MINERALIZED WOOD MATERIALS AND METHODS PROVIDING MINERALIZED WOOD MATERIALS

Abstract

The invention relates to a mineralized wood material comprising at least one metal salt MA in the lumina of the mineralized wood material, in particular in the lumina and the cell walls of the mineralized wood material and methods for providing said mineralized wood material.

Claims

1. A mineralized wood material comprising at least one metal salt of the formula MA in the lumina of the mineralized wood material, in particular in the lumina and the cell walls of the mineralized wood material.

2. The mineralized wood material according to claim 1, wherein the at least one metal salt MA comprises a weight in the range of 5 wt % to 40 wt % with respect to the weight of the unmineralized wood material.

3. The mineralized wood material according to claim 1, wherein M is selected from multivalent metals, in particular from earth alkali metals, more particularly from magnesium, barium or calcium and A is selected from organic or inorganic compounds, in particular from inorganic compounds, more particularly from sulfate, carbonate, borate, fluoride or phosphate.

4. A method for treatment of a wood material comprising the steps of: a) provision of a metal salt solution comprising at least one metal salt of the formula MX dissolved in a solvent and a salt solution comprising at least one salt of the formula YA dissolved in another solvent, b) treatment of said wood material by an impregnation cycle comprising a first impregnation step using one of said solutions and a subsequent second impregnation step using the other one of said solutions, or a diffusion step comprising a diffusion of the metal salt solution from one side and a diffusion of the salt solution from the other side into the wood material, providing a precipitation of a metal salt of the formula MA inside the wood material, wherein the solvents of the metal salt solution and the salt solution are characterized in that the metal salt MA has a low or almost no solubility in said solvents, in particular the metal salt MA has a solubility below 0.01 g per 100 mL in said solvents.

5. The method for treatment of wood according to claim 4, wherein in said first impregnation step said metal salt solution is used and in said subsequent second impregnation step said salt solution is used, providing a metal salt of the formula MA.

6. The method according to claim 4, wherein one of the solvents, in particular the solvent of the metal salt solution, is an organic solvent and the other one of the solvents is water, in particular the solvent of the salt solution is water.

7. A method for treatment of a wood material comprising the steps of: a) provision of a solution comprising at least one metal salt of the formula MX dissolved in dimethyl carbonate or diethyl carbonate, b) impregnation of wood with at least one impregnation step using said solution, c) hydrolysis of the impregnated wood with an aqueous solution, in particular with an aqueous solution comprising a pH range of more than 7, providing a metal carbonate.

8. The method according to claim 4, wherein M is selected from multivalent metals, in particular from earth alkali metals, more particularly from magnesium, barium or calcium.

9. The method according to claim 4, wherein A is selected from organic or inorganic compounds, in particular from inorganic compounds, more particularly from sulfate, carbonate, borate, fluoride or phosphate.

10. The method according to claim 4, wherein Y is selected from monovalent compounds, in particular from alkali metals, more particularly from sodium or potassium.

11. The method according to claim 4, wherein X is selected from nitrate, bromide, iodide or chloride, in particular from bromide, iodide or chloride, more particularly X is chloride.

12. The method for treatment of wood according to claim 7, wherein the pH is in the range of 8.5 to 9.5, in particular said pH is approximately 9.

13. The method according to claim 4, wherein the impregnation of step is performed for 2 to 24 hours and/or the impregnation cycle is performed for several times, in particular for 1 , 2, 3 or 4 times.

14. The method according to claim 4, wherein the concentration of the metal salt MX in the metal salt solution is in the range of 0.1 to 5 mol/l, in particular 0.5 to 2.5 mol/l, more particularly 1 to 2 mol/l, and the concentration of the salt YA in the salt solution is in the range of 0.1 to 5 mol/l, in particular 0.5 to 2.5mo1/1, more particularly 0.5 to 1.5 mol/l.

15. The method according to claim 7, wherein the solution comprises a concentration of the metal salt MX in the range of 0.1 to 5 mol/l, in particular 0.5 to 2.5 mol/l, more particularly 0.5 to 1.5 mol/l.

Description

SHORT DESCRIPTION OF THE FIGURES

[0151] FIG. 1: shows a reaction scheme concerning the use of a salt solution YA in the first impregnation step (a), concerning the use of a metal salt solution MA in the first impregnation step (b) or concerning the use of calcium carbonate (c) with respect to the mineralization of wood in an alternating solvent system;

[0152] FIG. 2: shows the mass gain of spruce, beech and ash based on the number (1 to 3 times) and duration (1 hours or 24 hours) of the reaction cycles obtained by a method according to the third aspect of the invention;

[0153] FIG. 3: shows scanning electron microscopic images of mineralized (a) beech, (b) ash and (c) spruce (4 cycles each 24 hours) obtained by a method according to the third aspect of the invention, wherein lighter areas indicate the presence of calcium carbonate in cell lumina as well as partly in cell walls;

[0154] FIG. 4: shows (a) a time-dependent heat release rate of native spruce (b) a time-dependent heat release rate of spruce-calcium carbonate composite obtained by a method according to the third aspect of the invention with 4 cycles each for 24 hours;

[0155] FIG. 5: shows a reaction scheme of calcium carbonate mineralization of wood using a hydrolysis step;

[0156] FIG. 6: shows SEM images of mineralized wood samples in the backscattered electron mode of beech (a, b) and spruce (c, d) and EDX point analysis of CaK -line at selected positions indicating a deposition within the wood cell wall (in FIG. 6b A indicates 8.84 Wt % (CaK), B indicates 6.68 Wt % (CaK) and C indicates 4.49 Wt % (CaK); in FIG. 6d A indicates 6.64 Wt % (CaK), B indicates 8.75 Wt % (CaK), C indicates 7.23 WT % (CaK) and D indicates 7.82 Wt % (CaK);

[0157] FIG. 7 shows temperature-dependent heat release rate of native spruce (unmodified spruce in a) and beech (unmodified beech in b) and wood/CaCO.sub.3 composites, namely (c) comprising a composite of spruce/CaCO.sub.3 (0.5 M DMC+0.5 M CaCl.sub.2), (d) comprising a composite of beech/CaCO.sub.3 (0.5 M DMC+0.5 M CaCl.sub.2), (e) comprising a composite of spruce/CaCO.sub.3 (1.0 M DMC+1.0 M CaCl.sub.2), (f) comprising a composite of beech/CaCO.sub.3 (1.0 M DMC+1.0 M CaCl.sub.2), (g) comprising a composite of spruce/CaCO.sub.3 (1.5 M DMC+1.5 M CaCl.sub.2), (h) comprising a composite of beech/CaCO.sub.3 (1.5 M DMC+1.5 M CaCl.sub.2), (i) comprising a composite of spruce/CaCO.sub.3 (prepared by 4 alternating impregnation cycles2 h per cyclebeginning with 1.5 M CaCl.sub.2 in ethanol followed by 1.0 M Na.sub.2CO.sub.3 in H.sub.2O), (j) comprising a composite of beech/CaCO.sub.3 (prepared by 4 alternating impregnation cycles2 h per cyclebeginning with 1.5 M CaCl.sub.2 in ethanol followed by 1.0 M Na.sub.2CO.sub.3 in H.sub.2O, (k) comprising a composite of spruce/CaCO.sub.3 (prepared by 4 alternating impregnation cycles24 h per cyclebeginning with 1.5 M CaCl.sub.2 in ethanol followed by 1.0 M Na.sub.2CO.sub.3 in H.sub.2O) and (l) comprising a composite of beech/CaCO.sub.3 (prepared by 4 alternating impregnation cycles24 h per cyclebeginning with 1.5 M CaCl.sub.2 in ethanol followed by 1.0 M Na.sub.2CO.sub.3 in H.sub.2O;

[0158] FIG. 8: shows Raman mapping of BaSO.sub.4/beech composites, (left side) shows the distribution of lignin emphasizing cell corners and middle lamella (aromatic ring stretching, 1554-1720cm.sup.1) (right side) shows the distribution of barium sulfate (958-1012 cm.sup.1) in beech fibers.

EXAMPLES AND INSTRUMENTS

[0159] ESEM-EDX. Environmental scanning electron microscopy (ESEM) in the low-vacuum mode was carried out on a FEI Quanta 200 3D coupled to an EDAX energy-dispersive X-ray spectrometer.

[0160] Pyrolysis combustion flow calorimetry. The heat of combustion of wood-calcium carbonate composites and reference wood was determined by oxygen consumption applied to the combustion gases in pyrolysis combustion flow calorimetry (PCFC) (Fire Testing Technology Instrument UK) with a pyrolysis temperature of 85-750 C. and a 80% N.sub.2/20% O.sub.2 gas mixture and operated at a heating rate of =1 K s.sup.1 and a combustion temperature of 900 C. The PCFC measurements were replicated at least five times for samples of approximately 5 mg. The char yield was determined directly after combustion. The HRR curves were baseline-corrected and fitted with multiple Gauss curves using the program OriginPro 8.1. Herein, the resulting peak sum (the total heat release) displayed residual values close to 1. The maximum heat release divided by the constant heating rate =1 K s.sup.1 gives the heat release capacity.

Examples According to the Second Aspect of the Invention

a) Calcium Carbonate Mineralization of Wood in a Two-Solvent Impregnation Cycle System

[0161] Highly mineralized wood (beech, spruce, ash) has so far been obtained by vacuum-assisted impregnation of bulk wood (edge length of the samples up to 2 cm) in 1.5 mol/L CaCl.sub.2 in ethanol and 1 M Na.sub.2CO.sub.3, in water in alternating reaction cycles (1-4 cycles) (FIG. 1). The wood pieces were placed in glass beakers and completely immersed in the reaction solution. Vacuum was applied at least three times to replace air within the wood tissue by the liquid. The reaction time was varied between 2 h to 24 h. The calcium carbonate mineralization of wood targets a significant improvement of fire retardancy without impairing mechanical strength of wood and wood-based products in practical applications.

b) Calcium Carbonate Mineralization of Wood in a Two-Side Diffusion System

[0162] An unmineralized wood body is placed in a reaction chamber within water resistant gaskets, giving two separate compartments, which are leakage free. In each compartment, the salt solution and the metal salt solution are given, respectively, which are separated by the wood body. The gaskets must prevent leakage of the two solutions, so that the diffusion and precipitation can occur exclusively through and in the wood respectively. In some embodiments, the metal salt solution comprises a concentration of the metal salt MX in the range of 0.001 mol/l to saturation concentration, depending on selected M, X and solvent (see solubility values in literature). In particular the metal salt solution comprises a concentration of the metal salt MX in the range of 0.5 to 2.5 mol/l, more particularly 1 to 2 mol/l. The salt solution comprises a concentration of the salt YA in the range of 0.001 mol/l to saturation concentration, in particular 0.5 to 2.5 mol/l, more particularly 0.5 to 1.5 mol/l, depending on selected Y, A and solvent. The concentrations of the metal salt solution and the salt solution, may be used in equimolar concentrations of MX and YA or as an excess of MX over YA or as an excess of YA over MX. In some embodiments, a mixture of metal salts MX in equimolar or with different concentrations is used. In some embodiments, a mixture of metal salts YA in equimolar or in different concentrations is used. In particular, 1 mol/l BaCl.sub.2 solution was placed in the reaction chamber on one side of the wood body and 1 mol/l Na.sub.2SO.sub.4 solution was placed on the other side of the wood body. The two solutions were let diffuse over time a certain time period (minimum 1 hour up to several weeks). The two solutions can be exchanged with fresh solutions in regular time intervals, depending on the desired mineralization degree. The final mineralized wood body comprises BaSO.sub.4 as the MA mineral phase.

c) Characterization of Calcium Carbonate/Wood Composites Regarding Weight Percent Gain

[0163] Using the process of the invention, high amounts of calcium carbonate can be incorporated into the wood structure tunable by varying the reaction conditions (number of reaction cycles, reaction time) for each type of wood (FIG. 2).

[0164] By using a short reaction cycle of 2 hours a mass gain of more than 5% (ash) up to more than 20% (beech) in only one cycle is achieved. By applying the alternating impregnation steps for 3 times the mass gain is in the range of more than 10% (ash) up to more than 25% (spruce or beech). The resulting mass uptake depends on the wood species, the sample geometry and other factors.

[0165] By using a long reaction cycle of 24 hours a mass gain of more than 15% (ash) up to more than 20% (spruce) in only one cycle is achieved. By applying the alternating impregnation steps for 3 times the mass gain is in the range of more than 20% (ash) up to nearly 35% (beech).

d) Mineralized Wood Material

[0166] Scanning electron microscopic images and Raman mapping indicate the incorporation of calcium carbonate inside the wood lumina and partially in the wood cell walls (FIG. 3 and FIG. 8).

e) Reduced Flammability of Wood-Calcium Carbonate Composites

[0167] The heat of combustion of spruce-calcium carbonate composites was determined by oxygen consumption in a pyrolysis combustion flow calorimetry (PCFC) probe. The peak heat released per unit mass and per degree of temperature assessing the specific flammability of the material was reduced from 1235 J g.sup.1 K.sup.1 in native spruce to 384 J g-1 K-1 (30% remaining) in the inorganic hybrid wood composite. This parameter reveals the tendency to ignite objects nearby and to maintain flame combustion. The net heat of complete combustion is also decreased to 2.60.4 kJ g.sup.1 (31%) compared to unmodified spruce (6.00.5 kJ g.sup.1). The char yield of the modified spruce is considerably higher than for native wood (382% compared to 161%) (FIG. 4).

[0168] A summary of the total heat release, the heat release capacity and the char yield for examples of mineralized wood materials is shown in table 2.

TABLE-US-00002 TABLE 2 Heat Reaction Total heat released [kJ g.sup.1] release capacity [J g.sup.1 K.sup.1] Char yield [%] conditions Spruce Beech Spruce Beech Spruce Beech 0 8.0 0.5 8.1 0.2 123 5 114 5 15.5 0.8 17.0 1.6 4 cycles 3.0 0.6 (38%) 3.4 0.6 (42%) 49 9 (40%) 34 2 (30%) 35.1 3.1 (226%) 33.9 2.9 (199%) (2 h/cycle) 4 cycles 2.6 0.4 (33%) 2.9 0.5 (36%) 38 4 (31%) 35 3 (31%) 38.2 2.4 (246%) 35.9 1.2 (211%) (24 h/cycle) Pyrolysis combustion flow calorimetry data of wood (spruce, beech) and CaCO.sub.3/wood composites prepared with 4 alternating cycles (2 h or 24 h per cycle) of 1.5 M CaCl.sub.2 and 1 M Na.sub.2CO.sub.3.

Examples According to the Third Aspect of the Invention

a) Calcium Carbonate Mineralization of Wood in a One-Solvent System

[0169] Blocks of spruce and beech wood (20 mm edge length) were immersed in an equimolar solution of CaCl.sub.2 and dimethyl carbonate (0.5 mol L.sup.1, 1.0 mol L.sup.1, 1.5 mol L.sup.1) under continuously stirring and vacuum-impregnated for several times. The controlled hydrolysis was initiated by adding an aqueous sodium hydroxide solution (e. g. concentration=1 mol L.sup.1) to the reaction solution. In this process only water-soluble by-products are formed, such as methanol (dimethyl carbonate), which do not interfere with the nucleation and growth of calcium carbonate (FIG. 5).

b) Mineralized Wood Material

[0170] SEM images of mineralized wood samples indicate the incorporation of calcium carbonate inside the wood lumina and partially in the wood cell walls (FIG. 6).

c) Reduced Flammability of wood-Calcium Carbonate Composites

[0171] A summary of the total heat release, the heat release capacity and the char yield for examples of mineralized wood materials is shown in table 3.

TABLE-US-00003 TABLE 3 Heat c (DMC) Total heat released [kJ g.sup.1] release capacity [J g.sup.1 K.sup.1] Char yield [%] [mol L.sup.1] Spruce Beech Spruce Beech Spruce Beech 0 8.0 0.5 8.1 0.2 123 5 114 5 15.5 0.8 17.0 1.6 0.5 4.2 0.5 (52%) 4.4 0.4 (53%) 57 3 (46%) 38 2 (46%) 29.9 2.1 (193%) 27.6 1.4 (162%) 1 2.9 0.4 (37%) 3.9 0.2 (48%) 52 4 (42%) 38 3 (42%) 33.1 2.0 (214%) 31.9 2.5 (187%) 1.5 2.5 0.2 (32%) 3.1 0.4 (38%) 45 5 (37%) 37 5 (37%) 37.7 1.7 (243%) 33.7 1.3 (198%) Pyrolysis combustion flow calorimetry data of wood (spruce, beech) and CaCO.sub.3/wood composites prepared by alkaline hydrolysis of dimethyl carbonate in the presence of CaCl.sub.2.