hydrophobicity of the wood and decreased moisture sorption is demonstrated in FIG. 2. As can be seen in FIG. 2, due to the hydrophobic character of the modification, the wood impregnated with Zirconium acetate and heat treated at 185° C. is displaying lower equilibrium moisture content at the same relative humidity compared to original/not treated wood reference.

Example 3

[0066] FIG. 3 shows enhanced hydrophobicity of the wood and decreased moisture content by dipping in water. The amount of the absorbed water in the wood impregnated with zirconium acetate and heat treated at 185° C. is much lower compared to untreated wood and only heat treated wood.

Example 4

[0067] In general when heat treating wood, there is a color change on the wood that can be connected to the amount of degradation occurring in the wood during the heat treatment process. An assessment on the color change of wood due to the heat treatment was made using not impregnated wood and zirconium salt impregnated wood. There was basically no change in colour before and after heat treatment in the zirconium salt impregnated wood. It was even evidenced that the presence of more zirconium salt could protect the wood against color change during the heat treatment at the given temperature. The impregnated wood with 3% and 10% zirconium acetate, heat treated at 185° C., were submitted for sensory panel evaluation. The sensory panel utilized individuals trained to compare wood products and evaluate color changes. Brownish color was ranked on a scale from 0 describing no brown color, to 5 describing very dark brown color. Untreated wood is ranked 0. Not impregnated but heat treated wood is ranked 3. According to the results shown in table 1 below, it can clearly be seen that the wood impregnated with 10% zirconium acetate solution could offer less color change, and hence less wood degradation, during heat treatment at 185° C. Evidently, the presence of zirconium salts in wood during the heat treatment process have a protecting role against thermal degradation to some extent. Table 2 below shows the color change evaluation of heat treated wood.

TABLE-US-00002 TABLE 2 Wood treatment according to Sensory panel evaluation invention of color change Original wood 0 Not impregnated but heat treated at 185° C. 3 3% Zirconium acetate + heat treatment at 3 185° C. 10% Zirconium acetate + heat treatment at 2 185° C.

Example 5

[0068] In order to further assess the invention, Solid-state 400 MHz NMR spectrometer was used to record the one-dimensional (1D) .sup.1H.fwdarw..sup.13C CPMAS spectra. Fine powders of all samples were prepared of the non-treated, heat treated and zirconium salt impregnated and heat treated wood for solid NMR recording. .sup.13C CPMAS NMR spectrum and signal assignment of Scots pine wood is displayed in FIG. 4 where Cr refers to crystalline, am to amorphous and h to hemicelluloses.

[0069] The recorded .sup.13C CPMAS NMR spectra of pine sapwood, “pine sapwood+ heat treatment 185° C.” and “pine sapwood impregnated with 3% zirconium acetate+heat treatment 185° C.” can be seen in FIG. 5. Firstly, the identification of the wood chemical components was performed qualitatively. The .sup.13C CPMAS NMR spectra of the wood samples is dominated by the signals assigned to cellulose. While further study of the hemicelluloses in the wood matrix is more complex due to the strong overlap of the signals assigned to hemicelluloses and cellulose, the signals of lignin are fairly without any interference (due to their different chemical nature).

[0070] During the heat treatment of wood, acetic acid is formed from the hydrolysis of acetyl esters in xylan. Hemicelluloses are depolymerized into oligomeric and monomeric units and further dehydrated to aldehydes under acidic conditions, leading to fewer hydroxyl groups and less hygroscopic wood. The effect of the heat treatment on the de-polymerization of cellulose is rather limited, instead by a small increase in cellulose crystallinity. Lignin is the least active component and can be cleaved to form phenolic groups only at high temperature. Therefore it's believed that the modifications of wood properties as well as the strength-loss of heat treated wood in general mainly is a result originating from the thermal degradation of hemicelluloses via an acidic autocatalytic reaction.

[0071] In order to form a comparative degradation study between the different treatments, the crystallinity of cellulose, determined as crystallinity index (CrI), was calculated by deconvolution from the area of the crystalline cellulose (86-92 ppm) C-4 signal, X, and the area of the amorphous cellulose (79-86 ppm) C-4 signal, Y (Wikberg, Hanne. 2004. Advanced Solid State NMR Spectroscopic Techniques. PhD thesis, Helsinki, Finland: University of Helsinki):

[00001]$\mathrm{Crl}=\frac{X}{X+Y}\times 100$

[0072] The more degradation in the amorphous area can be correlated to a higher crystallinity index CrI of samples (Table 2 and FIG. 6). Quantitative .sup.13C solid NMR show that the Cellulose crystallinity (ratio of the peak integrals of the “crystalline cellulose” to the “crystalline+ amorphous” cellulose) of the pine sapwood impregnated with Zirconium acetate and heat treated at 185° C. is less than the pine sapwood heat treated at 185° C. This means the degradation of the hemicellulose and amorphous cellulose is less when wood is impregnated with Zirconium acetate.

[0073] Quantative .sup.13C solid NMR show that the Cellulose crystallinity (ratio of the peak integrals of the “crystalline cellulose” to the “crystalline+ amorphous” cellulose) of the pine sapwood impregnated with Zirconium acetate and heat treated at 185° C. is less than the pine sapwood heat treated at 185° C. This means the degradation of the hemicellulose and amorphous cellulose is less when wood is impregnated with Zirconium acetate.

Example 6

[0074] The weight loss of the wood during heat treatment as a result of thermal degradation of biopolymers to small/volatile molecules is another sign of the degradation extent. The gravimetric analysis of the wood samples and amount of released low molecular weight volatile molecules during the heat treatment process was assessed by weighing the dry wood before heat treatment and after heat treatment at 185° C. The results display controlled degradation and mass loss of around 2% in the impregnated wood with 3% of Zirconium acetate Zirconium which is quite similar to the not impregnated wood.

[0075] As another evidence of the lower degradation of the wood structure to small molecules, the amount of the leached material after leaching test (EN 84) was measured. It can be concluded that heat treated (185° C.) zirconium impregnated wood leached out less than the heat treated (185° C.) and not impregnated wood, see FIG. 7.

Example 7

[0076] Table 3 below shows enhancements in water contact angle. As it can be seen, when using water, higher contact angles (CA) could be measured on wood impregnated with Zr salts and heat treated as compared to only heat treated wood.

TABLE-US-00003 Water Water contact contact Heat angle angle Wood sample Impregnation treatment initial 60s Original pine — — ~65 <30 sapwood Original pine — 135 ~65 ~65 sapwood Original pine — 185 ~65 ~65 sapwood Original pine 5% Zr.ac 135 ~85 ~85 sapwood powder Original pine 5% Zr.ac 185 ~85 ~85 sapwood powder Table 3

Example 8

[0077] Table 4, below shows dimensional expansion of the Pine sapwood dipped in water for 4 days. The chemical changes and the introduced hydrophobicity of the zirconium impregnated heat treated wood could lower the dimensional change of the wood samples in comparison to reference wood and only heat treated wood.

TABLE-US-00004 TABLE 4 Average dimensional change Heat (Expansion Wood sample Impregnation treatment in water %) Original pine sapwood — — 5,4 Original pine sapwood — 135 6,8 Original pine sapwood — 185 5,6 Original pine sapwood 3%Zr.ac 135 3,2 powder Original pine sapwood 3%Zr.ac 185 4,8 powder

Example 9

[0078] Soft rot protection is performed according to CEN TS 15083-2 (SS-ENV 807:2009). The performed soft rot test using standard SS-ENV 807:2009 displayed lower moisture content of the Zirconium impregnated/heat treated wood compared to the original wood and only heat treated wood at the same temperature, see FIG. 8. This lower moisture content can further decrease the biotic wood deterioration and damage caused by biological deterioration. The decrease in mass loss of the zirconium impregnated/heat treated wood compared to the original wood and only heat treated wood confirmed the efficiency of the heat treated zirconium impregnated wood against soft rot which can be due to both less moisture content and less digestible food sources of the wood. See FIG. 9.

Example 10

[0079] Water solution of soluble zirconium salts displayed minimum incompatibility with wood which make the impregnation process very efficient. For example, wood impregnation with 3% zirconium acetate solution at 11 bar yielded an impregnation wet uptake of up to 327 kg/m3 in just 3 hours meaning that almost all the sapwood part of the impregnated wood was saturated with zirconium salt water solution, see Table 5. The deep penetration depth of the zirconium solution will lead to an in depth protection of and longer durability of the final product. This experiment confirms the industrial viability of the invention.

TABLE-US-00005 TABLE 5 Wet Wood pH Impregnation Impregnation Impregnation uptake after Wood type Wood size formulation time presssure (kg/m3) impregnation Pine timber 28 mm* 120 3% Zirconium  60 minutes 11 bar ~290 4 (blend of mm *2300 mm acetate powder Sapwood and heartwood) Pine timber 28 mm* 120 3% Zirconium 180 minutes 11 bar ~327 4 (blend of mm *2300 mm acetate powder Sapwood and heartwood)

Example 11

[0080] In order to assess what happens to the zirconium salt water solution after using it in numerous impregnation cycles an inspection of the aged and reused (10 impregnation cycles) liquid was performed. It was confirmed by observation that minimum chemical and physical changes occurred (no or minimum leaching from wood substrate into the zirconium solution, no instability in the solution and no pH change in the liquid). The observed compatibility will further enhance production efficiency.

Example 12

[0081] In general a loss in bending modulus and strength is expected when wood is heat treated. This is also correlating to the degradation within wood obvious by the color change, mass loss and leeching properties of wood as discussed above. In order to further stress the benefits gained from the current invention a three point bending tests on the not treated pine sapwood (original), heat treated pine sapwood at 135° C. and 5% Zirconium acetate impregnated+ heat treated (135° C.) pine sapwood was performed. As expected the mechanical properties (both bending modulus and bending strength) were lowered in the heat treated wood case. On the contrary, for zirconium impregnated and heat treated wood, it was concluded that the wood keeps the mechanical properties as compared to untreated or heat treated wood or even enhances them, see FIG. 10.

Example 13

[0082] When subjecting samples treated according to the invention to EN 84/EN113 and classification according to SS-EN 350-1 we could see a good protection against both white (Coriolus versicolor) and brown rot (Coniophora puteana and Gloeophyllum trabeum), see Table 6 and 7. Pine sapwood impregnated with 10% Zirconium acetate solution and subsequently heat treated at 135° C. displayed a natural durability class 1 (very durable).

TABLE-US-00006 TABLE 6 Classes of natural durability of wood to fungal attack using laboratory tests based on EN 113 (Table from SS-EN 350) Laboratory test results Durability class Description expressed as x 1 Very durable x ≤ 0,15 2 Durable 0,15 < x ≤ 0,30 3 Moderately durable 0,30 < x ≤ 0,60 4 Slightly durable 0,60 < x ≤ 0,90 5 Not durable x > 0,90 x = average corrected mass loss of e1/average corrected mass loss of e2.1

TABLE-US-00007 TABLE 7 Impregnation Fungi Durability class 10% ZrAc Coniophora puteana 1 10% ZrAc Coriolus versicolor 1 10% ZrAc Gloeophyllum trabeum 1

Example 14

[0083] Paintability and further modification with other coatings was assessed. Zr impregnated wood, heat treated according to the invention generally exhibited very good compatibility with commercial coatings/paints. Wood impregnated with 10% Zr.ac powder and heat treated at 135° C. and further painted with 1 and 2 layers of commercially available alkyd based paints, aged for 1 year outdoor has still very good quality/properties.

Example 15

[0084] The present invention was assessed for mold and fungal Stain (blue stain) protection in wood. When treated samples of the invention and comparative wood samples were subjected to natural weathering conditions for 1 year it could be seen that the comparative samples that were not treated showed intensive fungal growth on the surface and deep into the wood while 10% Zirconium acetate impregnated+135° C. heat treated wood samples were by far less attacked.

[0085] The so generally described and exemplified invention has the following benefits. It is environmentally friendly: no halogens, no boric compounds, no phosphorous, no heavy metals, no pesticide, and no biocide. Chemicals are used with no toxic, no health hazard and no environmental hazard pictograms. No organic solvents, only water is used. The invention confers protection against rot and old/mildew protected (wood does not become gray very quickly in the surface and depth when exposed to outdoor climate). Further the invention provides hydrophobicity (increase of dimensional stability, less shrinking and swelling, less cracks) and while it is hydrophobic but still paintable and compatible with water based coatings. Still further, wood products of the present invention has minimal leakage of active components, degradation during the heat treatment is small and controlled and the mechanical properties are improved. Finally, only industrially viable chemicals are used and a process with lowest risk of composition preparation is admitted with an efficient wood impregnation/treatment and high durability/recycling of the corn position during the production cycles.