Production Method For Modified Lignocellulose Materials

Abstract

Production method for modified lignocellulose materials. The present invention relates to a production method for modified lignocellulose materials, comprising the impregnation of a lignocellulose material, especially wood, with a solution of an acid and an alcohol as well as treatment of the material with superheated steam at elevated temperatures.

Claims

1: A process for the preparation of a modified lignocellulose material is provided, comprising the steps of a) impregnating the lignocellulose material with an aqueous impregnation composition comprising i) an organic compound having more than one hydroxy group and ii) a organic carboxylic acid having more than one carboxylic group; b) treating the impregnated lignocellulose material at gat elevated temperature, wherein step b) comprises the treatment of the impregnated lignocellulose material with superheated steam, where the superheated steam has a temperature of >100° C.

2: The process of claim 1, wherein the aqueous impregnation composition is nitrogen-free.

3: The process of claim 1, wherein the aqueous impregnation composition is for formaldehyde-free

4: The process of claim 1, wherein the organic compound having more than one hydroxy group comprises a carbohydrate and/or a sugar alcohol.

5: The process of claim 1, wherein the organic compound having more than one hydroxy group is selected from sorbitol, glucose, glycerol, dextrines, xylitol, saccharose, fructose, mannitol, erythritol, lactit, isomalt, maltitol, hydrated starch hydrolysate (HSH), threitole, adonitole, arabitole, galaktite and inosite or mixtures thereof.

6: The process of claim 1, wherein the organic carboxylic acid having more than one carboxylic group is selected from oxalic acid, malonic acid, succinic: acid, glutaric acid, adipinic acid, fumaric acid, citric acid, maleinic acid, isocitric acid, aconitic acid, malic acid, oxalosuccinic acid, trimesic acid trimellitie acid, hemimellitic acid, or mixtures thereof.

7: The process of claim 1, wherein the impregnation composition furthermore comprises a catalyst, preferably selected from sodium hypophosphite, magnesium chloride, sulfuric acid, and hydrochloric acid.

8: The process of claim 1, wherein the ratio of compound i) to compound ii) is mol/mol—or, if there is more than one compound i) and/or compound ii), the ratio of the sum of the compounds i) to the compounds ii)—is ≥1:10 to ≤2, preferred≥1:5 to ≤1.5 and most preferred≥1:3 to ≤1.

9: The process of claim 1, wherein the ratio of compound i) to compound ii) mol/mol—or, if there is more than one compound i) and/or compound ii), the ratio of the sum of the compounds i) to the compounds ii)—are chosen so that X is ≥0.05 to ≤1, preferred≥0.06 to ≤0.5 and most preferred≥0.1 to ≤0.4, whereby X is calculated as follows: X=[X1/X2]/[X3/X4], with X1=the molar amount of compound i) X2=the number of hydroxy moieties in compound i) X3=the molar amount of compound ii) X4=the number of carboxylic acid moieties in compound ii)

10: The process of claim 1, wherein step b) occurs at a set temperature T.sub.A which is kept essentially constant throughout the treatment.

11: The process of claim 1, wherein the set temperature T.sub.A is 0° C. to =180° C.

12: The process of claim 1, wherein the set temperature T.sub.A is >100° C., to ≤140° C.

13: The process of claim 1, wherein step b) comprises the steps b1) to b3): b1) optionally heating the temperature up to ≥100° C. and generating a superheated stream atmosphere. b2) Heating the temperature to the set temperature T.sub.A with a heating rate, of 5° C. per hour b3) Treating the impregnated lignocellulose material at the set temperature T.sub.A

14: The process of claim 1, wherein step b) comprises the steps ba) to bc): ba) Heating the temperature up to a temperature T.sub.B lower than T.sub.A, whereby the difference between T.sub.B and T.sub.A is ≥15° C. preferably ≥20 more preferred≥25° C. and most preferred≥30° C. bb) Heating the temperature to the set temperature T.sub.A with a heating rate of ≤5° C. per hour bc) Treating the impregnated lignocellulose material at the set temperature T.sub.A

15: The process of claim 1, further comprising a step c) c) Cooling with a cooling rate of ≤10° C. per hour at a superheated stream atmosphere

16: Use of a process according to claim 1 for the modification of lignocellulose material.

17: A modified lignocellulose material obtained by the process of claim 1.

Description

[0140] FIG. 1 is a diagram showing the weight percentage gain after treatment for a first to fourth example of the present invention,

[0141] FIG. 2 is a diagram showing the relative swelling of the first to fourth example and a comparative example of the present invention,

[0142] FIG. 3 is a diagram showing the Anti-Swelling Efficiency for the first to fourth example of the present invention,

[0143] FIG. 4 is a photograph of the end grain surface of specimen according to the second comparative example and the fifth inventive example;

[0144] FIG. 5 is a photograph of an axially cut test specimen according to the second comparative example and the fifth inventive example;

[0145] FIG. 6 is a photograph of two fork test specimen according to the second comparative example and the fifth inventive example;

[0146] FIG. 7 is a diagram showing the cell wall bulking and weight percent gain of examples with different polyols; and

[0147] FIG. 8 is a diagram showing the weight percent gain and cell wall bulking before and after leaching of different wood types.

[0148] The invention will furthermore be described according to the following examples which are for illustrative purposes only and non-binding.

[0149] In the following four test specimen were provided according to the following procedure.

[0150] Scots pine sapwood specimens were fully impregnated with an aqueous solution of sorbitol and citric acid at molar ratios of 1:1 (Ex. 1 and 2) and 1:3 (Ex. 3 and 4).

[0151] In Example 1 and 3 an impregnation solution comprising 20 g of the combination of sorbitol and citric acid per 80 g water was used. In Example 2 and 4 an impregnation solution comprising 30 g of the combination of sorbitol and citric acid per 70 g water was used.

[0152] Wood specimens were impregnated with the respective impregnation solution in a vacuum-pressure impregnation process of 1 hr vacuum at 50 mbar followed by 2 hr overpressure at 12 bars. Fully impregnated specimens were dried and the modifying agents cured under superheated steam conditions at 140° C. For this, impregnated specimens were immediately after the impregnation (no pre-drying required) exposed to elevated temperature in a drying chamber with controlled air ventilation. Starting from ambient climatic conditions, the temperature was increased to ≥100° C. and the air inside the drying chamber exchanged by water vapor within a period of 10 hrs.

[0153] Afterwards a superheated steam atmosphere was created by heating ‘wet steam’ at temperatures≥100°. In a superheated steam atmosphere, the temperature was increased to 110° C. in steps of 0.1° C./hr. Afterwards, temperature was increased to 140° C. with 3° C./hr. The temperature remained at 140° C. for 24 hrs, before a cooling phase followed under superheated steam atmosphere until ca. 100° C., reducing the temperature in steps of 1° C./hr.

[0154] Further cooling happened from 100 to 50° C. with a rate of 2° C./hr at ca. 80% relative humidity. Finally, a conditioning phase followed at constant temperature of 50° C. and a relative humidity of 70% for 24 hrs.

[0155] As a comparative/reference example, an untreated sample was used.

[0156] FIGS. 1 to 3 show, respectively, the weight percentage gain, the relative swelling and the anti-swelling efficiency of the four inventive examples. As one can see, excellent properties can be obtained, especially when compared, as shown in FIG. 2., with an untreated sample.

[0157] FIG. 1 shows in detail the weight gain of the lignocellulose material according to examples 1 to 4, before (black) and after (striped) leaching for 14 days according to EN 84. Therefore, FIG. 1 shows the amount of reaction products of i) the organic compound having more than one hydroxy group and ii) the organic carboxylic acid having more than one carboxylic group, in the modified lignocellulose material.

[0158] FIG. 2 shows in detail the relative swelling of the lignocellulose material according to examples 1 to 4 and the reference (untreated sample), when being exposed to saturated water.

[0159] FIG. 3 shows in detail the anti-swelling efficiency (ASE) of the lignocellulose material according to examples 1 to 4.

[0160] Furthermore, a test specimen according to a fifth inventive example and a second comparative example was produced as follows:

[0161] According to the fifth inventive example, Scots pine sapwood (Pinus sylvestris L.) was impregnated according to inventive example 4. The impregnation process for inventive example 5 and comparative example 2 was identic to the one applied to the inventive examples 1— Impregnated specimens of the fifth inventive example had been dried in an superheated steam atmosphere according to inventive example 1-4. Impregnated specimens of the second comparative example had been dried under dry-conditions without steam. Like inventive examples 1-5, specimens of the second comparative example underwent the drying and curing immediately after the impregnation process.

[0162] According to the second comparative example, Scots pine sapwood (Pinus sylvestris L.) was impregnated with the same solution like it has been used for inventive example 4 and 5. Specimens of the second comparative example were dried at 103° C. for 8 hrs. Afterwards the temperature was increased to 110° C. within a period of ≤30 Min. Specimens were stored at constant temperature of 110° C. for 84 hrs. Finally, the temperature was increased to 140° C. within ≤60 Min. Specimens were stored at constant temperature of 140° C. for 24 hrs. Finally, the temperature was decreased to 50° C. and the specimens exposed to 50° C. for another 36 hrs.

[0163] FIGS. 4 and 6 show several photographs disclosing the differences between the comparative and the inventive example.

[0164] FIG. 4 shows the of specimen according to the second comparative example (the two specimens on the left) and the fifth inventive example (the two specimens on the right). At first it can be seen that the inventive examples have a brownish continuous coloring, whereas the comparative examples are much more lighter, but with irregular dark spots, which speaks for an uneven distribution of the impregnation material in the wood. This can also be observed in FIGS. 5 and 6.

[0165] FIG. 5 is a photograph an axially cut test specimen according to the second comparative example (upper two) and the fifth inventive example (lower two). When cutting the specimen (e.g. with a circular saw) for the comparative example a strong counter-force was observed, whereas the inventive examples could be cut smoothly and easily. This speaks for stronger strain and tensions in the comparative example than in the inventive one.

[0166] FIG. 6 is a photograph of two fork test specimen according to the second comparative example (left) and the fifth inventive example (right). The “fork test” shows a much stronger curvature of the comparative example, which again speaks for a much uneven distribution of the impregnation within the comparative example, as compared to the inventive one, and also for much greater strain and tension within the specimen according to the comparative example.

[0167] Table 1 shows further examples of the present invention that were carried out the same way as inventive examples 1 to 4, wherein various molar ratios of sorbitol and citric acid, various concentrations of these compounds in the impregnation solution, various curing temperatures and various curing times were used, as listed in the table.

[0168] The percentage weight gain of the sample (WPG) and the cell-wall bulking were measured before and after leaching the samples for 14 days according to EN 84. Additionally, the anti-swelling efficiency (ASE) was measured as before.

TABLE-US-00001 TABLE 1 Molar Curing Unleached Leached ratio temp. Curing WPG CWB WPG CWB ASE Ex. Sor:CA wt % [° C.] time [h] [%] [%] [%] [%] (1) (2) (3) (4) (5) 6 1:1 30 110 24 50 7.1 28 3.4 16 21 — — — 7 36 49 7.3 32 3.6 12 18 — — — 8 1:2 24 59 8.2 43 5.0 — — — — — 9 1:3 24 51 8.0 39 4.9 12 15 — — — 10 36 50 7.5 40 5.1 15 16 — — — 11 1:1 30 120 24 48 7.9 32 4.0 13 18 — — — 12 36 48 7.4 35 4.2 14 18 — — — 13 1:2 24 57 8.3 47 5.4 — — — — — 14 1:3 24 48 7.7 40 4.8 13 21 — — — 15 36 47 7.9 40 5.8 16 20 — — — 16 1:1 30 130 24 46 7.4 36 4.7 20 24 — — — 17 36 47 7.4 38 5.1 25 26 — — — 18 1:2 24 54 7.6 51 6.6 40 35 37 — — 19 1:3 24 45 7.6 42 6.0 27 27 — — — 20 36 46 7.9 43 6.4 27 26 — — — 21 .sup. 1:0.5 30 140 24 41 5.4 18 2.2 21 23 — — — 22 1:1 20 27 5.2 22 3.5 33 31 32 28 27 23 30 44 6.6 38 4.6 31 31 28 26 21 24 1:2 54 7.8 52 6.9 45 45 — — — 25 1:3 20 26 5.1 25 4.6 45 46 43 43 38 26 30 12 43 6.7 38 4.9 26 28 — — — 27 18 43 6.3 39 4.8 28 30 — — — 28 24 41 6.6 40 6.2 49 45 44 43 39 29 36 42 6.0 40 4.8 39 41 — — — 30 48 39 5.7 37 4.5 37 40 — — — 31 40 24 55 7.2 52 6.0 31 35 — — — 32 50 69 8.5 66 7.1 26 29 — — — 33 60 84 9.5 80 8.1 17 15 — — — 34 70 100 12.3 96 10.0 19 16 — — —

[0169] Table 2 shows further examples of the present invention that were carried out the same way as the previous example 4 (molar ratio Sor:CA=1:3 and 30 wt % total Sor/CA in the impregnation solution), wherein catalyst was added to the impregnation solution so that the impregnation composition comprises the catalyst in the given amount based on the total amount of impregnation composition.

TABLE-US-00002 TABLE 2 Curing Unleached Leached temp. WPG CWB WPG CWB ASE Ex. Catalyst wt. % [° C.] [%] [%] [%] [%] (1) 35 SHP 4 120 57 8 48 6 — 36 (sodium 6.5 61 9 48 7 — 37 hypophosphite) 8 67 8 49 6 — 38 4 140 49 7 45 7 — 39 6.5 51 8 41 8 — 40 8 56 8 38 7 43 41 MgCl.sub.2 × 6H.sub.2O 2 120 51 8 14 4 42 3 53 8 9 3 43 4 52 8 49 2 44 2 140 41 6 30 7 45 3 43 6 23 4 46 4 56 8 38 3 47 HCl 0.3 120 47 8 38 7 — 48 0.6 44 9 39 6 — 49 0.9 48 8 40 5 — 50 0.3 140 44 8 42 7 47 51 0.6 43 7 41 6 51 52 0.9 43 8 41 7 48 53 no catalyst 0 120 48 8 40 5 13 54 0 140 41 7 40 6 49

[0170] FIG. 7 is a diagram showing the cell wall bulking (B) and weight percent gain (WPG) in percent of examples with various polyols. The examples were prepared the same way as previous examples 1 to 4, wherein examples 55 to 58 were prepared using erythritol instead of sorbitol. Particularly, the examples were prepared according to the following table 3.

TABLE-US-00003 TABLE 3 organic compound having more than one hydroxy Molar ratio Ex. group used (polyol) polyol:CA wt % 55 erythritol 1:3 30 56 1:3 20 57 1:2 30 58 1:2 20 59 sorbitol 1:3 30 60 1:3 20 61 1:2 30

[0171] As can be seen from FIG. 7, similar results can be obtained from sorbitol and erythritol.

[0172] FIG. 8 is a diagram showing the weight percent gain (WPG) and cell wall bulking (Bulking) in percent, before and after leaching of samples from European beech and Scots pine. The examples were prepared the same way as previous examples 1 to 4, wherein different Sor:CA ratios (1:1 to 1:3) and different curing temperatures (120 to 160° C.) were used, as given in FIG. 8.

[0173] As can be seen from FIG. 8, different absolute values can be obtained for different wood types, wherein the trends between the examples remains comparable. Particularly, it can be seen from FIG. 8 that curing temperatures above 140° C. may be less favorable.

[0174] Furthermore, the following examples 62 and 63 were carried out, on 5 pinewood samples each (1.5×2.5×5 cm.sup.3 according to EN 113). The samples were held under a 10 mbar vacuum for 30 min. Afterwards the samples were submerged in impregnation composition for 1 hour at ambient pressure. After impregnation, the samples were held at 140° C. under superheated steam for 24 h, followed by leaching according to EN 84 and drying at 100° C. for 16 h.

[0175] In example 62, the impregnation solution comprised 20 wt. % sorbitol, 10.54 wt. % citric acid, 2 wt. % sulfuric acid as catalyst, and the rest water. In example 63, the impregnation solution did not comprise catalyst, i.e. the solution comprised 20 wt. % sorbitol, 10.54 wt. % citric acid, and the rest water.

[0176] Example 62 yielded in a weight loss of 9.9% from before leaching to after leaching, whereas example 63 had a weight loss of 45.4%, showing that the catalyst may lead to a better fixation of the impregnation solution.

[0177] The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.